The document discusses concentrating solar collectors, which focus direct sunlight onto a small area to achieve high temperatures efficiently. It outlines different types of concentrating collectors, including parabolic troughs, dish systems, and power towers, explaining their mechanisms and applications for generating electricity. The text highlights the advantages and roles of each system in harnessing solar energy, including the potential for thermal storage and hybrid setups with fossil fuels.

1. SOLAR ENERGY COLLECTION
Concentrating Solar Collectors
Dr.V.Malathi
Professor-EEE

2. INTRODUCTION-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.

3. TYPES OF CONCENTRATING COLLECTORS
• Two General Categories : Line Focusing and Point Focusing
• The line is a collector pipe and point is a small volume through which the
heat transport fluid flows
• The main types are:
• Parabolic trough collector
• Mirror strip reflector
• Fresnel lens collector
• Flate plate collector with adjustable mirrors
• Compound parabolic concentrator

4. PARABOLICTROUGH SYSTEM- LINE FOCUSING
COLLECTORS
 Solar radiation coming from particular direction
is collected over the area of the reflecting surface
and is concentrated at the focus of the parabola.
 If the reflector is in the form of a trough with
parabolic cross section, the solar radiation is
focused along a line.
 Parabolic trough reflectors have been made of
highly polished aluminium, of silvered glass or of
a thin film of aluminized plastic, on a firm base.
 Sometimes a transparent glass tube envelops the
receiver tube to reduce heat loss
 For proper focusing sun must be in such a
direction that it lies on the plane passing through
the focal line and vertex of the parabola.

5. • Since elevation of sun is always changing either the reflector trough or the collector pipe must
turn continuously about its main axis to maintain required orientation.
• Generally Oriented in East-West or North-South directions
• For East-West orientation , the collectors are laid flat on the ground.
• For North South orientation , north end of the trough is raised so that the collectors are sloped
facing South
• The slope angle to be changed periodically; it is simpler, but less efficient
• North-South Orientation permits more solar energy to be collected than the east-west arrangement

6. CONT…
Parabolic troughs often use single-axis or dual-axis
tracking.

8. WORK NG PR NC PLES OF CONCENTRAT NG
İ İ İ İ
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

9. 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
Parabolic trough with mirrored parabolic troughs

10. • The energy from the sun sent to the tube heats fluid 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 north south 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.
CONT…

11. • 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
CONT…

12. PARABOL C D SH SYSTEMS
İ İ
Parabolic dish collector with a mirror-like reflectors
and an absorber at the focal point [Courtesy of
SunLabs - Department of Energy
Crossection of parabolic dish
• 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.

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
CONT…

15. • 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.
CONT…

16. D SH SYSTEMS
İ
• 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.

17. COMB NAT ON OF PARABOL C D SH SYSTEM
İ İ İ İ
• 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.

18. POWERTOWER SYSTEM
Fig.
Fig. Heliostats
Heliostats
Fig. Power tower system

19. • A heliostat uses a field of dual axis sun trackers that direct solar energy
to a large absorber located on a tower.
• 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 .
CONT…

20. EXERCISE

21. • The power tower system with heliostats is shown in below.
CONT…

22. CENTRAL RECE VER SYSTEMS
İ OR POWERTOWER
SYSTEM
• 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.
• 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. Designs allow storage ranging
from 3 to 13 hours.

23. The process of molten salt storage
CONT…

24. MIRROR STRIP REFLECTOR

25. CONT…
• Number of slightly curved Mirror strips are mounted on a flat base
• The angles of the individual mirrors are such that they reflect solar radiation from a
specific direction on to the same focal line
• The angles of the mirrors to be adjusted to allow for changes in the suns elevation,
while a focal line remains a fixed position.
• Alternatively mirror strips may be fixed and the collector pipe moved continuously so
as to remain on the focal line.

26. CONT …

27. EXERCISE:

28. FRESNEL COLLECTOR

29. CONT…
• In Fresnel lens collector, solar radiation is focused into the absorber from the top, rather
than from bottom
• Insulation at the bottom and sides of the absorber pipe and a flat-plate over the top
reduce thermal losses
• It utilizes the focusing effect of a Fresnel lens
• The rounded triangular trough serves only as a container and plays no role in
concentrating the solar energy
• To be fully effective, Fresnel lens to be continuously aligned with the sun in two
directions namely, both along and perpendicular to its length.

30. CONT…
• This is achieved by orienting the troughs in the north south direction with the rotation
about the length wise axis
• North ends of the troughs are raised to increase the slope as the suns elevation
decreases
• Total solar radiation energy that can be collected annually is about 30% greater than for
an east-west orientation.

31. • Exercise

32. CONCENTRATING COLLECTORS; NON FOCUSING TYPE
 Simplest type of concentrating collector is the
mirror boosted, flat plate collector.
 It consists of a flat plate facing south with mirrors
attached to its north and south edges
 If the mirrors are set at the proper angle, they reflect
solar radiation on to the absorber plate.
 Thus the latter receives reflected radiation in
addition to that normally falling on it
 The mirrors cut off part of the scattered radiation
that otherwise have reached the absorber plate, and
only part of the scattered radiation falling on the
mirrors will be reflected on to the absorber

33. • Thus the concentration effect arises mainly from the increase in direct radiation reaching
the absorber plate.
• When number of collectors are combined in two or more rows, the rows must be set
further apart in the north south directions to allow for the additional sun shading caused
by the mirror extensions.
• For the mirrors to be more effective, the angles to be adjusted continuously as the suns
attitude changes.
• For these reasons, and they can provide only a relatively small increase in the solar
radiation falling on the absorber, flat plate collectors with mirrors are not widely used.

34. COMPOUND PARABOLIC CONCENTRATOR

35. • CPC(Winston Collector) is a trough like arrangement of two facing parabolic mirrors
• Unlike single parabolic trough, CPC is non-focussing but solar radiation from many
directions is reflected toward the bottom of the trough
• Because of this ;large proportion of the solar radiation, including diffuse radiation
entering the trough opening is collected on a small area.
• In addition to collecting both direct and diffuse radiations, it provides moderately good
concentration