This document discusses different types of concentrating solar collectors that can achieve higher temperatures than flat plate collectors. It describes four main types: parabolic trough systems, parabolic dish/engine systems, power tower systems, and stationary concentrating collectors. For each type it provides details on how it works, temperatures and efficiencies achieved, examples of implementations, and comparisons of features.

1. SOLAR
POWERCOMPLETE
DESCRIPTION By
A.S.Krishna

2. Putting Solar Energy to Use: Heating
Water by Flat Plate Collectors
 Two methods of heating water:
passive (no moving parts) and
active (pumps).
 In both, a flat-plate collector is
used to absorb the sun’s energy
to heat the water.
 The water circulates throughout
the closed system due to
convection currents.
 Tanks of hot water are used as
storage.

3. Heating Water: Active System

4. Concentrating collectors

5. Introduction
For applications such as air conditioning, central power generation,
and numerous industrial heat requirements, flat plate collectors
generally cannot provide carrier fluids at temperatures sufficiently
elevated to be effective.
They may be used as first-stage heat input devices; the temperature
of the carrier fluid is then boosted by other conventional heating
means. Alternatively, more complex and expensive concentrating
collectors can be used.
These are devices that optically reflect and focus incident solar
energy onto a small receiving area. As a result of this concentration,
the intensity of the solar energy is magnified, and the temperatures
that can be achieved at the receiver (called the "target") can
approach several hundred or even several thousand degrees Celsius.
The concentrators must move to track the sun if they are to
perform effectively.

6. Concentrating collectors
Concentrating, or focusing, collectors intercept direct
radiation over a large area and focus it onto a small
absorber area. These collectors can provide high
temperatures more efficiently than flat-plate collectors,
since the absorption surface area is much smaller.
However, diffused sky radiation cannot be focused onto
the absorber. Most concentrating collectors require
mechanical equipment that constantly orients the collectors
toward the sun and keeps the absorber at the point of
focus. Therefore; there are many types of concentrating
collectors

7. Types of concentrating
collectors
There are four basic types of concentrating collectors:
 Parabolic trough system
 Mirror strip (or)Parabolic dish
 Power tower
 Stationary concentrating collectors

8. Parabolic trough system
Parabolic troughs are devices that are shaped like the letter “u”.
The troughs concentrate sunlight onto a receiver tube that is
positioned along the focal line of the trough. Sometimes a
transparent glass tube envelops the receiver tube to reduce heat
loss
The parabolic trough sytem is shown in
the figure 1.2 below.
Their shapes are like letter “u” as
shown figure 1.1 below.
Receiver
Sun rays
Parabola
Tracking
mechanism
Figure 1.1 Crossection of parabolic trough Figure 1.2 Parabolic trough system .

10. Parabolic troughs often use single-axis or dual-axis tracking.
Figure 1.3 One Axis Tracking Parabolic Trough with
Axis Oriented E-W
Figure 1.4 Two Axis Tracking Concentrator
The below figure 1.3 shows one axis tracking
parabolic trough with axis oriented E-W.
The below figure 1.4 shows two axis
tracking concentrator.

11. Temperatures at the receiver can reach 400 °C and produce
steam for generating electricity. In California, multi-megawatt
power plants were built using parabolic troughs combined with
gas turbines
Parabolic trough combined with gas turbines is shown figure
1.5 below.
Figure 1.5 Parabolic trough combined with gas turbines [4].

12. ECONOMIC ASPECTS:
Cost projections for trough technology are higher
than those for power towers and dish/engine systems
due in large part to the lower solar concentration and
hence lower temperatures and efficiency.
However with long operating experience, continued
technology improvements, and operating and
maintenance cost reductions, troughs are the least
expensive, most reliable solar thermal power
production technology for near-term

13. Mirror Strip (or)Parabolic
dish systems
A parabolic dish collector is similar in appearance to a large
satellite dish, but has mirror-like reflectors and an absorber
at the focal point. It uses a dual axis sun tracker .
Figure 2.2 Parabolic dish collector with a mirror-like
reflectors and an absorber at the focal point [Courtesy of
SunLabs - Department of Energy]
The below figure 2.1 shows crossection
of parabolic dish.
Figure 2.1 Crossection of parabolic dish .
The Parabolic dish collector is shown in
the below figure 2.2.

