New research from the Cockrell School of Engineering at The University of Texas in the US has found that storing solar energy in batteries for nighttime use actually increases energy consumption and carbon dioxide (CO2) emissions.
The researchers assessed the trade-offs of adding home energy storage to households with existing solar panels, shedding light on the benefits and drawbacks of adding storage considering today’s full energy grid mix.
Although there is a growing interest in using energy storage to capture solar energy to reduce reliance on traditional utilities, only a few homes currently have on-site storage to hold their solar energy for later use in the home.
According to Michael Webber, a professor in the Department of Mechanical Engineering and deputy director of UT Austin’s Energy Institute, the study 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 who is now an American Association for the Advancement of Science fellow at the US 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 housed at UT Austin.
They found that storing solar energy for nighttime use increases a household’s annual energy consumption — in comparison with using solar panels without storage — because storage consumes some energy every time it charges and discharges. The researchers estimated that adding energy storage to a household with solar panels increases its annual energy consumption by about 324 to 591 kilowatt-hours (kWh).
Fares said he expected storage to lead to increased energy consumption but he was surprised to find about an 8% to 14% increase on average 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 primarily 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.
Adding storage would not make a household more green, Fares said, but it should not be dismissed either. Solar combined with storage is still cleaner than having no solar at all, he added.
For utility companies, the benefits are more clear cut. Solar energy storage reduces peak grid demand by 8% to 32% and the magnitude of solar power injections to the grid by 5% to 42%. This is good for the utility because it can reduce the amount of electricity generation and delivery capacity required.
In short, the analysis showed that storing solar energy today offers fewer environmental benefits than just sending it straight to the grid, because the energy lost to storage inefficiencies is ultimately made up with fossil-fuel electricity from the grid. “These findings challenge the myth that storage is inherently clean, but that, in turn, offers useful insights for utility companies,” Webber said.
“If we use the storage as the means to foster the adoption of significantly more renewables that offset the dirtiest sources, then storage — done the right way and installed at large-scale — can have beneficial impacts on the grid’s emissions overall,” Webber said.