PG&E, Other Utilities Test Hot Water Heaters as Virtual Grid Batteries

By Jonathan Marshall

Energy storage — the so-called “holy grail” application that can potentially support power grid reliability, balance out the swings of wind and solar energy, and so much more — doesn’t have to come in the form of big boxes with positive and negative poles called batteries.

With the right technology, it can be as mundane as the hot water heaters in millions of American homes.

A company called Sequentric made a big splash last November by announcing a new patent that regulates electricity on the grid, much like a battery, by permitting second-by-second changes in the amount of power demanded by electric water heaters.

The company estimates that there are about 50 million electric water heaters in North America. (Most water heaters in PG&E’s service area are fueled by natural gas, but about 10 percent are electric.) They can account for a significant portion of a home’s power draw — up to five kilowatts.

If utilities or grid operators could fine tune the collective draw of millions of such appliances, they could act like big batteries to absorb cheap surplus energy or cut back on energy demand when electricity supplies are relatively scarce and expensive.

All of that works on the assumption that customers are willing to live with a slightly wider range of water temperature—and forego scalding showers during periods of electricity shortages—in return for some kind of break on their electric rates.

That assumption seems reasonable, given that more than 100,000 PG&E customers participate in a program called SmartAC, which allows their air conditioners to be turned down briefly during periods of exceptional electricity demand. In August 2012, that program cut statewide electricity demand by about 100 megawatts during a “Flex Alert” day.

Sequentric isn’t the only company to offer such a solution for hot water heaters. Back in 2010, PG&E’s Applied Technology Services division in San Ramon reported the results of extensive tests of a General Electric  water heater hooked up to a SmartMeter and communications module. The appliance offered two heating modes and a variable thermostat, allowing a wide range of control over its energy use.

By sending a signal through the SmartMeter, the PG&E testers were able to slash the unit’s maximum power demand for short durations from 3.8 kW in standard electric mode to only 0.6 kW in a special high-efficiency mode. Lowering the thermostat setting from 135F to 100F cut the maximum power demand by another 90 Watts. (In practical application, actual demand reductions would probably be smaller.)

A large-scale demonstration of a similar application is now under way in five states, with participation by the Bonneville Power Administration, 11 distribution utilities, the U.S. Department of Energy and several technology partners including IBM. The system adjusts power demand every five minutes to keep the grid in balance, in part by sending signals to hot water heaters in 60,000 homes.

New Zealand utilities have used remote water heater controls since the 1950s for basic load management—to reduce electricity demand during peak periods, usually in the early evening hours during winter months. To reduce the burden, utilities cycle through their customers, turning off water heaters for short periods. Usually enough warm water remains in the tank for washing and other purposes.

The same principle of thermal energy storage can work in reverse – for example, using a building HVAC system to chill water off-peak for later use in cooling the building during afternoon peak hours. Check out NEXT100’s profile of such a money-saving application at Napa Valley Community College.

Such applications may become more widespread following a recent report by the state’s main grid operator calling for greater use of so-called “demand response” applications to help maintain electric reliability as California relies more and more on variable solar and wind energy.

Email Jonathan Marshall at


Comments are closed.

"PG&E" refers to Pacific Gas and Electric Company, a subsidiary of PG&E Corporation.
© 2014 Pacific Gas and Electric Company. All rights reserved.