Big-box stores can meet half of their energy needs with rooftop solar, study says
from WaPo’s Climate 202 Newsletter
A study finds that installing solar panels on the expansive, flat roofs of superstores such as Walmart, Target and Home Depot could generate enough electricity to meet half of their energy needs, The Post’s Tik Root reports.
The study, from the nonprofit Environment America Research and Policy Center and the nonpartisan research organization Frontier Group, calculates that there is about 7.2 billion square feet of roof space on superstores around the country, with about two-thirds of roofs suitable for solar — enough capacity to power about 8 million American homes.
Here’s the full story:
From Walmart to Ikea, a report finds that the rooftops of big-box stores offer enough solar potential to power the equivalent of 8 million American homes
Using data from the National Renewable Energy Laboratory, Wilson and his colleagues calculated that there are roughly 7.2 billion square feet of roof space on superstores in the continental United States. NREL estimates that about two-thirds of the roofs on large buildings overall are suitable for solar.
Fully building out that potential could produce 84.4 terawatt-hours of electricity each year and avoid more than 52 million metric tons of planet-warming carbon dioxide emissions annually, Wilson’s group reported. That’s roughly half of the electricity that the authors estimated big-box stores use in a year and, they say, the equivalent of powering 8 million American homes, or taking about 11.3 million passenger cars off the road for a year.
Rooftop solar capacity varies widely by both retailer and state. Walmart has by far the greatest potential, with nearly 784 million square feet of available space, more than three times the next closest retailer, Target. Across all companies, California, Texas, Florida and Ohio are the states with the most superstore solar opportunity.
Nonetheless, current levels of solar installation in the United States remain well below what’s possible. U.S. Energy Information Agency data shows that in 2020 the commercial sector produced roughly 12.9 terawatt-hours of solar power, or about 15 percent of what the latest report calculated was possible on superstore rooftops. But rooftop solar is catching on among big-box stores.
“Ikea is leading the way,” Wilson said. “They’re really ramping up their solar on-site. And Walmart and Target have done that to a lesser extent.”
Ikea reports having solar atop 90 percent of its U.S. locations. And Target ranks first in the amount of on-site solar generation, according to the Solar Energy Industries Association list of retailers with the most on-site solar power in the United States. The company says about a quarter of its more than 1,900 stores nationwide have solar on-site, with the systems providing from 15 percent to 40 percent of a property’s energy needs.
With roughly 2,000 stores in the United States, Home Depot ranks third among superstores in rooftop solar potential. The home-improvement retailer said more than 70 of its stores have solar installed on the roof.
Jim Fenton is the director of the Florida Solar Energy Center, which encourages companies to take the on-site approach. He said the building must first take steps to make sure it’s operating as efficiently as possible but that on-site solar has “the best internal rates of return.”
“The answer is efficiency, efficiency, efficiency,” Fenton said, “then solar.”
Solar will also be most cost-effective if it’s paired with battery storage, Fenton added. That’s because commercial electricity rates can be much higher during periods of high demand, such as in the evening. So if a company can store power during the day and use it when costs are elevated, it can lead to outsize benefits.
“You need to know your energy loads,” Fenton said. “If they have batteries in combination with the solar, they can really lower their demand charges.”
Fenton said that parking lots can offer even more solar potential, with panels not only providing electricity to the store but shade to cars and perhaps even power for electric vehicle chargers. Wilson’s group didn’t include parking lots in its calculations, but the report touches on the possibility.
“Most parking lots could be covered by a solar canopy,” it states, highlighting an Ikea store in Baltimore that installed what looks like solar awnings over the rows of cars in its parking lot. In a news release, Ikea said the move helped cut the store’s energy spending by 57 percent in the fall of 2020.
“We have these massive retail and grocery stores with very inviting roofs and parking lots,” Wilson said. “It just makes so much sense to put solar panels on these places.”