Storing solar power increases energyconsumption and emissions, study finds30 January 2017

Solarkraftwerk Waldpolenz, the first Solar 40-MW CdTePV Array installed by JUWI Group in Brandis, Germany.Credit: JUWI Group

Homes with solar panels do not require on-sitestorage to reap the biggest economic andenvironmental benefits of solar energy, accordingto research from the Cockrell School ofEngineering at The University of Texas at Austin.In fact, storing solar energy for nighttime useactually increases both energy consumption andemissions compared with sending excess solarenergy directly to the utility grid.

In a paper published in Nature Energy on Jan. 30,researchers assessed the trade-offs of addinghome energy storage to households with existingsolar panels, shedding light on the benefits anddrawbacks of adding storage considering today'sfull energy grid mix.

According to the Solar Energy IndustryAssociation, the number of rooftop solarinstallations grew to more than 1 million U.S.households in 2016. There is a growing interest inusing energy storage to capture solar energy toreduce reliance on traditional utilities. But for now,

few homes have on-site storage to hold their solarenergy for later use in the home.

"The good news is that storage isn't required tomake solar panels useful or cost-effective," said co-author Michael Webber, a professor in theDepartment of Mechanical Engineering and deputydirector of UT Austin's Energy Institute. "This alsocounters the prevailing myth that storage is neededto integrate distributed solar power just because itdoesn't produce energy at night."

Webber and co-author Robert Fares, a CockrellSchool alumnus who is now an AmericanAssociation for the Advancement of Science fellowat the U.S. Department of Energy, analyzed theimpact of home energy storage using electricitydata from almost 100 Texas households that arepart of a smart grid test bed managed by PecanStreet Inc., a renewable energy and smarttechnology company housed at UT Austin.

They found that storing solar energy for nighttimeuse increases a household's annual energyconsumption—in comparison with using solar panelswithout storage—because storage consumes someenergy every time it charges and discharges. Theresearchers estimated that adding energy storageto a household with solar panels increases itsannual energy consumption by about 324 to 591kilowatt-hours.

"I expected that storage would lead to an increasein energy consumption," Fares said. "But I wassurprised that the increase could be sosignificant—about an 8 to 14 percent increase onaverage over the year."

The researchers also found that adding storageindirectly increases overall emissions of carbondioxide, sulfur dioxide and nitrogen dioxide basedon today's Texas grid mix, which is primarily madeup of fossil fuels. The increase in emissions isprimarily due to the increase in energy consumption

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required to account for storage inefficiencies.Because storage affects what time of day ahousehold draws electricity from the grid, it alsoinfluences emissions in that way.

If a homeowner is seeking to reduce his or herenvironmental footprint, adding storage would notmake the household more green, but it shouldn't bedismissed either, the researchers said.

"Solar combined with storage is still a lot cleanerthan having no solar at all," Fares said.

For utility companies, the benefits are more clearcut. Solar energy storage reduces peak griddemand by 8 to 32 percent and the magnitude ofsolar power injections to the grid by 5 to 42 percent.This is good for the utility because it can reduce theamount of electricity generation and deliverycapacity required.

"However, if the utility is interested in reducingemissions, incentivizing home storage is probablynot a good idea," Fares said.

In short, the analysis showed that storing solarenergy today offers fewer environmental benefitsthan just sending it straight to the grid, because the energy lost to storage inefficiencies is ultimatelymade up with fossil-fuel electricity from the grid."These findings challenge the myth that storage isinherently clean, but that, in turn, offers usefulinsights for utility companies," Webber said.

"If we use the storage as the means to foster theadoption of significantly more renewables thatoffset the dirtiest sources, then storage—done theright way and installed at large-scale—can havebeneficial impacts on the grid's emissions overall,"Webber said.

More information: The impacts of storing solarenergy in the home to reduce reliance on the utility,Nature Energy , nature.com/articles/doi:10.1038/nenergy.2017.1

Provided by University of Texas at AustinAPA citation: Storing solar power increases energy consumption and emissions, study finds (2017,

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January 30) retrieved 28 July 2018 from https://phys.org/news/2017-01-solar-power-energy-consumption-emissions.html

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