Solar power plants in the Mojave Desert

There are several Solar power plants in the Mojave Desert which supply power to the electricity grid. Solar Energy Generating Systems (SEGS) is the name given to nine solar power plants in the Mojave Desert which were built in the 1980s. These plants have a combined capacity of 354 megawatts (MW) making them the largest solar power installation in the world. Nevada Solar One is a new solar thermal plant with a 64 MW generating capacity, located near Boulder City, Nevada. There are also plans to build other large solar plants in the Mojave Desert. The Mojave Solar Park will deliver 553 MW of solar thermal power when fully operational in 2011.

Insolation (solar radiation) in the Mojave Desert is among the best available in the United States, and some significant population centers are located in the area. This makes the Mojave Desert particularly suitable for solar power plants. These plants can generally be built in a few years because solar plants are built almost entirely with modular, readily available materials.

File:Usgs mojave desert.jpg

Extent of Mojave Desert. Green square is the area of a survey made by the USGS which covers 25,000 square miles (65,000 km²).

Overview

The southwestern United States is one of the world's best areas for insolation, and the Mojave Desert receives up to twice the sunlight received in other regions of the country. This abundance of solar energy makes solar power plants an attractive alternative to traditional power plants, which burn polluting fossil fuels such as oil and coal. Unlike traditional power plants, solar power stations provide an environmentally benign source of energy, produce virtually no emissions, and consume no fuel other than sunlight.

Currently, the cost of solar thermal produced energy can be close to 12 cents (US) per kilowatt-hour (kWh). However, many economists predict that this price will gradually drop over the next ten years to 6 cents per kWh, as a result of economies of scale and technological improvements.

While many of the costs of fossil fuels are well known, others (pollution related health problems, environmental degradation, the impact on national security from relying on foreign energy sources) are indirect and difficult to calculate. These are traditionally external to the pricing system, and are thus often referred to as externalities. A corrective pricing mechanism, such as a carbon tax, could lead to renewable energy, such as solar thermal power, becoming cheaper to the consumer than fossil fuel based energy.

Solar thermal power plants can generally be built in a few years because solar plants are built almost entirely with modular, readily available materials. In contrast, many types of conventional power projects, especially coal and nuclear plants, require long lead times.

Solar One and Solar Two

Aerial view of the Solar Two facility, showing the power tower (left) surrounded by the sun-tracking mirrors.

Solar power towers use thousands of individual sun-tracking mirrors (called heliostats) to reflect solar energy onto a central receiver located on top of a tall tower. The receiver collects the sun's heat in a heat-transfer fluid that flows through the receiver. The U.S. Department of Energy, and a consortium of U.S. utilities and industry, built the first two large-scale, demonstration solar power towers in the desert near Barstow, California.

Solar One operated successfully from 1982 to 1988, proving that power towers work efficiently to produce utility-scale power from sunlight. The Solar One plant used water/steam as the heat-transfer fluid in the receiver; this presented several problems in terms of storage and continuous turbine operation. To address these problems, Solar One was upgraded to Solar Two, which operated from 1996 to 1999. Both systems had the capacity to produce 10 MW of power.

The unique feature of Solar Two was its use of molten salt to capture and store the sun's heat. The very hot salt was stored and used when needed to produce steam to drive a turbine/generator that produces electricity. The system operated smoothly through intermittent clouds and continued generating electricity long into the night.

Solar Two was decommissioned in 1999, and was converted by the University of California, Davis, into an Air Cherenkov Telescope in 2001, measuring gamma rays hitting the atmosphere.

Solar Electricity Generating Systems

Sketch of a Parabolic Trough Collector system.

Aerial view of one of the SEGS plants.

Trough systems predominate among today's commercial solar power plants. Nine trough power plants, called Solar Energy Generating Systems (SEGS), were built in the 1980s in the Mojave Desert near Barstow. These plants have a combined capacity of 354 MW making them the largest solar power installation in the world. Today they generate enough electricity to meet the power needs of approximately 500,000 people.

Trough systems convert the heat from the sun into electricity. Because of their parabolical shape, trough collectors can focus the sun at 30-60 times its normal intensity on a receiver pipe located along the focal line of the trough. Synthetic oil circulates through the pipe and captures this heat, reaching temperatures of 390 °C (735 °F). 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. The SEGS plants are configured as hybrids to operate on natural gas on cloudy days or after dark, and natural gas provides 25% of the total output.

Nevada Solar One

Nevada Solar One has a 64 MW generating capacity and is located in Boulder City, Nevada. It was built by the U.S. Department of Energy, National Renewable Energy Laboratory, and Solargenix Energy.

Nevada Solar One uses parabolic troughs as thermal solar concentrators, heating tubes of liquid which act as solar receivers. These solar receivers are specially coated tubes made of glass and steel, and about 19,300 of these four meter long tubes are used in the newly built power plant. Nevada Solar One also uses a technology that collects extra heat by putting it into phase-changing molten salts. This energy can then be drawn at night.

Solar thermal power plants designed for solar-only generation are ideally matched to summer noon peak loads in prosperous areas with significant cooling demands, such as the south-western United States. Using thermal energy storage systems, solar thermal operating periods can even be extended to meet base-load needs.

The cost of Nevada Solar One is in the range of $220-250 million. The power produced is slightly more expensive than wind power, but less than photovoltaic (PV) power.

Nellis Solar Power Plant

In December 2007, the U.S. Air Force announced the completion of a solar photovoltaic (PV) system at Nellis Air Force Base in Clark County, Nevada. Occupying 140 acres of land leased from the Air Force at the western edge of the base, this ground-mounted photovoltaic system employs an advanced sun tracking system, designed and deployed by PowerLight subsidiary of SunPower. Tilted toward the south, each set of solar panels rotates around a central bar to track the sun from east to west. The 14-megawatt (MW) system will generate more than 30 million kilowatt-hours of electricity each year and supply approximately 25 percent of the total power used at the base. The Nellis Solar Power Plant is the largest solar photovoltaic system in North America.

Mojave Solar Park

Solel has signed a contract with Pacific Gas and Electric (PG&E) to build the world's largest solar plant in the Mojave Desert. When fully operational in 2011, the Mojave Solar Park will deliver 553 megawatts of solar power, the equivalent of powering 400,000 homes, to PG&E’s customers in northern and central California. The plant will cover up to 6,000 acres (24 km²) of land.

Stirling Solar Dish

A parabolic solar dish concentrating the sun's rays on the heating element of a Stirling engine. The entire unit acts as a solar tracker.

Stirling Energy Systems under an agreement with utility company Southern California Edison is planning to erect a 500 megawatt, 4,600 acre (19 km²), solar power plant to open some time after 2009. This will be the first commercial application of the Stirling Solar Dish which concentrates solar energy by the use of reflective surfaces and uses a Stirling heat engine to convert the heat into electricity.

Stirling Energy Systems have announced another agreement with San Diego Gas & Electric to provide between 300 and 900 megawatts of electricity.

Land use issues

Solar thermal power plants are large and seem to use a lot of land, but when looking at electricity output versus total size, they use less land than hydroelectric dams (including the size of the lake behind the dam) or coal plants (including the amount of land required for mining and excavation of the coal). While all power plants require land and have an environmental impact, the best locations for solar power plants are on land, such as deserts, for which there might be few other uses.

See also

• Deployment of solar power to energy grids
• List of solar thermal power stations
• Renewable energy commercialization
• Solar power
• Solar thermal energy

External links

• Nevada Solar One video
• Huge Solar Plants Bloom in Desert
• Solar plant planned in California desert