Solar-Powered Groundwater Pumping Systems for
Domestic Use in Developing Countries
Ryan Van Pelt
Department of Civil and Environmental Engineering, Colorado State University,
Fort Collins, Colorado 805231-1372
April 24, 2007
Abstract
Solar-powered pumping systems (SPPS) are becoming more common in the United
States and internationally. They have been utilized in the United States for over 20 years.
However, the operational knowledge required to properly size a SPPS and the initial costs
of installation tend to be more significant than an alternating current (AC) powered
pumping system. These two reasons contribute to why 90% of the users of SPPS are
developed countries like the United States, Canada, Europe, Australia, and Japan [1]. As
photovoltaic (PV) modules become more affordable and the energy efficiency of both the
modules and solar-powered pumps increases, SPPS will become a leading technology in
remote areas. Also, as usage of the systems increase, so does the knowledge of
improving the systems and avoiding common problems. Many of these common
problems can be avoided with feasibility analysis and proper installation.
The focus of this paper is solar-powered pumping systems designed for drinking water in
small villages where the water supply comes from a well and submersible pump. This
paper also focuses on small villages that are not on or in proximity to a rural power grid.
One of the main purposes of this paper is to list major considerations of feasibility before
installing a SPPS at a village. The feasibility of solar-powered pumps is discussed with
regard to regional and water demand constraints. The second purpose is to cover the
components of a SPPS along with their appropriate integration into the system. One
problem example is worked out and one case study is described of a successfully
implemented SPPS at a small village in Nicaragua.
I
Contents
1.
2.
Introduction ................................................................................................................. 1
Feasibility.................................................................................................................... 1
2.1
W-ater Source ..................................................................................................... 1
2.2
Power Source ...................................................................................................... 2
2.3
Realistic Expectations and Costs for a SPPS ...................................................... 5
2.4
Site Location ....................................................................................................... 6
2.5
Community Involvement & Ownership.............................................................. 7
2.6
Sustainability of System ..................................................................................... 7
2.7
System Security .................................................................................................. 8
3. SPPS Components ...................................................................................................... 8
3.1
Well ................................................................................................................... 10
3.2
Pump ................................................................................................................. 10
3.3
PV Array & Photovoltaic Cells......................................................................... 14
3.4
Pump Controller ................................................................................................ 16
3.5
Storage Tank ..................................................................................................... 16
3.6
Additional Components .................................................................................... 16
4. Example Problem ...................................................................................................... 18
5. Case Study ................................................................................................................ 20
6. Conclusion ................................................................................................................ 21
7. References ................................................................................................................. 22
II
1.
Introduction
Solar-powered pumping systems have been in use long enough that a preliminary
assessment can be conducted related to their efficiency and cost compared to other
alternative powered pumping systems. This preliminary assessment should be completed
before deciding if solar power is the best source of alternative power for a village water
supply system. Generally, alternative power is only considered when the cost of tapping
into the closest public power grid far outweighs the costs of using alternative power.
There are several technology alternatives for supplying power or lift to groundwater
systems including: wind turbines, windmills, generators, solar arrays, and hand powered
pumps. The main driving factors for selecting the appropriate technology are regional
feasibility, water demand, system efficiencies, and initial and long-term costs. Other
factors often include the need for power and water reserves in the form of batteries and
storage tanks. Solar-powered systems are often considered for use in developing
countries instead of other forms of alternative energy because they are durable and
exhibit long-term economic benefits.
This paper briefly covers the selection process needed before choosing solar power as the
appropriate alternative power source for a groundwater pumping system. Preference is
given to the drinking water supply of a small village. The paper also covers the design
process and the components of a SPPS when used with a well and submersible pump. A
significant amount of detail is directed towards selecting a pump when solar power is
selected as the appropriate technology.
2.
Feasibility
The selection of SPPS should only follow a thorough look at the feasibility and future
prospect of the technology. There are several important steps in this process. Not all of
them are covered here, but the key considerations are mentioned below. For a more
detailed feasibility study please refer to “Solar Pumping Systems (SPS), Introductory and
Feasibility Guide” by Green Empowerment [2].
2.1
Water Source
Selecting a water source involves making a detailed site map which shows changing
elevations, layout of the land, available water resources running through the site or near
the site, and present structures. If the selected water source is gravity-driven, like an
upper river or spring, the power supply can be avoided by the proper layout of a
distribution system. However, if the source is a well or surface water at a lower elevation
than the site, a powered pump or possibly even a ram pump will be needed.
Once the water source has been narrowed down to a well and alternative power is needed,
the village water demand needs to be determined. The average rate of consumption for
villagers used to traveling to get their water and carrying it home is 10 gallons per day
1
per capita [2]. It is general practice to add at least three days of storage to a SPPS for
cloudy days, nights, and emergencies [3].
2.2
Power Source
The next step is to rule out other sources of power or pumping devices. If the public
power grid is reliable and in proximity to the site, preferably less than 1/3 mile, then solar
power would most likely be a poor choice [4]. The cost of implementing a SPPS could
be significantly more than the cost to hook up to the local power grid and purchase an AC
pump. A 1/3 to 1/2-mile power line extension in the U.S. alone can cost $5,000 or more
[4]. With the exception of the storage tank, the most expensive element of a solarpowered system is usually the photovoltaic modules or panels. Table 1 lists the pros and
cons associated with different sources of alternative energy for water pumps and gives a
good comparison for SPPS.
