The document discusses solar thermal technology and its applications for rural India. It begins by explaining how solar thermal works by heating a liquid using sunlight. It then classifies solar thermal systems based on achievable temperature (low, medium, high) and concentration type (concentrating vs. non-concentrating). The main solar thermal devices discussed are flat plate collectors, evacuated tube collectors, compound parabolic concentrators, and cylindrical parabolic trough collectors. Applications include water heating, space heating, cooking, and industrial processes. The document also examines thermal energy needs across different sectors like household, industry, agriculture, and provides temperature ranges for various processes.

1. Solar Thermal Technology for
Rural India
Rural Energy Technology
Dr. Basudev Pradhan

2.  Solar Thermal is a clean, highly efficient means of using
renewable energy from the sun to provide hot water for
domestic, commercial and industrial process . Put in
simple terms, if you place a container full of liquid in
the garden on a sunny day, in a short time the contents
of the container become warm. Solar Collectors work in
much the same way, but are very more efficient.

3. Classification of Solar Thermal Systems
(A) On the basis of
Achievable
Temperature
(i)Low Temp.
T<100oC
(ii) Medium Temp
100o≤ T ≤ 300oC
(iii) High Temp
T>300oC

4. Classification of Solar Thermal Systems
(B) On the basis of
Concentration Type
Concentrating
CPT, CPC, CRS, DRS, Solar Cooker,
Parboloid
Non-Concentrating or
FPC Type
FPC, Solar Pond, Basin Type Still,
ETC
Imaging
CPC, DRS, Paraboloid
Non-Imaging
Solar Cooker, CRS, CPC
Line Focusing
CPT, Linear Fresnel
Point Focusing
Parboloidal Dish, Fresnel Lens

5. Solar Heating Applications and Systems
Temperature Applications Systems Imaging
Systems
Low Temperature
T<100oC
Water heating,
Space heating,
Drying,
Distillation
FPC, Solar Pond,
Solar Still
Air Dryer
Nil
Medium
Temperature
100o≤ T ≤ 300oC
Cooking, Air
heating,
Refrigeration and
AC, Distillation
FPC, CPC, Solar
Cooker, ETC,
Honeycomb CSD,
Linear Fresnel
Nil
High
Temperature
T>300oC
Process heat,
Power
CPT, Central
Receiver system,
Distributed
Receiver System,
Paraboloid
Paraboloid

6. S.N. Sector Conventional
Resources Used
Temperature
Range
1 Household Biomass, Coal, Oil,
Natural Gas
Low, Medium
2 Transportation Oil, Natural Gas --
3 Industry Coal, Oil, Natural Gas Low. Medium,
High
4 Agriculture Oil, Animal Power,
Biomass
Low, Medium
5 Commerce Coal, Oil, Natural Gas,
Biomass
Low, Medium
Thermal Energy Utilization Sectors/Resources

7. Sectors - Thermal Needs and Applications

8. Household Sector
Basic Needs Energy Activity Temp Range
Drinking Water Water distillation/purification Low
Food Cooking Low, Medium
Crop drying Low
Milk Pasteurization Low
Comfort Space heating Low
Water heating Low
Active space cooling and
refrigeration
Medium
Passive space heating, cooling
and lighting
Low

9. Industry Process Temperature (◦ C)
Dairy Pressurization 60–80
Sterilization 100–120
Drying 120–180
Concentrates 60–80
Boiler feed water 60–90
Tinned food Sterilization 110–120
Pasteurization 60–80
Cooking 60–90
Bleaching 60–90
Flours and by-products Sterilization 60–80
Tea Pre-heating 80-90
Drying 110-120
Industrial Sector : Food Industry-1
Mekhilef et al, Renewable and Sustainable Energy Reviews 15 (2011) 1777–1790

10. Industry Process Temperature (◦ C)
Meat Washing, sterilization 60–90
Cooking 90-100
Fish Washing, Sterlization 60-90
Drying 80-90
Beverages Washing, sterilization 60–80
Pasteurization 60–70
Industrial Sector : Food Industry-2

11. Industry Process Temperature (◦ C)
Textile Bleaching, dyeing 60–90
Drying, degreasing 100–130
Dyeing 70–90
Fixing 160–180
Pressing 80-100
Paper Pulp cooking, drying 60–80
Boiler feed water 60–90
Bleaching 130–150
Industrial Sector : Paper and Textile
Mekhilef et al, Renewable and Sustainable Energy Reviews 15 (2011) 1777–1790

12. Industry Process Temperature (◦ C)
Chemical Soaps 200–260
Synthetic rubber 150–200
Processing heat 120–180
Pre-heating water 60–90
Plastics Preparation 120–140
Distillation 140–150
Separation 200–220
Extrusion 140–160
Drying 180–200
Blending 120–140
Industrial Sector : Chemical Industry

