Enabling Solar Power with Residential Water Heater Load-Shifting

As governments and international organizations aim to increase renewable energy production in response to climate change, there is a growing demand for energy storage. A temporal mismatch in the daily profiles of solar energy production and residential energy use causes an imbalance between generation and demand. Load shifting presents a key grid control strategy that minimizes this mismatch and the resulting rapid ramp rates in fossil fuel-based electricity generation. Water heaters are a principal contributor to residential electricity consumption from the grid, and they offer a good potential for thermal energy storage due to low ambient energy loss and water’s high specific heat capacity. Load shifting of water heating loads maximizes self-consumption of solar power in residential buildings thereby improving homeowner utility costs and the ability of the electric grid to accept greater levels of intermittent solar generation. Water heating load data was generated using the U.S. Department of Energy Residential Prototype Building Models for a cycling 50-gallon (189 L) electric water heater in a single-family house in Los Angeles with a roof-mounted solar photovoltaic system. The effects of load shifting on the fraction of the water-heating loads to the total house electric loads, the fraction of the water heating load met by solar power, and end-user electricity bills using time-of-use (TOU) electricity rates were analyzed. This study shows that shifting the load of water heaters to coincide with the solar profile lowers electricity costs significantly more than a solar photovoltaic system without load shifting which sends power to the grid using a net metering agreement. The results suggest that widespread use of smart water heaters that optimize load shifting by predicting hot water consumption and the solar profile could present an important value for the integration of renewable energy onto the grid