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India: Heat and Electricity Production Combined for the First Time

Submitted by Baerbel Epp on November 19, 2008

parabolic trough collector of SLTL Collector for process heat: The troughs are connected mechanically through a tracking driver. Photo: SLTL





Worldwide, R&D departments in the industrial sector have taken an interest in the possibility to combine solar heat and solar electricity in one process. The Indian company Sahajanand Laser Technology Limited (SLTL) is currently developing such a combination, using a parabolic trough collector with an evacuated tube receiver and a thermoelectric transducer. The organic fluid (oil) inside the vacuum tubes is heated up to 300 °C. The heat is then transferred to the thermocouple device which converts it into electricity at approx. 6 % efficiency. The produced power is direct current and it will finally be converted to alternate current. At around 60 °C, a heat exchanger retrieves the waste heat. This way, the system produces approx. 150 litres of hot water per day as a byproduct. The collected heat is transferred to a semiconductor transducer which converts heat into electricity. The patent application for the system is pending as this is a very unique combination of two different technologies The efficiency of electricity generation is still worrying. The typical trough area is 1,400 X 400 mm2. Nearly 85 % of the radiation is reflected and 95 % absorbed. Calculating with a normal solar radiation of 700 W/m2, the net thermal input is 316 W per trough. This should give 18.9 W at conversion efficiencies of 6 %, respectively. Presently, the SLTL Research and Development model has achieved only up to 10 W output per trough (3.2 %). SLTL is making intense efforts to reach its target of more than 25 % efficiency within two years.

parabolic trough with tracking sensorParabolic trough collector with sensitive solar tracking. Photo: SLTL




The parabolic trough collectors are also used for the generation of industrial process steam in the range of 120 to 250 °C. SLTL plans to use these panels for solar cooling, utilizing a vapor adsorption technique. A suitable storage system can also save the heat for night-time electricity generation. Sahajanand Laser Technology Limited (SLTL), an ISO:9001:2000 certified company, is a leading manufacturer of laser-based CNC machines and special purpose machines for cutting, marking, welding, solar cell scribing and diamond processing. Its headquarters are located in Gandhinagar, India. It is internationally present in the U.S., in Germany as well as in China and just recently diversified in the field of solar power generation.

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This text was written by Jaideep Malaviya, an Indian journalist and solar thermal expert.