14. A parabolic dish system uses a computer to track the sun and
concentrate the sun's rays onto a receiver located at the focal point in
front of the dish. In some systems, a heat engine, such as a Stirling
engine, is linked to the receiver to generate electricity.
Parabolic dish systems can reach 1000 °C at the receiver, and
achieve the highest efficiencies for converting solar energy to
electricity in the small-power capacity range.
Figure 2.3 Solar dish stirling engine.

15. Engines currently under consideration include Stirling and
Brayton cycle engines. Several prototype dish/engine systems,
ranging in size from 7 to 25 kW have been deployed in
various locations in the USA. High optical efficiency and low
start up losses make dish/engine systems the most efficient of
all solar technologies. A Stirling engine/parabolic dish system
holds the world’s record for converting sunlight into
electricity. In 1984, a 29% net efficiency was measured at
Rancho Mirage, California ].

16. 3.3. Power tower system
A heliostat uses a field of dual axis sun trackers that direct solar
energy to a large absorber located on a tower. To date the only
application for the heliostat collector is power generation in a
system called the power tower .
Heliostats are shown in the
figure below.
Figure 3.3.1 Power tower system [4]. Figure 3.3.2 Heliostats [4].

17. A power tower has a field of large mirrors that follow the sun's
path across the sky. The mirrors concentrate sunlight onto a
receiver on top of a high tower. A computer keeps the mirrors
aligned so the reflected rays of the sun are always aimed at the
receiver, where temperatures well above 1000°C can be
reached. High-pressure steam is generated to produce
electricity [3].
The power tower system with heliostats is shown in the figure
3.3.3 below.
Figure 3.3.3 Power tower system with heliostats [4].

18. 3.4. Stationary concentrating
solar collectors
Stationary concentrating collectors use compound parabolic
reflectors and flat reflectors for directing solar energy to an
accompanying absorber or aperture through a wide acceptance
angle. The wide acceptance angle for these reflectors eliminates
the need for a sun tracker. This class of collector includes
parabolic trough flat plate collectors, flat plate collectors with
parabolic boosting reflectors, and solar cooker. Development of
the first two collectors has been done in Sweden. Solar cookers
are used throughout the world, especially in the developing
countries [3].

19. 4. Working principles of
concentrating collectors
Unlike solar (photovoltaic) cells, which use light to produce
electricity, concentrating solar power systems generate electricity
with heat. Concentrating solar collectors use mirrors and lenses to
concentrate and focus sunlight onto a thermal receiver, similar to a
boiler tube. The receiver absorbs and converts sunlight into heat.
The heat is then transported to a steam generator or engine where
it is converted into electricity. There are three main types of
concentrating solar power systems: parabolic troughs, dish/engine
systems, and central receiver systems.
These technologies can be used to generate electricity for a variety
of applications, ranging from remote power systems as small as a
few kilowatts (kW) up to grid connected applications of 200-350
megawatts (MW) or more. A concentrating solar power system that
produces 350 MW of electricity displaces the energy equivalent of
2.3 million barrels of oil

20. 4.1. Trough Systems
These solar collectors use mirrored parabolic troughs to focus the
sun's energy to a fluid-carrying receiver tube located at the focal
point of a parabolically curved trough reflector [5].It is shown in
the figure 4.1.1 below.
Figure 4.1.1 Parabolic trough with mirrored parabolic troughs [10].

21. The energy from the sun sent to the tube heats oil flowing
through the tube, and the heat energy is then used to generate
electricity in a conventional steam generator. Many troughs
placed in parallel rows are called a "collector field." The
troughs in the field are all aligned along a northsouth axis so
they can track the sun from east to west during the day,
ensuring that the sun is continuously focused on the receiver
pipes. Individual trough systems currently can generate about
80 MW of electricity.

22. Trough designs can incorporate thermal storage-setting aside
the heat transfer fluid in its hot phase allowing for electricity
generation several hours into the evening. Currently, all
parabolic trough plants are "hybrids," meaning they use fossil
fuels to supplement the solar output during periods of low
solar radiation. Typically, a natural gas-fired heat or a gas
steam boiler/reheater is used. Troughs also can be integrated
with existing coal-fired plants [5].