13. Industry Process Temperature (◦ C)
Timber by-products Thermo diffusion beams 80–100
Drying 60–100
Pre-heating water 60–90
Preparation pulp 120-170
Bricks and blocks Curing 60–140
Industrial Sector : Building Materials
Mekhilef et al, Renewable and Sustainable Energy Reviews 15 (2011) 1777–1790

14. Item/Detail Process Temperature (◦ C)
Food grain Drying 80–100
Parboiling
60–100
Fruit Drying 60-80
Pulp processing
100-110
Sericulture Cocoon processing
100
Pisciculture(Cold region) Reproduction/Growth
40-50
Poultry Chick brooding Growth
30-40
Plant conditioning Growth/quality
40-50
Agriculture: Crop/fruit

15. Solar Thermal Conversion Devices
and Utilization

16. Solar Thermal Collectors
Flat Plate Collector(FPC)
Spherical Parabolic
Concentrating Collector
Linear Cylidrical Parabolic
Concentrating Collector(CPC)
Evacuated Tubular Collector(ETC)

17. Collector
System
Detailed
Temperature
Range
FPC Flat Plate Collectors Low
Flat Plate Collectors with double glazing Medium
SP Solar Pond Low
ETC Evacuated Tubular Collectors Medium
CPC Compound Parabolic Concentrators Medium
CPT Cylindrical Parabolic Trough(linear) Medium-High
Cylindrical Parabolic Trough(Surface of
revolution)
High
CRS Central Receiver System High
Solar Thermal Conversion Collectors

18. Flat Plate Collector(FPC)

19. How Does it Work?

21. FPC
 It can easily achieve a temperature 60-80oC above ambient
temperature.
 It uses both beam and diffuse radiation.
 Does not require tracking.
 Requires little maintenance.
 Efficiency: ~ 45% at 80oC
 Applications: air heating,
water heating,
industrial process heating,
passive air conditioning
 15 % of all the thermal requirements are in this range*
* Mekhilef et al, Renewable and Sustainable Energy Rev. 15 (2011) 1777–1790

22. FPC - Section

23. Major parts of FPC
 A metallic flat absorber plate (cu, steel, aluminium
and having black coated( 0.5 mm to 1 mm)
 Tube or channels are soldered to the absorber plate
 A transparent toughened glass of 5 mm
 Fibre glass insulation of thickness 2.5 cm to 8 cm
 A container encloses the whole assembly in a box
made metallic sheet or fibre glass

24. Evacuated Tubular Collector(ETC)

25. ETC
 It can easily achieve a temperature 80-120oC above ambient
temperature.
 It uses both beam and diffuse radiation.
 Does not require tracking.
 Requires little maintenance.
 Mode: Heat pipe; U tube water; Integrated Collector/storage
 Efficiency: ~ 55% at 80oC(for water heating)
 Applications: air heating,
water heating,
industrial process heating,
passive air conditioning
 27 % of all the thermal requirements are in this range*
*Mekhilef et al, Renewable and Sustainable Energy Rev. 15 (2011) 1777–1790

26. ETC in heat pipe mode

27. ETC in Heat-pipe Mode
Glass-Glass
Evacuated tube
System
Heat Pipe
System

28. ETC in U-tube water mode

29. ETC performance
• Efficiency of ETC in heat pipe mode is better but pay back period of
U-tube/water in glass is very short.
• Evacuated tube of 58 mm ED is standard with centre to centre
spacing of 75 mm.
• Solar water heaters performance parameter Efficiency in terms of
ratio of tank volume to collector area ratio suggests that it is
highest(58%) for the ratio 75 L/m .
• Shorter tube 1800mm performed better than longer 2100mm due to
stagnation at the bottom.
• Angle has little influence on the thermal performance i.e. can be
installed vertically as well.
Zhang et al, Energy Conversion and Management, 2014

30. Concentrating Collector

31. Compound Parabolic Concentrating (CPC) collector
θc
• Concentration Ratio
• Highest for the given
Acceptance Angle
• Needs less tracking
• Temperature ~150oC
• Limitation:
CR~10

32. Cylindrical Parabolic Trough (CPT) collectors
Receiver tube
Glass
cover
Receiver detail
Receiver
Sun rays
Tracking
mechanism
Parabola
Schematic

33. Cylindrical Parabolic Trough (CPT) collectors
• Concetration Ratio ~10-80
• Needs one axis continuous
tracking based on mounting
• Higher the concentration ratio
more is the tracking
requirement
• Temp~400oC Su
n
ray
s

34. Parabolic Trough
The largest ‘solar thermal-electric’ installation of its kind in the world,
the Luz project in California’s Mojave Desert, has a peak output of some
350 megawatts and occupies several square kilometers of land

