5 Planning. Implementation, operation
and monitoring of ADS units
Hassan Fath and Vicente J. Subiela
5.1 INTRODUCTION
The need for providing communities with adequate water supply coupled with environmental
concerns regarding the burning of hydrocarbons has stimulated the interest in developing renewable
energy powered desalination systems. It often happens that the geographical areas where water is
needed are well gifted with renewable energy (RE) sources (solar, wind, geothermal, etc). Thus, the
obvious way is to combine those renewable energy sources to a desalination plant, in order to provide
water sources as required.
The viability of any RE desalination combination will mainly depend on:
- RE potential at the particular site and the form of useful energy which is available after conversion
from renewable sources, be it thermal, mechanical, electrical.
- the required production capacity from the desalination plant; this capacity somehow determines the
size of the energy collection subsystem.
- the availability of Operation & Maintenance (O&M) experienced personnel for plant operation at the
particular site.
- the total system cost.
The feasible renewable energy - desalination technology combinations are depicted in the form of a
tree in Fig. (5.1). From that tree of possibilities, the processes best suited for intermittent operation are
selected.
The most popular choice of desalination plants built is the Reverse Osmosis (RO) process, Table
(5.1), and the most popular choice of energy sources has been solar PV, Table (5.2). Therefore, the
most popular combination of desalination units driven by Renewable Energies (RE) is PV-RO,
although many other combinations have been tried. PV is particularly good for small desalination units
in sunny areas. For larger units, wind energy may be more attractive as it does not require anything
like as much ground.
Table (5.1) Desalination Processes used in Conjunction with RE
Process
RO
MED
World %
62
14
1
MSF
VC
ED
Other
10
6
5
4
2
Wind Energy
Mechanica
l
- MVC
- RO
Solar Energy
Electrical
- MVC
- RO
-EDR
Geothermal
Heat
- TVC
- MED
- MSF
Electrical (PV)
- MVC
- RO
-EDR
Electrical
- MVC
- RO
- EDR
(Thermal)
Heat Mechanical
Electrical
- TVC
- MVC
- MVC
- MED
- RO
- RO
- MSF
- EDR
Figure (5.1) Feasible technology for combination of RE and desalination
3
Table (5.2) Energy Sources for Desalination
Process
Solar PV
Solar Thermal
Wind
Hybrid
World %
43
27
20
10
Matching desalination to RE is fairly complex as desalination are best suited to continuous
operation, while the majority of RE are distinctly non continuous and are in fact intermittent often on a
diurnal basis. Desalination systems have traditionally been designed to operate with a constant power
input. Unpredictable and non-steady power inputs, of RE force the desalination plant to operate in nonoptimal conditions and may cause operational problems. A small energy storage system can be added
to ease the problem but this adds to total system cost. In general, the matching of RE sources to
desalination processes is a technical challenge with major problems associated to their intermittent
character and total system cost.
RE-desalination plant can be designed to operate coupled to the grid, and off-grid (standalone or
autonomous). The latter, named Autonomous Desalination System (ADS), poses the problem of
renewable energy variability because most renewable energy systems lack an inherent energy storage
mechanism. The produced power varies in time as wind speed or the level of solar irradiance. Power
has to be consumed directly or else it will be lost. The power consumer can be a desalination process
and water can be stored cheaply.
ADS are developed mainly for remote areas where no electricity and no fresh water are available.
Relatively small systems are used to cover the potable water needs. Over the last two decades,
numerous desalination systems utilizing renewable energy have been constructed. However, most of
theses systems have been built as research or demonstration projects and were consequently of small
capacity. At the moment there are no large-scale ADS applications. Nevertheless, the continuous
developments in both RE and desalination technologies will provide more reliable systems at cheaper
prices. These trends are liable to continue for the foreseeable future.
This chapter presents a guide to the ADS planning and Implementation. The guide aims to support
local installation under different local conditions, and will draw attention to the important technical,
social and economical aspects to be considered and the possible problems and solutions and actions to
be taken.
4
5.2 SITE SELECTION GUIDE, [1]
5.2.1 Site Selection Requirements
Proper site selection is very important for a successful installation and later operation of ADS.
Various aspects are affected by this selection, such as technology to be used, costs, time schedule,
sustainability, environmental impacts as well as political and social factors. The first step in the site
selection process is the candidate sites data collection, followed by the data analysis, then, the selection
of the site among more than one option.
Data sources such as ministries, universities, research institutes, meteorological stations, utilities,
research reports, feasibility studies and maps, and – most of all – on site visits have proven to be very
useful. The site technical, economical, social and other basic information, are gathered for every
candidate site, as given below in Tables (5.3) to (5.6). There might be other factors, not included in the
list, but may have an important influence on final evaluation of the site, or might even suddenly
become crucial for it’s selection or rejection.
Table (5.3) Technical Factors Affecting Site Selection
Factor
Discussion
Availability and quality
of feed water
A key factor influencing the technical design of the plant. Sea or
especially brackish water source needs to be thoroughly analyzed during
an extended period of time. Several complete analyses throughout the
period of 1 year are recommended to determine seasonal variations in
temperatures, quality as well as quantity of available water and whether a
change in water quality (esp. for ground water aquifer) over longer time
is expected. The results will greatly influence the desalting process
selection
how severe is the water shortage? Can existing source be further
exploited?
Present water supply
situation at a site,
existing fresh water
sources
RE sources
Complete atmospheric
data
Brine disposal
possibilities
Topography of the land,
seashore information
Geology, soils, seism city
solar radiation, wind, geothermal energy, etc. The intensity, daily
variations and duration throughout the year needs to be known. At a
system design stage exact, long-term measurement results are necessary.
Atmospheric parameters and processes that might influence the
operation of the unit or lead to catastrophic events: humidity,
temperatures, sand storms, hurricanes, tsunamis, etc. should be analyzed
in advance.
Must also be considered from technical, environmental and legislation
point of view. The concentrate disposal point should be close to the unit
for economical reasons.
Area available, slope, accessibility and special issues (cliffs, potential
flooding, etc.) will affect complicity and type of earthworks (and so time
and money to be spent) and the risks involved.
Data important for sustainability analysis and risk assessment
Table (5.4) Economic Factors Affecting Site Selection
Factor
Discussion
Economic parameters
Costs of land, labor, transportation, energy, taxes, fees, cost-benefit analysis.
Water selling price
Can the users pay for water, how much and on what conditions
5
Rules and regulations
Applicable standards need to be identified and analyzed. Environmental
constraints imposed by both local and national regulations greatly influence the
site selection, construction, and operation of desalting plants [4]. Regulations
like seashore line protection and need for permissions (i.e. for digging wells,
erecting a building or disposing brine) need to be taken into account. Possibility
of obtaining subsidies due to governmental programs must be checked.
Table (5.5) Social Factors Affecting Site Selection
Factor
Discussion
Social benefit from
planned installation
To what extend will it improve people’s life standards and change their
lives? How drastic this change will be?
Social situation and
willingness
of
local
community to cooperate
Social studies must be made and personal contacts (surveys, workshops,
meetings) during site visits are very important. This problem will be addressed
in more detail.
Quality and quantity
of fresh water needed
Needs to be estimated according to planned usage of water (drinking,
household, irrigation, other), number of users and average consumption per
person or household. Possible future fluctuations (i.e. due to increased land
cultivation, increasing population or life standards) must be taken into account
based on surveys among future users and analysis of present situation. One
cubic meter of water per day (m³/d) can typically supply 20 to 50 people in the
developing world and the recommended salinity of drinking water is less than
500 mg/L TDS and up to 1000 mg/L TDS may also be perfectly acceptable in
some cases).
Technical level and
skill of local people,
local
subcontractors,
suppliers
Employment
situation
Low level may eliminate the possibility of installing more sophisticated
devices or increase costs due to intensive training or bringing external
specialists.
Involving local community in works before, during and after installation can
improve this situation, thus creating an added value.
6
Table (5.6) Infrastructure Factors Affecting Site Selection
Factor
Discussion
Existing
infrastructure
Distance
from
electricity grid
Distance from the
user
Wells, channels, buildings, water distribution network, pumps. Possibility of
utilizing those highly simplifies the installation and decreases investments.
In case of accessible electricity grid in the proximity of candidate site, the
use of RE might not be economically justified.
Municipality, beneficiary community) to the water source will also influence
the design and thus costs of the installation. Pumping water over longer
distances requires more energy and materials to be used, but where other forms
of transportation are not available (rough terrain, no other means of transport)
this might be justified. Responsible person must also have the possibility to visit
the plant regularly.
Availability
of
construction materials,
Including spare parts, maintenance products, etc.
local products and services are always preferred
Figure (5.2) Typical Rural Bedouin Communities in need of Fresh Water
At this point it is worth emphasizing the importance of proper identification of beneficiary
community’s needs, Figure (5.2). Practice shows that this social factor is very often completely omitted
in the site selection process as well as in later phases of projects. Analysis of many abandoned units of
all types (including rural electrification and desalination), indicating the lack of this social engineering
or technology not properly fitted into local conditions as two most common errors, confirms those
words. Therefore again it is very important to keep the basic principles in the social sciences in mind
and try to:
 communicate well with the beneficiary community,
 make them aware of the degree in which the installation will change their lives,
 make sure they really want it and are willing to participate in the project,
 test their motivation and determination by already giving them some tasks and noticing how
they deal with difficulties and tackle problems
 start creating a feeling among the people that what is supposed to be installed in their village
will be for them, will belong to them and whether it will run continuously improving their
lives, or will be abandoned after the first major problem is in their own hands.
In case of lack of cooperation or real interest at such an early stage, maybe it’s better to turn back to
some other candidate site or go through the site selection process again, thus avoiding yet another
useless and expensive installation. Those people are obviously not in real need of desalting unit, even if
our analytical data says so.
7
5.2.2 Data Analysis & Site Selection
5.2.2.1
Data Analysis
The second step is the analysis of gathered data. The most important criteria for specific installation
should be clearly identified and ordered according to their relevance. The order will largely depend on
the character and purpose of the installation (commercial, aid project, technology testing, regional
development program). In some cases, like in aid or regional development projects, social benefit and
improving current situation will overweight many other factors, which would otherwise be more
important (like economic parameters or existing infrastructure). In those cases appropriate technology
needs to be selected according to specific site conditions.
In cases like pilot installations, technology testing or ready commercial products to be installed, a
site which best fulfills specified conditions (esp. water and energy source) must be found in order to
make the best use of chosen technology. In those cases (where the technological solution has been
chosen in advance) evaluation criteria will depend on the process used for desalting, energy supply
system, purpose of installation, and technical particularities of planned units.
5.2.2.2
Site Selection
The third step is the selection of a site out of some selected candidates sites. There generally are two
theoretical approaches to site selection:
1. Comparative approach: all potential sites are compared to a reference site which can be either a site
of an existing and well functioning unit, or a model, being a list of required and acceptable criteria.
2. Numerical classification approach: the various desalination sites are compared to each other in a
numerical manner using marks, or relevance weight factors. This is a more systematic and
transparent approach. It also leaves less room for subjectivity and personal judgment.
In practice, the site selection process requires mixing the two approaches. It is recommendable to
create a table consisting of a list of analyzed criteria, their weights (%) and ratings (i.e. a 0 – 5 scale)
for each site considered. Summation of every criterion’s rating multiplied by its corresponding weight
will lead to a rating (same scale) of each site. A basic exemplary comparison of two sites in such a
manner is presented in a Table (5.7) below.
Table (5.7) Quantifying & Selection Sites, [1]
Criteria
Criterion
weight
%
SITE 1
Ratin
SITE 2
Result
g
Raw water proximity
Raw water quality
Existing water supply
RES availability
Distance
Brine disposal
Materials, spare parts, etc.
Costs
Skill of local labor/contractor
Social benefit
Local regulations
TOTAL:
10
10
10
15
5
5
5
15
5
10
10
100
8
Ratin
Result
3
3
3
2
4
3
3
4
5
2
2
0,3
0,3
0,3
0,3
0,2
0,15
0,15
0,6
0,25
0,2
0,2
2,95
g
4
1
1
5
2
3
2
4
3
4
4
0,4
0,1
0,1
0,75
0,1
0,15
0,1
0,6
0,15
0,4
0,4
3,25
At some sites, it can turn out to be very difficult to obtain some information, perform certain
measurements or establish local contacts. Certain problems might arise due to cultural and educational
differences, no reliable sources of information or human misunderstandings. This should however not
influence objectivity, fair judgment of actual conditions and truthful reporting to the decision makers. It
is important to really identify the most suitable site for an installation, best fulfilling the project aims
and bringing relief to the local community, rather than selecting one just because it will be easier there.
9
5.3 DESALINATION PROCESSES SELECTION GUIDE
5.3.1 Process Selection Basic Issues, [1] & [2]
Desalination technology should be implemented only if the renewable water resources have been
exhausted and no simpler water purification technology can be applied. When this is the case, we are
still left with a number of possible desalination methods and ways of supplying them with necessary
energy.
A number of basic parameters should be investigated before the desalination process selection. This
includes mainly the plant size, renewable energy resources, evaluation of feed water resources (quality
and quantity), product water quality and use, technical staff availability, brine disposal, budget
constraints, and the cost of water that the users will and could pay, Table (5.8).
Table (5.8) Parameters Affecting Process Selection
Parameter
Discussion
Plant size
This is normally dictated by demand for water (potable) in the
(based on demand, area. This should be assessed before any work is undertaken.
saline water resources, Dealing with brackish water plants, a survey of the availability of
storage capacity)
brackish water should be carried out. Clearly, the plant size cannot
exceed the availability of the feed water. Comparing the available
water resources and water consumption, it is feasible to estimate
the real amount of water required. Also, for size plant’s
optimization, any available storage capacity and the operation
pattern should be determined. In case where the determination of
the water demand in a certain location is not feasible an average of
120 Lit/d per capita in winter period and a 180 Lit/d per capita in
summer period (EU countries). Consumptions in the range of 45 to
78 Lit/capita per day (Morocco: 60 Lit, Algeria: 45 Lit, per capita
per day) have been reported.
RE resources
A survey of all of the potentially available energy resources
should be carried out. RE type; solar / wind / others , available
trend and value solar intensity or wind velocity, conversion, to
thermal or electrical, energy storage,…etc. The most likely
sources to be encountered and exploited in rural areas are wind
and solar. Solar may be used as thermal energy or as electrical
energy through PV conversion.
Desalination
The selection of the appropriate desalination process depends
Technology
on a number of factors. These include, plant size, feed water
(Membrane / Thermal / salinity, remoteness, availability of grid electricity, technical
..ect)
infrastructure and the type and potential of the local renewable
energy resource.
