Cost-competitive heat prices can be a convincing argument for solar thermal in India. That shows the case study of a solar hot water system for the college hostel of the Symbiosis Institute of Business Management (SIBM) in the city of Hyderabad in the south of India. The calculations by solar thermal system supplier Emmvee Solar Systems result in a solar heat price of 3.2 Indian Rupees (INR) per kWhth (39 EUR/MWh) over a life cycle of 10 years, whereas electric water heaters would cost the university 6.7 INR/kWhth (82 EUR/MWh) – double as much. The price per kWh from an oil boiler would even be as high as 8 INR/kWhth (100 EUR/MWh). Thippegowda Srinath, Technical Director at Emmvee Solar Systems, presented the case study during the panel discussion New Business Models for the Solar Thermal Industry at the international conference SMEThermal 2014 in Berlin, Germany, on 18 February.
Photo: Stephanie Banse
“Originally, the management team of the Symbiosis institute wanted to install electric heaters for the hot water needs of the students,” Srinath said during the discussion. “However, after a rough calculation and a couple of visits, they were convinced, because they understood that solar will save them a lot of money.” So, Emmvee installed 18 individual thermosiphon systems with different sizes on the roof of the hostel in December 2013.
Emmvee tried to avoid a solar thermal collector field with a pump-driven circuit because the frequent power cuts in the region can cause high stagnation temperatures, which would interrupt operation, because water would be blown off through the pressure valves. “Based on our experiences, thermosiphon systems are very reliable. The piping is done in such a way that if one system develops a problem, the local technician just turns a few knobs and the hot water bypasses the damaged system,” Srinath explained.
|Total solar water heating capacity (storage capacity in decentralised thermosiphon tanks)||26,800 litres per day|
|Number of collectors||218 collectors, 2 m² each|
|Date of commissioning||December 2013|
|Backup heating||Air source heat pumps|
(6 times 500 litres/hour)
|Total investment costs, including storage and installation||INR 8,020,000|
|Specific costs||224 EUR/m²|
|Annual solar yield calculated over 300 days (not counting two monsoon months)||575 kWh/m²a|
|Resulting solar heat price over ten-year life cycle (no interest rate, no incentive)||3.2 INR/kWhth |
|Resulting solar heat price over ten-year life cycle (annual interest rate 12% on 100% of the investment costs, annual inflation 7%, no incentive)||3.98 INR/kWhth|
|Heat price with electric water heaters (90% efficiency)||6.7 INR/kWhth|
Key figures of the feasibility study of a solar hot water system for the SIBM college hostel, Hyderabad (1 Euro = 82 Rupees)
Calculation method of solar yield
According to Emmvee, the solar yield is based on the following assumptions. The total solar water heating capacity of 26,800 litres is reduced down to 24,000 litres, because after using 90% of the hot water, the rest will be mixed with incoming cold water, so that the temperature is too low for bathing. The temperature difference is 30°C between the cold water at 25°C and the hot water at 55°C. The daily solar yield is calculated in the same way by multiplying 24,000 litres with the heat capacity of water of 4.18 kJ/kg*K and the temperature difference of 30 K and is then converted into kWh, which results in a daily total solar yield of 836 kWh. The table above shows this yield to be achieved in 300 days. This means that the annual yield produced by 436 m² of collector area is 250,800 kWh, resulting in a specific yield of 575 kWh/m²a.
Calculation method of solar heat price
The solar heat price is calculated by dividing the total investment costs of INR 8,020,000 through the total solar yield over 10 years (250,800 kWh times 10), which results in a specific solar heat price of 3.2 INR/kWh (39 EUR/MWh). “Based on our experiences, the performance degradation of a solar water heating system is negligible if the system was designed properly,” Srinath said, “That´s why our calculation is based on the assumption that the solar thermal system will have the same heat output over 10 years.”
The technical director also explained that many Emmvee clients for larger installations are social institutions, such as hospitals or educational institutions, which are non-profit, so they receive low-interest loans. Hence, the basic calculation does not include any financing costs for the investment. According to Emmvee, a typical bank loan over 10 years would be available at an annual interest rate of around 12%. Considering 7% annual inflation, the investment would have a current value of INR 9,969,362, resulting in an increased solar heat price of 3.98 INR/kWh (49 EUR/MWh).