Electricity production using solar thermal technologies

1. 3.
ELECTRICITY GENERATING Solar
thermal collectors

2. • Conversion of thermal energy into electricity requires conversion
at two stages – first a fluid is converted into steam and second
steam is used to rotate a turbine (and alternator). The solar
thermal technology used for electrical power generation must
raise the temperature of the fluid such that it gets converted into
steam and can rotate the turbine. Solar thermal technologies used
for this purpose is called Concentrated Solar Power (CSP)
Technology.
• CSP technologies use mirrors to reflect and concentrate sunlight
onto receivers that collect solar energy and convert it to heat.
Thermal energy can then be used to produce electricity via a
turbine or heat engine driving a generator.
• Because CSP technologies collect solar energy and convert it to
thermal energy that can be stored before powering a generator,
they can be used either as a flexible provider of electricity, such as
a natural gas “peaker” plant, or as a baseload source of electricity
similar to a traditional nuclear or coal plant.

3. • CSP can also be deployed as fossil-fuel
backup/hybridization that allows existing fossil fuel
projects to run cleaner while operating at the same or
lower cost.
• The CSP technologies are primarily classified according
to the way the mirrors are concentrating the sun rays
for raising the temperature of the fluid kept in the
container. They are classified as:
– Parabolic trough
– Parabolic dish
– Power tower
– Linear fresnel reflector

5. Parabolic Trough Reflector
• Parabolic trough power plants use a curved, mirrored trough which
reflects the direct solar radiation onto a glass tube containing a fluid
(also called a receiver, absorber or collector) running the length of the
trough, positioned at the focal point of the reflectors.
• The trough is parabolic along one axis and linear in the orthogonal axis.
• For change of the daily position of the sun perpendicular to the receiver,
the trough tilts east to west so that the direct radiation remains focused
on the receiver. However, seasonal changes in the angle of sunlight
parallel to the trough does not require adjustment of the mirrors, since
the light is simply concentrated elsewhere on the receiver.
• Thus the trough design does not require tracking on a second axis. The
receiver may be enclosed in a glass vacuum chamber. The vacuum
significantly reduces convective heat loss.
• A fluid (also called heat transfer fluid) passes through the receiver and
becomes very hot. Common fluids are synthetic oil, molten salt and
pressurized steam. The fluid containing the heat is transported to a heat
engine where about a third of the heat is converted to electricity.

6. Parabolic Dish Collector

7. Parabolic Dish Collector
• With a parabolic dish collector, one or more parabolic dishes concentrate
solar energy at a single focal point, similar to the way a reflecting
telescope focuses starlight, or a dish antenna focuses radio waves. This
geometry may be used in solar furnaces and solar power plants.
• The shape of a parabola means that incoming light rays which are
parallel to the dish's axis will be reflected toward the focus, no matter
where on the dish they arrive.
• Light from the sun arrives at the Earth's surface almost completely
parallel, and the dish is aligned with its axis pointing at the sun, allowing
almost all incoming radiation to be reflected towards the focal point of
the dish.
• Most losses in such collectors are due to imperfections in the parabolic
shape and imperfect reflection.
• Losses due to atmospheric scattering are generally minimal. However, on
a hazy or foggy day, light is diffused in all directions through the
atmosphere, which significantly reduces the efficiency of a parabolic
dish.
• In dish stirling power plant designs, a stirling engine coupled to a
dynamo, is placed at the focus of the dish. This absorbs the energy
focused onto it and converts it into electricity.

8. Power tower

9. Power tower
• A power tower is a large tower surrounded by tracking mirrors called
heliostats. These mirrors align themselves and focus sunlight on the receiver at
the top of tower, collected heat is transferred to a power station below.
• This design reaches very high temperatures. High temperatures are suitable for
electricity generation using conventional methods like steam turbine or a
direct high temperature chemical reaction such as liquid salt.
• By concentrating sunlight, current systems can get better efficiency than simple
solar cells. A larger area can be covered by using relatively inexpensive mirrors
rather than using expensive solar cells. Concentrated light can be redirected to
a suitable location via optical fiber cable for such uses as illuminating buildings.
• Heat storage for power production during cloudy and overnight conditions can
be accomplished, often by underground tank storage of heated fluids. Molten
salts have been used to good effect. Other working fluids, such as liquid
metals, have also been proposed due to their superior thermal properties.
• However, concentrating systems require sun tracking to maintain sunlight focus
at the collector. They are unable to provide significant power in diffused light
conditions.
• Solar cells are able to provide some output even if the sky becomes cloudy, but
power output from concentrating systems drops drastically in cloudy
conditions as diffused light cannot be concentrated.

