Salt River Project (SRP) said it has already begun to receive power from the recently completed Hudson Ranch I geothermal plant in the Salton Sea region of Southern California.
The plant, operated by EnergySource, is now providing enough power to supply about 26,000 average-size family homes.
At a recent dedication the plant was renamed the John L. Featherstone Plant in honor of a technology pioneer and innovator in the Salton Sea geothermal resource.
SRP, a municipal power and irrigation district in Tempe, Ariz., signed a 30-year agreement in 2007 to purchase 49 megawatts (MW) of geothermal energy from Hudson Ranch I. Following on from this, SRP, which has 950,000 customers and is the largest provider of electricity to the greater Phoenix area, signed another agreement last year.
Under the terms of the second deal SRP has agreed to purchase another 49 MW of geothermal from Hudson Ranch II, a second plant operated by EnergySource, which is expected to be completed by 2014, with drilling commencing in the third quarter of 2012.
Construction of the Hudson Ranch I project cost an estimated $400 million. The Salton Sea geothermal field is very hot and very amenable to liquid penetration, but the rocks also contain a high concentration of minerals which makes the drilling and developing more challenging.
Geothermal power comes from capturing the heat emitted naturally by radioactive rocks beneath the surface of the earth. Developers capture the energy by cracking open the rocks and pumping water through them and back up to the surface. The water comes up boiling and the steam rotates a turbine.
Hudson Ranch I has four injection wells for water to flow through the rocks and three production wells that capture the steam. Creating between 15 and 40 MW of power each, the wells are some of the largest geothermal producers in the world.
Unlike other forms of renewable energy such as solar or wind, geothermal offers the advantage that it can produce power without break, regardless of the time of the day or weather conditions. A drawback of geothermal, however, is the major investment needed to start operations: scouting out suitable sites and drilling down to the geothermal rocks is a costly and lengthy process.