Mirrored parabolic troughs concentrate solar energy onto pipes containing synthetic oil.

The Department of Energy has offered conditional loan guarantees totaling $2 billion to two concentrated solar projects in California, Energy Secretary Steven Chu announced yesterday.

Both projects employ mirrored parabolic solar thermal troughs that reflect and concentrate solar energy to heat pipes containing heat transfer liquid, usually synthetic oil. That hot liquid is then used to generate steam and power a turbine generator that produces electricity.

Specifically, a $1.2 billion loan guarantee has been offered to the 250-megawatt Mojave Solar Project in San Bernardino County. Once fully operational, the farm is expected to generate enough electricity to power 53,000 homes annually.

Due to increased thermal efficiency of the system compared to older concentrated solar plants, the Mojave Solar Project will be able to operate without a fossil fuel backup system, such as natural gas, during periods when sun power wanes, according to project sponsor Abengoa Solar.

The Mojave Solar Project is expected to create 830 construction jobs and 70 operational jobs. About 80 percent of all equipment and labor to build the project will be sourced from within the U.S., with the plant's receiver tubes being made in New Mexico, and its parabolic trough mirrors coming from Arizona, according to Abengoa.

The DOE has also offered $681.6 million in the form of a loan guarantee to the Genesis Solar Project, which, when complete, will consist of two 125-megawatt concentrated solar farms in the Sonoran Desert roughly 25 miles from Blythe, Calif.

The Genesis Solar Project had already been granted use of those public lands by the Bureau of Land Management shortly after October 2010 when Department of the Interior Secretary Ken Salazar approved a program to facilitate land-use grants for renewable energy projects.

The Genesis Solar Project is expected to create 800 construction jobs and 47 operating jobs. Once complete, it should generate enough electricity to power the equivalent of 48,000 homes annually, according to project sponsor NextEra Energy Resources.

NextEra already operates seven solar projects in the Mojave Desert region, according to the company.

The electricity generated by both the Mojave Solar Project and the Genesis Solar Project will be sold to the Pacific Gas and Electric Company, according to the DOE.