10. Linear fresnel reflector

11. Linear fresnel reflector
• A linear Fresnel reflector power plant uses a series of long, narrow, shallow-
curvature (or even flat) mirrors to focus light onto one or more linear receivers
positioned above the mirrors. On top of the receiver a small parabolic mirror
can be attached for further focusing the light.
• These systems aim to offer lower overall costs by sharing a receiver between
several mirrors (as compared with trough and dish concepts), while still using
the simple line-focus geometry with one axis for tracking. This is similar to the
trough design (and different from central towers and dishes with dual-axis).
The receiver is stationary and so fluid couplings are not required (as in troughs
and dishes). The mirrors also do not need to support the receiver, so they are
structurally simpler.
• When suitable aiming strategies are used (mirrors aimed at different receivers
at different times of day), this can allow a denser packing of mirrors on
available land area.
• Rival single axis tracking technologies include the relatively new linear Fresnel
reflector (LFR) and compact-LFR (CLFR) technologies. The LFR differs from that
of the parabolic trough in that the absorber is fixed in space above the mirror
field. Also, the reflector is composed of many low row segments, which focus
collectively on an elevated long tower receiver running parallel to the reflector
rotational axis.

12. Concentrating solar power (CSP)

13. Concentrating solar power (CSP)
• Concentrating solar power is largely utilized in power generation
• The main component of power generation resemble a conventional
coal/gas power plant – except that the coal combustion process is
replaced by solar thermal heat generation

14. Concentrating solar power (CSP)

15. Concentrating solar power (CSP)
• The power plant work on the
principle of Rankine Cycle
• Through this cyclic process, heat
energy (Qboiler) is converted into
mechanical work output (Wturbine)
through rotation of turbine shaft.
• An electrical generator is fitted in
front of the turbine to convert the
mechanical shaft work to
electricity.
• Some additional pump work
(Wpump) is required to be done and
some heat is rejected to the
environment (Qcondenser)
Qboiler +Wpump = Qcondenser + Wturbine
Wpump , Qcondenser can not be zero
Wpump << Wturbine , Qcondenser < Qboiler

16. Concentrating solar power (CSP)
Qboiler +Wpump = Qcondenser + Wturbine
Wpump , Qcondenser can not be zero
Wpump << Wturbine (almost negligible)
Qcondenser < Qboiler
𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 1 −
Qcondenser
Qboiler
Qboiler Qcondenser

17. Concentrating solar power (CSP)
• T is temperature of steam or water in Kelvin
• So higher the difference between the temperatures, higher is the theoretical
efficiency
• As a result, to practically achieve higher power generation efficiency, it is
better to have high steam temperature coming out of the solar field
• The storage tanks are there as a buffer system to stabilize the temperatures
𝐻𝑖𝑔ℎ𝑒𝑠𝑡 𝑝𝑜𝑠𝑠𝑖𝑏𝑙𝑒
𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦
= 1 −
Tcondenser
Tboiler
Tboiler
Tcondenser

18. Concentrating solar power (CSP)
• Therefore higher concentration is always desirable
• Four major technologies are available
– Parabolic trough collector (PTC)
– Paraboloid dish collector (PDC)
– Central Power Tower – heliostat
(CPT or SPT)
– Liner Fresnel reflector (LFR)
• Now if you wish to concentrate radiation then you can use it larger area of
mirrors.
• So effectively you are collecting same amount of energy available but
collecting them on smaller area
Reflector/ mirror
Absorber/receiver
Sunlight

19. Concentrating solar power (CSP)

20. Concentrating solar power (CSP)
Receiver

21. Concentrating solar power (CSP)

22. Concentrating solar power (CSP)

23. Concentrating solar power (CSP)

24. Concentrating solar power (CSP)
• Important factor for CSP technologies commercial success
1. Direct normal irradiance (DNI)
2. Land requirement
3. Thermal energy storage
4. Water requirement
5. Availability of transmission and supporting infrastructure
6. Potential for auxiliary supply
• Threshold value (5 to 5.5 kWh/m2/day)~(1800 to 2000 kWh/m2/year)
• Now the threshold energy available must be through direct beam only, therefore only
limited areas in India have the potential for CSP based power generation unlike solar PV
based technology
• Andhra Pradesh, Gujarat, Maharashtra, Rajasthan, Tamilnadu, Ladakh Region
• 1.6 ha/MW to 8.36 ha/MW
• 300 L/MWh to 4500 L/MWh, 90% for cooling and 10% for washing of mirror

