A couple of weeks ago, we wrote about all the state “firsts” that specialty furniture retailer IKEA is making when it comes to rooftop solar installations, and is continuing that push. But big-box retailer Walmart has got IKEA beat when it comes to the sheer capacity of clean solar energy that is now powering its stores — especially in the state of California.

Walmart just finished its 100th project in California with the completion of its San Diego store. (The roof is pictured above.) Last year, the retailer committed to extending its rooftop solar portfolio to more than 75 percent of its stores in the state (approximately 130) by the end of 2013.

So far, Walmart supports solar photovoltaic installations on about 150 stores, giving it about 62 megawatts of capacity. It is shooting for about 90 megawatts across almost one-quarter of its U.S. stores (about 1,000 locations) by 2020.

The solar installations in California handle 10 percent to 30 percent of each facility’s electricity load, so they are offsetting other sources. The combined output of the systems in the state so far is estimated at 70 million kilowatt-hours annually.

Walmart began piloting solar installations in 2008, targeting states where utility rates are particularly high such as California, Hawaii, Puerto Rico, Ohio and Connecticut. The company is also installing fuel cells and wind turbines, including a 1.1-megawatt turbine in Red Bluff, Calif., due to start up by the end of August.

IKEA Plugs in Philadephia-area Installations

Walmart may beat other retailers when it comes to sheer solar capacity, but IKEA is farther ahead when it comes to the percentage of its entire store system that have some sort of solar capacity.

Recently, the company switched on the largest rooftop solar installations in Michigan, Virginia and Florida. This week, it plugged in several more systems in the Philadelphia area to support two stores and its U.S. Service Office in Conshohcoken, Pa.

IKEA owns its solar installations, while Walmart typically constructs them on a leased basis (SolarCity is Walmart’s partner for 70 of the 100 projects in California).

IKEA’s latest systems in the Philadelphia area have an overall generating capacity of 2,208 kW, and they use 9,198 solar panels among them. The projects will produce approximately 2.65 million kilowatt-hours of electricity annually.

IKEA’s solar construction partner for the Philadelphia area installations was Gehrlicher Solar America.

Eventually, IKEA plans to supply 89 percent of its U.S. stores with solar technology, representing a total generating capacity of 38 megawatts. More than 250,000 panels have already been installed on IKEA stores and offices around the world; the company also owns and operates 110 wind turbines in Europe.