Feed water
Product water
The feed water source will normally be either brackish water or
seawater. Distillation desalination processes tend to be used for
seawater desalination, while the membrane processes are used for
a wide range of salinity from brackish to seawater. Application of
the electro dialysis process is limited to brackish water
desalination (energy consumption is directly related to the feed
water salinity).
The determination of the quality of the produced water depends
10
quality & use
on the purpose of the desalination plant (for potable, agricultural
or industry needs). Distillation processes are used for the
production of distillate water while membrane processes are used
for the production of potable water.
Need for Technical
staff
(remoteness,
technology
simplicity,
local community type,
..ect.)
If the plant is to be remotely sited, the technology of choice
should be robust and as independent of support from outside of the
area as possible both in respect of spare parts and chemicals as
well as operator expertise. This means that process selection is not
entirely dominated by energy consumption considerations.
Membrane processes usually have lower energy costs but may
require more chemicals and expertise in their operation.
Brine disposal
The brine disposal from a desalination plant can be a major
problem that should be determined before plant’s installation. For
a seawater or brackish water desalination plant on the seacoast the
brine disposal is not usually a problem. However, in cases where
the plant has to be located inland (specially for brackish water
units), care should be taken so that to dispose the concentrate brine
reject without polluting local water resources. A solution, although
of high cost, is the use of evaporation ponds. Another, less costly
alternative is the operation of the plant at as high as possible
recovery ratio, in order to decrease the amount of the brine
disposal and reduce the ultimate disposal system.
Budget constraints
The total capital cost as well as operation and maintenance
costs of the RES - desalination system should be compared to the
available budget and expected income to be paid by potential
users. Possible financing and water price subsidy schemes by local
or international organizations should be carefully examined, see
section (5.5) below.
Total
production cost
water
As a general rule, the cost of the produced water by renewable
energy driven desalination is normally higher than conventional
electricity sources (fossil fuel). If the cost of transported water is
high, compared with the ADS water cost, then ADS have a credit.
5.3.2 Comparison Between Desalination Processes, [2]
The choice of one process over the other is very site specific and depends on a number
of factors need to be taken into consideration. Discussion of these factors is given in
Table (5.9).
Table (5.9) Factors Affecting Comparison between desalination processes
Factor
Feed water
Comparison
Thermal and RO processes are used for the desalination of seawater
11
type
while RO and ED are used to desalt brackish water. Comparing the two
membrane processes, at low feed salinity, ED becomes a more attractive
alternative for large potable water desalination plants. For higher feed
water salinity its main competitor, RO, usually becomes a cheaper
option. Feed water treatment for RO is important and can be expensive.
Product
water quality
In general, thermal processes produce distillate water with very low
TDS, around 10 to 20 ppm. By contrast the TDS of product water from
RO and ED is usually around 350-500 ppm (potable). The post-treatment
required varies according to the use of the produced water. For potable
use, the water produced should be treated according to WHO’s
standards. With regard the distillate water produced by thermal
processes, there are concerns about its desirability for potable use over a
long time period, although this question has not been settled
conclusively.
Plant
capacity
MSF & MED plants are typically available in large unit capacities.
VC process which is used in small and medium scale applications. MSF
units are best suited to large-scale operation (economy of scale). MED
process is used in medium and large-scale applications. Small-scale
MED plants have also been developed. Membrane plants can be easily
adapted to any plant size and can be found in all capacity ranges. Both
technologies, RO and ED are suitable for small and large-scale
applications.
Economics
of
desalination
Cost figures for desalination have always been difficult to obtain.
Desalination costs are largely depended on the process, feed water type,
product water quality requirements, electricity price, etc.
The total cost of water produced by a desalination plant includes the
investment cost as well as operating and maintenance cost. In a
comparison between seawater and brackish water desalination the cost of
the first is about 3 to 5 times the cost of the second one for the same
plant size.
Investment
Generally, the investment includes equipment, installation, and other
civil works. Distillation plants have higher investment costs and lower
operational costs than membrane processes. Additionally, land
requirements for thermal processes are higher than these for membrane
processes.
Operating
&
maintenance
costs
Operating and maintenance costs include energy requirements, labor,
and process consumables, including chemicals and membranes
replacement (for membrane processes).
System
O&M
The maintenance of a desalination plant includes the feed water pretreatment, periodic cleaning of the system, replacement of mechanical
equipment and control instruments. The most important maintenance
requirement concerning membrane processes is membrane replacement
which constitutes a major cost factor.
Operational and maintenance costs are less for thermal processes.
Scale prevention and corrosion control are important factors particularly
with plants operated at high temperatures. Chemical requirements for
pre-treatment and post-treatment processes are strongly dependent on the
feed water quality. In general, distillation processes require less
12
chemicals for the feed water pre-treatment than membrane processes.
Labor
requirements
Generally, the specific cost of labor for a large plant is slightly lower
than for a small one. In small plants, labor requirements are slightly
lower for distillation processes than for reverse osmosis, however they
become equal for larger plants.
Energy
requirements
The theoretical absolute minimum energy required for desalination is
about 0.8 kWh/m3 of water produced, depending on the salt content and
regardless of the process used. In any desalination process, the energy
consumption depends on a variety of factors, such as sea water
concentration, temperature of operation for membrane processes, as well
as performance ratio, heat losses, temperature difference etc., for thermal
processes.
Processes that rely on a change in water phase as in thermal processes,
usually involve higher energy consumption, see Table (5.10), [2], than
processes that do not require a change of phase. Thus, distillation
processes are found mostly in countries with cheap fuel (e.g. Saudi
Arabia, U.A.E.). However, thermal processes (MSF, MED) operating
with steam supplied by exhaust or bleeding steam from back pressure or
extraction steam turbines, are economically attractive and comparable
with RO energy cost. For membrane processes the energy required
depends on the ions selective Transport and is proportional to the salinity
of the feed water used and product obtained. For medium and large RO
systems an energy recovery system can be used, recovering about 40%
of the input energy.
Total costs
The total specific costs of the major large capacity desalination
processes, of a typical plant size between 10 000-20 000 m3/d, with
exception of VC which exists in the range below 2500 m 3/d, are shown
in Table (5.11), [2].
Constructio
In terms of the time of construction, a thermal process requires more
n time
time than a membrane process. The construction time for very large MF
plants can take from three to five years. Large RO plants can be
produced installed and commissioned in periods ranging from 18 to 24
months. Small RO plants can be produced and installed in almost one
month.
13
Table (5.10) Estimated energy consumption of Major Desalination Processes, [2]&[3]
Process
MSF
MED
VC
SWRO
Steam
Energy
kWh/m3
7.5 - 11
4-7
---
BWRO
ED
---
Electrical Energy
kWh/m3
2.5 – 3.5
2
7 - 15
4 – 6 with energy
recovery
7 – 13 without energy
recovery
0.5 – 2.5
0.7 – 2.5
Equivalent
Electrical Energy
kWh/m3
10 – 14.5
6–9
7 - 15
4 – 6 with energy
recovery
7 – 13 without
energy recovery
0.5 – 2.5
0.7 – 2.5
Table (5.11) Total Specific Costs of Major Desalination Processes, [2]&[3]
Proces
s
MSF
MED
VC
SWRO
BWRO
ED
Investm
ent
Euros/
(m3/day)
1000–
2000
900 –
1800
900 –
2500
800 –
1600
200 –
500
266 324
Energy
Euros/
m3
0.6–1.8
0.38–
1.12
0.56–
2.4
0.321.28
0.040.4
0.060.4
Consumab
les
Euros/ m3
0.03-0.09
0.02-0.15
0.02-0.15
0.09-0.25
0.05-0.13
0.05-0.13
Labor
Maint.
Euros/
m3
0.030.2
0.030.2
0.030.2
0.030.2
0.030.2
0.030.2
Euros/
m3
0.020.06
0.020.06
0.020.08
0.020.05
0.004.02
.006.009
Tot. O &
M
Euros/ m3
0.68-2.15
0.45-1.53
0.63-2.83
0.46-1.78
0.12-0.75
0.15-0.74
5.3.3 Appropriate Technology
It should be made clear at this point, that there is no straightforward way to select the appropriate
RE desalination technology. Rather, an iterative approach is most probable to be followed, involving
careful assessment of selected criteria and technical parameters. Furthermore, every candidate process
option resulting from the previously described process should be further screened through constraints
such as site characteristics (accessibility, land formation, etc.) and financial requirements.
Appropriate technology is that which makes the best use of available resources, such as labor,
capital, and natural assets, taking into account operation and maintenance as well. The proper
identification of the appropriate technology for a particular rural water supply necessitates the
evaluation and comparison of alternative methods, including all costs and benefits [1]. A well designed
rural water supply project should be:
 Simple, robust and reliable
 Relatively labor-intensive
 low capital cost and little import of foreign material
 Accepted and supported by the local community with minimum change to social sphere
 Organized at local level with relatively simple training
 Sustainable
14
When several alternative ADS schemes are applicable for a specific case, the final decision
concerning the most prominent combination should be based, once again, on criteria such as:
- Commercial maturity of technology (an appropriate way to validate this is by examining the
performance of similar existing applications).
- Availability of local support (installers, technicians, machine shops, etc.)
- Simplicity of operation and maintenance of the system
The above factors, in conjunction with available technical information (feed water quality, output
water requirements (quality and quantity) as well as the type of RE resource available) provide a
starting point for the engineer and the decision maker.
Table (C.1), Appendix (5.C), provides a guidance towards the applicability of each ADS technology
option, according to the above mentioned technical factors. It provides an assessment of each
technically feasible application. The remarks presented in this table stem directly from the analysis of
the various technology options analyzed in [4].
15
5.4 ADS ECONOMICS & FINANCING
5.4.1 Cost analysis
Cost Analysis of ADS usually aims to estimate the cost of a liter or a cubic meter of fresh water, and
calculates the contribution of each cost item to the total cost. This identifies immediately the most
significant cost items and attracts the attention to what should first be examined for possible
improvement and cost reduction.
The calculation should always take into account both ongoing and future costs. Unit product cost is
mainly affected by:
 Unit capacity – larger units require higher investment, but the product water cost is lower due to
higher production.
 Quality of feed water – for RO & ED technologies, for example, the lower the feed water TDS
concentration, the smaller the energy consumption and fewer chemicals necessary for pretreatment. Thermal systems are relatively independent of feed water quality
 Energy cost –is closely connected to average wind velocity, solar radiation or availability of other
RE sources
 Type of technology – determines requirements for pre- and post-treatment, energy efficiency and
costs of equipment and its installation as well as O&M cost.
 Site conditions – existing infrastructure (wells, water distribution network) can decrease the
investment costs
 Costs of land and labor
 Additional costs – like taxes, permissions, fees, brine disposal, etc.
It should be however noted, that for a given desalination technology, cost analysis is site-specific
and usually cannot be generalized for applications in other situations. As a general rule, the cost of the
produced water by ADS is normally higher than conventional electricity sources (fuel energy).
However in the remote areas far from fresh water resources as well as areas where the economic driven
is tourism, the water price is acceptable. The developments currently underway suggest that the
desalination applications are going to become more wide spread. As this happen, price will fall and
technology will then become more viable, specially, in the developing countries.
The total capital cost as well as O & M costs of ADS should be compared to the available budget
and the expected income to be paid by potential users. Table (5.12) shows a general rang of the costs of
produced water for each technology combination. It indicates that, the cost of transported water in
remote areas is high.
16
Table (5.12) Range of Cost (Euros/m3) for Various RES Technologies, [3]
Cost in Euros/m3
Water
Type
Fresh
B
B
B
B
B
ADS
1
2
3
4
5
6
7
8
9
1
0
Tankers to remote areas
Conventional Energy +
RO,ED
PV - RO
PV - ED
Wind - RO
Wind - ED
S
Conventional Energy +
RO,ED,MED,MSF, VC
S
PV - RO
S
Wind - RO
S
Wind - VC
S
Solar Thermal - MED
S
Geothermal - MED
B= Brackish Water , S= Sea Water
5.4.2 Decision Support Tool (DST)
To aid the process of cost calculation for a specific desalination technology and situation, a Decision
Support Tool (DST) is being developed within the ADIRA Project. For a more detailed economic
analysis of your system, please refer to DST software, [4]. For analysis, the DST authors, [4], suggest
to divide the cost of ADS into following categories, Figure (5.3):
Figure ( 5.3) DST Cost Categories, [4]
1. Cost of feed water system and pre-treatment, including all necessary investment and related
expenses required for the supply of brackish or sea water to the desalination main system
17
2. Cost of desalination unit itself
3. Cost of supporting Renewable Energy Source (RES), supplying all the energy needs for the
desalination unit, feed water pumps and brine disposal.
4. Cost of Brine water disposal, which could be anything from minimal to very expensive depending
upon specific conditions
5. Other costs
Some more details of these categories is given in Table (5.13).
Table (5.13 ) DST Cost Categories Details, [4]
Category
Cost of Feed
Water Supply system
Details
The required investment and running cost of this part of the system depends
very much on the nature of each case, the elevation and horizontal distance of
the water source to the desalination machine, the type and size of the piping
system, etc. In most cases the Feed Water Supply System will require a
pumping system (motor and pump) which will consume part of the energy
offered by the Renewable Energy System of the configuration (RES). Drilling
for underground water may be the most important cost item under this heading.
Depending upon the depth of the water basin it could be anything between a
few hundred to many thousand euros. The cost of borehole and associated fixed
equipment is treated very much like the costs of desalination and RES system
costs.
Cost
of
Desalination System
The cost of the Desalination System consists of the purchase and installation
cost of all the pieces of equipment required for the actual desalination. This
may include some kind of pre-treatment items, the desalination unit itself,
possible motor and pump. Sometimes, if the Brine Water Disposal System is
not significant, it is assumed and treated as part of the Desalination System.
Each ADS needs some means of fresh water storage because of the irregular
nature of the energy resource availability. The bigger the volume of the water
tank, the more secure the water supply. However, the size of the tank is limited
by the size of the desalination system and cost & effectiveness considerations
which must be taken into account before sizing the water storage.
Cost
of
Supply system
The Renewable Energy System, exploiting the energy of the sun, the wind,
etc. is supplying the desalination and supporting systems with the required
energy in order to function properly. Its investment cost includes purchase and
installation of the system1. As the availability of the RES involves an element
of uncertainty, each ADS may have an associated energy storage (battery)
system, which, in combination with the fresh water storage system, smooth the
fluctuations of the RES.
RE
The optimal size of battery and fresh water tank can only be estimated with
very detailed weather data, which may not be available, in which case sizing is
based on less rigorous methods.