A preliminary guidance for the feasibility of using a SPPS versus a generator powered
system or hand pump can be found in Table 2 by Green Empowerment [2]. This table is
based on water demand and required pumping head. Note that this table does not appear
to account for all of the recent advances in SPPS technology and may be very
conservative.
2
Table 1
Pros and Cons of Alternative Forms of Energy for Pumps
“Solar Pumping Systems (SPS) Introductory and Feasibility Guide,” Green Empowerment [2]
3
Table 2
General Feasibility of SPPS Compared to a Hand Pump and Diesel Generator
“Solar Pumping Systems (SPS) Introductory and Feasibility Guide,” Green Empowerment [2]
4
2.3
Realistic Expectations and Costs for a SPPS
A solar-powered pumping system is not recommended for community indoor plumbing
needs. Most economical SPPS will not provide enough water and pressure for the
required demand of community indoor plumbing, but can meet the demands of a single
building similar to a small community center or medical center. SPPS is also not
adequate for large-scale irrigation, but can work for small-scale drip irrigation systems.
A large-scale SPPS can be considered one that serves over 240 peoples or serves a water
demand of over 2,400 gpd [2]. The cost of a system that serves 500 people or more can
easily reach $34,300 (see Example Problem in section 4). If the village is over 500
people it may be more practical to use a generator and AC pump. As the size of the
village population approaches 500 people, the costs of the required storage starts to rise
sharply due to the recommended backup storage volume for three days of demand and the
limited daylight hours of water pumping.
For a basic comparison of running a pump on a diesel generator compared to solar power
refer to the study conducted in the United States and Bangladesh where a 1 kW, 50 meter
pump head SPPS is compared to a 2 kW, 50 meter pump head conventional diesel
generator pumping system. This study was published in Renewable and Sustainable
Energy Reviews [1]. The main assumptions in the cost comparison are as follows:
1. The projected costs were for a 25 year project lifetime of each system.
2. Net profit is calculated as the difference between the variable costs of a dieselpowered pumping system and variable costs of a SPPS.
3. All costs are given in US dollars, where US $1.00 = 69.49 Bangladesh Taka.
4. Local materials and local skills are used wherever possible.
5. Cost of PV modules are approximated at US $4.5/Watt power.
6. Manual labor costs are significantly less in Bangladesh than the USA.
7. Diesel fuel costs and original equipment costs (excluding local accessories) are
the same in both countries.
8. Diesel fuel prices increase 10% every year.
9. Transportation costs are significantly less in Bangladesh and expected to increase
by only 1% per year.
10. Operation and maintenance costs per year are considered constant for the systems.
11. Diesel generator system is maintained everyday for turning off/on and refueling.
12. SPPS system is checked once per week.
13. Costs of replacement items such as pumps and generators are considered constant
through the projected lifetime of the systems.
14. The SPPS pump and controller are replaced every 10 years.
15. The diesel generator is replaced every 5 years.
16. The excess water storage recommended for a SPPS is not accounted for in the
cost comparison.
The report indicates that although the initial costs of the generator powered system were
much less than the SPPS, based on total costs of operation, after 10 years of operations
the SPPS system cost less to operate annually than the generator system (see Figure 1).
5
This cost difference is mostly attributed to the long-term fuel costs associated with
operating a diesel-powered system.
Figure 1: Year by Year Total Cost Comparison for SPPS versus a Diesel Generator System
Meah K. et all, Renewable and Sustainable Energy Reviews. October 2006 [1]
2.4
Site Location
The site location plays a major part in the feasibility of a SPPS. Peak sunlight hours
(PSH) differ widely across the globe. The PSH is based on the number of equivalent
daily hours that provide solar irradiance equal to 1 kW/m2. If a graphical plot of sun
radiation versus hours of the day is created and the area under the curve is integrated and
divided by 1,000 W/m2, the resulting value would be PSH [2]. It is difficult to find in the
literature a recommended cut-off value for PSH at which point a SPPS is not practical.
The general guidance is that the less PSH available, the more expensive the required
photovoltaic (PV) array and pump. System costs also increase when more storage is
needed to compensate for the very limited exposure of the PV array to peak sunlight
hours. The majority of the successful SPPS systems installed in developing countries
appear to be located in areas where the PSH is at least 4. To obtain the PSH for a region,
please refer to (www.solar4power.com). The maps accessible from this website give
yearly low peak sunlight hours. Another factor is the climate of the region. Solarpowered systems are not typically designed for extremely cold weather (temperature less
than -200C). However, the systems can be well insulated to handle fairly cold winters.
For example, with the proper insulation they have proven effective in the northern United
States in places like New York State [4].
6
2.5
Community Involvement & Ownership
Local acceptance is an important factor to consider. A survey and assessment should be
conducted among the village leaders and some of the households to determine if the
villagers will be willing to embrace the technology and use it wisely. The assessment
should consider local skills, materials, and labor in order to estimate how the community
could be involved in the installation, operation, and maintenance of the system. It is also
generally a good idea to contact the local government officials in the country and make
sure that they are accepting of the solar system and aware of what it is being used for.
