The Alamosa Solar Generating Plant is a 37 MWp (30.72 MWAC) concentrator photovoltaics power station, the largest in the world when it was completed, in May 2012. It is located in the sunny San Luis Valley, along with several other solar farms. It was built by Mortenson construction using 492 dual axis Amonix 7700 panels each of which contains 7,560 fresnel lens to concentrate sunlight 500 times, and multi-junction solar cells, allowing a greater efficiency than other photovoltaic power plants. It uses all three of the methods available to increase efficiency—dual-axis tracking, concentrating photovoltaics, and multi-junction cells. The systems are certified for operation for 50 years, but the multi-junction cells will need to be replaced in 25 years. The output is being sold to Public Service of Colorado, a subsidiary of Xcel Energy, under a long term Power Purchase Agreement.