35. Solar Bowl Concentrator
•HIGHEST ACHIEVABLE TEMP=260oC
•AUROVILLE (Pondicherry)

36. Fresnel lens collector
Made of an acrylic plastic sheet, flat on one side,
fine longitudinal grooves on the other side
Angle of grooves~ line focus
CR ~ 10 to 80
Temp~ 150 to 400o C

37. Solar Water Heater

38. Solar Water Heater

39. Solar Water Heat

40. Solar Water Heating

41. A thermosyphon system

42. A double-cycle system with forced circulation with a conventional boiler
for back-up heating

43. A solar district heating system

44. Solar Water Heater
(Forced Circulation)

45. Industrial Solar Thermal Process Heat
System(Forced Circulation)

46. Solar Cooking

47. Benefits of Solar Cooking
 Consumes no fuels/wood
 No loss of trees & habitat
 Trees sequester carbon
 Generates no air pollution
 Generates no greenhouse
gases
 Produces no smoke
 Cooking smoke kills over 1.6
million people each year,
mostly women & children,
according to a recent report
 Eliminates fire dangers

48. More Benefits of Solar Cooking
 Eliminates work
 No daily search for
firewood
 2 Billion people rely on
wood for cooking fuel!
 No risks to women and
children
 Frees time for other
activities
 No need to stir food
 Helps to liberate
women

49. More Benefits of Solar Cooking
• Cooks foods slowly and
thoroughly
• Preserves nutrients
• Foods will not burn
• Pots are easy to clean;
less clean water is
needed
• Use for canning
vegetables
• Use for dried fruit
• Kill insects in dry grains

50. Solar Cooking
How Long Does it Take?
 Vegetables: 1.5 hrs
 Rice/wheat: 1.5-2 hrs
 Beans: 2-3 hrs
 Meats: 1-3 hrs
 Bread: 1-1.5 hrs

51. SOLAR COOKERS
Three types of cookers
1. Box type: for boiling type cooking
2. Concentrator type: for boiling, frying,
baking, roasting
3. Advanced type: for indoor cooking

52. Box-type
 Boiling type cooking
 Low temperature cooking
 Nutrition value
maintained

53. Box type
 Double walled box with insulator in between. The inner
box is metallic and is inclined at 45 deg and coated black
on top. Which cooking pots (coated black outside) are kept
over the inner box. Booster mirror.
 50 cm x 50 cm x 14 cm
 Covered with two clear window glasses(70cm x 70 cm)
fixed in a frame hinged on one side of the box.
 Over 10 lakh such cookers distributed in India.

54. Box type cooker

55. Concentrating type
 Boiling, frying possible
 Out of various types, the
paraboloid concentrator
solar cooker(PCC) can meet
that demand by delivering
power up to 0.6kW which
can boil 3-4 litres of water in
about half an hour.
CONCENTRATOR TYPE
0.70 m2 area
700 W

56. SCHEFFLER COOKER FOR COMMUNITY
COOKING AT SHIRDI
Also at Tirupati Balajee Temple, Tamilnadu and Prajapita
Brhmakumari, Mount Abu, Gujarat

57. Solar Power Tower
In 1995 Solar One was converted into Solar Two, by adding a second ring
of 108 larger 95 m² (1,000 ft²) heliostats around the existing Solar One,
totaling 1926 heliostats with a total area of 82,750 m² (891,000 ft²)

58. Solar Dish
Stirling Energy Systems‘ solar dish technology is the world’s most efficient
device for the conversion of solar energy to grid-delivered electricity,
nearly twice as efficient as any alternative solar technology.

60. Solar Pond
 Top layer at ambient
temp, whereas bottom
layer temp 60°- 85°C
 surface convection zone
 2.concentration
gradient zone
 3. Lower convective
zone
Artificially designed pond filled with salty water maintaining a define concentration
gradient is called a “Solar Pond”
Three basic zones: 1. surface convective zone(SCZ)(thickness 10-20 cm),
2. Non-convective zone(NCZ) (half the depth of the pond, as insulator layer)
3. Lower convective zone(LCZ)(nearly same as NCZ, constant temp. and conc.

