27-09-2012, 03:05 PM
Solar Thermal Electricity The Ultimate Renewable Resource
Solar Energy.ppt (Size: 2.96 MB / Downloads: 37)
What is Solar Energy?
Originates with the thermonuclear fusion reactions occurring in the sun.
Represents the entire electromagnetic radiation (visible light, infrared, ultraviolet, x-rays, and radio waves).
Solar Thermal Electricity
Solar energy can also be used to make electricity. Some solar power plants use a highly curved mirror called a parabolic trough to focus solar light on a pipe running down a central point above the curve of the mirror. The mirror focuses the solar light to strike the pipe, and it gets so hot that it can boil water into steam. That steam can then be used to turn a turbine to make electricity.
WORKING OF PARABOLIC MIRRORS
The solar electric generating system plants use long parabolic mirror
with pipes at the focus point, where circulating oil is heated to 700 F (350 C). The oil is
pumped through heat exchangers which boil water to make high-pressure steam, which
drives turbine generators to make electric power.
Recently, new technology has placed in service the PS-10 power tower system, which employs a
field of reflectors which move in two dimensions to focus light at the top of a tower,
A large pressure tank, or “steam accumulator”, stores energy as pressurized hot water and
allows the plant to continue generation in cloudy conditions for up to an hour.
Solar-Thermal Electricity:Parabolic Dishes and Troughs
Focus sunlight on a smaller receiver for each device; the heated liquid drives a steam engine to generate electricity.
The first of these Solar Electric Generating Stations (SEGS) was installed in CA by an Israeli company, Luz International.
Output was 13.8 MW; cost was $6,000/peak kW and overall efficiency was 25%.
Through federal and state tax credits, Luz was able to build more SEGS, and improved reduced costs to $3,000/peak kW and the cost of electricity from 25 cents to 8 cents per kWh, barely more than the cost of nuclear or coal-fired facilities.
The more recent facilities converted a remarkable 22% of sunlight into electricity.
Direct Conversion into Electricity
Photovoltaic cells are capable of directly converting sunlight into electricity.
A simple wafer of silicon with wires attached to the layers. Current is produced based on types of silicon (n- and p-types) used for the layers. Each cell=0.5 volts.
Battery needed as storage
No moving partsdo no wear out, but because they are exposed to the weather, their lifespan is about 20 years.
Solar Panels in Use
Because of their current costs, only rural and other customers far away from power lines use solar panels because it is more cost effective than extending power lines.
Note that utility companies are already purchasing, installing, and maintaining PV-home systems (Idaho Power Co.).
Largest solar plant in US, sponsored by the DOE, served the Sacramento area, producing 2195 MWh of electric energy, making it cost competitive with fossil fuel plants.