23. 4.2. Dish Systems
Dish systems use dish-shaped parabolic mirrors as reflectors to
concentrate and focus the sun's rays onto a receiver, which is
mounted above the dish at the dish center. A dish/engine system
is a stand alone unit composed primarily of a collector, a receiver,
and an engine. It works by collecting and concentrating the sun's
energy with a dishshaped surface onto a receiver that absorbs the
energy and transfers it to the engine. The engine then converts
that energy to heat. The heat is then converted to mechanical
power, in a manner similar to conventional engines, by
compressing the working fluid when it is cold, heating the
compressed working fluid, and then expanding it through a
turbine or with a piston to produce mechanical power. An
electric generator or alternator converts the mechanical power
into electrical power.

24. Each dish produces 5 to 50 kW of electricity and can be used
independently or linked together to increase generating
capacity. A 250-kW plant composed of ten 25-kW
dish/engine systems requires less than an acre of land.
Dish/engine systems are not commercially available yet,
although ongoing demonstrations indicate good potential.
Individual dish/engine systems currently can generate about
25 kW of electricity. More capacity is possible by connecting
dishes together. These systems can be combined with natural
gas, and the resulting hybrid provides continuous power
generation [5].
Figure 4.2.1 Combination of parabolic dish system [4].
The right figure 4.2.1 shows
the combination of parabolic
dish system.

25. 4.3. Central Receiver Systems
Central receivers (or power towers) use thousands of individual
sun-tracking mirrors called "heliostats" to reflect solar energy
onto a receiver located on top of tall tower. The receiver
collects the sun's heat in a heat-transfer fluid (molten salt) that
flows through the receiver. The salt's heat energy is then used to
make steam to generate electricity in a conventional steam
generator, located at the foot of the tower. The molten salt
storage system retains heat efficiently, so it can be stored for
hours or even days before being used to generate electricity [5].
In this system, molten-salt is pumped from a “cold” tank at 288
deg.C and cycled through the receiver where it is heated to 565
deg.C and returned to a “hot” tank. The hot salt can then be
used to generate electricity when needed. Current designs allow
storage ranging from 3 to 13 hours [4].

26. Figure 4.3.1 shows the process of molten salt storage.
Figure 4.3.1 The process of molten salt storage [11].

27. 5. Technology Comparison
Towers and troughs are best suited for large, grid-connected
power projects in the 30-200 MW size, whereas, dish/engine
systems are modular and can be used in single dish applications
or grouped in dish farms to create larger multi-megawatt
projects. Parabolic trough plants are the most mature solar power
technology available today and the technology most likely to be
used for near-term deployments. Power towers, with low cost
and efficient thermal storage, promise to offer dispatchable, high
capacity factor, solar-only power plants in the near future.

28. The modular nature of dishes will allow them to be used in
smaller, high-value applications. Towers and dishes offer the
opportunity to achieve higher solar-to-electric efficiencies and
lower cost than parabolic trough plants, but uncertainty remains as
to whether these technologies can achieve the necessary capital
cost reductions and availability improvements. Parabolic troughs
are currently a proven technology primarily waiting for an
opportunity to be developed. Power towers require the operability
and maintainability of the molten-salt technology to be
demonstrated and the development of low cost heliostats.
Dish/engine systems require the development of at least one
commercial engine and the development of a low cost
concentrator [4].

29. Highlights the key features of the three solar technologies.
Parabolic Trough Dish/Engine Power Tower
Size 30-320 MW 5-25 kW 10-200 MW
Operating Temperature
(ºC/ºF)
390/734 750/1382 565/1049
Annual Capacity Factor 23-50 % 25 % 20-77 %
Peak Efficiency 20%(d) 29.4%(d) 23%(p)
Net Annual Efficiency 11(d)-16% 12-25%(p) 7(d)-20%
Commercial Status
Commercially Scale-up
Prototype
Demonstration AvailableDemonstration
Technology
Development Risk
Low High Medium
Storage Available Limited Battery Yes
Hybrid Designs Yes Yes Yes
Cost USD/W 2,7-4,0 1,3-12,6 2,5-4,4
(p) = predicted; (d) = demonstrated;
Table 5.1 Key features of the three solar technologies [4].

30. 7. Economic and Environmental
Considerations
The most important factor driving the solar energy system
design process is whether the energy it produces is economical.
Although there are factors other than economics that enter into
a decision of when to use solar energy; i.e. no pollution, no
greenhouse gas generation, security of the energy resource etc.,
design decisions are almost exclusively dominated by the
‘levelized energy cost’. This or some similar economic
parameter, gives the expected cost of the energy produced by
the solar energy system, averaged over the lifetime of the
system.

