MIDDLE EAST TECHNICAL UNIVERSITY
DEPARTMENT OF PHYSICS
PHYS 471
SOLAR ENERGY -1
INDUSTRIAL
PROCESS HEAT
by
Savaş GÜMÜŞTOP
Instructor: Prof. Dr. Ahmet ECEVIT
2004-1
TABLE OF CONTENT
1. Introduction.............................................................................................. 1
2. Components of Industrial Process Heat System.................................... 5
3. Solar Collector Technology.......................................................................7
3.1 Flat Plate Collectors.........................................................................9
3.2 Compound Parabolic .Concentrators.............................................10
3.3 Evacuated Tubular Collectors.......................................................12
3.4 Parabolic Through Collectors........................................................14
3.5 Solar Ponds.......................................................................................16
4. Industrial Process Heat Systems..............................................................19
4.1 Industrial Solar System Without Heat Storage............................22
4.2 Industrial Solar System With Heat Storage..................................23
5. Industrial Process Heat System Design...................................................25
5.1 Hot Water Industrial Process Heat System..................................26
5.2 Hot Air Industrial Process Heat System.......................................29
5.3 Steam Industrial Process Heat System ........................................30
PAGE
6. Guidelines for Evaluation and System Design.........................32
6.1 Feasibility Analysis...........................................................33
6.1.1 Sellection of Appropriate Interfaces for the
Coupling of a Solar System......................................................34
6.1.2 Influence of the Working Temperature................35
6.1.3 Continuity of the Load and Storage......................36
6.2 Guidelines for System Design...........................................37
6.2.1 Solar Collector Field...............................................38
6.2.2 Storage......................................................................39
7. Conclusion....................................................................................40
References....................................................................................41
1. Introduction
The industrial sector is a major energyconsuming sector in our country, using about
50% of the total commercial energy.
A major portion of industrial energy
consumption is in the form of thermal
energy. And primary sources of this thermal
energy are fossil fuels like coal, lignite, oil
and gas. But upon combustion, these fuels
release large quantities of pollutants [1].
Solar technology may replace fossil fuels. It offers
various cost-effective enduses without endangering
the environment. Commercial and industrial
buildings may use the same solar technologies photovoltaics, passive heating, daylighting, and
water heating - that are used for residential
buildings. These nonresidential buildings can also
use solar energy technologies that would be
impractical for a home. These technologies include
ventilation air preheating, solar process heating, and
cooling [2].
Industrial process heat is the thermal energy used
directly in the preparation or treatment of
materials and items manufactured by an industry.
Large portion of industrial process heat is at
sufficiently low temperatures which can easily be
supplied by solar energy [1].
Beyond the low temperature applications there are
several potential fields of application for solar
thermal energy at a medium and medium-high
temperature level (80ºC -250ºC). The most
important of them are: heat production for
industrial processes, solar cooling and air
conditioning, solar drying, distillation and
desalination [3].
2.Components of Solar Industrial Process
Heat System
Solar process heating systems are designed
to provide large quantities of hot water or
space heating for nonresidential
buildings. A typical system includes solar
collectors that work along with a pump, a
heat exchanger, and/or one or more large
storage tanks [4].
Components
Collectors
 Pump
 Heat exchanger
 Storage tanks

3.Solar Collector Technology
Solar energy collector is the most
important component of any solar
energy utilization device. Different
types of collectors and systems are
used in process heat industries. Due to
the needs and opportunities several
types can be use. Here are some of
them.
*Flat-plate
*Compound Parabolic Concentrator (CPC)
*Evacuated Tubular Collectors
*Parabolic Through Collectors
*Solar Ponds
3.1 Flat Plate Collectors

Flat-plate collectors are characterized by durability,
dependability, simplicity, and high solar collector
efficiency. At low temperatures, the flat-plate collectors
operate at high optical and thermal efficiency
compared to concentrators. However, as the collection
temperature goes on increasing, the efficiency of a
concentrator decreases very slowly while the flat plate
collector efficiency decreases very fast. Therefore, the
most obvious choice is flat plate collectors for
applications below 80 ºC [5].
3.2 Compound Parabolic Concentrator
(CPC)
To reduce the heat losses of a solar collector
consists in reducing the area of absorber with
respect to the collecting area, since the heat
losses are proportional to the absorber area
and not to the collecting area. This
concentration can be obtained using reflectors
that force the radiation incident within a
certain angle into the collector aperture in
direction to the absorber after one or more
reflections. Compound parabolic concentrator
is shown in figure 1.
Fig. 1 : Compound Parabolic Concentrator [6].
3.3 Evacuated Tubular Collectors

