On April 6, San Diego, California Mayor Jerry Sanders and SunEdison announced the successful deployment of a 945-kilowatt solar array at the city’s Otay Mesa water treatment facility.

SunEdison, a subsidiary of MEMC Electronic Materials, is the United States’ largest solar energy services provider and the first to introduce a solar power purchase agreement, or PPA, for homeowners and businesses wanting to install solar without the large, upfront costs that getting such a system requires.

Although solar panel prices have fallen in the past two years, largely in response to declining silicon prices and one of the worst recessions since the 1930s, a good, traditional solar system (comprised of silicon-based solar panels, producing 5 kilowatts) costs about $7 per watt installed, or about $27,500.

This is considerably better than solar panel prices before the recession, when installed prices ran as high as $12 per watt, and today’s prices can be reduced even further by state and regional incentives like that provided in New Jersey and California.

The Otay Mesa solar field array is covered by a 20-year PPA, during which the city can buy the electricity generated at what are current retail rates, with a guaranteed, long-term rate that will likely come in well under future electricity rates, which historically have only risen over time. This enables the city to more easily predict and regulate the cost of delivering water to the city’s residents.

Delivering 1.5 million kilowatt-hours the first year, and 27 million kilowatt-hours over the 20-year lifespan of the PPA, the Otay Mesa solar array will also prevent more than 29 million pounds of carbon dioxide emissions over its lifetime, which is – according to the Greenhouse Gas Equivalencies Calculator developed by the U.S. Environmental Protection Agency – the same as taking more than 2,800 cars off the road until 2030.

Otay Mesa is the second step in the city’s plan to develop and use 5 megawatts of solar energy. The first step, also installed by SunEdison, is a 1.1-megawatt solar field array at the Alvarado water treatment plant, completed in 2007.

According to Mayor Sander, San Diego is the biggest solar city in California – a fact confirmed by the 2008 report from Environment California (too bad more recent updates aren’t available).