25. Concentrating solar power (CSP)
Commercial CST Technology
Central Tower
Paraboloid
Dish
Fresnel
Reflector
Parabolic
Trough
• Temperature: (°C)
upto 300
• Line Focusing
• Linear receiver
• Fixed absorber row
• Working fluid: water/steam
• Flat or curved concentrator:
mirror
• Commercially under
development
• Heat storage possible
• Water requirement:
(L/MWh)
3800-3800
• Land
requirement:(acre/MW)
2.5: Direct
• CUF(%) : 22-24
• Temperature: (°C)
upto 400
• Line Focusing
• Linear Receiver tube
• Concentrator: Parabolic
mirror
• Working Fluid: Thermic
fluid, steam
• Highly commercially
available
• Require flat land
• Heat storage feasible
• Water
requirement:(L/MWh)
300-3500
• Land
requirement:(acre/MW)
6.2: Direct
• CUF(%): 25-43
• Temperature: (°C)
120 to 750
• Point Focusing
• Dish Concentrator
• Stirling engine/ micro-turbine
• Working fluid: air
• Dry cooling/ no cooling
required
• Highest efficiency
• Heat storage difficult
• Commercially under
development
• Water requirement: (L/MWh)
76: Mirror washing
• Land requirement:(acre/MW)
2.8: Direct
• CUF(%): 25-28
• Temperature (°C)
450 to 1500
• Point Focusing
• Flat Concentrator: mirror
• Working fluid: thermic fluid,
water, air
• Concentrator: heliostat
• Commercially experience in
needed
• Feasible on non flat sites
• Heat storage feasible
• Water requirement:(L/MWh)
340-2800
• Land
requirement:(acre/MW)
8.9: Direct
• CUF(%): 25-55

26. Concentrating solar power (CSP)
Source: A. Kumar et. al (2017),H.L. Zhang et. al (2013),M.I. Serrano (2017),
T.V. Ramchandra et. al (2011)
Source: V. Siva Reddy et al (2013), IEA,IRENA
CSP Technology Efficiency (%)
PTC 10-16
LFR 9-15
PDC 18-25
SPT 14-20
CSP Technology Temperature (°C)
PTC 20-400
LFR 50-300
PDC 120-700
SPT 250-1500
8
10
12
14
16
18
20
22
24
26
PTC LFR PDC SPT
Efficiency
(η)
%
Efficiency Range
Parabolic trough collector (PTC) , Liner Fresnel reflector (LFR), Paraboloid dish collector (PDC), Central Power Tower – heliostat (CPT or SPT),

27. Concentrating solar power (CSP)

28. Concentrating solar power (CSP)
Source: S. Ong et. al 2013 [10]
Land Requirement for Different CSP Technologies
Parabolic trough collector (PTC) , Liner Fresnel reflector (LFR), Paraboloid dish collector (PDC), Central Power Tower – heliostat (CPT or SPT),

29. Concentrating solar power (CSP)
S.
no
.
Plant Technolo
gy used
Capacit
y (MW)
Solar field
area (m2)
Solar field
temp. (°C)
Storage
type/capacity
HTF Turbine
Design
Power
cycle
1. Abhijeet PTC 50 - - None Therminol VP-1 SST-700 Rankine
2. Acme solar CT 2.5 16,222 218-440 None Water/steam - Rankine
3. Diwakar PTC 100 - - 4h, two tank
indirect-molten
salt, 1010 MWht
Synthetic oil SST-700 Rankine
4. Godawari Green
Energy
PTC 50 392,400 293-390 None Dowtherm SST-700 -
5. Gujarat Solar One PTC 25 326,800 293-393 9h, two tank
indirect- molten
salt
Diphyl - Rankine
6. India One Schefller
Dish
1 46,200 150-260 cast iron block,
16 h
Steam - Rankine
7. KVK Energy PTC 100 - - 4h, two tank,
indirect, molten
salt
- SST-700 -
8. Megha Engineering PTC 50 366,240 293-393 8h, molten salt Xceltherm®MK1 - Rankine
9. Rajasthan Solar One PTC 10 - - 8h, molten salt Molten salt - Rankine
10
.
Rajasthan Sun
Technique
LFR 125 - - None - - Rankine
11
.
NSTPF NISE PTC/LFR 1 8175/7020 293-393 None Therminol VP-1 - Rankine

30. Other applications of solar thermal

31. Other applications of solar thermal

32. Other applications of solar thermal

33. Other applications of solar thermal

34. Other applications of solar thermal

35. Other applications of solar thermal

36. Other applications of solar thermal

37. Other applications of solar thermal

38. Other applications of solar thermal

39. Other applications of solar thermal