Cost
Water
system
of Brine
Disposal
The brine water which remains after desalination, should be disposed in a
way that does not harm the feed water or the environment in general. In the
case of sea water source, the problem is minimal, since brine can be re-directed
1
Installation costs of the RES may be significant. In some cases, for example when the RES is based
on PV electricity, it might be necessary to prepare a fairly expensive construction to place the PV
panels.
18
to the sea. However, in the case of drilling underground water, brine has to be
sent back into the ground, sometimes in depths much deeper than the feed
water location.
The cost of Brine Water disposal is very much site dependent and has to be
studied for each individual case for a meaningful estimation of the required
expense.
Other Costs
Costs under this heading are mainly costs of buildings, constructions or
equipment supporting the operation of the ADS.
Costs of other equipment are handled at exactly the same manner as other
investment categories. In the case that an investment in this category is shared
with other uses, only the proportion corresponding to the ADS use is
considered
The usefulness of categorising costs as above allows estimation of each unit costs and facilitates
comparisons, such as for example, between using different RES with the same desalination system,
measures the cost of being autonomous, increases the scope of sensitivity analyses and helps to
optimise system configuration.
Most, if not all, of the above categories have (a) an investment and (b) a running cost. The first
reflects the annual cost of purchasing and installing equipment or other fixed asset, while the second
relates to annual expenses and the cost of various consumables which are necessary. The cost per litre
or cubic metre of fresh water is estimated by dividing the sum total of all annualised investment plus
running costs of all categories by the volume of fresh water produced.
19
5.4.3 Costs of Typical Applied Cases
i- PV-RO unit in Lampedusa-Italy, [3]
The ADS unit uses sea water to produce 5 m3/hr of <500 ppm water quality. The total cost of the
produced water is around 6.5 Euros/m3. The capital cost as well as the O & M costs are shown in the
following Table (5.14). The unit was operated under the supervision of water utility of part time
experienced staff. The cost of personnel will remain elevated if the plant does not coexist with an
organization capable to operate it. with part time of its own personnel
Table (5.14) Cost of PV-RO unit of Lampedusa
Equipment
PV array
Batteries
RO unit
O & M Cost
Staff (1 employee)
Energy
Chemicals
Membrane Replacement
Spares
Electricity Production Cost
Total Water Cost
Cost
10,000
125
19,000
Units
Euros/kWp
Euros/kWh
Euros/m3.hr
20,000
0.7
0.1
0.25
0.05
0.7
6.5
Euros/year
Euros/m3
Euros/m3
Euros/m3
Euros/m3
Euros/kW.hr
Euros/m3
ii- Wind – Diesel – RO Plant at Jandia, Fuerteventura, Spain, [3]
The unit produces 56 m3/day and is driven by a 225 kW wind energy converted and two 160 kVA
diesel engines. The plant serves an isolated village in isolated island of Canary island far from the grid
and far from other communities. O & M costs are shown in the following Table (5.15). No detailed cost
figures are given for the plant capital.
Table (5.15) Estimated O & M Cost per Year
O & M Cost
Euros / Year
O & M Staff
Wind generator
Diesel
Fuel for Diesel
Total
20,000
2,000
12,000
12,000
46,000
A main observation during system operation, concerned the mismatch between the power output
from the wind generator and the load of the system. The generated energy exceeds the energy demand
at the site, and hence a large dump load was required in order to make-up with the excess power. In
such cases, a careful sizing of equipment is required, not only to reduce the investment costs, but also
to properly tune the operation. More cases can be obtained from Reference [3].
5.4.4 Financing Mechanisms
A project can be considered successful only when all costs are covered. Ensuring financing after the
completion of the project can also increase sustainability. Possible financing and water price subsidy
schemes by local or international organizations should be carefully examined.
20
Most of RE projects need considerable investments and cooperative financing. Each project is
financed differently, depending on the purpose, country, unit size and other particularities. One can
however distinguish several typical ways to finance such projects [1]:








Personal savings, assets from users and/or promoters
Subsidies or grants to support technological innovations
Loans from International Funding Agencies (e.g. World Bank Group, Global Environment
Facility, Regional Multilateral Development Banks)
National Funding Agencies
NGO’s
European Commission Programmers (like Europe Aid)
Combined projects with strong financial partners - Private Sector Investment
Financing of the project with limited guarantees over the future cash flows
According to the previous experiences with the financing of RE, a fee for service is essential for the
success of a project. Therefore, an appropriate tariff system for the users should be implemented.
Implementation models
Due to high initial costs of RE powered desalination a good implementation model is necessary.
Some of the possible models are briefly discussed below [2]:
 Cash sales - The companies sell their systems to end users directly (possibly via retailers). End
users own the system as soon as they have paid.
 Consumer credit – Manufacturers (dealers) sell systems directly to end users, but here users can
pay for the systems in installments. Hence, the dealer grants credit. Depending on the agreement,
users either own the system as soon as they receive it or when payment has been completed.
 Credit institution - Companies sell the systems to end users, with a third institution granting
credit to the users. Depending on the agreement, the system either becomes the property of the user
upon delivery or upon final payment.
 Lease - The companies or a financial intermediary lease the system to users, who can purchase it
at the end of the leasing period. However, during the leasing period, the lesser retains ownership of
the system and is also responsible for maintenance and repairs.
 Fee for service - A company or institution (also public water supplier) owns the system and makes
it available to users, who in return pay a usage fee. A financial institute (bank, lease company) can
be involved to share the risk. The provider retains responsibility for maintenance and repairs, and
users never become owners.
Which model (or mix of elements of various models) is best suited for a project depends on the
specifics. Thus, the financial concept must be planned exactly at the outset, and local features must be
taken into consideration. The model should be selected to fit into the local water and energy markets
and suit users’ standard of living. In any of the models it will always be the matter of selling products
and services in order to fulfill clients’ water (possibly also energy) needs. Table (5.16) provides an
overview of these models, [1].
Table (5.16) Implementation of Financial Models [1]
Cash sales
Capital needed by
the company
little
Consumer
credit
medium
most
medium
Access for users
difficult
without means
little
Medium/hig
Infrastructure
h
required
Not
Credit
Political
necessarily
generally has to
framework
needed,
but be regulated
helpful
21
Credit
institution
low
medium
good
high
Fee
for
service
highest
Lease
high
to
medium
good
high
to
best
high
Possibly
Lease
Concessio
development
contract designs ns to sell
and
water and related tax water
(and
supply aid
issues
energy)
helpful.
Users,
in
Responsibility for some
cases
installation
and dealer
will
maintenance
carry out the
installation
End-User,
(for dealer until
Risk allocation
warranty period
expires)
Users,
possibly
installing
company
Usually the
Initially
Owner
installing
technicians
(company,
company,
from installing public water
possibly users company
supplier)
Distributed
Distributed
Distributed
All
among
all among
all among
all with
parties, highest parties
parties, highest owner
with the dealer
with the lessor
Note must be taken that all of those models assume that the users are paying for water, which not
always is the case. The financial actor may fully or partially take on this responsibility, when dealing
with poor village communities.
22
risk
the
5.5 SOCIAL IMPACTS & ACTORS PARTICIPATION
Social Impacts, [5]
Social aspects have received less consideration than techno-economical ones, even though they are
of considerable importance to the successful and sustainable operation of any technology, but
particularly those in remote areas. For example, membrane technology is prone to membrane fouling
which requires careful management in remote locations. Problems like this can give the technology a
poor reputation which does not reflect on the technology itself, but rather the way it has been
implemented and is managed. Therefore, and in order to be socially sustainable, such technologies
must:
• be accepted by the community,
• meet their water needs, and
• be within their capacity to operate and maintain.
Another general consideration all water resource planners should keep in mind is that the cheapest,
easiest and most environmentally friendly water supply plan always includes demand management and
careful use of naturally available and renewable water resources (rainfall, rivers and renewable
groundwater). A community should resort to desalination only after these options have been exhausted.
The social aspects of desalination technologies should ideally be considered before a new
technology is introduced. This can be carried out by examining the water uses and needs of a
community, the human resources available for the management and operation of desalination unit, and
the response of communities in remote areas [5]. These communities usually have essential services
such as power and water supplied through a community council, which also employs an Essential
Services Officer (ESO) to look after a number of small sites that the broader community to a prototype
of such a unit. A field trip for testing ADS site and installation will provided the opportunity to
investigate these social factors using social science research methods such as small-scale interviews
and surveys, and theoretical insights from the fields of appropriate and sustainable technologies. The
practical application of these theories to the case study can result in an assessment of the prototype’s
suitability, and the identification of strategies to contribute to the successful development and
implementation of ADS units in remote areas.
Table (5.17) summarizes few basic principles in the social sciences that should be kept in mind for
ADS social study, [1].
23
Table (5.17) Basic Principles in the social sciences, [1]
Principle
The sociotechnical
approach
Focus
people
on
Learning
Participati
on,
independence
& autonomy
Process
orientation
Sustainabi
lity
Realism
Discussion
A system can only run optimally when the interdependency and interaction of
people, technologies, and organizations are taken into account. This approach aims to
link the social and technical aspects within the system in order to jointly optimize
them. If users are viewed as an active part of the system, it is much easier to design
the technology adequately.
People affected by the project must be put in the foreground. It means letting them
provide input into important decisions, but also recognizing and respecting their
values, as in such projects people with quite different values often interact. This
becomes easier the more the actors involved identify with the target group. Users
should be included in the planning and design of the project at an early stage.
In order to be able to benefit from new technologies such as RE powered ADS,
people have to learn. The possibility of learning and receiving training has to be
provided at the outset, so that the knowledge gained can be put into practice in a
second step. The sooner those affected are given the opportunity to learn and provided
with resources for this purpose, the greater are the chances that problems can be
remedied and project will be successful.
Users must actively take part in the preparation, design, and implementation of a
project. Any of the actors involved can take the initiative to participate, but
participation does not mean that all of those involved have to take part in all activities
at the same time. The willingness of potential users of installed systems to collaborate
largely depends on the degree of independence they have experienced and the
autonomy permitted. That means that those affected should be able to make decisions
about their lives themselves. They can thus also control where they allow changes to
take place and where they consciously reject innovations.
The general frameworks and conditions for rural water supply change quickly.
Inflexible methods are not able to cover the great variety of needs to ensure the
success of projects. For this reason, procedures should be flexible, which means that
no unified strategies or generally applicable procedures can be drawn up and
recommended for the implementation of projects. Rather, strategies have to be
process oriented to be able to react to changes.
Sustainability means that the actors will support a project after it has been
completed, and the systems will remain in operation. Continuation of the projects
even under changing conditions and in the face of difficulties is especially desirable.
Checks of sustainability are only possible once a project has ended - sometimes only
years later. Factors that influence sustainability have to be detected as early as
possible - at best, during planning and implementation. Sustainability criteria have to
be defined and formulated for each project. All project activities will then address
them and be evaluated based on these criteria at a later date. In this manner, the
degree to which the goals of the project were met can be assessed and quality
improved.
The planned objectives and results should not be too demanding or unrealistic. A
distinction has to be made between the feasible and the desirable. Modest goals can
protect the project and the partners from being overtaxed by excessive expectations.
Realistic project designs require consideration of the conditions for the project. Each
of the countries for which projects are planned has its own reality. Getting to know
this reality and analyzing it should be a central task in preparing the project. Both the
actors and the local population should develop a feeling for the project’s feasibility
alongside the ideal.
5.5.1 Social aspects & Social Sustainability, [5]
As noted above, the technical, economic and environmental aspects of small-scale renewable
powered desalination units have already received considerable attention whilst the social environments
24
for which they are being suggested have been studied less closely. A review of the literature relating to
small-scale desalination units highlights a number of attributes which have been identified as important
contributors to their success and ongoing social sustainability. These can be summarized as the:• capacity of the unit to produce sufficient water quality and quantity to fulfil local needs;
• capacity of the local community to construct (where appropriate), operate and maintain the unit;
• ability of the unit to operate reliably and independently in a decentralized context;
• response of the community to the unit and thus it’s ability to operate with minimal disruption caused
to the local community.
Interestingly, many of these attributes are common to small-scale desalination systems in very
diverse social settings, from rural communities in Egypt [6]
An examination of renewable energy (RE) power supply systems in remote areas should also
provide some insights regarding the social sustainability of such technologies. A review of such
systems in remote Australian communities found that inadequate maintenance support, caused by a
lack of “effective trained personnel to maintain and service RE systems” [5], was a major contributor to
the failure or sub-optimum operation of such systems. The distance of systems from service centers
was also a problem, and a strong influence upon maintenance costs. Responses highlighted that
pastoralists tended to be most concerned about the high costs of renewable energy systems, while
Indigenous communities had concerns about their reliability. Some solutions suggested to these social
issues include training programs for maintenance providers and accreditation for system installers,
education about energy demand management for consumers, and the development of more reliable
systems (hardware).
On the other hand, social sustainability for ADS has to be assessed in the selected remote
area. This will involve examining ADS compatibility with or ability to be adapted to relevant
aspects of the social environment, such as:
• water quality and quantity needs,
• the human resources available to operate and maintain such a unit, and
• the attitudes of community members to a prototype of ADS.
This approach is illustrated schematically in Fig. (5.4).
Social Context
Technology
Unit Performance
Product Water Quality
Concentrate Quality
Maintenance Need
Is ADS
Compatible
with Social
Contexts in
remote site
Water Quality
& Quantity Needs
- Human
Resources
- Response to
ADS
Figure (5.4) Schematic of Approach to Evaluate Social Sustainability
It is worth mentioning here that the concept of appropriate technology has been incorporated in
‘sustainable technologies’, which are defined as those technologies which are “compatible with or
readily adaptable to the natural, economic, technical and social environment”. Sustainable technologies
are no longer limited to applications in developing countries, and expand the environmental and social
focus of appropriate technology to incorporate economic and technical considerations. In The factors
have been highlighted in the literature as playing an important role in the social sustainability of such
small-scale units are identified below. Further work in form of a scoping study is in progress to
complete this list of factors for Central Australian applications.
25
5.5.2 Applied Social Methodology
Two social science research methodologies can be applied. The first is a case study approach using
interviews and site visits is considered to be the best methodology for studying in greater detail the
social aspects of water use and provision in different types of remote settlements. The second
component relates to gathering feedback from community members (community response) about
attitudes to ADS via a questionnaire. Both methods are described in greater detail below.
