Every hour, the sun provides the earth with as much energy as all of human civilization uses in an entire year. At just 10 percent efficiency -- that is, if only 10 percent of that solar energy was converted to electricity -- a 100-miles-square area of land could produce enough electricity to power the entire United States. Yet a century after Albert Einstein explained the photoelectric effect, solar technology remains a trivial player in global energy. That may be beginning to change.

In October, 2005, Walmart launched its wide-ranging sustainability initiative and set a goal (among others) to be supplied 100 percent by renewable energy. It’s the goal where they have made the least headway. In Fall 2007, Environmental Defense Fund (EDF) and Walmart initiated a partnership to advance the development of emerging photovoltaic technologies – collectively known as thin-film solar -- into commercially viable, consistent, and cost effective sources of renewable energy.

Today, Walmart, one of EDF’s most prominent corporate partners, announced its plans to add solar generating systems to another 20 to 30 sites in California and Arizona, and the majority of these locations will feature thin film technology. Two different thin film systems will be assessed -- cadmium telluride and copper indium gallium selenide, known as CIGS.

Thin film-based semiconductors, about 1 micron thick (in comparison, a human hair is 40 to 120 microns in diameter), are a less material-intensive alternative to traditional crystalline silicon wafers. Thin film technology enables lighter solar panels; their lighter weight means they could be used in more locations, including flat roofs in states where the potential for snow accumulation precludes the use of heavier traditional solar panels. Because thin film installations usually lie flat, they won’t interfere with skylights. Thin film has also proven more efficient at converting sunlight to energy in fog or smog-prone settings. In advanced applications, thin film solar can even be incorporated into the building envelope itself, further reducing life-cycle cost.

Our partnership with Walmart seeks to create market demand for a product with great potential but which both parties acknowledged being at an early stage of technological development when we initiated the effort. Launching an experimental project in the world’s largest company proved to be far more daunting than anticipated; lawyers and finance people alike are not fond of uncertainty. But the Walmart energy team with whom EDF worked remained resolute, and we slowly progressed from formal partnership agreement to a joint request for proposals (RFP) in late 2008 to the selection of contractors and product to today’s announcement. We actually benefited from the delay -- along the way, the project grew tenfold, from an anticipated two to three store-sized pilots to 20 to 30.

The project’s success will be measured by the extent to which it delivers significant and measurable amounts of renewable energy and significantly reduces greenhouse gas emissions generates reliable projections showing that, when produced and installed at commercial scale, thin-film solar technology will generate electricity at an average cost equal to or less than the average price of utility-delivered electricity while meeting required rates of return for any capital investment; and accelerates the time to market of commercially available thin-film solar products.   

When complete, the new solar installations on Walmart roofs are expected to produce more than 22.5 million kilowatt hours of energy per year, enough to power more than 1,750 average U.S. homes and provide up to 20 to 30 percent of each location’s total electric energy needs. The use of solar energy will also avoid production of more than 11,650 metric tons of GHG, akin to taking more than 3,000 cars off the road each year.

Leveraging Walmart’s scale to benefit the environment is EDF’s reason for staffing an office in Bentonville. Since the thin film project was first discussed in 2007, other retailers have initiated and implemented a wide variety of solar projects, including some thin film installations. And even when Walmart completes new solar installations on all 30 new sites, they (at last count) have some 8,350 facilities to go. In truth, we’re still waiting for a truly Walmart-sized effort toward achieving the renewable energy goal.

But ... with more than 2,700 supercenters whose combined roof area alone exceeds 500 million square feet, Walmart still represents extraordinary potential for on-site renewable energy generation and commensurate GHG savings. Over the next two years, we will work together to assess -- and publicize -- the results of this new technology pilot.

Here’s to bright, sunshine-filled days ahead.

Michelle Mauthe Harvey co-leads Environmental Defense Fund's on-site partnership with Walmart in Bentonville, Arkansas, advancing sustainable business practices throughout their operations and supply chain. This content is cross-posted at the EDF Innovation Exchange. 

Underlying image licensed by Flickr user Dave Dugdale.