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Solar Trough System
Trough systems predominate among today’s commercial solar power
plants. Trough systems convert the heat from the sun into electricity.
Because of their parabolic shape, troughs can focus the sun at 30 to 60
times its normal intensity on a receiver pipe located along the focal
line of the trough. Synthetic oil captures this heat as the oil circulates
through the pipe, reaching temperatures as high as 390°C (735ºF).
The hot oil is pumped to a generating station and routed through a heat
exchanger to produce steam. Finally, electricity is produced in a conventional
steam turbine.
Parabolic trough solar power plants produce electricity
from the heat of the sun. Trough technology is the most cost-effective
solar technology available today, with potential for significant cost
reduction. This technology has the advantage over other renewable technologies
(e.g., wind) in that it can be augmented with fossil fuels or with the
addition thermal storage, allowing trough technology to provide electricity
on demand.
The first parabolic trough solar power plant became operational in 1984.
It continues to provide commercial power to this day. In total, nine trough
power plants ranging in size from 14 MWe to 80 MWe are currently in operation
and have a combined operational experience of more than 110 years. Together,
they have produced about 7.5 billion kWh of electricity.
Parabolic trough solar power plants produce electric power by converting
the sun's energy into high-temperature heat through the use of parabolic-trough
collectors. The sun's energy is concentrated by the parabolic-shaped mirrors
(or reflectors) with focus light onto a receiver pipe running located
at the focus of the collector mirrors. This energy heats oil flowing through
the pipe, and the heat energy is then used to generate electricity in
a conventional steam turbine.
A collector field comprises many troughs in parallel rows aligned on
a north-south axis. This configuration enables the single-axis troughs
to track the sun from east to west during the day to ensure that the sun
is continuously focused on the receiver pipes. Individual trough systems
currently can generate about 80 megawatts of electricity, enough to power
a city of 110,000 people. Of course, individual systems can be grouped
to provide more power.
Because trough technology relies on sunshine, it is often "hybridized"
with fossil fuel systems to allow generation of power around the clock.
Typically a natural gas-fired heat or a gas steam boiler/reheater is used;
troughs also can be integrated with existing coal-fired plants or high
efficiency combined-cycle plants. Trough designs can incorporate thermal
storage-setting aside the heat transfer fluid in its hot phase-allowing
for electricity generation several hours into the evening.
These attributes, along with impressive solar-to-electric conversion
efficiencies, make trough technology an attractive renewable energy option
in the Southwest and other sunbelt regions worldwide.
Parabolic trough technology is in the family of concentrating solar power
technologies, also called solar thermal electric technologies.
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