5.5.2.1
Case study context analysis
The first component of the research relates to determining ADS compatibility with social aspects of
water use. As mentioned above, this requires a consideration of water quality and quantity needs, and
the human resources available to operate and maintain the unit. A case study approach is to be taken,
which involved examining the existing water provision mechanisms and interviewing the person
responsible for the management of the existing water provision system at each site. In all cases this
person had been exposed to ADS by virtue of it having been operated at their site for a period of 2–10
days. They were shown the unit while it was functioning and had an opportunity to ask questions of
engineers working on the project. These respondents were then interviewed about the following items:
• Population at the site
• Main socio-economic activities undertaken at the site
• Existing water system, including the number and quality of bores available and other water sources
• shortfalls they observed in water quality and quantity
• responsibility for water system management, operation, maintenance and financing.
By developing an understanding of these aspects of the water system at each site, an assessment of
ADS’s potential compatibility can be made.
5.5.2.2
Community response to ADS
The second research activity relates to gathering the feedback of a range of people relating to ADS.
As mentioned above, a questionnaire was prepared to gather this feedback. The choice of a
questionnaire rather than interviews was made because questionnaires are simpler to execute and allow
for a greater number of responses to be gathered using fewer resources. The completion of a
questionnaire in private also allows for unbiased information to be gathered by avoiding the
interactions required with an interview, and when they are anonymous can encourage respondents to
give more honest responses.
The topics covered by the questionnaire included the views of respondents regarding:
• their opinions of the combination of desalination and renewable energy (on a scale from poor to
excellent)
• what they liked most about ADS
• what they felt most needed to be improved about ADS
• the situation / location in which they felt ADS would be most useful
• their concerns (if any) about consuming water from ADS
• any other comments they wanted to make about ADS.
By gathering responses to such questions, the community response to ADS can be evaluated, which
will contribute to a determination of its social sustainability.
5.5.3 Actors Participation, [1]
There are different actors (Stakeholders) involved in the ADS installation process . They should be
introduces, pointing out their main interests, influence on the project and possible contributions. A
step-by-step Stakeholder analysis scheme should be used to identify them and analyze their role,
relation to the project.
26
Key stakeholders are those individuals or institutions that may (directly or indirectly, positively or
negatively) affect or be affected by the outcomes of the project. In addition to the main project
management team; (1) Project coordinator, (2) Project partners, and (3) Project Consultants, the other
stakeholder and their interest, influence on the project, and potential contributions is shown in Table
(5.18). In addition, the ‘Informers’, (i.e. ministries, universities, research institutes, consultants,
meteorological stations, utilities) are of particularly important in the site selection process, where data
collection plays a key role.
5.5.4 Stakeholder-Analysis
The following steps are to be taken for the stakeholder analysis, [1],
1. Start with identifying the various stakeholders, who
might be affected by or might affect the project
might become useful project partners
might become conflict partners
will anyway be involved in the project
2. Categorize them according to their role
partner, financial, beneficiaries, supporters, controllers etc.
3. Characterize them from a social and organizational point of view
social and economic characteristics (take gender into account)
structure/organization
status, etc.
4. Analyze them with regard to expectations and relationships
interests and expectations
the links and relationships between the various stakeholder groups
5. Characterize their sensitivity towards and respect to certain issues (gender equality, environment)
6. Asses the potential, resources and capacities of the stakeholders
strengths on which the project could be build up
potential contributions
existing deficiencies
7. Draw conclusions and make recommendations for the project
Table (5.18) Stakeholder and their Relation to the Project, [1]
Stakeholder
Interest
Governments,
ministries or local
authorities
Environmental impacts, costs
of water production, wellbeing
of the community, employment
and
regional
development,
support to R&D
The beneficiary
community
Availability, costs of product
water employment possibilities,
regional
development,
environmental impacts, technical
simplicity,
sustainability,
training
Investors,
financial partners
Minimizing the site related
risks (such as environmental
risks), water selling price, life
time period
Business
Installing
companies,
subcontractors
27
Influence on
the Project
Laws
and
regulations
Potential
contributions
Subsidies, reduced
import duties, tax and
fiscal
incentives,
awareness
raising,
promotion campaigns,
quality control.
User,
acceptance
or
rejection of the
project. CRUICAL
for the success of
the project
Information about
the site, participation in
planning, building and
maintenance, possibly
buying water
Financing
Supply of capital,
Know-how...
Financing
Installation
maintenance of
system
and
the
Land owners
earning money, keeping land
intact,
minimizing
environmental impacts, adhering
to
regulations,
ensuring
sustainability,
Providing
water, need
agree
of
to
Know-how of the
site,
help
in
maintenance
5.6 ADS INSTALLATION AND O & M GUIDE
Once the site, technology, actor's participation and local contacts have been decided, as described in
the previous sections, the specific process of installing and operating the system should be made
according to the following suggested plan:
5.6.1 Selection of Suppliers
5.6.1.1
Tender process
The tender process can be summarized as follows:ADS owner will select a team of specialized persons in the ADS fields to write the tender
documents; tender call specifications & conditions and tender call advertisement in both
English and national (Local) languages
2. The tender call specifications & conditions, should cover
(i)
tender call advertisement,
(ii)
scope of work,
(iii)
civil works, which includes; well digging (if needed) or feed water supply
system, fences, Building / rooms for ADS operation & control panel,
components and spare parts storage, operator & meeting room (if needed), pipes
and electricity connections, entrance advertisement,
(iv)
electro-mechanical works which includes; specification of product water rate &
quality, ADS type (RO, ED, MD, Thermal), Pre & post treatment, Electricity
generating unit (PV, wind), power & water storage tanks sizes, Brine disposal
methods, instruments and control devices,
1.
In all above items; the detailed specifications required should be included.
General Conditions including; place of manufacturer (if needed), Codes to be
used, Guarantee certificates, Letter of credits, training needed, engineering
drawings, Time schedule, Components and equipment catalogs and performance
charts, one or two envelopes (technical & environmental), O&M requirements,
spare parts, training, and general conditions related to local requirements.
(vi)
Payment conditions; down payment and Bank Guarantee letter, periodical
percentage of payment, last payment, delayed payment for devices warrantee,
(vii)
The tender call conditions & specifications may also include introduction about
the ADS owner, introduction about the ADS related project,
The Tender Call Advertisement is a summary of the above Tender call Conditions &
Specification. It also include the closing date (and hour) and address of submission. This
advertisement
(v)
3.
Appendix (A) shows a Typical Tender call conditions & Specification for small
Thermal ADS unit to be installed In Egypt.
4.
The Tender Call Advertisement should be advertised in well known and local news paper,
international ADS magazine(s), the project and ADS owner web sites. Direct e-mail or mail /
fax, telephone calls to companies in the field may help spreading the advertisement as well as
clarifying all inquires from interested companies.
28
5.6.1.2
Offers Analysis
At the tender call closing date, hour & place, the selected ADS team will receive the company's both
technical and financial offers (in two separate envelops). At the closing hour, the team leader will
receive the offers (at least three offers should be received otherwise the call may be repeated – unless
there is only less than three companies produce this type of ADS required).
The technical offers will be opened one by one, in front of all companies' representatives, and the
detailed received documents from each offer are written in official minutes. The financial offers will be
sealed and kept with ASD owner. The team, team leader and the companies representatives will sign
the minutes. The team leader announces the date of opening the financial offers, after a suitable time
for reviewing the technical offers.
The ADS team leader will distribute copies of the technical offers to the reviewing and team for
evaluation. Each has to check if the received documents satisfy the tender call conditions &
specifications. If some parts are not clear, official letters clarifications will be sent to the respected
company through the team leader.
The offers which agree with the tender call conditions & specifications will be technically evaluated
with prioritization criterion. Each criterion will be give a marking value (weight) or percentage. These
values will be added and the total represents the offer total technical value. In addition to the direct
contacts between the members, more than one meeting ma be needed for ADS reviewing team for
discussion of the offers details and clarifications. However, the evaluation will be separate. In the last
meeting, all evaluations will be compiled into one sheet where the average of the reviewers will be
calculated. The offers will then be ranked based on the top down numbers or percentage. Examples of
the criterion for selection of tenders are given in Table (5.19).
After the technical offers are evaluated and marked, the ADS evaluation team leader will contact the
companies to confirm the financial offers opening date. At that date, the sealed financial offers will be
brought and opened in the presence of the company’s representatives. The financial offers total costs as
well as cost break downs will be tabulated. The minutes of this opening activity (including the financial
offers table(s), will be written, signed by the ADS team members and the companies’ representatives.
ADS team will meet to review evaluate and discuss the financial offers. Some criterion may be put
for the evaluation including; the total financial offer, the break down, the equivalent values the local
currency (or unified currency), Taxes, Customs, and other conditions.
29
Table (5.19) Examples of the criterion for selection of tenders
General
Mechanica
l Works
1
Previous Experience
2
Financial Stand
Materials
Used
3
ADS Schedule
Submerged
Pump
4
Engineering Drawings
Connecting
Pipes
5
PW specification
Electrica
l Works
ADS design
Motors
Operation
& Protection
Panel
Electricit
y Generation
Unit
Storage
Batteries
Auxiliaries
Materials
Used
Instrument
ation
& Control
Measuring
Devices
Monitoring
&
Data
Records
Civil
Works
Fences and
its Ancillaries
Water Well
Tanks and
its Ancillaries
Building
and
its
Ancillaries
Advertising
Panel
6
7
8
9
1
ADS Technology
ADS Performance
Environmental Impact
Manufacturer Origin
Maintenance & Spare
0
Parts
1
Future Extension
1
1
Training
2
1
Equipment Guarantee
3
5.6.1.3
Selection of Bidder(s)
Bidders financial offers are ranked in top-down order. In general, If all technical offers are accepted,
the lowest financial offer will be chosen as the selected one. However, there may be a strong reason(s)
put another offer to the top even if it is not the least cost. An example for this case, in some countries
there may be a national law that support national companies and give them privilege over the foreign
companies. Egyptian law, for example, gives privilege to national companies over foreign companies if
the national company’s offer is within 15 % higher than the foreign companies.
After through discussion of the ADS team, the final decision will be taken, written and signed by the
team. ADS team leader will inform the ADS owner or the funding authority of the team decision. Once
he gets their approval, the team leader (or the owner / authorized person) will officially inform all
bidders with the final decision. Their should be one winner and one or two (in order) as standby.
It should be indicated that all theses activities should be well documented, signed by those who have
to sign, informed by all to be informed. Local, national and international authorities might need to
review these documents.
5.6.2 Bid Finalization & Contacting
After the bidder has been selected, a series of technical meetings will be carried out, between ADS
team and the wining bidder (contractor), in order to discuss in details of the final design, schedule, bill
of quantities, and make the necessary action plan. Technical discussions may include new ideas to
30
improve the proposed design from the supplier to be adapted to the local conditions. Visits to the site
and suppliers will be needed at this stage to finalize the design and select out of alternatives (if needed).
Adjustment of the technical drawings, some design re-calculations might also be needed at this stage.
The updated design might need schedule and technical drawing updating. All should be approved by
both the ADS owner and contractor.
A draft of the contract is written (either in English or local language or both). The contract will be
reviewed, updated and finalized by both parties (ADS owner & contractor). The contract will identify
the role of both parties. For the contractor; the equipment delivery, installation, testing, unit overall
commissioning, O & M, staff training and documents to submit (such as Bank guarantee, catalogs,
equipment specifications, …etc). For ADS owner, the payment schedule, supervision, etc.). Two
originals of the contract are signed and stamped by both parties. One copy is kept with each party.
5.6.3 Local Actions
ADS owner should contact local and national authorities for different permits to install the ADS
unit. Permits includes the well digging, construction of civil works, use of sea water & intake system,
brine disposal to sea or to under ground, possible electrical power connection to net work, …etc.
Contacts to ministries of water, environment and energy as well as local city councils, governorate
staff, local NGO(s) and local community heads should be carried out.
Figure (5.1) Signing A Protocol of Agreement Between ADS Owner & Local Authorities
It will be advisable if the ADS owner sign a protocol of cooperation (or similar agreement with local
/ national authorities) and get them involved as part of the process. Figure (5.1) shows a signing a
protocol of cooperation between ADIRA –ADS partner and the Head of West Coast Development
Authority and the local governorate.
5.6.4 ADS Installation & Commissioning, [11]
5.6.4.1
Transport and Local Delivery
As per the contact (agreement between contractor & ADS owner), and according to the scheduled,
the contractor starts his civil works, the transportation of equipment from the manufacturer site to the
ADS site. Some equipment might be locally available or manufactured and others may be imported. All
these should be taken into account in the project schedule. Appendix (B)shows a proposed schedule for
a small ADS system.
In general, there are many of the ADS components has to be delivered from EU countries. These
components have to be shipped to the site under the supervision of the contractor. This shipment
container may contain ADS main components ( as the solar collectors and support structure, distillation
module components, PV panels, RO or Distillation membranes,…etc) in addition to instrumentation &
control devices ( data acquisition devices and sensors and some of the controlling devices). Upon the
container arrival, it will be transported to the site. Cautions have to be taken during these processes
specially for handling sensitive devices and components. The contractor organizes and carries out the
transport of the container from port to the site.
5.6.4.2
Preparation of ADS Set-up;
A preliminary meeting for ADS installation team and the contractor to discuss the steps to be
performed and the action plan to take place. Within this meeting all scheduled tasks should be
discussed and the selection of components to be imported or locally supplied to be defined and
31
finalized. The meeting should also address the feed water source ( directly from sea, taken from an
existing or newly beach well at the site, …etc.). The quality of the water had to be analyzed and the
results provided to all parties specially the ADS manufacturing company to readjust the system design
accordingly. Similarly, the supporting systems (as the cooling water for the thermal distillation unit),
the water & energy consumption for pumping and the different solution and alternatives proposed
within the scope of the project should be addressed.
The organization of the set-up of the components and the necessary work for preparation should be
discussed with the project contractor. This includes piping plans for the complete installation, the
foundations of the components, the construction & installation of water tanks (feed, product & brine),
the controlling components (as far as possible, standard components with no or low energy
consumption to be used with some of the features to be modified and adapted to the needs of ADS
installation), the measuring devices and data acquisition system.
The site preparation; (i) pavement of the land & the concrete foundations and fences, (ii)
construction of labor, storage and control panel room(s) and other civil works, (iii) water connection
for feed water supply and brine disposal, (iv) water tanks insulation if needed, (v) electrical connection
for the pumps and data acquisition system, and other components.
The set-up could be very well supported by local authorities and community. In dealing with
difficulties and unexpected problems, local authorities & NGOs will assist ADS team admirably. The
set-up should be performed in very close collaboration with these parties, and a helping hand missing
somewhere to be made available in an easy and co-operative atmosphere.
