Sierra Sun Tower is a 5 MW commercial concentrating solar power (CSP) plant built and operated by eSolar. The plant is located in Lancaster, California and is the only CSP tower facility operating in North America.

The Sierra SunTower facility is based on power tower CSP technology. The plant features an array of heliostats which reflect solar radiation to a tower-mounted thermal receiver. The concentrated solar energy boils water in the receiver to produce steam. The steam is piped to a steam turbine generator which converts the energy to electricity. The steam out of the turbine is condensed and pressurized back into the receiver.

eSolar unveiled the 5 MW Sierra Sun Tower plant, a commercial facility in Lancaster, California that demonstrates the company's technology. Sierra SunTower is interconnected to the Southern California Edison (SCE) grid and, as of spring 2010, is the only commercial CSP tower facility in North America.

The project site occupies approximately 8 hectares (20 acres) in an arid valley in the western corner of the Mojave Desert at 35° north latitude.

Sierra Sun Tower includes two eSolar modules. 24,000 heliostats, divided between four sub-fields, track the sun and focus its energy onto two tower-mounted receivers. The focused heat converts feedwater piped to the receivers into superheated steam that drives a reconditioned 1947 GE turbine generator to produce electricity. The steam passes through a steam condenser, reverts back to water through cooling, and the process repeats.

During the 12 months of construction, Sierra SunTower created over 300 temporary jobs. In operation, the site employs 21 permanent employees.

Concurrent with the plant’s official unveiling, California Governor Arnold Schwarzenegger praised the eSolar solution, “…proving that California’s energy and environmental leadership are advancing carbon-free, cost-effective energy that can be used around the world.”

Sierra Suntower has been certified by the California Energy Commission as a renewable energy facility. Power from the facility is sold under a Power Purchase Agreement (PPA) with SCE, providing clean, renewable energy for up to 4,000 homes.

The 5 MW output from Sierra SunTower reduces CO2 emissions by 7,000 tons per year, an amount equivalent to planting 5,265 acres of trees, removing 1,368 automobiles from the road, or saving 650,000 gallons of gasoline.

Sierra Sun Tower was designed to validate eSolar's technology at full scale, effectively eliminating scaleup risks. The solar thermal equipment operating at Sierra SunTower forms a blueprint from which future plants will be built.

Sierra Sun Tower Awards

In December 2009, editors of Power Engineering magazine selected Sierra SunTower as the winner of the “Best Renewable Project”. Each year, Power Engineering magazine recognizes the world's best energy projects. The award distinguishes Sierra as an exceptional power generation project toward meeting growing global demand.

In February 2010, Sierra SunTower won Renewable Energy World’s “Renewable Project of the Year” award. The award recognizes eSolar's achievements in the clean energy industry by naming Sierra SunTower an exceptional breakthrough in the commercialization of solar thermal technology.

The 5 megawatt (MW) Kimberlina Solar Thermal Energy Plant in Bakersfield, California is the first commercial solar thermal power plant to be built by AREVA Solar, formerly Ausra. The Kimberlina renewable energy solar boiler uses Compact Linear Fresnel Reflector (CLFR) technology to generate superheated steam. Each solar boiler has a group of 13 narrow, flat mirrors, that individually track and focus the sun's heat onto overhead pipes carrying water. The water boils directly into steam. The steam can then spin a turbine to generate electricity or be used as industrial steam for food, oil and desalination processes. The Kimberlina solar boiler currently achieves 750-degree F superheated steam. The next generation solar boiler under construction is designed to achieve 900-degree F superheated steam.

AREVA Solar's boiler is the first and only solar boiler certified with an S-Stamp by the American Society of Mechanical Engineers (ASME).

The Kimberlina Solar Thermal Power Plant was the first of its kind to be built in California in more than 20 years, with the previous plant being the Solar Energy Generating Systems, which employs solar troughs.

Nevada Solar One is a concentrated solar power plant, with a nominal capacity of 64 MW and maximum capacity of 75 MW. The project required an investment of $266 million USD and electricity production is estimated to be 134 million kilowatt hours per year.

It is the second solar thermal power plant built in the United States in more than 16 years and the largest STE plant built in the world since 1991. It is on the southeast fringes of Boulder City, Nevada and was built in that city's Energy Resource Zone which requires renewable generation as part of plant development permits; Nevada Solar One was approved as part of Duke Energy's larger El Dorado Energy project that built 1 GW of electrical generation capacity. The solar trough generation was built by Acciona Solar Power, a partially owned subsidiary of Spanish conglomerate Acciona Energy. Lauren Engineers & Constructors (Abilene, TX) was the EPC contractor for the project. Acciona purchased a 55 percent stake in Solargenix (formerly Duke Solar) and Acciona owns 95 percent of the project. Nevada Solar One is unrelated to the Solar One power plant in California.

A year earlier, Arizona Public Service's Saguaro Solar Facility opened, in 2006, using similar technology, located 30 miles north of Tucson, and producing 1 MW. Nevada Solar One went online for commercial use on June 27, 2007. It was constructed over a period of 16 months. The total project site is approximately 400 acres (0.6 mi² / 1.6 km²), while the solar collectors cover 300 acres (1.2 km²).

Nevada Solar One uses 760 parabolic troughs (using more than 180,000 mirrors) made by Flabeg AG in Germany that concentrate the sun's rays onto thermos tubes placed at the focal axis of the troughs and containing a heat transfer fluid (solar receivers), in contrast to the power tower concentrator concept that California's original Solar One project uses. These specially coated tubes, made of glass and steel, were designed and produced by Solel Solar Systems as well as by Schott Glass in Germany. Motion control was supplied by Parker Hannifin, from components by Ansco Machine Company. The plant uses 18,240 of these four-meter-long tubes. The heat transfer fluid is heated to 735 °F (391 °C). The heat is then exchanged to water to produce steam which drives a Siemens SST-700 steam turbine, adapted to the specific requirements of the CSP technology.

Solar thermal power plants designed for solar-only generation are well matched to summer noon peak loads in areas with significant cooling demands, such as the southwestern United States. Using thermal energy storage systems, solar thermal operating periods can be extended to meet base load needs. Given Nevada's land and sun resources the state has the ability to produce more than 600 GW using solar thermal concentrators like those used by Nevada Solar One.

Nine parabolic concentrator facilities have been successfully operating in California's Mojave Desert commercially since 1984 with a combined generating capacity of 354MW for these Solar Energy Generating Systems. Other parabolic trough power plants being proposed are two 50 MW plants in Spain (see Solar power in Spain), and two 110 MW plants in Israel.

It has been proposed that massive expansion of solar plants such as Nevada Solar One has the potential to provide sufficient electricity to power the entire United States.