As Walmart unveiled its 100th rooftop solar installation in California this week, the world’s largest retailer reaffirmed its commitment to sustainability.

The solar array helps Walmart toward its goal of getting 100 percent of its energy from renewable sources, said Walmart spokeswoman Brooke Buchanan.

“Last year we made a commitment to install solar on 75 percent of our stores in Califoria,” Buchanan said. “Together, they are expected to generate 70 million kilowatt hours of electricity.”

That’s enough to power roughly 5,400 homes, she said.

Each of the solar installations on Walmart store roofs use different technologies and produce between 10 and 30 percent of the energy the store needs, depending on how large the store is, Buchanan said.

Walmart’s approach to solar in California is just the beginning, she said. There is also solar installed on Walmart rooftops in Colorado, Arizona, Louisiana, Massachusetts and China. Those markets have the most attractive rebate and incentive packages for solar.

“We’re looking to expand into other markets as well,” Buchanan said.

The retailer expects to have almost a fourth of its more than 4,500 U.S. stores powered at least partially by solar by 2020.

The new solar installation at the Walmart located on College Avenue in San Diego brought the company’s U.S. solar energy portfolio to 62 megawatts. Buchanan said Walmart expects to reach 90 megawatts by the end of 2012.

Walmart works with local contractors on each of its solar installation projects. The San Diego project was installed by SolarCity, which has hired 1,213 employees since announcing its first Walmart project in September 2010. The company has installed about 70 of Walmart’s 100 rooftop solar projects.

Each Walmart solar installation requires about 48 contractors. The company launched its solar pilot program in 2007 and has continued t support it since, installing solar on more and more of its stores.

The aim, according to a press release from the retailer, is to reduce overhead expenses and further drive down the cost of goods.