According to research from the Cockrell School of Engineering at the University of Texas, Austin, homes with solar panels do not require on-site storage to reap the economic and environmental benefits of solar energy. In fact, storing solar energy for nighttime use actually increases both energy consumption and emissions, compared with sending excess solar energy directly to the utility grid.
Researchers assessed the trade-offs of adding energy storage to households with existing solar panels, shedding light on the benefits and drawbacks considering today’s full energy grid mix.
“The good news is that storage isn’t required to make solar panels useful or cost-effective,” said co-author Michael Webber, mechanical engineering professor and deputy director of UT Austin’s Energy Institute. “This also counters the prevailing myth that storage is needed to integrate distributed solar power just because it doesn’t produce energy at night.”
Webber and co-author Robert Fares, a Cockrell School alumnus and an American Association for the Advancement of Science fellow at the U.S. Department of Energy, analyzed the impact of home energy storage using electricity data from almost 100 Texas households that are part of a smart-grid test bed managed by Pecan Street Inc., a renewable energy and smart technology company at UT Austin.
They found that storing solar energy for nighttime use increases a household’s annual energy consumption—compared with using solar panels without storage—because storage consumes energy when it charges and discharges. The researchers estimated that adding energy storage increases energy consumption by between 324 to 591 kilowatt-hours.
“I expected that storage would lead to an increase in energy consumption,” Fares said. “But I was surprised that the increase could be so significant—about an 8–14 percent over the year.”
The researchers also found that adding storage indirectly increases overall emissions of carbon dioxide, sulfur dioxide and nitrogen dioxide based on today’s Texas grid mix, which is mainly made up of fossil fuels. The increase in emissions is primarily due to the increase in energy consumption required to account for storage inefficiencies. Because storage affects what time of day a household draws electricity from the grid, it also influences emissions in that way.
While adding energy storage would not make a household greener, it shouldn’t be dismissed.
“Solar combined with storage is still a lot cleaner than having no solar at all,” Fares said.