Walmart is inching closer to its goal of using 100 percent renewable energy with a new deal bringing rooftop solar power to five Puerto Rico stores.

Solar panel image CC licensed by Flickr user Mountain/\Ash

The arrangement with SunEdison could lead to rooftop solar systems at an additional 23 stores over five years. Each system will provide between 25 percent and 35 percent of the electricity consumed by the host store.

The deal is similar to a slew of previous announcements by retailers looking to add renewable energy to their operations without a large capital investment. SunEdison will finance, own, build and operate the solar arrays over a 15-year contractual period, guaranteeing Walmart a long-term source of green power at a predictable rate.

JCPenney is working with SunPower Corp. to install at 10 stores solar energy systems that will be financed, owned and operated by SunPower. Gap, AT&T, and Constellation Wines have also entered power purchase agreements for solar power produced on their property by generating systems owned and operated by others.

The move is part of a wave of initiatives undertaken by the world's largest retailer since it publicly committed to improving its environmental performance in 2005. Although the company has stated publicly its goal of achieving 100 percent renewable energy, Walmart has declined to say how far along it is in its effort. In a conference call with reporters in late 2008, the company demurred, responding only, "It's very early."

The company announced in 2007 a major solar power purchase agreement that led to 20 completed solar installations in Hawaii and California, followed by a joint agreement with BP Solar in April that will provide solar power arrays at another 10 to 20 locations in California. In November, the company finalized a deal that will provide enough wind power to satisfy 15 percent of its needs in roughly 350 Texas facilities. The company operates more than 4,100 facilities in the U.S.

“Today, our new Walmart stores are 21 percent more energy-efficient than our original 2005 stores,” Walmart Puerto Rico President and CEO Renzo Casillo said in a statement. “Through the implementation of energy-saving strategies and the installation of energy-efficient equipments, last year we achieved an 8.7 percent reduction in energy consumption compared to the previous year. With this solar energy project we'll continue to broaden our efforts towards our main objective and commitment of being supplied 100 percent by renewable energy."

The Puerto Rico solar energy arrays will vary in capacity from 795 kW to 1,239 kW. The first location to break ground will be a 895.4 kW installation at Walmart’s Caguas store beginning later this year.

Walmart is billing the five-store Puerto Rico project, at a total of 4.7 megawatts once complete, as the largest ever developed the island’s history. According to its research, the largest project to date involves two warehouse rooftop installations that generate 375 kW.

The company also installed what it called the largest photovoltaic solar energy system in Latin America earlier this year, a 1,056-solar panel system spanning 2,173.5 meters in Aguascalientes, Mexico.

Walmart uses a variety of arrangements to use solar energy at its stores. In 2006, it issued a request for proposal (RFP) to install rooftop solar energy systems in five states, which at the time was the largest solar procurement proposal ever. The company asked bidders for offers that were either turnkey solar systems that would be purchased outright by the world’s largest retailer, solar installations that were built, owned and operated by the supplier, or leased installations.