Solar-powered-pumping systems are gaining ground in developing countries, but rarely
are they installed without the funds and supervision of non-government organizations
(NGOs). There are significant upfront costs and community training required for the
successful implementation of a SPPS. NGOs will usually be involved in the initial
phases of the project including design, installation, and training needed to operate and
maintain the systems.
Community ownership is key to the longevity of the SPPS. The community should take
pride in their water system and gain a sense of ownership from the service it provides.
Most NGOs recommend a fee based system for the water users, even if it is only
equivalent to 2 to 3 $U.S. per family per month. The fees are used to pay a water system
manager in the village and to maintain and upgrade the system as needed. NGOs like
AsoFenix [14], based out of Nicaragua, will also help with the training of villagers to
install the system and to understand its basic operation. Other NGOs may require a water
committee or water management system to be in place before they will complete
installation tasks or do additional work on the SPPS.
Other concerns often overlooked are the community socio-economic needs. If having
water delivered to them more conveniently significantly takes away from their socioeconomic structure, the village may begin to resent the system, making it more prone to
vandalism or unintended uses [2]. There are several good guides for considering socioeconomic factures published by USAID and NGOs like Life Water International. For
Life Water International’s technical library and US AID publications, refer to the website
(http://www.lifewater.org/resources/tech_library.html) [5].
2.6
Sustainability of System
The long-term costs and ability of the SPPS to be adaptable to changing demands should
be implemented into the feasibility of the system. This process is also significantly
related to the ability of the village to adapt to changing demands. Photovoltaic modules
should last 20 – 25 years. This is dependent on being maintained (kept clean and
securely mounted) and protected from strong winds, lightning and hail storms, and falling
objects such as tree branches. The solar pumps should be expected to last about 10 years
[2]. The other electronics and controls should be designed to last at least 10 years with
little electrical maintenance [1]. The overall lifetime of the complete system should be
7
designed and maintained to last 25 years taking into account future growth projections of
the community. The system should be inspected at least once per week checking the
pumping rate, operation of controller, condition of PV modules, tanks, wires, and pipes
(for leaks/corrosion). More information can also be found in the Life Water International
technical notes. Table 3 shows a list of some of the NGOs that provide support for water
resource projects in developing countries.
Table 3
Non-Government Organizations (NGOs) Involved in Supporting
Water Resource Projects in Developing Countries
NGOs
Base
Country
Type of Aid
Web Site
Green Empowerment
U.S.
financial, build, design
http://www.greenempowerment.org
Asofenix
Nicaragua
design
(no website)
New Earth Foundation
U.S.
financial
http://www.newearthfoundation.org
EnerGreen Foundation
U.S.
financial
http://www.energreen.org
UNICEF
U.S.
financial
http://www.unicef.org
Fundacion Natura
Ecuador
design
http://www.fnatura.org/index.htm
Greenstar
U.S.
design
http://www.greenstar.org
Sustainable Village
U.S.
design, research
http://www.sustainablevillage.com
EWB
Enersol
U.S.
U.S.
design, build
owns & maintains system
villagers pay back over time
http://www.ewb-usa.org
http://www.enersol.com
2.7
System Security
Another important aspect to consider is security. Can the PV array be secured properly
or will it be stolen or vandalized? It is obvious that without a functioning PV array, a
SPPS is worthless. The PV array is one of the most expensive components of the system
(~50-75%) and should be protected from theft, vandalism, and livestock [1]. For instance,
due to the realized value of the modules in South Africa, there have been several reported
cases of modules being stolen in the region [6]. It is strongly recommended that
provisions be made to put a fence with a lockable gate around the array. The fence needs
to have enough set-back that it does not cast a shadow on the array.
3.
SPPS Components
A solar-powered pumping system for a village should consist of the following minimum
components:
1.
2.
3.
4.
5.
water well
PV array
array mounting bracket and rack
pump controller
electrical ground for controller
8
6. DC pump with safety ropes, mount, and well seal
7. wiring
8. discharge tubing or piping
9. storage tank
10. tank floatation switch
11. water taps or access points
12. security
The flotation switch is used in the tank to turn off the pump when the tank is full. The
pump should be specifically designed for solar power. It is strongly recommended to
have the pump controller purchased from the same manufacturer as the pump. To use
another manufacturer could cause several unforeseen problems and even invalidate the
pump’s warranty. If the pump does not contain a built-in check valve, one should be
installed in the system to keep the water from flowing back into the well. Very few
pumps can handle reverse flow without reducing the life expectancy of the pump. The
pumps that are designed to drain during non-operation are meant for extremely cold
conditions to keep water from freezing in the lines. The pump should be no deeper than 2
feet above the bottom of the well to help prevent heavy silt and sand from entering the
pumps intake and causing it to seize. The storage tank should be sized to hold at least
three days worth of water demand to account for evenings and cloudy days. A security
fence should be placed around the PV modules and controller. If the controller is not
attached to the array mounting bracket it can be placed in a secure shed or pump house,
preferably water tight and dust free. See the following figure for a schematic diagram of
a typical system.