5.6.4.3
ADS Commissioning
The set-up and start of operation of the ADS will take place once the unit's components arrive to the
site. The installation of the measuring devices, controlling equipment and the co-ordination of the setup work is carried out by the contractor under the supervision of the ADS installation team. Some
amendments to the set-up to improve the performance may be needed. Installed the ADS followed by
the system start-up. The plant is then set into commissioning stage of operation.
It might take few days to reach steady state operating conditions (as heat up the storage tank in
thermal unit). Afterwards the parameters of the control devices are to be determined and adapted to the
operating conditions. After a first period in which the system is left to equilibrate, the system well be
investigated again.
The data acquisition equipment should be monitored to run reasonably well. In the demonstration
plants, the measured data is stored through online measurement channels. This includes; (i) Thermal
system temperatures (ADS loop, mixing unit, storage tank, distillation unit); (ii) volumetric flows
(ADS loop, storage output, heat exchanger inlet, distillate production); (iii) ambient temperature; (iv)
wind speed; (v) solar irradiation on collector area; (vi) conductivity of distillate, (vii) electrical power
generated from PV panels & wind mill units.
32
5.6.5 ADS Operating
5.6.5.1
Monitoring ADS Operation Condition
Starting from the day of installation, a regular transfer of measuring data has to be performed. At the
start of the period, several problems (as the stability of the electricity supply) may prevent continuous
operation. These and similar problems will be overcome by specialized operation staff. The acquired
data has to be regularly evaluated and in very close co-operation between operator, contractor & ADS
team, the results of the evaluation have to be used to optimize the operation strategy of the whole
system.
5.6.5.2
Evaluation & Supervision
In order to assure that the system is sustainable in social, ecological and economic regards, ADS
project has to be continuously evaluated. This will assess building up expertise and collect additional
arguments for the introduction of ADS. The projects should be evaluated systematically using
qualitative and quantitative methodology. Usually the operators carry the responsibility for evaluation
and to react to problems with measures to optimize or to enlarge the system performance and economy.
However, from a scientific point of view it can also be done by external members of a project team.
5.6.5.3
Changes in operation mode
Several unexpected operational handicaps caused the need for changes in the operation strategy as it
was planned before set-up of the system. Example of this could be a windshield is be fixed around the
ADS unit in order to decrease wind losses from the solar collectors in thermal system, and fix
insulation on the pipes. Another example for ADIRA solar stills units in Egypt, It was observed during
testing similar solar stills, Figure (5.2) that the product water and brine temperature are 5-15 C above
the feed water. A system for energy recovery was proposed to improve the still performance.
Figure (5.2) Testing and Improving still efficiency through the recovery of lost energy
With product water and brine
5.6.5.4
Hand over and withdrawal
If an outside entity (such as scientists or NGOs) initiates the implementation of an ADS and they do
not plan to operate it for themselves, the hand over to the further operator and the withdrawal of this
organization from the project has to be planned thoroughly. Apart from securing suitable mechanisms
of organization and for financing, they should provide long term support and technical assistance to the
community and/or the operator.
Appendix (C), [3], summarizes typical operational experiences & lessons learned from selected
ADS applications.
5.6.6 ADS Maintenance, [10]
5.6.6.1
Introduction
There are many problems involved that arises from coupling a desalination plant to a renewable
energy source. Each desalination system has specific problems when it is connected to a variable power
system, [1]. For example;
33
-
-
RO system has to cope with the sensitivity of the membrane regarding fouling, scaling as well as
unpredictable phenomena due to start-stop cycle and partial load operation during periods of
oscillating power supply
The VC system has considerable thermal inertia and needs to consume a great deal of energy to get
to normal working point.
ED system has the same problems as RO about the sensitivity of membranes regarding scaling and
fouling and is not able to desalt seawater.
The performance of the ADS unit should assure to be very satisfactory, nearly as designed. Looking
at the data, the low performance of the ADS concept may indicate the failure or malfunction of
component(s). The ADS unit may be opened, therefore, to check the major points of maintenance
referring to the former experience. There are two types of maintenance; (a) preventive maintenance and
(b) predictive maintenance. These two types will be discussed below for a typical ADS component;
pumps, while Appendix (D) summarizes the maintenance needed for some ADS components
5.6.6.2
Preventive maintenance
Preventive maintenance aims at preventing unscheduled equipment failure. Depending on the
circumstances, an unscheduled failure will be very inconvenient and can be extremely costly. A
successful program of preventive and routine maintenance will reduce equipment failures, extend the
life of the equipment, and reduce the overall operating costs. The preventive maintenance should be
carried out per the manufacturer’s recommendations. This includes; daily visual inspection of the
various parts, monthly check lubrication of bearings (if any), monthly check of packing and seals for
wear (the first sign of wear is a loss of the pressure and eventually water leaks), motor and pump
alignment for proper torque transfer, and pump mounting. Example of preventive maintenance of
plunger pump is shown in Table (5.20).
34
Table (5.20) Example of preventive maintenance of plunger pump, [10]
Frequency
Oil level
Oil leaks
Water leaks
Belt/pulley
Pluming
Initial
oil
change
Oil change
Seal change
Valve change
accessories
d
aily



Wee
kly
50
hrs
500
hrs
1500
hrs
3000
hrs







A thorough maintenance inspection should be scheduled annually and may include; cleaning of the
pumps, check (replacement) of bearings and drive belts for indirectly coupled pumps, annual
inspection of motor( temperature and vibration)
Detecting wear in the early stages can reduce repair costs and downtime. Prolonged operation with
worn parts can result in costly repairs. Wear parts, such as shaft seals, bearings, and casing wear rings
have defined service lives and should therefore be replaced per the manufacturer’s recommendations.
5.6.6.3
Predictive maintenance:
Predictive Maintenance (PDM) can also be performed. Maintenance is scheduled based on the
analysis of data collected during the monitoring of the condition of the pump, not necessarily on any set
maintenance program. This requires close monitoring of the pumps performance, noise, vibrations, and
temperature of the motor.

Overheating of motors is a sign of bad bearings, mechanical overload (plugged
pump outlet or locked rotor), or insulation failure in the motor windings.

Leakage of water is a sign that the mechanical needs replacement.

Noise is an indication of cavitations, rubbing and bad bearings

Vibration – is an indication the beginning of a failure
35
5.6.7 O&M Staff Training, [9]
At each site, the responsibility for the ADS lays with either the site manager and/or operator(s).
They will carry out the day-to-day operation and maintenance of the system and call specialists when a
greater level of expertise is required. These people should have a good level of knowledge about ADS
unit's system, components and water/energy storage. There is a necessity to train them to be able to
cope with the requirements the system poses on them, [9].The over all aims of the training are to;
- ensure long lasting operation of the ADS,
- increase user satisfaction,
- prevent or minimize problems arising from inappropriate use and wrong expectations,
- react to arising problems in a competent way.
For the process of training several steps have to be carried out in order to make sure each O&M staff
member receives the kind of training s/he needs to ensure the sustainability of the system, i.e., training
will be different (adapted) to each member to be trained. The design of the training process consists of
the following steps:
1. Situation Analysis
2. Training Needs Assessment for each group of trainees
3. Planning of the training for each group of trainees
4. Realization
5. Evaluation of the training
Table (5-21) Training Checklist, [9]
Who
What
Who are the stakeholders that are involved with the ADS? What is their role
concerning the project and the long-term sustainability of the ADU (e.g.
operation and maintenance, administration, use etc.)?
Which are the goals of the project and how can they be supported by training?
What kind of problems can arise in the course of the project and which of them
can be addressed or prevented by training?
When
How
By whom
Where
Evaluation
Resources
needed?
Training Schedule: At which stage of planning and installation? Before, while
or after?
Methodology?
Trainers?
Location? Timing? Can everyone reach this location? Is there enough space?
Indicators, methods, time of sampling?
Financial resources? Time? Knowledge and qualification of the trainers?
Material? What is needed? What is available?
For each step the social and economic aspects of all kinds of trainees have to be considered as well
as the technical requirements of the ADS unit. A checklist was propose, [9], with important questions
that have to be asked in order to develop a training that helps to bridge the gaps between people and
technology optimally, Table (5.21). An example of training contents can be found in Table (5-22).
Training will be carried out in class rooms (knowledge), workshop (skills) in addition to the On the
Job Training (OJT). It is important to realize that training is a process which has to be repeated
continuously.
Table (5.22) Example training contents for end users
36
General
Information about
the benefits of the
ADU
Organisational
Information:
Technical
Information
Quality, quantity
and availability of
water
and
restrictions of the
ADU
The wise use of
water
Payment
- Drinking clean water protects family members from sickness
- Accessible safe water saves women's and kid’s time, improves welfare of
women and provides
more time for family care or income-producing activities.
- The renewable energy source reduces costs and enhances sustainability
It also has to be made clear that:
- Improved water supply will only lead to benefits if linked with proper use
- the community must assume responsibility for the ADS
- Water is precious and is worth paying
- the general organization of the ADS
- ownership and responsibility.
- Role of the key person/guard/caretaker
- Amount of water available for every household
- Distribution among the households and persons responsible for the
distribution and controls
- Components of the ADUS: e.g. the desalination unit and its most important
features; the renewable energy source and it’s most important features (e.g. the
solar panel, the battery ); displays informing about the state of the water supply
- Use of the ADS: e.g. the steps to withdraw the water from the system; pre
treatment and post treatment; what kind of problems can arise from
inappropriate use; how to determine whether there is enough water in the tank;
dangers such as high pressure in the RO-Unit
- Maintenance and Monitoring: e.g. flushing operation to clean the
membrane, the regular cleaning of the PV-Module, the cleaning of taps or the
removal of brine; who to contact in case of problems and how
The restrictions in the use of water have to be explained thoroughly and it
has to be made sure that every user accepts these in order to prevent
disappointment.
- The water has a very high quality, but if it stays in the tank too long,
bacteria can grow
- The amount of water that is produced per day is restricted.
- If there is no wind/no sun, no water can be produced.
- The ADS produces a noise that might be disturbing
The water produced by the ADS is likely to be still a scarce resource and the
users have to be made aware of that. It is important that they do understand that
they must not waste this.
- The wise use of water: ways of saving water and ways of keeping the water
clean; suitable and
unsuitable uses of water.
- how costs arise and modes of payment
37
5.7 REFERENCES
[1] Vicente J. Subiela et. Al. "Installation Guide Lines for ADIRA Project", ADIRA internal Project,
June (2005)
[2] S. Loupasis, "Technical analysis of existing RES desalination schemes – RE Driven Desalination
Systems REDDES", Report, Contract # 4.1030 / Z /01-081 / 2001, May (2002)
[3] CRES et. al., "Desalination Guide using RE", (2000)
[4] P. G. Soldatos, . Mohamed and D. Assimakis, " Autonomous Desalination Systems
(ADS) Sizing and Cost Analysis: Methodology", ADIRA document under preparation, AUA,
Greece (2007).
[5] M. Werner and A. I. Schafer " Social aspects of a solar powered desalination unit for remote
Australian communities", Desalination 203, 375–393 (2007)
[6] H.E.S. Fath, F.M. El-Shall, G. Vogt and U. Seibert, "A stand alone complex for the production
of water, food, electrical power and salts for the sustainable development of small communities in
remote areas", Desalination, 183 (2005) 13–22.
[7] UNESCO, " RE powered desalination systems in the Mediterranean region", April (2000)
[8] J. A. Carta, J. Gonzalez, and V Subiela, " The SDAWES project: an ambitious R & D prototype
for wind powered desalination:, Desalination 161, 33–48 (2004)
[9] Co-ordination Action for Autonomous Desalination Units Based on Renewable Energy Systems
(ADU-RES): GUIDELINES", WP 6 - Deliverable 6.2, Co-ordinated by Fraunhofer ISE, INCO –CT2004-50 90 93, May (2006).
[10] Co-ordination Action for Autonomous Desalination Units Based on Renewable Energy
Systems (ADU-RES): GUIDELINES", WP 4 – Technical Report on Cost Reduction Strategy, INCO –
CT-2004-50 90 93, Nov. (2005).
