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Facts about Solar Power Plants
from: Forsgrens
A solar power plant is a power plant that collects, stores, and processes the heat of the sun to generate energy that will power homes and commercial establishments. Solar energy has been tapped as a cleaner, cheaper, and more abundant alternative source since the 1990’s, and the ability to do so is starting to come about in the early 2000’s with the use of solar power plants.
There are 2 main types of solar power plants, the Concentrating Solar Power (CSP) plants, and the Solar Chimney.
The Solar Chimney is a relatively low technology solar power plant. This utilizes air that is heated by the sun that passes under a very large glass house (2–30 km in diameter). The heated air is then channeled up towards a convection tower. Then, the heated air naturally rises and is used to drive turbines to generate electricity. Economically and profitable systems with a kilowatt–hour price of 2 cents – 12 cents are only possible on a large scale.
On the other hand, concentrating solar power plants use various mirror configurations to convert solar energy into high temperature heat. Heat is then channeled through a regular generator to be converted to electricity. The amount of power generated by a CSP plant depends on the amount of direct sunlight.
CSP plant sizes range from village power size (10 kilowatts), to grid connection applications (maximum 100 megawatts). Some systems use thermal storage during cloudy days or during night. Other systems are combined with natural gases to produce high value power. Such systems have produced world record solar–to–electricity conversion efficiencies, making CSP an attractive, renewable energy option in sunbelt areas of the world. Four CSP technologies are being promoted internationally.
1) Parabolic Trough Systems
Parabolic trough–shaped reflectors concentrate solar energy onto a receiving pipe that runs along the inside of the reflector’s curved surface. This heats oil flowing through the pipe, then the heat energy is used to generate electricity in a typical steam generator.
In a collector field, many troughs are aligned in parallel rows on a north–south axis. This enables the single–axis troughs to track the sun from east to west during the day, ensuring the continuous focus of sunlight on the receiving pipes. This system can generate approximately 80 megawatts of electricity.
The trough design incorporates thermal storage, setting aside the heat transfer fluid in its hot phase, allowing electricity generation for several hours into the evening.
All parabolic trough plants presently use fossil fuel to supplement the solar output during periods of low sunlight. Generally, a natural gas–fired heater or gas steam boiler is used in this system, but troughs can also be used in coal fired plants.
2) Power Tower Systems
Power Tower systems use many large, sun tracking mirrors, or heliostats, to focus sunlight on a receiver at the top of a tower. The receiver then heats a fluid to generate steam. The steam is then used in a typical turbine–generator to produce electricity.
Early models use steam as a heat transfer fluid. Current US designs use molten nitrate salts due to its superior heat transfer and energy storage capabilities. Present European designs use air as a heat transfer medium because of its high temperature and manageability.
Individual commercial plants produce 50 to 200 MW of electricity.
3) Parabolic Dish Systems
Dish systems use large, reflective dishes that are similar to the shape of satellite TV dishes. These dishes focus all the sunlight that strikes it onto a receiver at a focal point. Dishes are mounted on structure with a two–axis tracking system that follows the sun.
A heat engine mounted on the receiver that moves with the dish directly uses the collected heat. Stirling or Brayton cycle engines are used to convert the heat to electricity. Such systems have been constructed to contain up to 5 MWe. Systems with a 50 kWe maximum size have achieved up to 30% net peak efficiencies.
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