A rooftop photovoltaic installation

Household solar storage increases emissions, study concludes

Image credit: Lucas Braun

Contrary to popular belief, household storage for solar power doesn’t reduce cost or emissions, an American study suggests.

As charging and discharging a home battery itself consumes energy, feeding surplus solar power into the storage device instead of into the grid results in higher overall electricity consumption for the household, as well as higher emissions because the increased consumption needs to be covered by fossil fuel-based energy.

This increase is quite substantial – up to 591KWh annually.

“I expected that storage would lead to an increase in energy consumption,” said Robert Fares from the Cockrell School of Engineering at the University of Texas at Austin, “but I was surprised that the increase could be so significant - about an eight to 14 per cent increase on average over the year.”

Fares, together with Professor Michael Webber, analysed 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 Austin-based renewable energy and smart technology company Pecan Street Inc.

The results are relevant for Texas, where the majority of grid electricity comes from fossil fuels. As a result, the increased consumption due to storage technology leads to higher carbon, sulphur and nitrogen dioxide emissions.

The situation, however, is different for utility companies, which could reduce their peak grid demand by up to 32 per cent thanks to solar energy storage and cut down the magnitude of solar power injections to the grid by up to 42 per cent.

“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."

The study was published in the journal Nature Energy.

According to the Solar Energy Industry Association, the number of rooftop solar installations grew to more than one million US households in 2016. There is a growing interest in using energy storage to capture solar energy to reduce reliance on traditional utilities.

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