An evacuated-tube collector is a shallow
box full of many glass, double-walled
tubes and reflectors to heat the fluid
inside the tubes. A vacuum between the
two walls insulates the inner tube, holding
in the heat. Evacuated tubular collectors
are shown in figure 2.
Fig. 2 : Evacuated Tubular Collectors [6].
3.4 Parabolic Troughs
Collectors

Parabolic troughs are long, rectangular,
curved (U-shaped) mirrors tilted to focus
sunlight on a tube, which runs down the
center of the trough. This heats the fluid
within the tube. Some parabolic trough
collectors are shown in figure 3.
Fig. 3: Parabolic Trough Collectors [6].
3.5 Solar Ponds

A solar pond is a body of water that collects
and stores solar energy. Solar energy will warm
a body of water (that is exposed to the sun), but
the water loses its heat unless some method is
used to trap it. Water warmed by the sun
expands and rises as it becomes less dense.
Once it reaches the surface, the water loses its
heat to the air through convection, or
evaporates, taking heat with it.
The colder water, which is heavier, moves
down to replace the warm water, creating a
natural convective circulation that mixes the
water and dissipates the heat. The design of
solar ponds reduces either convection or
evaporation in order to store the heat
collected by the pond. They can operate in
almost any climate [5].
Types of Solar ponds
* Nonconvecting ponds,
which reduce heat loss by preventing
convection from occurring within the
pond.
* Convecting ponds,
which reduce heat loss by hindering
evaporation with a cover over the surface
of the pond [5].
4. Industrial Process Heat Systems
The economic and technical feasibility of any solar
industrial process heat (SIPH) system depends on
four factors [1].
 Heat must be supplied in sufficient quantity,
 Heat must be of adequate quality, i.e. at an
appropriate temperature,
 Heat must be transferred directly from the solar
collector to the process where it is to be used,
and
 Solar energy must be used profitable.
Each industrial plant has unique requirement
and hence the SIPH system is to be carefully
designed. Because of the specific intermittent
nature of solar radiation, SIPH must be backed
up with alternate fossil-fuel system so that the
industry gets uninterrupted supply of process
heat. Generally SIPH has one of the following
two possible modes :
 Solar
Augmentation without energy
storage, and
 Solar Augmentation with energy storage
[1].
4.1 Industrial Solar System Without Heat Storage
In most of the industries heat demand is so high that there
is no need to store heat. Eliminating storage cost it is
possible to build a low cost solar system. The simplest case
is an industrial solar system supplying heat for a process
with a continuous operation and a load always higher than
the solar gains (process operating at least 12 hours per day
during daytime). In these cases, the solar system can be
conceived without storage. The solar heat produced will be
fed directly to the process or to the heat supply system [7].
Figure 4 shows solar system without storage.
Fig. 4 : Solar System Without Storage [4].
4.2 Industrial Solar System With Heat Storage
If, as it is mostly common, the industrial process operates
only 6 or 5 days a week and it is idle during the
weekend, the system can be designed considering
storage of the energy collected during these weekendbreaks. The collected energy will be used during the
rest of the days of the week.
Storage may also be necessary if there are strong
fluctuations of the process heat demand during the
operational periods (demand peaks, short breaks of
operation) [7].
Figure 5 shows solar system with heat storage.
Fig. 5 : Solar System With Heat Storage [7].
5. Industrial Process Heat System Design
The process heat in various industries is supplied
generally in the following three modes [1].



Process hot water,
Hot air, and
Process steam.
5.1 Hot Water Industrial Process Heat System

In hot water process systems both the direct
solar water system where the heated water
from the solar collector is directly supplied as
process heat and indirect solar hot water
system where a heat exchanger is used between
the collector loop and delivery loop are used. In
cold climates, an indirect water system is used
with some antifreeze mixtures in the collector
and storage loop. Direct systems although work
at higher efficiency are preferred only in hot
climates or during the day time or in special
process industries or with some precautionary
measures for protecting it against damage due
to freezing.
In industries large amounts of hot water in
the temperature range of 50-100 °C is
required for applications like cooking,
washing, bleaching etc. The solar preheated water can also be used as feed
water to boilers [1].
Schematic diagram of the solar energy
system is shown in figure 6.
Fig. 6 : Schematic Diagram of The Solar Energy System [4].
5.2 Hot Air Industrial Process Heat System