[11] H. Müller-Holst, "SMALL SCALE THERMAL WATER DESALINATION SYSTEM USING
SOLAR ENERGY OR WASTE HEAT", MEDRC Series of R&D Reports, MEDRC Project: 97-AS024b, April (2001)
38
Appendix (A)
ADS Technology Selection
Table (A.1) Evaluation of the various RES - desalination options, [3] & [4]
Water
Quantity
Output(2)(3)
Inpu
Bracki (2)potable
t (1)
low
sh
Reqs
Resource
solar
availability
medium
large
Bracki
potable
low
wind
distillate
most applicable
PV - ED
PV - RO
PV - ED
limited experience
because of high cost of PVs only recommended for
quantities of output water
PV - RO
PV - ED
because of high cost of PVs only recommended for
quantities of output water
medium
Wind - RO
Wind - ED
most applicable
large
Wind - RO
Wind - ED
low
solar
medium
low
Solar Still
wind
most applicable
MED not recommended for brackish water
desalination, not used for low quantities of output water
Solar thermal - MSF
MSF not recommended for brackish water
desalination, not used for low quantities of output water
high cost due to large land requirements
Solar thermal - MED
Solar thermal - MSF
MED not recommended for brackish water
desalination
MSF not recommended for brackish water
desalination, not used for low quantities of output water
Solar Still
Solar thermal - MED
Solar thermal - MSF
significant large land requirements
MED not recommended for brackish water
desalination
MSF not recommended for brackish water
MVC not used for low quantities of output water,
desalination
not recommended for brackish water desalination
Wind - MVC
sh
medium
large
not recommended because of high storage costs of
autonomous wind energy systems
Solar thermal - MED
Solar Still
large
distillate
Remarks on technology applicability
most applicable
sh
Bracki
Desalination
feasible
Wind - RO
Wind - ED
sh
Bracki
REStechnically
PV - RO
Technology
Wind - MVC
Wind - MVC
39
MVC not
desalination
MVC not
desalination
recommended
recommended
for
for
brackish
brackish
water
water
35
Table (C.1) Evaluation of the various RES - desalination options, [3] &[4]
Water
Quantity
Output Reqs (3)
Input
Brackis
distillate
(1)
(2)
h
low
Resource
geothermal
availability
medium
RESDesalination
technically
feasible
Remarks on technology applicability
Geothermal - MED
MED, MSF- not used for low quantities of output water, not recommended
Technology
Geothermal - MSF
for brackish water desalination
Geothermal - MED
Geothermal MSF
large
Sea
water
potable
low
solar
medium
large
Sea
water
potable
low
medium
wind
MED not recommended for brackish water desalination
MSF not recommended for brackish water desalination and for low quantities
of output water
Geothermal - MED
Geothermal - MSF
MED, MSF not recommended for brackish water
desalination
PV - RO
most applicable
PV - ED
ED not recommended for sea water desalination due
to high energy requirements
PV - RO
because of high cost of PVs only recommended for low
quantities of output water
PV - ED
ED not recommended for sea water desalination due
to high energy requirements
PV - RO
because of high cost of PVs only recommended for low
quantities of output water
PV - ED
ED not recommended for sea water desalination due
to high energy requirements
Wind - RO
most applicable
Wind - ED
ED not recommended for sea water desalination due
to high energy requirements
Wind - RO
most applicable
Wind - ED
ED not recommended for sea water desalination due
to high energy requirements
Wind - RO
not recommended because of high storage costs of
autonomous wind energy systems
large
Wind - ED
not recommended for sea water desalination due to
high energy requirements and high storage costs of autonomous wind
energy systems
40
Table (C.1) Evaluation of the various RES - desalination options, [3] & [4]
Water
Quantity
Output Reqs (3)
Input
Sea
distillate
(1)
(2)
water
Sea
water
distillate
Sea
water
distillate
low
Resource
solar
availability
RESDesalination
technically
feasible
Solar Still
Technology
Remarks on technology applicability
most applicable
medium
Solar thermal - MED
Solar thermal MSF
Solar Still
MED not used for low quantities or output water
MSF not used for low quantities of output water
high cost due to large land requirements
large
Solar thermal - MED
Solar thermal - MSF
Solar Still
most applicable
MSF not used for low quantities of output water
high cost due to large land requirements
Solar thermal - MED
Solar thermal - MSF
most applicable
Wind - MVC
Wind - MVC
Wind - MVC
Geothermal - MED
Geothermal - MSF
MVC not used for low quantities of output water,
most applicable
most applicable
MED, MSF not used for low quantities of output water
medium
Geothermal - MED
most applicable
large
Geothermal - MSF
Geothermal - MED
MSF not used for low quantities of output water
most applicable
low
medium
large
low
wind
geothermal
Geothermal - MSF
3
(1) Brackish water: 3000- 11 000 ppm TDS, sea water: 35 000 ppm TDS
(2) potable: 250- 700 ppm TDS, distillate: < 20 ppm TDS
3
3
3
(3) low: 1-50 m / d, medium: 50- 250 m /d, large:> 250 m /d
41
Appendix (5.B)
Desalination Technologies
Table (B.1) Thermal Desalination Process
Multiple-stage flash distillation
Process
Multiple stage flash (MSF) distillation is the most widely used desalination process, in terms of capacity. The performance ratio
Description
(mass of distillate produced per unit mass of steam consumed) is an important parameter used for gauging the performance of a
plant. A performance ratio of 8-10 is the practical upper limit for this type of plant.
An MSF plant can contain from 4 up to 40 stages. Increasing the number of stages reduces the heat transfer surface that is
required, reducing the capital cost. This has to be offset against the cost of providing extra stages. Complicated optimization
calculations have to be undertaken where the main parameters are capital cost versus operating cost. MSF plants usually operate at
top brine temperatures of between 90-120 C, depending on the feed water treatment. Operation at higher temperatures than 120 C is
not workable because of problems of scale deposition in the brine heater. Looking for methods to increase TBT (new anti scalant or
Nano Filtration) or the flashing range will increase the system performance, productivity and, therefore, water production cost.
The advantages of the “ brine recirculation” configuration are that the sea water pre-treated is in the order of only one third of the
once-through design. However, new configurations as mixed and brine recirculation with higher make-up rate (up to once through)
are considered for future developments. The majority of the tube bundles work with de-aerated brine water with lower corrosion
and the in-condensable gases released are reduced thus achieving higher efficiency of the stages. In general, MSF plants are
relatively easy to operate. Special attention is required in order to avoid scaling and corrosion of materials. With the appropriate
maintenance, modern plants can operate with long intervals between shutdowns. Life spans of up to 40 years are now being
predicted for large plants in the Arabian Gulf area.
Technology
deployment
MSF distillation process has played a vital role in the provision of water in many areas, particularly in the Middle East. The
installed capacity of the process has grown considerably over the last twenty-five years.
MSF has been developed and adapted to large-scale applications, usually greater than 5000 m3/d. At present, the largest MSF
plant, contracted or in operation is of 60 000 m3/d product water capacity. Plans for 75,000 – 100,000 m3/d are under consideration.
The process is widely used in the Gulf countries with 75% of the global total installed capacity. In Europe the MSF process is
mainly used in Italy and in Spain.
Manufacturing
Concerning manufacturing, Japanese and Korean manufacturers produce 45% of the world production of the MSF plants.
European manufacturers produce 43% of the total production and the USA 8% .
42
Economics
The capital cost as well as the energy cost of an MSF plant are significant (see Table 5.10). The main energy requirement is
thermal energy. Electricity demand is low and is used for auxiliary services such as pumps, dosifiers, vacuum ejectors, etc. For
instance, for a plant that operates at a performance ratio equal to 8 the thermal energy consumption is around 290 kJ/kg of produced
water while the electricity consumption can be ranged from 4 to 6 kWh/m3, (see Table 5.11).
Multiple effect distillation
Process
Description
Multiple effect distillation (MED or ME or MEE) was the first process used for seawater desalination. It is widely used in the
chemical industry where the process was originally developed. The MED process is similar to the MSF process since it also
operates in part by flashing, however, the majority of the distillate is produced by boiling.
Most of the new MED plants have been built around the concept of operating at lower temperatures. Some of the more recent
plants have been built to operate with top temperatures (in the first effect) around 70 C reducing the potential for scaling within the
plant. MED plants tend to have smaller number of effects than MSF stages. Usually 8-16 effects are used in typical large plants, due
to the relation of the number of effects with the performance ratio (which cannot exceed the number of effects of the plant). As in an
MSF plant, special attention is required concerning the operating temperature to avoid scaling and corrosion of materials. Also,
extra care is required concerning the control of the brine level in each effect.
Technology
deployment
MED has been widely used for industrial applications (e.g. for sugar production by juice distillation) and for salt production by
seawater distillation. Some of the early water distillation plants used the MED process, but this process was displaced by the MSF
units because of cost factors, fewer operating problems, and their apparent higher efficiency. However, interest in the MED process
has increased and a number of new designs have been developed. MED units of more than 5000 m/d in capacity have been
constructed. However, small single and multiple effect units are more common.
MED process is primarily used in the former USSR, which accounts 39% of the global MED installed capacity, 10% in the
Caribbean islands, 7.2% in USA, and 12.7% in Europe.
Manufacturing
A number of European companies are developing innovative MED designs which offer lower energy consumptions than
conventional MSF. The desalination market is particularly conservative and there is a reluctance to move from the well-proven
MSF design.
43
Economics
The cost of an MED plant heavily depends on the performance ratio. Capital and energy costs are significant factors, (see Table
5.10). The main energy requirement is thermal energy. For a plant operating with a performance ratio equal to 8 the thermal energy
consumption is around 290 kJ/kg of produced water. Electrical energy demand is low around 2.5-3 kWh/m3 (see Table 5.11).
Vapor compression
Process Description
There exist two vapor compressor (VC) processes. The first configuration is mechanical vapor compression (MVC), in
which a mechanical compressor is used. The second, is thermal vapor compression (TVC), in which a thermo compressor or
ejector is used to increase the vapor's pressure. Both types are widely used.
The fundamental concept of this process is inherently simple, in that after vapor has been produced it is then compressed
to increase its pressure and consequently its saturation temperature before it is returned to the evaporator as the heating
vapour for the evaporation of more liquid.
Technology
Deployment
Vapor compression plants have been in use since the end of the 19th century. The vapor compression process is usually
used for small and medium scale water desalination units in a range of 20-2500 m3/d. Many applications for this process
have been found. Because of its compactness, ease of operation and transportability, military versions have been developed.
The process is mainly used in Western countries. 20% of the total installed capacity is in USA, 13% in the Middle East,
and 22% in Europe.
Manufacturing
Concerning VC manufacturing, 48% of the capacity was sold by European companies, 32% by US companies and 18% by
an Israeli company.
Economics
Capital and energy costs are significant factors in the determination of the total water production cost. The energy demand
mainly required to drive the vapour compressor motor. Its operation and maintenance sometimes covers half of the total
operating and maintenance cost.
However, the energy requirements of VC plants have been reduced (from 20 kWh/m3) and currently range between 8 to
12 kWh/m3 - with the potential for further reduction.
44
Table (B.2) Membrane Desalination Process
Reverse osmosis
Technology
Description
Reverse osmosis (RO) is the most widely used process for seawater desalination. RO process involves the
forced passage of water through a membrane against the natural osmotic pressure to accomplish separation
of water and ions.
A typical RO system consists of four major subsystems; pre-treatment system, high pressure pump,
membrane modules, post-treatment system
Feed water pre-treatment is a critical factor in the operation of an RO system due to membranes sensitivity
to fouling. Pre-treatment commonly includes feed water sterilization, filtration and addition of chemicals in
order to prevent scaling and bio-fouling. The post-treatment system consists of sterilization, stabilization and
mineral enrichment of the product water.
The pre-treated feed water is forced by a high-pressure pump to flow across the membrane surface. RO
operating pressure varies from 17-27 bar for brackish water and from 55-82 bar for sea water. Part of the
feed water, the product or permeate water, passes through the membrane, removing from it the majority of
the dissolved solids. The remainder together with the rejected salts emerges from the membrane modules at
high pressure, as a concentrated reject stream (brine). In large plants the reject brine pressure energy is
recovered by a turbine, recovering from 20% up to 40% of the consumed energy.
Two types of RO membranes are used commercially. These are the spiral wound (SW) membranes and
the hollow fiber (HF) membranes. SW and HF membranes are used to desalt both seawater and brackish
water. The choice between the two is based on factors such as cost, feed water quality and product water
capacity. Now SW is dominated as the only HF company was sold.
Due to the R0 unit operation at ambient temperature, corrosion and scaling problems are diminished in
comparison with distillation processes. However, effective pre-treatment of the feed water is required to
minimize fouling, scaling and membrane degradation. In general, the selection of the proper pre-treatment as
well as the proper membrane maintenance are critical for the efficiency and life of the system
45
A large number of RO plants has been installed for both sea water (SWRO) and brackish water (BWRO)
applications. The process is also widely used in manufacturing, agriculture, food processing and
pharmaceutical industries. 32% of the total RO units installed capacity is found in the USA, 21% in Saudi
Arabia, 8% in Japan, and 8.9% in Europe.
RO units are available in a wide range of capacities due to their modular design. Large plants are made up
of hundreds or thousands of modules which are accommodated in racks. Also, very small units (down to 0.1
m3/d) for marine purposes, for houses or hotels are available.
Manufacturing
The main membranes manufacturers are in USA and Japan. Concerning RO systems manufacturing 23%
are produced in USA, 18.3% in Japan and 12.3% in Europe.
Economics
As a general rule, a seawater RO unit has low capital cost and significant maintenance cost due to the high
cost of the membrane replacement. The cost of the energy used to drive the plant is also significant. The
major energy requirement for reverse osmosis desalination is for pressurizing the feed water. Energy
requirements for SWRO have been reduced to around 5 kWh/m 3 for large units with energy recovery
systems, while for small units this may exceed 15 kWh/m 3. For brackish water desalination the energy
requirement is between 1 to 3 kWh/m3, (see Tables 5.10 & 5.11)..
46
Electro-dialysis
Process
Description
ED is an electrochemical process and a low cost method for the desalination of brackish water. Due to the
dependency of the energy consumption on the feed water salt concentration, the Electro-dialysis process is
not economically attractive for the desalination of seawater.
In electro-dialysis (ED) process, ions are transported through a membrane by an electrical field applied
across the membrane. An ED unit consists of the following basic components; pre-treatment system,
membrane stack, low pressure circulation pump, power supply for direct current (rectifier), post-treatment
The principle of electro-dialysis operation refers to the following, When electrodes are connected to an
outside source of direct current, like a battery, in a container of water, electrical current is carried through the
solution, with the ions tending to migrate to the electrode with the opposite charge. Positively charged ions
migrate to the cathode and negatively charged ions migrate to the anode. If between electrodes a pair of
membranes (cell), anion permeable membrane followed by a cation permeable membrane is placed, then, a
region of low salinity water (product water) will be created between the membranes. Between each pair of
membranes, a spacer sheet is placed in order to permit the water flow along the face of the membrane and to
induce a degree of turbulence. One spacer provides a channel that carries feed (and product water) while the
next carries brine. By this arrangement, concentrated and diluted solutions are created in the spaces between
the alternating membranes.
ED cells can be stacked either horizontally or vertically. In practice, several membrane pairs are used
between a single pair of electrodes, forming an ED stack. Feed water passes simultaneously in parallel paths
through all the cells, providing a continuous flow of product water and brine to come out from the stack.
Stacks on commercial ED plants contain a large number, usually several hundred of cell pairs.
Concerning the maintenance of an ED plant, extra care is required for the feed water pre-treatment to
prevent membrane degradation.
A modification to the basic electro-dialysis process is the reversal electro-dialysis, EDR. An EDR unit
operates on the same general principle as a standard ED plant, except that both, the product and the brine
channels are identical in construction. In this process the polarity of the electrodes changes periodically of
time, reversing the flow through the membranes. This inhibits deposition of inorganic scales and colloidal
substances on the membranes without addition of chemicals to the feed water. This development has
47
enhanced the viability of this process considerably as the process is now self-cleaning. In general, EDR
requires minimum feed water pre-treatment and minimum use of chemicals for membrane cleaning.
Technology
deployment
Electro-dialysis has been in commercial use since 1954, over ten years before RO Since then, this process
has seen widespread applications for a number of purposes, of which the production of potable water is one
of the most important. Due to its modular structure, ED is available in a wide range of sizes, from small
(down to 2 m3/d) up to large product water capacities.
ED is widely used in USA with a 31 % of the total installed capacity. In Europe ED process accounts a
15% while in the Middle East a 23% of the total installed capacity.
The EDR process was developed in the early 1970s. Today, the EDR process is in use in over 30 countries
around the world with 1,100 installations. Typical industrial users of EDR include power plants,
semiconductor manufacturers, pharmaceutical industry, food processors, etc.
Manufacturing
Manufacturing of ED and EDR plants is largely controlled by one company, Ionics of U.S.A. Ionics
company was sold to GE.
