Electric Hot Water Heater Primary Frequency Control

Residential electric hot water heaters present a massive distributed energy storage resource. By allowing for temperature variation of the water in the lower part of the water heat tank, as much as several kWh of energy storage could be realized per water heater. It is estimated that there are millions of residential electric hot water heaters in the Pacific Northwest of the United States, which puts the total energy storage resource on the order of several thousand MWh of storage. This paper presents a cost effective modification of the operation of the lower element of an electric hot water heater to allow the hot water heater to participate in frequency regulation, effectively storing energy when the grid frequency is high, and allowing the water heater to coast when the frequency is low. It is demonstrated that each water heater can easily provide 5% frequency regulation (4500 W per 3 Hz) without a significant impact to the temperature of water withdrawn by the home user.