Credit: Cockrell School of Engineering at The University of Texas at Austin
According to a study from the Cockrell School of Engineering at The University of Texas at Austin, homes with solar panels do not need on-site storage to enjoy the biggest financial and environmental benefits of solar energy. In reality, solar energy stored for nighttime use actually increases both emissions and energy consumption compared with transmitting surplus solar energy directly to the utility grid.
In a research article published in the January 30 issue of Nature Energy, researchers evaluated the trade-offs of incorporating home energy storage to households using exisiting solar panels, shedding light on the advantages and disadvantages of incorporating storage, considering today's full energy grid mix.
According to the Solar Energy Industry Association, in 2016 the number of rooftop solar installations increased to over one million U.S. households. There is increasing interest in utilizing energy storage to capture solar energy to decrease dependence on traditional utilities. But for now, few homes have on-site storage to contain their solar energy for future use.
The good news is that storage isn’t required to make solar panels useful or cost-effective. This also counters the prevailing myth that storage is needed to integrate distributed solar power just because it doesn’t produce energy at night.
Michael Webber, Professor, The University of Texas at Austin
Webber and co-author Robert Fares, a Cockrell School alumnus who is currently an American Association for the Advancement of Science fellow at the U.S. Department of Energy, studied the impact of home energy storage using electricity data from nearly 100 Texas households that are part of a smart grid test bed operated by Pecan Street Inc., a renewable energy and smart technology company based at UT Austin.
They discovered that solar energy stored for nighttime use increases the annual energy consumption of a household compared to using solar panels without storage, which was because storage consumes a small of amount of energy every time it charges and discharges. The researchers estimated that incorporating energy storage to a household with solar panels increases its yearly energy consumption by roughly 324 to 591 kW-hours.
I expected that storage would lead to an increase in energy consumption. But I was surprised that the increase could be so significant — about an 8 to 14 percent increase on average over the year.
Robert Fares, U.S Department of Energy
The researchers also discovered that incorporating storage indirectly increases total emissions of sulfur dioxide, carbon dioxide, and nitrogen dioxide according to the current Texas grid mix, which is primarily composed of fossil fuels. The increase in emissions is principally due to the increase in energy consumption required to make up for storage inefficiencies. As storage influences what time of day a household utilizes electricity from the grid, it also impacts emissions in that way.
If a homeowner wants to decrease his or her environmental footprint, incorporating storage would not make the household more eco-friendly; however it should not be shunned either, the researchers said.
“Solar combined with storage is still a lot cleaner than having no solar at all,” Fares said.
For utility companies, the advantages are more precise. Solar energy storage decreases the magnitude of solar power injections to the grid by 5 to 42 % and peak grid demand by 8 to 32 %. This is beneficial for the utility since it can decrease the amount of electricity generation and delivery capacity needed.
“However, if the utility is interested in reducing emissions, incentivizing home storage is probably not a good idea,” Fares said.
In short, the study revealed that storing solar energy today provides fewer environmental advantages compared to just transmitting it straight to the grid, as the energy lost due to storage inefficiencies is finally compensated 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. 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.
Michael Webber, P rofessor, The University of Texas at Austin
This research received financial support from Pecan Street Inc., the Electric Reliability Council of Texas, and The University of Texas at Austin Energy Institute.