The Solana Generating Station is a 280-megawatt (MW) concentrating solar power (CSP) plant to be built 70 miles southwest of Phoenix, near Gila Bend, Arizona. The plant will be located on the northwest corner of Interstate 8 (I-8) and Painted Rock Dam road.
It will produce enough energy to serve 70,000 APS customers when operating at full capacity. The plant will be built by Abengoa Solar Inc., and is scheduled to provide renewable energy beginning in 2012.
Spanish for “sunny place,” Solana will not emit greenhouse gases and will provide APS with more solar electricity per customer than any utility in the U.S. The facility also would be the largest solar power plant in the world if in operation today.
There are several ways to create electricity using the sun’s energy. Two common methods are concentrating solar power and photovoltaic. Both applications have their appropriate place for helping meet the future energy needs of Arizona.
Solana will use concentrating solar power (CSP) technology with storage capability. Unlike a photovoltaic solar plant, which uses sunlight to produce electricity, CSP uses the sun’s heat.
Solana’s parabolic mirrors focus the sun’s heat on a heat transfer fluid. The fluid can reach a temperature of 735 degrees Fahrenheit. To produce electricity, the hot fluid transfers its heat energy to water, creating steam. The steam is then used to run conventional steam turbines. The heat energy in the fluid also can be stored and used at a later time to generate electricity.
Large thermos-like buildings containing molten salt will be located next to the steam boilers. At select times, instead of immediately creating steam, the heat transfer fluid will heat the molten salt. Then, if electricity is needed when the sun is not shining, the fluid can be heated by running it through the hot salt instead of through the mirrors. Using this process, electricity can be made from heat energy that was created up to six hours earlier.
Concentrating Solar Power
Parabolic mirrors focus solar energy onto a heat transfer fluid. To produce electricity, the heated fluid transfers its heat energy to water, creating steam. The steam is then used to run conventional steam turbines. The heat energy in the fluid also can be stored and used at a later time to generate electricity.
Solar trough technology uses long rows of mirrors which track the sun from east to west in order to best focus sunlight onto the receiver pipes (heat collecting element). The receiver pipes are filled with fluid that is heated by the sun’s energy, much like a huge magnifying glass. The heated fluid is then sent to a heat exchanger where steam is created, and that steam is then used to turn a turbine. Large insulated tanks filled with molten salt can be used with concentrating solar power to store the heat from the fluid. This stored heat can then be used to produce energy during periods of low or no sun, including the evening hours.
Using thermal storage allows energy provided by the sun to be distributed over a longer window of time. In the example above, the stored energy is used to provide heat for the electricity generation well into the night. APS’ peak summer demand occurs in the early evening, often as late as 7 p.m., long after the sun has provided its most intense radiation. Thermal energy storage allows the solar trough to supply electricity when energy is most needed by APS customers.
Arizona and Solar Energy: A Great Match
Regardless of the technology used to produce it, generating energy requires fuel. This fuel can take the form of fossil fuels like coal or natural gas, or it can take the form of renewable fuels like the wind or the sun. With abundant sunshine, Arizona offers one of the best renewable resources in the world, and is well situated to provide reliable electricity to APS customers.
Among the most important factors in considering a resource for electricity production is the reliability of the fuel. Arizona’s solar climate provides a resource that is both dependable and predictable. The solar resource in Arizona is virtually unlimited, with more than 300 days of sunshine each year. In addition, Arizona has sizeable quantities of wide-open, flat landscape that is ideal for the installation of large-scale solar equipment.
Near-optimal landscape, weather, proximity to electric transmission and other essential factors make Arizona one of the best solar climates in the nation.
Development of large-scale solar electricity generation plants requires a unique set of conditions. Although solar intensity is high in most of Arizona and some other areas of the southwest, other considerations reduce the area practically available for development of this resource. Optimal areas would include generally flat (less than 1 percent slope) land that is not affected by summer monsoons or heavy blowing dust, proximity to transmission lines and available water for plan operation. In addition, when selecting sites for solar generation, consideration must be given to the desert ecosystem and sensitive species that inhabit it. As this map shows, Arizona is one of the few places in the United States where the solar resource is world class and the rigorous development requirements are met.