61. Salt Gradient Solar Pond
1. There are 3 distinct layers of water in the pond:
a) The top SCZ layer, which has a low salt content.
b) The bottom LCZ/SZ layer , which has a high salt content.
c) An intermediate insulating NCZ/GZ layer with a salt gradient,
which establishes a density gradient that prevents heat
exchange by natural convection
2. Solar collector-cum-storage system
3. Average storage temperature ~ 80oC
4. Large collection and storage capacity, Efficiency ~ 14%
5. The lowest thermal energy cost amongst all solar & conventional
technologies.
6. Applications: water purification, water heating, space
heating, refrigeration, power
7. Drawbacks: low temperature, instability, environmental
problems

62. ElPaso
Solar Pond,
Texas
The El Paso Solar Pond project is a research, development, and demonstration
project initiated by the University of Texas at El Paso in 1983. It has operated since
May 1986 and has successfully shown that process heat, electricity, and fresh water
can be produced in the southwestern United States using solar pond technology. An
organic Rankine-cycle engine generator was installed on site in 1986, making it the
first in the U.S. to generate grid connected power, producing up to 70kW. Most of
this power has been delivered to Bruce Foods Corporation for peak power shaving.
This demonstrates one of the primary benefits of solar ponds: power on demand --
even at night or after long periods of cloudy weather.

63. Solar pond
 Largest solar pond: Bet ha Arava in Israel, area 250,000m2
generate 5 Mwe of electrical power with an organic fluid
working rankine cycle principle
 India 1st solar pond: area 1200 m2 was built at Central salt
Research Institute, Bhavnagar in 1973,
 6000 m2 , built at Bhuj(Gujarat), 2nd largest in world, it
provides daily 90,000 litres of hot water at 80c as process
heat for can sterilization, -temp 99C, capable of generating
150 kW of power

64. The Solar Pond
BIRD’S EYE VIEWS

65. Storage Zone temperature
Reflectivity=0.3

66. This picture of the Solar pond at
Pyramid Hill (near Kerang in
Northern Victoria) shows the
mesh of pipes running down
the wall of the pond. These run
across the bottom of the pond
and up the other side. Fresh
water (or radiator coolant) is
circulated through them, and is
heated by the saline pond water.
This hot fluid is then used to
heat glass houses, boil
refrigerant in a rankine engine
to make electricity, or (in the
case of Pyramid Hill) used to
heat air to flash dry gourmet
salt products.
(The plastic rings visible on the
surface of the water are used to
reduce water movement caused
by wind)

67. Passive Solar
 Passive Solar is accommodated in
the design of some homes where
living rooms are south facing with
large windows and floors and
sometimes walls have a large thermal
mass.
 While it is necessary to use the solar
to heat in winter overheating in
summer has to be avoided, this is
normally done by having a roof
overhang which blocks the high
summer sun but not the low winter
sun.
 While it can provide some free heat it
doesn’t supply hot water and there
are design constraints.
 The key is designing a passive solar
home to best take advantage of your
local climate.

68. Passive Solar

69. Solar crop drying
 Air inside is heated and
natural air circulation starts
 Temperature inside ranges
from 50 to 75C
 Drying time for products like:
dates, grapes, apricots,
Cashew nuts and chillies
from 2 to 4 days
 Large scale drying: seasoning
of timber, corn drying, Tea
processing, tobacco curing,
fish and fruit drying

70. Solar crop drying

71. Solar kilns
Heating and drying of products on a large scale, like tea, corn, fruits, timber, etc is done
using solar energy.

72. Solar kilns

73. Solar Distillation
Arid, semiarid and costal area
Salt works, Bhavnagar, capacity: 1000 m3/day, Evaporating area: 350 m2 for
drinking water for workers in salt works sea water

74. World Water Resources
Salt Water
Fresh Water The Worlds Water
 97% Sea Water
 3% Fresh Water
California Coastline
http://www.windycityart.com/californiawallpa
per/ocean%20wallpaper.jpg
Solar Powered Desalination

75. World Fresh Water Resources
Ice
Ground Water
Riparian Areas
The Worlds Fresh
Water
 77% Ice
 22% Ground Water
 1% Rivers, Lakes and
Streams
Solar Powered Desalination

76. Desalination
The separation and removal of
ions, salts and other dissolved
solids from water.
 Heat Based
 Membrane Based
Evaporation pool (Saudi Arabia)
http://www.cea.fr/gb/publications/Clefs44/an-
clefs44/clefs4481a.html
Solar Desalination

77. Water Distillation
 Process that removes impurities & contaminants
 How?
 Heat water to point of vaporization
 Water vapor condenses on cooler surfaces
 Condensate runs off into collection bin

78. Patent & Periodical Research Results
 Beneficial Ideas
 Troughs
 Water height < 2 cm
 Mirrors
 Beneficial Information
 Asymmetrical superior to
other designs
 30% more efficient

80. Market Search Rainmaker 550TM
•Unit Cost - $479.00•Estimated cost $400-$600
•Built & supplied by aid
organization
El Paso Solar Energy Association
(EPSEA) Aid Project
•Not currently in
production
•Very low output
The Water Cone®

81. Looking Towards The Future
Due to the impending global water scarcity crisis,
many human rights organizations are funding
research on desalination in order to provide
people with adequate drinking water.
Everyone need water
http://news.bbc.co.uk