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Solar Thermal for Electricity

   

Solar Thermal for Electricity

Production of electricity from renewable resources means using water (dams and oceans), wind (turbines) and solar (photovoltaic's and thermal). Nuclear can not be considered a renewable resource as the radioactive material does not renew, nor is there a satisfactory method to dispose of the waste radioactive material. Nuclear does not produce carbon dioxide in the production of electricity however.

Several large scale solar thermal electrical plants are in production today. These plants have an advantage over natural gas and coal plants from a hedging perspective. Once in production, they produce electricity for the same cost per kilowatt, year after year. You never know what the price of natural gas and coal is going to be a year from now.

Putting a price on carbon, such as California's 2006 law AB32 which requires a 25% cut from 2006 emission levels by 2020, makes solar thermal electrical production a hands down winner over coal or gas production!

Suitable for Solar Thermal Electrical Plants

 

Solar Thermal Parabolic Trough

Both the International Energy Agency and the World Bank state that solar thermal power plant technology is the most economical way to generate electricity from solar energy. And over the past 20 years the solar thermal parabolic trough power plants know as the California Solar Energy Generating Stations (SEGs) have generated over 12,000 gigawatt hours of electricity.

Parabolic trough power plants consist of numerous trough-shaped parabolic mirrors that concentrate sunlight onto receivers (absorber tubes), such as the SCHOTT PTR 70, that are located along the focal line. Inside these specially coated receivers, concentrated solar radiation heats a special heat resistant transfer fluid to temperatures of up to 400° Celsius (752 °F).

 parabolic trough solar electric collector

This fluid is pumped to the central generating unit. It passes through several downstream heat exchangers and, as in conventional power plants, generates the steam that is required to drive the turbines that produce electricity. [Figure 2]

solar thermal electric process

 

Certain regular maintenance is needed on the mirrors, collectors and turbines. For instance, the receivers and mirrors need to be periodically washed.

The largest cost involved in solar thermal parabolic trough power plants is the initial capital cost to build the plant rather than operating costs – the opposite of cheap to build, expensive to operate fossil fuel power plants.

The collectors used at the Californian SEGS have been used for almost 20 years and are still working fine.

Solar thermal parabolic trough power plants have the added advantage over other forms of solar electric generation in that it is possible to generate electricity even during unfavorable weather and at night using heat storage systems.

The vast amount of heat transfer fluid circulating in the solar field already represents a considerable storage capacity which can bridge short term cloudy phases.

Molten salt storage tanks provide additional power even when the sun goes down. In Spain’s planned AndaSol power plant, a mixture of 25,000 tons of sodium and potassium nitrate will be heated to 384° C (723° F.) This should allow the power plant to operate for well over 6 hours after the sun goes down. The Spanish national carrier has given this kind of power plant system the same reliability rating as power plants using fossil fuels. The output of solar thermal power plants is thus available continuously.

 

Power Tower Systems

Solar Two Power Tower

Solar One was a pilot solar-thermal project built in the Mojave Desert. Solar One was completed in 1981 and was operational from 1982 to 1986. Later redesigned and renamed Solar Two. The project produced 10 MW of electricity using 1818 mirrors (1926 mirrors as Solar Two). It was operational again, as Solar Two, from 1995 to 1999.

The 17 MW Solar Tres in Sevilla Spain will be the first commercial molten-salt central receiver plant in the world. With a 15-hour molten-salt storage system and a high-temperature, high-efficiency thermal cycle, the plant will generate 110.6 GWh/yr.

Solar Power Tower Schematic

 

Dish/Engine Systems

Solar Dish/Engine

This solar dish-engine system is an electric generator that "burns" sunlight instead of gas or coal to produce electricity. The dish, a concentrator, is the primary solar component of the system, collecting the energy coming directly from the sun and concentrating it on a small area. A thermal receiver absorbs the concentrated beam of solar energy, converts it to heat, and transfers the heat to the engine/generator.

Sterling Energy Systems Inc. are leaders in the field of small sterling engine based solar power systems. They presently have two projects under development that would roll out thousands of their SunCatchers for a combined generating capacity of 1,750 MW.

 

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