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What Is Solar Thermal Electric?

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Posted by pautrey2 on November 12, 2008, 7:29 pm
 
What is Solar Thermal Electric?

Solar thermal electric power is achieved through the use of
concentrating solar power technologies.

Concentrating solar power technologies utilize reflective materials
such as mirrors to concentrate the sun's energy. This concentrated
heat energy is then converted into electricity.

Technologies
Select images to enlarge
Trough Collectors
Parabolic trough systems use curved mirrors to focus sunlight on an
absorber tube filled with oil or other fluid. The hot oil boils water
to produce steam, which is used to generate electricity.

Since 1985, nine power plants in the Mojave Desert called the Solar
Electric Generating Systems (SEGS) that use parabolic trough
technology have been in full commercial operation.

Power Towers
Power tower systems use a large field of sun-tracking mirrors, called
heliostats, to concentrate sunlight onto a receiver on the top of a
tower. The sun heats a fluid inside the receiver.

An early U.S. demonstration plant, Solar One, used water as the fluid,
generating steam in the tower to drive a turbine to generate
electricity. The plant was later converted to Solar Two, which used
molten salt as the fluid. The hot salt could be stored, then used when
needed to boil water into steam to drive a turbine.

Dish/Engine Systems
A dish/engine system uses mirrors in the shape of a dish to collect
and concentrate the sun's heat onto a receiver. The receiver transfers
the solar energy to a heat engineusually a Stirling cycle enginethat
converts the heat into mechanical energy, which drives a generator to
produce electricity. The receiver, heat engine, and generator are
integrated into one assembly that is mounted at the focus of the
mirrored dish.

An alternative approach, called the open Brayton cycle, passes air
through a porous medium in the receiver, causing the air to heat and
expand rapidly. The hot air is then fed into a separate gas turbine
that drives a generator to produce electricity.

Issues
Mirror Technologies
Concentrators use reflective surfaces of aluminum or silver on the
front or back surface of thin glass or plastic. Researchers are
developing new reflective materials, such as advanced polymer films,
that are less expensive to produce than glass.

Stretched membranes are thin reflective membranes stretched across a
rim or hoop. Another membrane stretched on the back creates a partial
vacuum. This forces the membranes into a spherical shape, which is the
ideal concentrator shape.

Hybrid Systems
Researchers are working with utilities on experimental hybrid power
towers that run on solar energy and natural gas. A similar solar/
fossil fuel hybrid is being developed for dish/engine systems. One
advantage of hybrid systems is that they could run continuously.

Manufacturing Costs
Concentrating solar power is the least expensive solar electricity for
large-scale power generation, and has the potential to make solar
power available at a very competitive rate. As a result, government,
industry, and utilities have formed partnerships with the goal of
reducing the manufacturing cost of concentrating solar power
technologies.


Information courtesy of US Department of Energy

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More Information:

US Department of Energy EERE web site
Guide to Tribal Energy Development: Dish/Engine Systems
State Energy Alternatives  Concentrating Solar Power
US DOE Energy Efficiency and Renewable Energy (EERE) Subject Index
National Renewable Energy Laboratory (NREL) web site
Parabolic Trough Power Plant System Technology
Parabolic Trough Solar Field Technology
Concentrating Solar Power: Energy from Mirrors (PDF document - 227KB)
UTC Molten-Salt Power Towers (PDF document - 2529KB)

http://www.reia-nm.org/solar_thermal_electric.html

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