Figure 2: Schematic Diagram of a Typical SPPS
“Solar Photovoltaic Water Pumping for Remote Locations, University of Wyoming, 2006 [1]
9
3.1
Well
The entire solar system design depends on the yield of the well and the water demand of
the village. Therefore, all precautions should be taken to place the well into a clean, high
yield, groundwater aquifer. It is also recommended to avoid extremely shallow water
tables. The diameter of the well should be at least 6 inches. This allows enough
tolerance for the addition of a sand shroud on a 4 inch pump. In developing countries,
threaded 40-schedule PVC casing and screen are usually used. The screen slots are sized
appropriately for the filter pack and native material. The well should be sealed at the
surface to prevent surface water intrusion. This guide does not go into the details about
installing a well, but appropriate guidelines should be followed to ensure the best possible
installation, development, and pump test the project budget can afford. Having a bad
well is equivalent to having an unreliable power source. If at all possible, it is
recommended to use standard practice procedures used in developed countries to install
the well, like ASTM standard (ASTM DRILL99-99) [7]. These standards are not
specifically intended for supply wells, but do cover the essential aspects of installing a
well and conducting a groundwater investigation.
3.2
Pump
Pumps designed specifically for solar power utilize direct current (DC) and tend to be
very energy efficient, but they usually cost more than their otherwise equivalent
alternating current (AC) pump. Surface mounted pumps can be used for a SPPS, but are
discouraged because of their suction limitations when used in deep wells compared to the
achievable lift of a submersible pump. Based on the specifications from several
manufactures such as Shurflow, Gaiam, and Dankoff, the typical suction abilities for
surface pumps designed for solar power are between 10 and 20 feet. Surface pumps also
have greater exposure to the climate making them more vulnerable to freezing and harsh
weather. Submersible pumps are more protected from the climate and use the
groundwater as a natural priming fluid.
The reliability and efficiency of submersible pumps designed for solar power have
increased tremendously over the last 10 years. Solar powered pumps are designed to
have a low starting torque requirement. Modern solar powered pumps have an average
daily solar energy to hydraulic efficiency of more than 4% [8]. Energy efficiency in its
most basic definition is output/input. In regards to pumps, it is more appropriately
considered the product of the motor and lift mechanism efficiency [9]. For example, if
the motor is 80% efficient and the lift mechanism is 50% efficient, than the overall pump
efficiency is 40%. Most submersible pumps designed specifically for solar power have
an overall efficiency of 40 to 70%.
Currently, there are four main types of lifting mechanisms used in submersible solarpowered pumps: diaphragm, reciprocating piston, centrifugal, and helical rotor (screwtype device). Some of them are more efficient and easier to maintenance than others, like
the helical rotor, but sacrifice other abilities like flow rate. The four main types of lift
mechanisms are listed below:
10




Centrifugal pumps elevate the water through a series of spinning impellers
(commonly called stages) that suck the water in and force it up the pump.
Centrifugal pumps are usually used with high lift and flow demands.
Helical rotor pumps rely on one moving part that acts as a screw type approach to
trapping the water in the suction side of the pump and moving it upwards.
A diaphragm pump uses sealed diaphragms and often consists of 3 chambers to
move water.
A piston pump relies on a piston to draw water into a chamber using an inlet valve
and forces it to the outlet using the outlet valve.
The centrifugal and helical rotor pump are less susceptible to high ambient pressures
created at submersion depths greater than 164 feet compared to the piston and diaphragm
pumps. Most piston and diaphragm pumps display observable pumping efficiency losses
and escalating starting torque requirements in submersion at depths of 33 feet or more
[10].
There are also different motor devices in the pumps. However, most of the solarpowered pumps either rely on a brush or brushless permanent magnet (PM) and most
centrifugal pumps also have a variable speed motor. The brushless PM motors are
designed to reduce the frictional wear forces created in other conventional pumps and
seem to be the most durable and energy efficient.
Several of the more common submersible solar-powered pump manufacturers are listed
in Table 4. This table also indicates general operating parameters for selecting a pump.
If using this table, particular attention needs to be given to the footnotes. Following are
pictures of a Grundfos SQFlex centrifugal and helical rotor pump.
Figure 3: Grundfos SQFlex Centrifugal Pump
Grundfos Pumps (www.grundfos.com) [11]
11
Figure 4: Grundfos SQFlex Helical Rotor Pump
Grundfos Pumps (www.grundfos.com) [11]
12
Table 4
Manufacturers of Submersible Solar-Powered Pumps
Brand
Model or Series
Type
Lift
Motor
Mechanism
Diameter
(inches)
Power Requirement/Ranges
Voltage Range
Power
Max. Current
(Volts)
(Watts)
(Amps)
Max Lift
Main
Headquarters
(feet)
Max
Capacity
(gpm)
Divwatt
Solastar-3B
RP
PM Brush
Con-D
34 - 85 DC
1200
12
656
6.0
South Africa
Fluxinos
Solaflux
RP
PM
3.9
20 - 70 DC
20 - 300
~4
492
4.2
Italy
Lorentz
PS150, PS1800
PS200, PS600, PS1200
C
HR
PM Brushless
PM Brushless
3.8 / 3.9
3.9
12 - 50 DC
24 - 48 DC
450 / 1400
1200
~12.5
Con-D
39 - 197
165 - 760
21.7 - 72.0
10 - 45
Germany
16SQF-10, 25SQF-3, 25SQF-6,
C
PM Brushless
3.9
30 - 300 DC or 90 - 240 AC
1400
Con-D
50 - 100
25 - 75
Denmark
3SQF-2, 3SQF-3, 6SQF-2, 11SQF-2
HR
PM Brushless
2.9
30 - 300 DC or 90 - 240 AC
900
Con-D
325 - 525
3.0 - 11
Denmark
Kyocera
SD -series
SC-series 500 and 1000
D
C
Con-D
PM Brushless
3.8 - 4.6
3.8
12 - 30 DC
60 - 120 DC
20 - 140
140 - 1000
10
14
100 - 230
98.4 - 525
2.4 - 4.5
3.7 - 43
Japan
Solarjack
SDS Series - no longer made
SCS Series - no longer made
D
C
Con-D
PM Brushless
3.8 - 4
~4
12 - 24 DC
30 - 180 DC
Con-D
140 - 2880
Con-D
Con-D
Con-D
800
Con-D
50.0
U.S.A.
