Homes with solar panels do not require on-site storage to reap the biggest economic and environmental benefits of solar energy, says the study from the Cockrell School of Engineering at The University of Texas at Austin.
According to the Solar Energy Industry Association, the number of rooftop solar installations grew to more than 1 million U.S. households in 2016, but few have on-site storage to hold their solar energy for later use in the home.
“The good news is that storage isn’t required to make solar panels useful or cost-effective,” said Michael Webber, a professor in the Department of Mechanical Engineering 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.”
The study looked at electricity data from almost 100 Texas households that are part of a smart grid test bed managed by Pecan Street, 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.
“I expected that storage would lead to an increase in energy consumption,” said Robert Fares, a fellow at the US Department of Energy who also worked on the study. “But I was surprised that the increase could be so significant — about an 8 to 14 percent 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 the electricity grid using fossil fuels. he 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.
For utility companies, the benefits are more clear cut. Solar energy storage reduces peak grid demand by 8 to 32 percent and the magnitude of solar power injections to the grid by 5 to 42 percent. This is good for the utility because it can reduce the amount of electricity generation and delivery capacity required.
“These findings challenge the myth that storage is inherently clean, but that, in turn, offers useful insights for utility companies,” said 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,” he said. “Solar combined with storage is still a lot cleaner than having no solar at all,” added Fares.
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