One method of utilyzing solar energy is through a clean, large-scale solar thermal technology known as concentrating solar power (CSP). Three types of CSP technologies are currently being looked at: Trough Systems, Dish/engine Systems, and Power Towers. These technologies each use a different kind of mirror configuration to convert the sun's energy into high-temperature heat. This heat energy, in turn, is then used to generate electricity in a steam generator.

So instead of burning gas or coal, a CSP system collects sunlight. The dish, a concentrator, is the primary solar component of the system. It collects the energy coming directly from the sun and concentrates 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. The heat then turns water into steam that turns the generator and electricity is produced.

The Trough System

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 through mass production and engineering improvements. This technology also has the advantage over other renewable technologies (e.g., wind) in that it can be augmented with fossil fuels and/or exceess heat production can be stored in thermal storage units for later use, 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) which focus light onto a receiver pipe 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 also incorporate thermal storage units which set 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.

Trough Technology along with its sister CSP systems have relatively low cost and the ability to deliver power during periods of peak demand—when and where we need it. This means that CSP can be a major contributor to the nation's future needs for distributed sources of energy.