Economics
In a general rule electro-dialysis is an economically attractive process for low salinity water. In capital
cost terms, EDR requires some extra equipments (timing controllers, automatic valves etc.), in comparison
with ED, but reduces or almost eliminates the requirement for chemical pretreatment.
In general, the total energy consumption, under ambient temperature conditions and assuming product
water of 500 ppm TDS, would be around 1.5 and 4 kWh/m3 for a feed water of 1500 to 3500 ppm TDS,
respectively. Additionally, pumping energy requirements are minimum.
48
Appendix (C)
ADS Technologies, [4]
Solar thermal ADS plant
Description
Solar thermal distillation plants include a field of solar collectors, where a thermal fluid is heated. This hot fluid, by means of a
heat exchanger, is used to warm up the brine circulating through the distillation plant. The collectors must be able to heat the
thermal fluid up to medium temperatures so that after appropriate heat transfer, the brine fed to the evaporator reaches
temperatures between 70 C and 120 C.
Power
matching
The solar field may comprise flat or parabolic trough collectors, according to the desired temperature in the water. One major
component of the system is some sort of heat accumulator or storage tank, in order to keep the feed water to the required
temperature and compensate for the night hours or the cloudy days. The distillation unit may be either a multistage flash (MSF) or
a multi-effect (ME) evaporator.
The main parameters to be considered in this system are the heat efficiency of solar collection (percentage of solar radiation
received that is used for heating), the solar fraction (percentage of solar energy in the overall energy consumption, when other
energy sources are also used). The performance ratio of the evaporator (water produced per heat supplied) and the auxiliary
electricity consumption are also of interest. Heat rate is sometimes used in this type of plants where heat is provided via hot water
and not from steam.
Operational
features
From the energy point of view, the main supply to the desalination plant is a large thermal input. Like all thermal processes,
distillation demands a high-energy input (due to the energy required for change of phase). Besides, some auxiliary electricity is
also required for pumping (electricity could be produced via photo voltaic).
On the other hand, the solar thermal systems are so much dependent on the radiation (day/night) that some heat storage is
always required. The accumulator may thus become the main subsystem of the plant and the adopted control strategies become of
particular importance.
For MSF evaporators, the performance ratio increases with temperature, so that high temperatures (up to 120 oC) are preferred.
This in turn increases the chances of suffering from scaling and corrosion. MED evaporators operate nowadays at lower
temperatures (around 70 oC) and those hazards are reduced.
Finally, the control of such evaporators must be very accurate, and particularly the flash equilibration in MSF. The system is
unstable in small sizes. This leads to the use of medium and large size evaporators (thousands of m3/day capacity) which do no
49
quite fit with the sizes and capacities usually applied with renewable energies, unless a huge solar field could be built, which in
turn implies large ground surfaces. Therefore, the combination solar thermal - distillation seems best suited for medium and high
production capacities.
In spite of the operational drawbacks, distillation processes have a number of advantages, the most important one being the
high quality of the product water (low salinity, distilled water), which makes those processes particularly suitable when distilled
water is required (for boiler makeup, industry, some particular crops, or even blending with other waters).
Both sides of the combination (energy and desalination) are well developed nowadays as far as equipment is concerned. Solar
collectors and evaporators are available. However the combination is not widespread, and not many examples can be found-, with
high-energy demand and large energy storage requirements being among the reasons.
Cost
According to figures reported in 1996, the capital cost for such a unit, solar thermal - MED of around 80 m3/day, can reach the
value of US$ 2 136 667, including solar field, heat accumulator and evaporator, as well as an auxiliary diesel generator. Operation
and maintenance cost is around 1 Euro/m3. The total water cost being in the area of about 7 Euro/m3.
A projected cost for larger solar thermal - MED units, up to 5000 m3/d, establishes a water cost around 2 Euro/m3.
Applications
Solar thermal distillation applications are “ solar assisted” rather than stand alone, since they all need an electric supply. These
units are perhaps suitable when low enthalpy energy is available (otherwise improperly called waste heat).
There is a relevant example of ME evaporator assisted with solar thermal energy located in Abu Dhabi (United Arab Emirates).
Another example is located at the Platform Solar de Almeria (Spain). More reference cases can be found at S. Luis de la Paz
(Mexico) where a double solar field (194 m2 flat collectors plus 160 m2 concentrating) provide heat for a 10 m3/d MSF unit, with
10 stages. The plant was commissioned in 1980.
Another plant was built at EI Paso by the University of Texas, USA. The combination this time was somewhat unusual
involving a 3355 m2 solar pond and a cogeneration system, producing electricity in a rankine cycle and water in a 24 stage MSF
evaporator capable for 19 m3/d. One more example is found in Italy, again with a solar pond as the energy collection system. The
pond is located since 1988 at Margherita di Savoia (Apulia), with a surface area of 25 000 m2, 5 meters deep, and coupled to an
evaporator capable of producing 10 m3/d distillate. The evaporator operates on the thermal vapor compression principle
(incorporating a steam ejector), although it is also capable of operating as a three effect multi effect unit.
50
Solar PV-RO / ED
Description of
The electricity from PV panels can be used for electro-mechanical devices such as pumps for RO units or in a direct current
the system
(DC) device, for ED units. The main advantage of PV desalination systems is the ability to develop small size desalination plants.
The energy production unit consists of a number of photovoltaic modules, which convert solar into direct current (DC)
electricity. The appropriate desalination processes for this combination should use electricity in some CD or AC form. Therefore,
reverse osmosis (RO) and electro-dialysis (ED) appear as the most suitable choices to be coupled with PV systems.
Reverse osmosis usually uses alternating current (AC) for the pumps, which means that DC/AC inverters have to be used. On
the other hand, ED uses direct current for the electrodes at the cell stack, and hence it can use the energy supply from the PV
panels without major modifications. Yet, some kind of power conditioning is required in this case as well for a typical PV-ED
system design.
Energy storage is again a matter of concern, and batteries are used for PV output power smoothing or for sustaining system
operation when no sufficient solar energy is available.
Operational
features
The main design parameters in this combination are; - solar energy, - PV modules efficiency, - PV installed capacity. Of course
the electricity consumption from the desalination process also plays a major role when assessing the feasibility of this
combination.
An advantageous feature this time is the fact that the process operates at ambient temperature (no hot parts), which reduces
scaling and corrosion. Besides, all required energy can be provided from PV, and no auxiliary supply is required.
The performance of membrane processes is very sensitive to the feed water salinity (product flow and quality). The type of feed
water intake and the feed water pre-treatment are determinant in the performance and operational results of the desalination unit.
However, the membranes usually provide product water with higher salinity than distillation. Finally, electro dialysis is only
available on a commercial basis for brackish water desalination.
Availability and
cost
PV systems and membrane desalination units are available anywhere, and their prices also tend to decrease. Most important,
RO plants are available in small sizes (fractions of m3/h). Small size (compact) PV-RO units to supply water for small villages or
even single houses can be built.
According to published reports the water cost of a PV seawater RO unit ranges from 5.5 to 20 Euro/m3 for product water
capacity of 120 m3/day to 12 m3/day, respectively. Also, for PV-RO brackish water desalination a unit water cost of around 5
51
Euro/m3 for PV-RO systems of 250 m3/day has been reported in the literature. For the same system size and same feed water
salinity a cost of 4 Euro/m3 for PV-ED system has been also reported in the literature.
The water cost is affected, in addition to the unit size, by factors such as; - feed water concentration; - hours of operation; frequency of components replacement; - assumed rate of return, etc.
Applications
The typical PV-RO or PV-ED applications are of the stand-alone type, and there exist some interesting examples. A wellknown case is in Lampedusa, Italy. Other installations have been reported in Egypt and Algeria. The first one is located at EI
Hamrawein, edge of Red Sea, since 1986. The PV array is rated at 19.84 kWp, delivering voltage at 104 V for the pumps as main
consumption, plus a secondary array rated 0.64 kWp at 24 V for instruments and control. The battery storage unit has a capacity of
208 kWh and is designed for three-day autonomy. The RO plant production capacity is 10 m3/h with a brackish water feed 4400
mg/Lit TDS, and operating at 13 bar pressure. Unit energy consumption is 0.89 kWh/m3.
The second is located in Hassi-Khebi, Algeria, running on feed water of 3,200 mg/Lit TDS, and provided with a 2.59 kWp PV
array, featuring a Pelton energy recovery turbine delivering 300 W. The RO plant production is 0.95 m3/h, at 11 bar operating
pressure. Unit consumption this time reaches 1.86 kWh/m3.
In the city of Tanote, in Rajhastan, India, a small plant was commissioned in 1986, featuring a PV system capable of providing
450 Wp in 42 cell pairs. The ED unit includes 3 stages, producing 1 m3/d water, from brackish water 5000 mg/Lit TDS. The unit
energy consumption is 1 kWh/ kg salt removed.
An unusual application is reported from Japan. PV technology is used to drive an ED plant fed with seawater, instead of the
usual brackish water when ED is used. That is because a partially desalinated water storage system is used, depending on the
obtained electric output from the PV cells. The solar field consists of 390 panels with a peak power of 25 kWp, which can drive a
10 m3/d ED unit. The system is located at Oshima Island (Nagasaki) and is operating since 1986. Product water quality is reported
below 400 ppm TDS, and the ED stack is provided with 250 cell pairs.
A small experimental unit was reported in Spencer Valley, New Mexico, USA. Two separate PV arrays are used there: two
tracking flat arrays, 1000 WP power, 120 V, with DC/AC inverters for pumps, plus 3 fixed arrays 2.3 kWp, 50 V for ED supply.
The ED design calls for 2.8 m3/d product water from a feed around 1000 mg/Lit TDS. This particular feed water contains uranium
and radon, apart from alpha particles. Hence an Ion exchange process is required prior to ED. Unit consumption is 0.82 kWh/m3
and the reported cost is 11 065 Euro.
52
Wind - RO / ED / VC
System
A combination that is growing in use is the coupling of wind energy conversion devices and some desalination unit, which can
description
be chosen from a number of alternatives: reverse osmosis, electro-dialysis, and vapor compression.
The selection of the appropriate desalination technology depends on the available feed water quality and the required product
water quality. Membrane systems usually produce water with higher salinity than distillation systems (around 500 ppm TDS the
former, whereas distillation can produce water below 20 ppm TDS). Besides, desalination by ED is usually used for brackish water
(up to around 6000 ppm TDS). In all these alternatives, the energy supply comes from a single wind turbine or a wind farm.
The main characteristic of wind energy systems is the random nature of the wind velocity, which has no predictable variation.
There is no trend or model like the day/night type for solar energy. Hence the amount of energy available is difficult to predict.
Appropriate power control and conditioning systems are required for the matching of the input power to the desalination load.
The power supply must provide alternate current (AC) for RO and VC, while ED requires direct current (DC). Inverters, rectifiers,
and variable frequency devices are used in most designs. Power matching requires some form of energy dissipation or storage
device, hence, in all cases the power control system includes dump loads, or flywheels, or storage in batteries, or their
combinations.
Parameters of special interest for the design include: the wind velocity distribution; the available power distribution; the
desalination unit energy consumption; the feed water salinity. The design of the control system (how the load follows the supply or
inversely) is the most critical and challenging part.
There have been a number of attempts to combine wind energy with RO, ED, or MVC desalination systems. A number of
plants have actually been operated. However, most of them were of small size, mainly for research purposes. Therefore not many
conclusions have been reached in terms of expertise and know how.
It is still difficult to control the usage of wind in a cost effective way. Coupling of a variable energy supply system, as
mentioned earlier, to a desalination unit requires either power or demand management, and there is not much experience on it.
However, the prospects of this combination are high mainly due to the low cost of wind energy. The operational experience
from early demonstration units is expected to contribute to improved designs and a large number commercial systems are expected
to appear in the market place soon.
53
Cost
The experience on wind powered MVC seawater desalination figures out that if the plant runs in a stand-alone mode (between 5
and 12.5 m3 distillate per hour), the mean water cost varies between 3.07 Euro/m3 and 3.73 Euro/m 3.
In another stand-alone wind-diesel desalination system, that includes an MVC desalination plant, the costs reported are: 60
Euro/MWh for the cost of wind energy produced and 1.30 Euro/ m3 for the cost of water produced. It is assumed that 100% of the
wind energy is utilised.
Additionally, according to another published report the water cost of a wind brackish water reverse osmosis unit (large system,
about 250 m3/day) is of the order of 2 Euro/m3 while, for the same feed water salinity and size, the water cost of a windelectrodialysis unit is around 1.5 Euro/m3.
Applications
Two types of applications are usually referred as wind energy and desalination couplings. The first type concerns the coupling
of the wind generator and the desalination plant on a small size autonomous electricity grid. The second concerns the direct
coupling of these two for the sole purpose of production of water.
There has been a number of successful applications of the first type. Small autonomous grids are usually powered by diesel
generators. The larger the size of the local grid (in terms of installed power and minimum load) the easier to implement such a
configuration. If the wind turbine and the desalination plant size are comparable to the size of the local grid, then special controls
are required.
Depending on the relative sizes of wind, desalination and diesel as well as the control applied to it, the system may be
considered as a wind desalination system with diesel backup or as a hybrid system. lf the local grid is big enough and no special
controls are applied to the wind generator or the desalination plant, it is debatable if this constitutes a wind desalination coupling
(in a technical sense).
Systems exhibiting direct coupling of the wind and desalination units are of most interest here because their applicability does
not depend on the existence of a local grid.
Only a few applications are known of combining wind energy with evaporation systems. A pilot plant was installed at the
German island of Borkum in 1991 where a wind turbine with a nominal power 45 kW was coupled to a mechanical vapor
compression (MVC) evaporator in a system capable of desalinating seawater and producing up to 48 m3/d of fresh water. The
compressor required 36 kW power, and the system was controlled by varying the compressor speed, and assisted by a resistance
heating when the compressor run at its speed limit.
54
The experience was followed by another larger plant at the island of Rügen in 1995 [27]. The wind turbine was now rated at
300 kW and the MVC unit at a maximum 12.5 m/h. Again a resistance heating is used for auxiliary power when required. The
energy consumption ranges between 9 and 20 kWh/m3.
The cost for such a system is around 1.48 million Euro. The operation costs were calculated between 3.03 Euro/m3 and 3.69
Euro/m3. If the system is operated on a grid connected basis, the costs would reduce to 2.38 Euro/m3. As regards wind energy and
reverse osmosis combinations, a number of testing units have been designed and tested. As early as 1982, a small system was set
at Ile du Planier, France. A turbine providing 4 kW, coupled to a 0.5 m3/h RO desalination unit. The system was designed to
operate via either a direct coupling or batteries.