Hot air systems are employed for drying or
dehydration processes in industries and such systems
are safe from damage due to freezing. The hot air if
sufficiently heated by Solar Energy can be directly
supplied for drying/dehydration or can be further
heated by an auxiliary heater before it goes to process
load. An alternative to direct hot air system is the use of
liquid collectors (since they are better than air
collectors) and a liquid-to-air heat exchanger (which
reduce the efficiency) and finally heated air can be
supplied to the process load [4]. Heated air can be
directly used for ventilation and heating such
application in Fed-ex Denver can be seen in figure 7.
Fig. 7 Solar system used for ventilation and heating [4].
5.3 Steam Industrial Process Heat System
In industries the largest share of process heat (two thirds
of all industrial process heat) is met by steam.
Significantly different approaches is used for producing
steam using solar energy then that for air or water
process heating. Following three possible ways to
supply steam with solar collectors are tried :
 Circulation of pressurized water in the collectors
with subsequent flashing to steam in a flash tank,
 Use of high temperature fluid in the collectors with
heat transferred to an unfired boiler, and
 Boiling of water in collectors [1].
Figure 8 shows schematic diagram of the solar process
steam system using a flash tank.
Fig. 8. Schematic Diagram of The Solar Process Steam System Using
A Flash Tank [1].
6. Guidelines for Evaluation and
System Design
6.1 Feasibility Analysis
6.1.1 Selection of Appropriate Interfaces for
the Coupling of a Solar System
First of all most appropriate interfaces
(processes) of coupling a solar system to the
existing heat supply have to be selected. The
selection criteria are the following [7].



Low temperature level: Solar heat at
temperatures above 150  C is technically
feasible but not economically reasonable at
present system costs. Applications at low
temperature (<60  C) are best,
Continuous demand (otherwise storage is
needed), and
Technical possibility of introducing a heat
exchanger for the solar system in the existing
equipment or heat supply circuit [7].
6.1.2 Influence of the Working Temperature
The upper limit for the working temperature depends
on the climate. As a rule thumb, it can be stated that
solar systems for temperatures above 100 °C are only
recommendable in high radiation regions (southern
regions). In the northern regions only low temperature
systems should be considered. It has to be taken into
account that working temperature in the solar system is
always somewhat higher than the required process
temperatures , due to losses in the piping and the
temperature drop in heat exchangers.
6.1.3 Continuity of the Load and Storage
In order to obtain a reasonable economic performance,
solar systems should be designed close the ideal of
100% utilization. This means that the heat demand
should always be higher than the maximum possible
output of the solar system. Otherwise, and if no storage
is used, the useful heat drawn from the solar system is
reduced [3].
6.2 Guidelines for System Design

6.2.1 Solar Collector Field
While selecting collector type, operating
temperature is most imported aspect. Other
aspects such as the possibility of roof integration
or system size have to be considered as well . By
an adequate design of flow rates, pipe diameters
and pipe insulation, the electricity consumption
for fluid circulation can be below 1% of the
overall heat gains. Thermal losses in the piping
and storage should not be above 5% of the overall
heat gains for medium and large size systems [3].
Table 1 shows the selection criteria of collector
type for different applications.
Table 1. The selection criteria of collector type for different
applications [6].
6.2.2 Storage

Short-term heat storage is recommended whenever a
mismatch between available solar radiation and heat
demand occurs. For short-term storage (several hours)
storage volumes about 25 liter /m2 are recommended.
Short-term storage may even be recommended for
continuously operating process, in order to lower the
mean working temperature of the solar system and
thereby improving its efficiency, especially if low cost
solar collectors with high thermal loss coefficients are
used. The larger the system’s size the more effective the
heat storage over longer periods (e.g. weekends) [3].
7.Conclusion

The industrial sector is a major energyconsuming sector in every country, using about
50% of the total commercial energy. In general,
industry is highly energy-intensive and its
energy efficiency is well below that of
othersectors. Moreover, on account of high
specific fuel consumption, it becomes difficult
for the developing countries products to be
competitive globally. A major portion of
industrial energy consumption is in the form of
thermal energy.

And primary sources of this thermal energy are fossil
fuels like coal, lignite, oil and gas. But upon
combustion, these fuels release large quantities of
pollutants such as suspended particulate matter, SO2,
NOx, CO2 and CO. Thus, there is an urgent need to find
alternative technologies that not only address everworsening energy situation but also are enviromentally
benign. Solar technology is one of such options. It offers
various cost-effective enduses without endangering the
environment. By virtue of having built-in energy
storage, it can be used irrespective of time and season.
In industry, where there is a demand of thermal energy
in a number of energy intensive processes, SIPH can
offer cost-effective solutions.
References







[1] Advances in Solar Energy Technology, Garg H.P, Volume
2 (Industrial Application of Solar Energy), D.Reidel
Publishing Company, 1987
[2] http://www.teriin.org/division/eetdiv/reta/docs/abs02.htm
[3] Poship Final Report : http://www.aiguasol.com/poship.htm
[4] http://www.nrel.gov/clean_energy/solarprocessheat.html
[5] http://www.eere.energy.gov/consumerinfo/factsheets
/aa8.html
[6] http://www.solarnetix.com/vacuumtubesolar.htm
[7] http://www.eere.energy.gov/consumerinfo/factsheets
/aa8.html