Shurflo
9300
D
PM
3.8
24 DC
155
4.6
230
2.0
U.S.A.
Sun Pumps
SDS-series
SCS-series (1/2 to 2 HP motors)
D
C
Con-D
PM Brushless
3.8 - 4.5
3.9 - 4.0
12 - 30 DC
30 - 180 DC
95 - 184
320 - 2070
6
7.1 - 11.5
115 - 230
30 - 65
1.3 - 5.0
4.0 - 70
U.S.A.
NAPS
SP-series 400 and 1500
Con-D
Con-D
Con-D
150 - 1600
Con-D
43 - 656
0.64 - 30.1
Africa
1.
Grundfos
40SQF-3, 40SQF-5, 60SQF-3, 75SQF-3
1.
Grundfos
2.
45 - 90 DC
Notes:
Not all manufactures of solar powered pumps are listed.
Where possible from internet resources, all listed specifications are from manufactures and not the distributors.
The operational ranges for most of the pumps listed were based on tests performed with 6kWh/m2/day of solar irradiance, Lorentz pump specifications were between 5.2 and 7.0 kWh/m2/day.
Actual flow rate depends on perfect sunlight hours at installation site.
The listed wattage is based on the performance ranges of the pump, but because of inefficiencies in solar energy conversion it is recommended that the solar modules be sized with a factor of at least 1.25 X the pump demands.
Manufacturers only have distributors in certain regions of the world. Before deciding on a solar powered pump make sure your region is served, or it is economical to ship the pump there.
1.
2.
AC
C
Con-D
D
DC
HR
PM
RP
TDH
Grundfos pumps are very versatile and can operate off a wide range of DC or AC.
The specifications for the NAPS pumps were difficult to understand and the listed voltage may not be correct.
Alternating Current (power grid, generator)
Centrifugal
Contact Distributor
Diaphragm, most listed diaphragm pumps are 3 chambered
Direct Current (solar power, batteries, wind turbine)
Helical Rotor
Permanent Magnet
Reciprocating Piston
Total Dynamic Head
13
The size of the pump will depend on several factors including: available water supply,
available power, available storage, total dynamic head (TDH), diameter of well, and
village demand (including 25 year growth projection). Assume that the pump will only
be operating during peak sunlight hours. Try to install the most efficient and simplest
system that meets the project demands. Before the village starts using the system, the
storage tank should be filled. This allows the rest of the distribution system to be
designed with a semi-constant pressure head. It also reduces the demand on the pump by
allowing it to cycle, starting again when the volume in the tank is approximately ½
depleted.
It is important to determine the total dynamic head. For a SPPS, total dynamic head can
be referred to as the head pressure required to overcome the sum of the static lift of the
water, the static height of the storage tank, and the frictional losses in the pipe network
[4]. Following are some preliminary calculations for determining TDH and the flow rate
of the pump needed:
TDH = (depth from static water table to top of well + drawdown at sustainable or desired
pumping rate + elevation difference from top of well to top of storage tank) x 1.1


1.1 accounts for other head losses and frictional losses in system [2]. For
a more accurate measurement of frictional losses, Hazen-William’s
equation should be used along with tables that show the frictional loss per
foot of pipe length. Minor and local losses in fittings should also be
accounted for.
The desired pumping rate should not be greater than the sustained well
yield.
An estimate of the required flow rate of the pump can be determined by the following
equation [4]:
Flow Rate (gpm) 
demand in gpd
hr
x
PSH per day
60 min
The next step is to take the well diameter, TDH, and desired flow rate and refer to
Table 4 or other manufacturers not listed to determine what type of pump will fulfill the
system needs. The final selection of the pump should be based on a system parameter
match with the manufacturer’s pump curve.
3.3
PV Array & Photovoltaic Cells
Solar power comes from photovoltaic (PV) cells that convert the sun’s energy into usable
DC electricity. A module consists of PV cells and an array consists of several modules.
PV cells are primarily made from silicon and come in three different types:
monocrystalline, polycrystalline (multicrystalline), and amorphous. The following figure
shows the three types of cell modules.
14
Figure 5: Types of PV Modules
Guide to Solar-Powered Water Pumping Systems in New York State
New York State Energy Research and Development Authority (NYSERDA) [4]
The efficiency of the PV module relates to the area of active cell area exposed to the
sunlight [9]. Monocrystalline are the most efficient, converting approximately 15% of
the sun’s energy to electricity, but they are also the most expensive of the three.