Another case where wind energy and reverse osmosis was combined is that of Helgoland, also a German island, in 1988. The
wind turbine in this case was rated at 1.2 MW and used to drive two RO units, 480 m3/day each, with seawater feed. Reports
indicate that some time later the turbine was dismantled, and other supplementary sources were used.
More recently some R&D projects have been carried out, such as the wind desalination system built at Drepanon on a cement
plant, near Patras, Greece. The project, including a 35 kW wind turbine, was initiated in 1992, and completed in 1995. The project
called for full design and construction of the wind generator turbine (blades, etc.), plus installing two RO units with a production
capacity of 5 m3/d and 22 m3/d. Unfortunately, since 1995, operational results have been poor due to the low wind regime.
Currently, only the first RO unit is operating, driven by a diesel engine generator.
A very interesting experience has been carried out at a test facility in Lastours, France where a 5 kW wind turbine provides
energy to a number of batteries (1500 Ah, 24 V), and including a phase inverter. The energy is supplied to an RO unit with 1.8 kW
nominal consumption, and 2.76 kW actual consumption at 60 bar.
The energy consumption is around 20 kWh/m3, which is high according to the standards for a conventional plant. The reason is
the extremely small size of RO unit (140 l/h). Besides, significant maintenance and filtering work is required in such a small unit.
A larger plant (15 kW wind turbine) is planned at Sardinia.
A major project awarded by the European Commission was the so-called PRODESAL (Towards the large scale development of
decentralised water desalination) developed in the island of Tenerife, Spain within the DGXII APAS Programme. The project
included for a 200 kW wind turbine, which would operate on average wind velocity 7.5 m/s, with an expected yearly energy yield
around 600 MWh. This amount of energy is capable of producing over 200 m3/d water.
In order to stand the discontinuous mode of operation, a new reverse osmosis membrane was developed, incorporating
55
advantages of both spiral wound and plate and frame designs. A plunger pump and a Pelton recovery turbine are also used.
Another large project was awarded under JOULE III and is known as SDAWES (Sea water desalination plants connected to an
autonomous wind energy system), carried out at the island of Gran Canaria, Spain. This facility is provided with two 230 kW wind
turbines, and includes three different desalination systems (RO, ED and distillation).
56
Geothermal – distillation
System
description
The most intuitive way of using geothermal energy for water desalination is by applying geothermal heat to a distillation plant. This source is ideal
for the stability of thermal processes. The technology of extracting hot water streams directly from underground aquifers or similar is relatively
mature and well proven.
Concerning MSF operation powered by geothermal heat no application has been reported. MED powered by geothermal energy is preferred due to
the lower energy requirements in comparison with the MSF process. In the case of MED powered by geothermal energy, two different configurations
can be though of:
- geothermal water is fed into the distillator
- heat is removed from the geothermal water to heat up the feed water
The second alternative is preferable, even if it is more expensive, due to the possible high concentration of heavy metals in the geothermal water
and/or due to a social negative reaction to the idea of drinking geothermal water.
Technical problems, mainly related to fouling in the heat exchangers, arise when the geothermal water is above 70 oC or when the salinity is high.
Variation in the chemical composition of the extraction stream can also cause operational problems if the stream is itself being used as the brackish
water source.
Cost
Water costs of less than 1 Euro/m3 are possible, which makes the combination very attractive. Geothermal energy applications tend to be very site
specific and design decisions for one location may not be valid for the other. Common examples are:
- how deep to drill (depth affects temperature which in turn determines the number of effects which can be used in the desalination plant),
- how far to place the well from the sea,
- how long to operate the plant and
- whether to use the geothermal ground water itself as the feed water for the desalination plant in preference to using its heat exchanger to desalinate
sea water.
Concerning geothermal energy - MED coupling, a wide range of pre-feasibility studies have been carried out. Results from studies carried out in
Greece indicate significant potential for commercial exploitation. For example, the use of low enthalpy geothermal energy to power a distillation plant
in Kimolos island which has been studied within the THERMIE Programme (Contr. No GE/00438/94), EC DGXVII. The innovative aspect of the
system is the use of low enthalpy geothermal energy as the heating medium in a vertical tubes MED sea water desalination plant with evaporation
under vacuum, operating on low temperatures (temperature of over 52 C and up to 65 C). The desalination unit is designed to produce up to 150
m3/day of distillate water. The exploitation of low enthalpy geothermal energy in the proposed unit results in the substitution of at least 1000
TOE/year. The produced water cost is estimated of the order of 2.22 US$/m3, (including only annual operation costs).
57
Hybrid systems
System
description
Besides the various combinations between RE and desalination technologies already presented, there are other intermediate
solutions, usually concerning the energy supply side, and including the use of renewable and some conventional fossil fuel. Hybrid
systems seem to be an appropriate power supply for small to medium size desalination loads. Examples are either the combination
of wind energy and a diesel generator or PV plus the diesel generator.
One example of the first type was developed in the Middle East where a wind turbine rated at 11 kW was used to drive a 25
m3/d RO unit, also equipped with a Pelton turbine for energy recovery. The feed is seawater (38 000 to 44 000 mg/l TDS), and the
unit consumption 11 kWh/m3, including feed pumping (1.5 kWh/m3), pre-treatment 2.5 (kWh/m3), the high-pressure pump (6.5
kWh/m3), and post-treatment (0.5 kWh/m3). The energy supply was supplemented with a diesel generator in case of lack of wind.
A more recent example is located at Fuerteventura, Canary Islands, Spain, where a wind turbine and two diesel generators
provide the full energy demand of a small village. Several other examples can be found in the literature.
58
Solar Stlls
Process
Description
Solar distillation (in solar stills) is a process in which the energy of the sun is directly used to evaporate
fresh water from sea or brackish water. The process has been used for many years, usually for small scale
applications. In solar distillation plants the solar radiation is trapped in the solar still by the greenhouse
effect.
Still
A simple solar still consists Solar
of a shallow
basin of brine, Figure (B.1 a), lined with some black material to
get good radiation absorbtivity, and covered by a vapor proof, transparent roof designed to act as a
condenser. The vapor produced by the evaporation of seawater is condensed on the cool surface of the stills’
roof, and the condensate collected as product water. Well-designed units can produce around 2.5 Lit/m2 per
day with a thermal efficiency of 50%. Solar stills are simple in operation and maintenance. The only
maintenance required is the cleaning of the plant, especially of the glass roof.
Other Types of stills, is the wick (Fleece) still, where the absorber is a black cloth (wick) with thin film of
water flow through, Figure (B.1 b). Improving still efficiency requires the recovery of lost energy as
condensation, product water and brine heat.
(a)
(b)
Figure (B.1) Solar Stills
(a) Schematic Diagram of Simple Solar Still (Basin Type) (b) Two Solar Stills in Alexandria University (Egypt)
Technology
deployment
Economics
The main development of this technology was in the 1960s and 1970s, concerning the improvement of the
solar stills efficiency and the reduction of construction cost. Over this period many distillation plants were
constructed around the world. Several small-scale plants have been built in Saudi Arabia, in Greek islands,
etc. However, most of them are not in operation today.
Solar distillation is usually suitable for small-scale applications. In remote areas, where low cost land is
available and solar radiation is high, solar distillation can be viable.
Construction costs as well as large land area requirements are the main parameters in the determination of
the total water cost produced by solar stills. Electricity requirements is only for pumping and are minimum.
59
Membrane Distillation (MD)
Process
Description
MD is relatively new technique implemented in solar-driven stand-alone desalination. It combines advantages of
membrane separation and distillation. Its several important advantages are:
- System efficiency and high product water quality are practically independent of feed water salinity
- Intermittent operation is possible. Unlike with RO membranes, there is no danger of membrane damage if it gets dry
- Chemical pre-treatment in not necessary (MD membranes are tested against fouling and scaling)
Operating temperatures are at levels (60 - 80ºC) at which solar collectors perform well
Heat
Exchang
er
Condenser
Feedwa
Heat
Sourc
e
ter
Distillat
e
Evaporator
Brine
Membrane
Figure (B.2) Membrane Distillation Principles
Peocess
Performance
It has been reported that a very simple compact system with less than 6 m² and without heat storage can produce 120 to
160 L/day of distilled water during a summer day in a southern country [10]. Process simplicity & low maintenance
requirements make MD a very attractive alternative to RO in regions with high solar irradiation.
Figure (B.3) MD Compact System
60
Technical
Wvaluation
MD process have not reached the commercial stage. There are a number of pilot units with different degrees of success.
MD has many advantages over solar stills:
- MD recovers the condensation energy and almost duplicate or triple the yield / m2 of collector area.
- The pre treatment required is much less than RO membrane technology.
- Water quality is similar to distillation processes (Low TDS of order of 5 – 25ppm based on feew water salinity.
- Maintenance required is expected to be less than RO membrane technology
61
Appendix (D)
Maintenance needed for some ADS components, [10]
Component
Pre-treatment
and
feed water system
Maintenance Needed
Maintenance tasks concerning the pre-treatment process consist mainly of checking frequently the level of chemical tanks as well as checking
the filters. Cartridge filters must be replaced when the difference between the output and input pressure is equal to or greater than specified in the
maintenance manuals provided by their manufacturers. Sand filter must be backwashed if pressure drop between the input and output of the sand
filter exceeds 0.5 bars.
The systems for dosing of chemicals rarely present problems if have been made of adequate materials, except the diffuser of acid to the feed
line, that is usually replaced yearly.
When membrane fouling is prevented or minimized by effective pre-treatment, maintenance requirements in the entire RO plant are minimal.
High pressure pumps
Pump failure tends to be caused by one or more of four following conditions:
Inadequate pump (type, sizing);

Improper installation;

Inappropriate operation; and

Incorrect and irregular servicing.
Failure to follow the recommendations of the manufacturer (OEM spare parts, ...)
Operating a pump in dry conditions, as the motor will overheat and burn out. Water is needed for lubrication and
heat dissipation.



Positive displacement pumps use more components that are subject to wear. For this reason, maintenance requirements are higher than with
other pump types. Under normal operating conditions, diaphragms need replacement every 2 to 3 years. The seals in a piston-type pump may last
3 to 5 years.
Labour cost for maintenance depends on the country and is on the average €5/hour in addition to spare parts and consumables
62
Pump motor
Brushless DC and AC motors require little maintenance aside from preventing water and dust from entering the motor housing (in the case of
open motors). Brushless DC and AC motors can last 10–20 years or more under ideal conditions.
Brushed DC and AC motors require periodic replacement of brushes. Brushes are inexpensive but the unit must be stopped for this operation
(downtime costs). The replacement should be performed according to the manufacturer’s recommendations. Depending on the duty, a small
brushed-motor may last 4 to 8 years. The bearings motors require grease lubrication and sometimes replacement after about 5000 hours of
operation. Maintenance requirements depend also on the type of coupling (direct, drive, gear).
63
ENERGY
RECOVERY
SYSTEMS
STORAGE OF
BATTERIES
BEFORE
INSTALLATION
PV SYSTEMS
Maintenance tasks will vary among the different configurations offered. However, available energy recovery systems usually have little
maintenance needs.
Lead-acid batteries, before installation, should be stored in a dry and cool atmosphere. The long time storage at high temperature will have a
detrimental effect on life as the corrosion of the lead electrodes is accelerated at elevated temperatures. Humid atmosphere will create a leakage
current flowing over the battery cover between the positive and negative terminals. In the long run, but much faster than due to the internal self
discharge, the battery will be deeply discharged decreasing thus the battery life due to sulphation of the electrodes.
It is recommended to recharge batteries periodically (typically every six months), if they are to be stored for a long time. The capacity drain is
otherwise very harmful to the battery life since self-discharge, going on inside the battery. Permanent damage is created if the self-discharge of
the battery drains the battery completely
Batteries can be protected against deterioration when stored before installation by a process called dry charging. The battery is then shipped
fully charged but in dry condition and the acid is not filled in the cells until it is to be installed.
Such dry charged batteries can usually be stored for almost two years without important degradation. When acid is introduced, the battery
becomes operational very quickly.
Operation and maintenance (O&M) costs can be significant for PV installations. For small PV systems, one maintenance visit per year can
offset the value of energy produced per year by the system. Improving the reliability and fault tolerance of systems and equipment can have a
significant effect on reducing O&M costs, and can improve overall system performance. While there have been very few problems associated
with PV modules and arrays, a number of reliability issues have been identified with inverters and power conditioning equipment in gridconnected and AC systems. Over fifty percent of these installations have experienced problems with power conditioning subsystem components
that required a site visit to correct the problem and return the system to normal operation [3]. Unscheduled maintenance has been required to
change out complete inverters, replace fuses, reset circuit breakers, and upgrade software. Based on the amount and value of energy produced
from these systems, the estimated costs for maintenance have ranged from 0.04 to 0.20 € per kWh ac during the first year of operation. Other
studies have identified O&M costs ranging from 0.01 to 0.16 per kWh ac [4]. Challenges to reduce PV system maintenance costs include
64
WIND ENERGY
developing inverter designs that offer improved reliability and fault-tolerant features consistent with those for PV modules.
There are several maintenance needs for a wind turbine such as the alternator bearings replacement, yaw bearings replacement with their
significant loading. Dust, debris, and even insects in the wind will eventually erode the most durable blade materials, leading edge tapes, and
paint coatings. Tail bushings and governor components, subjected to dirt and moisture; inevitably wear as the turbine governs in storms or during
windy periods. Paint coatings, subjected to sunlight, moisture, and temperature extremes will eventually deteriorate. If the wind turbine system
has a gearbox, the lubricant will degrade over time. Typically direct driven wind turbines costs about 1% of the installed cost per year for the
O&M costs, and 2% for wind turbines with gearbox.
Figure 1. Typical PV-wind hybrid system components
STORAGE 8.5
TANKS
Water storage tanks do not involve any operation costs. Also the maintenance requirements are very low under normal conditions. All that has
to be done is to have the tank drained, cleaned and professionally evaluated every three to five years. In addition in regular basis tanks should be
checked for obvious problems like leakages or vandalism. Should such circumstances occur tank engineers have to be called in for repairing the
damage.
If these very simple maintenance procedures are followed water tanks can be functional for many decades, much longer than any autonomous
desalination unit has ever operated.
Tanks made of reinforced concrete or steel are more probable to require some maintenance operations than plastic tanks. Steel tanks are
subject to corrosion, while concrete tanks may be affected by trees growing close to them. Additionally, those kind of tanks are coated and the
coating may deteriorate needing repair.
65
HANDBOOK Chapter 2 - Region identification and Site Selection.