Basics of Solar Thermal

SOLAR THERMAL POWER PLANTS TECHNOLOGIES (DEMONSTRATION UNITS)

The scenario has thrown new fears on renewable energy resources like solar, wind, Biogas etc. Renewable technologies promise not only energy security at affordable cost but can speed up the development of rural areas. Among renewable resources Concentrating Solar Power Plants is one of the best suited technologies to help, in an affordable way, mitigate climate change as well as reduce the consumption of fossil fuels. There are two types of Solar Thermal Technologies that are mature and are being installed in many developed places such as USA, Spain, Israel, Greece, and developing countries like Mexico, Morocco, India and Egypt. These technologies are as follows:

Solar Dish Stirling Engine Technology:

A solar dish/engine system utilizes solar energy as the source energy to heat the working fluid of a Stirling engine which drives an electric generator. Essentially the system consists of parabolic solar concentrator, tracking system, receiver and Stirling engine with generator. The compactness of the system makes it well suited for remote operations. The power-generating equipment, i.e. solar heat exchanger/ receiver and Stirling engine, is mounted at the focal point of the solar dish. The engine converts heat to mechanical power by compressing the working fluid (Helium or Hydrogen) when it is cold, heating the compressed working fluid, and then expanding the fluid with a piston to produce work. The engine is coupled to an electric generator to convert the mechanical power to electric power. The capacity of a single unit is typically from 5 to 25 kW. These are ideal for stand alone and or other decentralised application. Fig-1

Solar Parabolic Trough Technology:

This system also utilizes solar energy as a heat source to generate steam which in turn runs a steam turbine which is used to generate electricity. Essentially the system consists of collectors, the fluid transfer pumps, the power generating system, the natural gas auxiliary subsystem, and the controls. In this system solar radiation incident on the parabolic trough is reflected on to a receiver tube in which flows the working fluid. This fluid is heated up to 300 ºC. This hot fluid is then used to produce steam to run the steam turbine. Steam cycle power plants up to 80 MW capacity using parabolic trough collectors have been in commercial operation for more than 15 years. Nine plants with a total of 354 MW of installed power are feeding the California electric grid with 800-million kWh/ year at a cost of about 10-12 cents/kWh. Fig-2

Advantages of the Technology:

The potential life cycle of the Stirling engine is extraordinarily high since there is no internal pollution of the piston & bearing due to combustion of fuels. Parabolic trough concentrator can be used for utility scale generation of solar steam for process heat application and solar power generation. Both the dish and parabolic trough technologies can be additionally be powered by fossil or bio-mass (i.e. biogas). Thus the system is also available to operate during the cloudy or night-time. The systems fulfill all the requirements that can be demanded from a future-oriented, environmentally friendly energy system. Tracking system of the dish/collectors is controlled by sun sensors to meet the peak power demands during summer time and its sales bring greatest revenue. Thermal storage for at least 3 hours further reduces the cost of delivered energy. Reduce dependence on the fossil fuels.