Photovoltaic modules have typical warranties of 20 – 25 years, with life expectancies
approaching 30 years [4]. The following table relates the differences between the three
main types of PV cells:
Table 5
Types of PV Cells and their Efficiency
Research Institute for Sustainable Energy (rise), Murdoch, Western Australia [9]
Type of cell
Efficiency range
Comments
Monocrystalline
14 to 16%
Highest price, affected by temperature
Polycrystalline
12 to 14%
Medium price, affected by temperature
Amorphous Silicon
8 to 9%
Medium to low price, not affected by
temperature
Modern research is developing PV cells that have cell efficiencies approaching 30%, but
modules containing these cells still are not easily available in the global market [9]. The
design of the PV array is fairly straightforward and depends on PSH, energy losses, and
the desired power supply to the pump. A factor of 1.25 times the pump wattage
requirements is often used to determine the preliminary size of the required array [4].
This accounts for the energy losses in the modules and controller. If batteries and a
regulator are added into the system, the PV array demand will be higher. The addition of
an inverter to run an AC pump would also increase the demand on the PV array. Some of
the pump manufacturers listed in Table 4 also sell compactable PV arrays and should be
consulted for the final size of the needed array. How the PV modules are connected,
series versus parallel will depend on the required output voltage and current. If they are
all connected in parallel, it will increase the available current. If they are all connected in
series, it will increase the available voltage. It is best to get the recommended layout of
the modules from the distributor of the pump and controller.
15
The PV array needs to be mounted securely to a tilted rack that is fixed to the ground. A
tracking system can be used, but as mentioned earlier, a tracking system mount is not
always recommended. The selection of the mount should include all factors of
maintenance, latitude of region, wind, and the project budget. If the modules are fixed,
the orientation of the tilt is to the south and should be equal to the site latitude. If they
are on an adjustable mount, the tilt should be the latitude minus 10 to 15 degrees in the
summer and the latitude plus 10 to 15 degrees in the winter [3].
3.4
Pump Controller
The pump controller is a highly specialized item and can vary significantly between
pump manufacturers. A technical term for a pump controller is a linear current booster.
The purpose of the pump controller is to regulate and match the flow of DC electricity to
the needs of the pump [4]. The pump controller also contains the recognition
components for the storage tank floatation switch and the low-well switch. The
controller should be expected to last approximately 10 years [1].
3.5
Storage Tank
The storage tank should have enough volume to hold at least three days worth of average
demand [3]. This is not only to account for peak demands, but primarily to compensate
for nights and cloudy days, especially when other backup systems are not used. The
general cost for water storage is estimated to be between 1 and 2 $U.S. per gallon [2].
All pressure analyzes and standard distribution calculations should be accounted for,
including water hammer effects. Make sure the internal velocities and pressures are
appropriate for the pipe material and desired flow rates.
3.6
Additional Components
There can be several additional components to a SPPS that can enhance the performance
of the system or add backup energy reserves:
1. Batteries: Deep-cycle batteries are often used as a power backup. They are
recharged during the day through the PV array and drained at night or during
cloudy days. The batteries should be lead-acid so they can be trickle charged
indefinitely once they reach full charge. The pump controller is usually installed
after the batteries. The addition of batteries requires a charge regulator between
the batteries and the PV array. The charge regulator needs to monitor the battery
voltage to prevent over-charging because the DC solar energy fluctuates
throughout the day. It is also recommended to install blocking diodes before the
charge regulator [3]. A diode in the system should prevent the PV array from
draining the batteries in low light conditions. A diode is usually just a twoelement electron tube or a semi-conductor through which current can pass freely
in only one direction.
16
2. Wind Turbine: Wind turbines can be a very cost effective backup to solar power
in areas with average wind speeds above 7 mph [11]. Usually wind turbines are
low maintenance and tend to perform best during the winter and spring.
3. Generator: If sufficient water storage is not available, some systems may need a
backup generator to run the pump during low sunlight periods. If a generator is
used with a DC pump, an inverter is usually required. However, generators are
directly compatible with some pumps like the Grundfos SQ Flex pumps [11].
Grundfos does recommend an interface controller when using a generator to
automatically switch back to solar power when it is available (see Table 4). The
life expectancy of a generator is typically 5 years [1].
4. AC Pump: An AC pump can also be used instead of a DC pump but this will
require an inverter when used with solar power.
5. Solar Tracking System: A solar tracking device can be added to the PV array to
increase the power yield. Tracking systems are often sold by the manufacturers of
PV modules. Trackers are attached to the mounting bracket and control the
degree to which the array is tilted towards the sun. They can either be controlled
passively (sun’s heat exposure) or electronically through part of the converted
energy from the PV array. Passive trackers contain liquid (often Freon) that when
heated from the sun moves from one cylinder to another causing the rack to tilt
more into the sun. Tracking devices have been reported to increase the daily
energy yield up to 40% at certain latitudes in New York State [4]. However, they
are not recommended for areas near the equator or which are susceptible to high
winds. They can also add approximately 25% of additional maintenance costs [1].
