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Solar Thermal Technology (Page 2/2)

A financial requirement of about $162 million has been projected for the 11th Five-Year Plan for energy-efficiency related initiatives. A number of pilot and demonstration projects have been taken up for load management and energy conservation through reduction of transmission and distribution losses in the system. In the area of building energy efficiency, building plans will not be approved by local authorities unless they comply with the Energy Conservation Building Codes (ECBCs) after 2009. The ECBCs will make it mandatory for buildings not to exceed 140 kilowatt/hour per square meter annually.

Solar thermal technology uses flat and concentrating absorbers that collect heat energy from the sun for such processes as crop drying, food processing, water and space heating, industrial process heat, and electricity generation.

Solar water heating systems, such as the ones pictured in China’s Yunnan Province, 20 consist of a solar collector and a storage tank. The collector is typically a rectangular box with a transparent cover, through which pipes run, carrying water that is heated by the sun. The pipes are attached to an absorber plate, which is painted black to absorb the heat. As the sun’s heat warms the collector, the water is heated and passed to the storage tank, which stores the hot water heated for domestic use. As explained by the National Renewable Energy Laboratories, “Solar water heating systems can be either active or passive. Active systems rely on pumps to move the liquid between the collector and the storage tank, while passive systems rely on gravity and the tendency for water to naturally circulate as it is heated. Simpler versions of this system are used to heat swimming pools.”

Solar heating systems to dry food and other crops can improve the quality of the product while reducing waste. Solar driers outclass traditional open-air drying and have lower operating costs than mechanized fuel-based driers. The three types of solar driers are natural convection, forced convection, and tent driers. In natural convection driers, air is drawn through the dryer and heated as it passes through the collector, then partially cooled as it picks up moisture from the product drying. The flow of air is caused by the lighter warm air inside the dryer moving toward the cooler outside air. In forced convection, a fan is used to create the airflow, reducing drying time by a factor of 3 and the area of collector required by up to 50 percent. A photovoltaic panel can be used to generate electricity for the fan. Tent driers combine the drying chamber and collector and allow for a lower initial cost. Drying times are not much lower than for open-air drying, but the main purpose is to provide protection from dust, dirt, rain, wind, and predators; tent driers are usually used for fruit, fish, coffee, or other products for which wastage is otherwise high.


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