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1. ERG 211 RENEWABLE ENERGY AND GREEN
TECHNOLOGY (1+1)
Practical - 13
Performance evaluation of solar water heater
Aim: To assess the performance of solar water heater.

2. Solar water heaters
Solar water heating system (SWHS) is a device which
supplies hot water at 60°C to 80°C using only solar thermal
energy without any other fuel.
In the case of smaller systems (100 – 2000 litres per day),
the hot water reaches the user end by natural (thermo –
siphon) circulation for which the storage tank is located
above the collectors.
In higher capacity systems, a pump is used for forced
circulation of water.

3. Solar water heaters
The two types water heating system are flat plate solar
water heaters and evacuated tube solar water heaters
i) Flat plate solar water heaters
A flat plate solar water heating system is used for
domestic & industrial applications for heating water upto
60 to 70 °C.
A flat plate collector is simple in design and consists of
flat collector or absorber, glass cover, insulation, pipes
and storage tanks.

4. Solar water heaters

5. Solar water heaters
ii) Evacuated tube solar water heaters
Evacuated Tube Collector is made of double layer
borosilicate glass tubes evacuated for providing insulation.
The outer wall of the inner tube is coated with selective
absorbing material. This helps absorption of solar radiation
and transfers the heat to the water which flows through
the inner tube.
Due to vacuum in the evacuated tube collector, there is no
medium which take the heat away from the absorber plate.

6. c) Solar water heaters
ii) Evacuated tube solar water heaters
Therefore, there are less heat losses. Thus, in evacuated
tube collectors, the water temperature close to 100°C can
be obtained.

7. Performance evaluation of solar water heater
Theory:
Solar water heater converts solar energy into thermal
energy and produces hot water.
The performance such as hot water generation,
temperature of hot water, efficiency of hot water system
etc. can be assessed.
Instruments required:
Pyranometer and Thermometer

8. Performance evaluation of solar water heater
Procedure
1. Measure the collector area and note down the capacity of
the solar water heater.
2. Fill the cold water tank up to the solar water heater
capacity.
3. Record the ambient temperature, solar radiation and
initial temperature of water.
4. Check the hot water outlet for the water temperature (Th)
and note the time taken

9. Performance evaluation of solar water heater

10. Performance evaluation of solar water heater
Parameters to be measured
Solar insolation in the study period, SD = W m-2
Capacity of hot water system, Q = lpd
Length of the collector, l = m
Width of the collector, w = m
Number of collectors, n = n
Atmospheric temperature, Ta = °C
Specific heat of water, Cp = kJ/kg °C
Cold water temperature, Tc = °C
Hot water temperature, Th = °C

11. Performance evaluation of solar water heater
Economics of solar water heater
It is considered that the economics of solar water heater
is compared with electrical heaters.
The cost required for solar hot water system and
electrical systems are calculated and the pay-back period
is calculated.
Cost of solar water heater = Investment, Rs.
Daily thermal energy requirement (QE) kWh
= QU / (0.95 x 3600)
Where QU is the daily heat energy required to heat water

12. Economics of solar water heater
(Considering the efficiency of the electrical water
heating system as 0.95)
Cost of electricity per day, PE, Rs. = QE × Unit Price
Assuming 300 days of annual utilization of SWH system,
Annual saving, Rs. = PE x 300
Investment, Rs.
Simple payback period =
Annual savings, Rs.

13. Performance evaluation of solar water heater
Problem - 1
Calculate the thermal efficiency of solar water heater and
payback period with given data:
Capacity of hot water system = 200 lpd
Number of collectors = 2
Length of the collector = 2 m
Width of the collector = 1 m

14. Performance evaluation of solar water heater
Problem - 1
Cold water temperature = 15°C
Hot water temperature = 80°C
Solar insolation = 1353 W/m2
Specific heat of water = 4.19 KJ/Kg°C
Time = 8 hr/day
Investment of solar water heater = 20,000.
Unit price of electricity is Rs. 3.00
Assume other necessary data if required.

15. Performance evaluation of solar water heater
Problem – 1 - Solution
Thermal Efficiency = 34.946 %
QU = Q x Cp x (Th – Tc) = 54470
QE = 15.92
PE = 47.78
Annual savings = 14334
Pay back period = 1.395 or 1 year 4 months

16. Performance evaluation of solar water heater

17. Performance evaluation of solar water heater
Problem – 1 - Solution
Thermal Efficiency
200 x 4.19 x (80 – 15), KJd-1
= x 100 %
(1353 x 2 x 2 x 1 x 8 x 3600) / 1000 KJd-1
Thermal Efficiency = 34.946 %
Investment, Rs.
Simple payback period =
Annual savings, Rs.
Annual saving, Rs. = PE x 300

18. Performance evaluation of solar water heater
Problem – 1 – Solution
Annual saving, Rs. = PE x 300
Cost of electricity per day, PE, Rs.= QE × Unit Price
Daily thermal energy requirement (QE) kWh
= QU / (0.95 x 3600)
Where QU is the daily heat energy required to heat water
QU = Q x Cp x (Th – Tc) = 54470
QE = 54479 / (0.95 x3600) = 15.92
PE = 15.926 x 3 = Rs.47.78

19. Performance evaluation of solar water heater
Problem – 1 – Solution
Annual saving, Rs. = PE x 300 = 47.78 x 300 = Rs. 14334
Investment, Rs.
Simple payback period =
Annual savings, Rs.
Pay back period = 20000 /14334
= 1.395 or 1 year 4 months

20. Performance evaluation of solar water heater
Problem - 2
From the following Solar Water Heater Performance
Evaluation System, Calculate the thermal Efficiency from the
Observations taken below:
Capacity of Water system = 30 lit/day;
Length of collector &Width of collector 6 ft and 3.25 ft
respectively;
Number of Collector= 2;

21. Performance evaluation of solar water heater
Problem – 2 Contd….
Specific Heat Capacity = 4.184 kcal/kg0c;
Initial Temperature= 28.50 C;
Final Temperature = 620 C;
Rise in Temperature is 33.50 C;
Solar Insolation = 350 Watts / m2;

22. Performance evaluation of solar water heater
Problem – 2 – Contd…..
If the electrical water heating system has efficiency of 0.90,
cost of solar water heater is Rs. 13500, annual utilization of
the system is 290 days and the unit price of electricity is Rs.
0.80, calculate the payback period also.
Assume other necessary data if required.

23. Performance evaluation of solar water heater
Problem – 2 – Solution
Thermal Efficiency
30 x 4.184 x 4.184 x (62 – 28.5), KJd-1
= x 100 %
(350 x 2 x 1.83 x 0.99 x 8 x 3600) / 1000 KJd-1
Thermal Efficiency = 48 %
QU = 17593.53
QE = 5.14
PE = Rs. 4.114
Annual savings = 1234.5
Pay back period = 10.93 or 10 year 9 months

24. Performance evaluation of solar water heater
Problem – 2 – Solution
Annual savings = 1234.5
Pay back period = 10.93 or 10 year 9 months