6. Weather Insulation: Weather proofing and insulation should be added for
extremely harsh environments, especially in areas where temperatures reach
minus 200C, which is the minimum temperature rating of several pumps.
7. Low Well Switch: In low yield wells, where the drawdown of the well exceeds
the pumping capacity, the addition of a shutoff switch is needed in the well to
keep the pump from running dry. Some pumps advertise they can run dry without
damage to the pump, but allowing any pump to continually run dry is a bad idea.
Ideally, the pump should shut off when the water level gets within 2 feet of the
pumps intake to reduce air intake and turbulence. Some pumps come preinstalled with a safety shut-off switch.
8. Sand Shroud: A sand shroud may be needed around the intake zone of the pump.
Sand shrouds are recommended for use in wells that have high sediment loads or
that were not properly installed. They are particularly recommended in open
boreholes which are not screened through the saturated zone of the well. This
type of drilled well is often installed in places like Uganda where the water is
coming in through rocky areas. The pump manufacturer can usually provide a
compatible sand shroud.
17
9. Hand Pump: If the water table is fairly shallow and only low yields are needed, a
simple hand pump could be installed in the same well as the solar-powered pump
to act as an additional backup. This would only be practical if space allows, such
as in a large diameter well or hand-dug well. It would also require a solid
concrete slab over the well and a drainage system. See the following web link for
more detail: (file:///D:/CSU%20Course%20Work/Research%20Project%202007/
Hand%20Pumps/hand&PV-power-water-pump.htm).
Both inverters and batteries significantly reduce the efficiency of an SPPS and should be
avoided if at all possible. Batteries along with the charge regulator can produce a power
loss of up to 25% of the total array output [10]. If plenty of water storage is available, the
batteries may not be necessary. The initial cost of an efficient DC pump (designed for
PV power) is usually greater than an equivalent AC pump. However, compared to
running and maintaining an AC pump off a generator, the cost should be regained in 5 to
10 years of operation [12].
4.
Example Problem
To put SPPS into perspective, the following example is given based on a Grundfos 25
SQF-6 centrifugal pump and a large-scale SPPS. General costs and multiplier values are
preliminary estimates taken from the Green Empowerment Feasibility Guide [2]. The
listed cost of the pump and controller is a conservative price based on the suggested retail
price and the price taken from varies on-line distributors of Grundfos pumps:
Assuming no reserve battery systems and 3-days of demand water storage, a large-scale
SPPS can meet the needs of up 500 people at a TDH of 90 feet. This region is in Uganda
and has 5 hours a day of peak sunlight hours.
Calculate preliminary estimate of demand: 500 people x 10 gpd/capita = 5,000 gpd
Calculate preliminary estimate for required flow rate:
Flow Rate (gpm) 
demand in gpd
hr
5,000
hr



 16.67gpm
PSH per day 60 min
5
60 min
Looking at Table 4 and following up the selection with the manufactures pump curves, a
Grundfos 25 SQF-6 pump curve matches the flow and head parameters well. At 90 feet
of TDH and 16.7 gpm, the pump needs 725 watts of power being delivered directly to the
pump. The efficiency losses of energy in the PV modules and other electronics would
require an array capable of producing approximately 900W or 1.25X the pump
requirement. A cost of $6/W for PV module energy output is used which is about the
mid cost reported. The pump curve for a Grundfos 25 SQF-6 is shown in Figure 6. The
total estimated cost of this system is approximately $34,300. Other assumptions and
details are shown in the following table.
18
Table 6
Item and Cost for Example of Large-Scale SPPS
Item
Amount
Cost/Amount
(U.S. $)
Cost
(U.S. $)
People Served
TDH (ft)
Pumping Rate (gpm)
Pump DC Demand (W)
Peak Sunlight Hours
Required PV Array (W)
Fixed Mount with Rack (per module)
assuming each module 100W
Grundfos 25 SQF-6 Centrifugal Pump
Grundfos CU 200 Pump Controller
Pump Shut-off Switches and Misc.
Wiring (ft)
Piping (ft)
Installation of SPPS
(not including well or storage tank)
Well (ft)
Storage Tank for 3 days demand (gal)
500
90
16.7
725
5.0
906
9
-----$6.0
$75.0
-----$5,438
$675
1
1
1
100
500
$1,500
$300
$500
$1.50
$1.25
$1,500
$300
$500
$150
$625
1
65
15,000
$1,000
$25
$1.50
$1,000
$1,625
$22,500
Total Cost
$34,313
Figure 6: Grundfos Pump Curve for 60 SQF-3 Solar Powered Pump
Grundfos Pumps (www.grundfos.com) [11]
19
Notice that the high water demand of this example SPPS caused the water storage cost
for three days of backup supply to outweigh the PV array costs. In developing countries,
solar powered pumping systems that approach the scale of this example SPPS are
generally considered very high end and in some cases unpractical. If the demand of the
village is this high and the project budget or property constraints of the site do not allow
for this much water storage, it may be more practical to go with a generator and an AC
pump.
5.
Case Study
A village in Nicaragua called Candelaria consisted of 240 people. Due to the severe
summers of the area and recent droughts, many of the men in the village were forced to
relocate to Costa Rica for work picking coffee beans. The women would walk for hours
to collect water and carry it home. Their average day would consist of three trips to
collect water. This village sought out help for funding a community water project and
joined with the NGOs called Asociancion Fenix (AsoFenix) and Green Empowerment.