31. Commercial applications from a few kilowatts to hundreds of
megawatts are now feasible, and plants totaling 354 MW have
been in operation in California since the 1980s. Plants can
function in dispatchable, grid-connected markets or in
distributed, stand-alone applications. They are suitable for fossil-hybrid
operation or can include cost-effective storage to meet
dispatchability requirements. They can operate worldwide in
regions having high beam-normal insolation, including large areas
of the southwestern United States, and Central and South
America, Africa, Australia, China, India, the Mediterranean
region, and the Middle East, . Commercial solar plants have
achieved levelized energy costs of about 12-15¢/kWh, and the
potential for cost reduction are expected to ultimately lead to
costs as low as 5¢/kWh [6].

32. 8. Conclusions
Concentrating solar power technology for electricity generation
is ready for the market. Various types of single and dual-purpose
plants have been analysed and tested in the field. In
addition, experience has been gained from the first commercial
installations in use worldwide since the beginning of the 1980s.
Solar thermal power plants will, within the next decade, provide
a significant contribution to an efficient, economical and
environmentally benign energy supply both in large-scale
gridconnected dispatchable markets and remote or modular
distributed markets. Parabolic and Fresnel troughs, central
receivers and parabolic dishes will be installed for solar/fossil
hybrid and solar-only power plant operation. In parallel,
decentralised process heat for industrial applications will be
provided by low-cost concentrated collectors.

33. Following a subsidised introduction phase in green markets,
electricity costs will decrease from 14 to 18 Euro cents per
kilowatt hour presently in Southern Europe towards 5 to 6
Euro cents per kilowatt hour in the near future at good sites
in the countries of the Earth’s sunbelt. After that, there will
be no further additional cost in the emission reduction by
CSP. This, and the vast potential for bulk electricity
generation, moves the goal of longterm stabilisation of the
global climate into a realistic range. Moreover, the problem of
sustainable water resources and development in arid regions
is addressed in an excellent way, making use of highly
efficient, solar powered co-generation systems. However,
during the introduction phase, strong political and financial
support from the responsible authorities is still required, and
many barriers must be overcome [7].

34. References
 [1]http://aloisiuskolleg.www.de/schule/fachber
eiche/comenius/charles/solar.html
 [2]http://www.tpub.com/utilities/index.html
 [3]http://www.canren.gc.ca/tech.appl/index.asp

35. Some Other Useful
Data

36. Types of solar collectors
Motion Collector type
Absorber
type
Concentration
ratio
Indicative
temperature
range (°C)
Stationary
Flat plate collector (FPC) Flat 1 30-80
Evacuated tube collector (ETC) Flat 1 50-200
Compound parabolic collector (CPC) Tubular
1-5 60-240
Single-axis
tracking
5-15 60-300
Linear Fresnel reflector (LFR) Tubular 10-40 60-250
Parabolic trough collector (PTC) Tubular 15-45 60-300
Cylindrical trough collector (CTC) Tubular 10-50 60-300
Two-axes
tracking
Parabolic dish reflector (PDR) Point 100-1000 100-500
Heliostat field collector (HFC) Point 100-1500 150-2000
Note: Concentration ratio is defined as the aperture area divided by the receiver/absorber area of the collector.
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37. Modes of Tracking
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38. Comparison of energy absorbed
for various modes of tracking
Tracking mode
Solar energy (kWh/m2) Percent to full tracking
E SS WS E SS WS
Full tracking 8.43 10.60 5.70 100.0 100.0 100.0
E-W Polar 8.43 9.73 5.23 100.0 91.7 91.7
N-S Horizontal 6.22 7.85 4.91 73.8 74.0 86.2
E-W Horizontal 7.51 10.36 4.47 89.1 97.7 60.9
Note: E - Equinoxes, SS - Summer Solstice, WS -Winter Solstice
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39. Parabolic Trough System
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40. Parabolic trough collectors
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41. Parabola detail
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42. Receiver detail
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43. Central receiver system
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44. Heliostat detail
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45. Central receiver-1
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46. Central receiver-2
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47. Central receiver-3
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48. Central receiver-4
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49. Central receiver-5
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50. Central receiver-6
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51. Central receiver-7
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52. Central receiver-8
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53. Solar energy should be given a
chance if we want to protect the
environment.
We own it to our children, our
grandchildren and the
generations to come.
Thank you for your attention,
any questions please….
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