Grid Scale, Solar, Storage, Wind Power

Water Heaters as Energy Storage a Significant Potential Grid Resource, Brattle Group Says

Water heaters used as energy storage is an attractive opportunity for improving the reliability, economics and environmental footprint of the power grid, according to a new report from The Brattle Group.

The report, which was released on Feb. 10, analyzes the economics of advanced electric water heating load control and energy efficiency strategies that utilities and demand response aggregators could implement to reduce total system costs. According to the report, flexible load in the form of demand response or behind-the-meter energy storage is a possible solution for reliably integrating renewables into the power system.

“Electric water heaters are essentially pre-installed thermal batteries that are sitting idle in homes across the U.S.,” Brattle Group said in the report. “By heating the water in the tank to store thermal energy, water heaters can be controlled in real-time to shift electricity consumption from higher-priced hours when less efficient generating units are operating on the margin to lower-priced hours when less costly generation is operating on the margin and, in some cases, there may be excess supply of energy from low- or zero-emitting resources, such as wind power.”

New grid interactive water heaters also can be controlled over short time intervals and with near instantaneous response, allowing them to provide frequency regulation and other grid balancing services that deliver value in markets with rapid fluctuations in supply.

Brattle Group prepared the report for the National Rural Electric Cooperative Association (NRECA), the Natural Resources Defense Council (NRDC), and the Peak Load Management Alliance (PLMA).

Minnesota-based cooperative Great River Energy joined NRECA, NRDC and PLMA on Feb. 10 for the launch of an initiative designed to promote growth in community-based energy storage, also called community storage.

Great River Energy currently manages a community storage program that has been able to store a gigawatt-hour of energy each night by controlling the electric resistance water heaters of 65,000 end-use members, according to the co-op.

“At Great River Energy, we believe there’s a battery hidden in basements all across our service territory,” Gary Connett, director of member services at Great River Energy, said in a statement. “When the wind is blowing or the sun is shining, large capacity water heaters can be enabled to make immediate use of that energy to heat water to high temperatures. The water heaters can be shut down when renewables are scarce and wholesale costs are high.”

In the report, Brattle Group examined peak shaving, in which load is curtailed during peak hours on a limited number of days per year; thermal storage, in which the water is heated each night to avoid higher priced hours during the day; and fast response, which would provide balancing services in the form of quick load increases and decreases.

Brattle Group determined that the peak shave strategy is suited for market conditions in which there is a peak demand-driven need for generation and transmission capacity, a relatively flat energy price profile, and a limited ability to promote adoption of larger electric resistance water heater tank sizes.

A thermal storage strategy, Brattle Group said, can increase benefits relative to the peak shave strategy, at little incremental cost, if offered to customers with larger water tanks in market conditions with a significant price differential between peak and off-peak periods. A fast response strategy, Brattle Group added, can increase benefits over the other two load control strategies in markets with a need for resources that can quickly ramp load up and down.

Lead image: Plumber and water heater. Credit: Shutterstock.

This article was updated on Feb. 19 at 12:00 p.m. EST to correct gigawatt-hour from gigawatt.