Green Empowerment and AsoFenix started raising funds, designing, and initiating the
project. The Nicaraguan water authority became part of the project once the NGOs got
involved and they agreed to drill the well for the system. Other NGOs helped fund the
project through Green Empowerment including New Earth Foundation, International
Foundation, Energreen Foundation, and Empresa Nicaraguense de Acuedactos
Alcantarillados (ENACAL). The Nicaraguan water authority had support from United
Nations Children’s Fund (UNICEF). The system design ended up being a SPPS. The
community mobilized in the efforts to have clean water and the NGOs brought education
and training into the community, including sanitation and good hygiene practices. All
locally available supplies were purchased in country and the bulk of the technical
components of the SPPS were purchased from the U.S. distributor called Sun Pumps
(also listed in Table 4). The community became responsible for the long-term
management and maintenance of the system. After conducting a local survey of the
community, AsoFenix helped establish affordable usage fees (tariffs) of 30 cordobas, or
approximately 2 $U.S. per household per month. A community treasurer became
responsible for depositing the money in a local bank and seeing that the money was used
for maintenance and needed improvements to the SPPS [13]. The SPPS was installed
between 2003 and 2004 and was a great success. It quickly became the envy of
surrounding communities that came to appreciate the importance of clean water and
better sanitation practices. The awareness of the surrounding villages also led to more
installations of SPPS initially funded through NGOs and with help from the local water
authority. The specifications not including the tank volume, of the system are listed
below [14]:






People Served =
Dynamic Head =
Well Depth =
Well Test (yield) =
Design Flow =
Pump Model =
240 people
210 feet
140 feet
15 gpm
8 gpm
Grundfos 11-SQF-2
20



6.
PV Array =
12 Isofoton, 94W, 24V panels
PV Array Capacity = 1,128W
Project Cost =
$44,665
Conclusion
Solar-powered pumping systems are making headway in becoming leading and
appropriate technology for small-scale water systems in developing countries. This is
partly due to the many NGOs funding and supporting the effort. However, other
important reasons for the global use of the technology are cost reductions in the
equipment, greater output efficiencies, low maintenance requirements, and durability of
the systems. Not including the recommended three days of demand water storage, the PV
modules are usually the most expensive element of the system, but the average 25 year
life span of well-constructed PV modules may be the most attractive aspect of a SPPS.
The technology has also been around for over 20 years, so many of the once common and
costly installation mistakes can be avoided through a thorough feasibility study, research,
and appropriate training.
21
7.
References
[1]
Meah K. et al. Solar photovoltaic water pumping–opportunities and challenges.
Renewable and Sustainable Energy Reviews 2007:1-14.
[2]
Ratterman W., Cohen J., Garwood A. Solar Pumping Systems (SPS) –
Introductory and Feasibility Guide. Green Empowerment, no date indicated: 1-64.
[3]
Solar Engineers. The Promise of Clean Reliable Energy [On-line], available at:
(http://www.solarengineers.com). retrieved in March 2007.
[4]
Sinton C.W., Butler R., Winnett R. Guide to Solar-Powered Water Pumping
Systems in New York State. New York State Energy Research and Development
Authority (NYSERDA). [On-line], available at: (http://www.nyserda.org/
publications/solarpumpingguide.pdf), retrieved in March 2007.
[5]
Life Water International Technical Library and US AID Water for the World
Technical Notes. [On-line], available at: (http://www.lifewater.org/resources/
tech_library.html), retrieved November 2006.
[6]
Short T.D., Thompson P. Breaking the mould: solar water pumping – the
challenges and the reality. Solar Energy 2003;75(1):1-9.
[7]
American Society for Testing and Materials. ASTM Standards on Ground Water
& Vadose Zone Investigations. ASTM International. Edition: 2. September 1,
1999. ISBN 0803127189.
[8]
Practical Action. technical brief release. Solar (Photovoltaic) Water Pumping.
Intermediate Technology Development Group Ltd. Patron HRH. [On-line]
available at: (http://www.practicalaction.org), retrieved in March 2007.
[9]
Research Institute for Sustainable Energy (rise). Solar Water Pumping Module 2.
[On-line], available at: (http://www.rise.org.au/info/Education/SPS/swp002.html),
retrieved March 2007.
[10]
Villers I. Divwatt Ltd. Ensuring a bright future for solar powered water pumps.
World Pumps, February 1999:1-4.
[11]
Grundfos Pumps. Technical Specifications for SQFlex series pumps, [On-line]
available at (http://www.grundfos.com), retrieved in March 2007.
[12]
Meah K. et al. Solar photovoltaic water pumping for remote locations. Renewable
and Sustainable Energy Review 2006:1-16.
22
[13]
Refocus. Energia Solar-The Rising Solar Solution in Rural Latin America.
Elsevier Ltd. May/June 2005:32-34.
[14]
Green Empowerment. Nicaragua Solar Water Pump – Bringing Potable Water to
the People of Candelaria. [On-line], available at:
(http://www.greenempowerment.org/Nicaragua%20Solar%20Water%20Pump%2
0Project%20Profile.pdf), retrieved on March 25, 2007.
23