Net Zero Energy Houses with Dispatchable Solar PV Power Supported by Electric Water Heater and Battery Energy Storage

Over a year, net zero energy (NZE) houses produce and feed zero net metered electrical energy to the grid. Technical challenges, notably the `duck curve' arise due to the fact that peak solar generation and load demand are seldom coincident. Common approaches to mitigate this limitation include the curtailment of solar power, and the use of storage. Surplus solar energy may be stored in a battery, which can subsequently be discharged to supply the home electricity needs when demand is in excess. In addition to batteries, less expensive electric water heaters, which are ubiquitous, can be modified as energy storage systems, functioning as `uni-directional batteries' by virtue of their high thermal mass. This paper proposes the use of a hybrid energy storage system including both batteries and variable power electric water heaters in NZE residences. It is demonstrated that the hybrid energy storage system along with solar PV generation coordinated and virtual power plant (VPP) controls would reduce the required battery size and ratings while still harvesting the maximum solar energy potential. The proposed control strategy enables the NZE homes to produce dispatchable power or behave like controllable loads, and benefits at the utility level are demonstrated by interconnection of NZE homes with an IEEE 13 node test feeder system. The technology has the potential to mitigate all issues related to solar power variability.