Elsevier

Solar Energy

Volume 226, 15 September 2021, Pages 489-500
Solar Energy

Control optimization of PV powered electric storage and heat pump water heaters

https://doi.org/10.1016/j.solener.2021.08.059Get rights and content
Under a Creative Commons license
open access

Highlights

  • Electric water heaters require special controls to take advantage of excess PV power.

  • Smart controls can create highly efficient PV powered electric water heaters.

  • Experimental results show PV powered water heaters reduce grid electricity by 85%

  • Water tanks can act as thermal batteries, reducing stress on the electricity grid.

  • Transition to all electric homes powered by rooftop PV systems.

Abstract

Domestic rooftop photovoltaic (PV) systems are typically installed without energy storage and power generated in excess of the building electric load must be exported to the grid or curtailed. In this paper the use of excess PV electricity for water heating is investigated, with the hot water storage tank acting as a low-cost thermal battery. A 3.6 kWp PV system installed on a domestic house with a 315 L storage hot water heater is analysed. It is shown that advanced control of the water heater is critical to make effective use of local intermittent PV power. Without appropriate controls the excess PV power can only reduce the grid energy consumption of an electric storage water heater by approximately 13%. However, with appropriate control, savings of purchased grid electricity above 80% can be achieved for electric storage water heaters. Similarly, using a heat pump, the consumption of purchased grid electricity for water heating can be reduced by close to 90% by making use of excess PV power. The use of excess PV electricity for water heating purposes can also significantly reduce export PV electricity, thereby also assisting the voltage and frequency stabilisation of the electrical distribution network.

Keywords

PV water heating
Control of electric storage and heat pump water heaters
PV self-consumption
Efficient use of excess PV power
Low cost energy storage
Water heating efficiency

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