Up to 20 Wal-Mart stores in California will be discounting their carbon footprints by adding solar power. The retailer will nearly double its solar power purchases in California by adding 10 megawatts of photovoltaic panels.

Wal-Mart won't own the panels at its store locations, which will provide between 20 and 30 percent of the energy needs. BP Solar will manage the equipment and provide the electricity under a power purchase agreement. Wal-Mart expects the solar panels will reduce its carbon footprint by 10,000 metric tons.

The addition of solar power is another step towards the companies goal of using 100 percent renewable energy, according to Kim Saylors-Laster, Wal-Mart's Vice President of Energy. She said the company hasn't set a deadline for its goals, which also include generating zero waste.

Someday the solar power could be used to charge customer electric vehicles. Saylors-Laster believes "there is a potential for (vehicle) charging stations around the country," but the company has not committed to installing any at this time.

Wal-Mart is also considering adding wind and geothermal as clean energy alternatives, according to Saylors-Laster. The company has developed a prototype of a new store that will reduce energy consumption by 30 percent.

According to Wal-Mart's 2009 annual sustainability report, the company recycled or reused 55 percent of its waste during the prior year.