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.

家用屋顶光伏 (PV) 系统通常安装在没有能量存储的情况下，产生的超过建筑电力负荷的电力必须输出到电网或削减。在本文中，研究了将多余的光伏电力用于水加热，其中热水储罐充当低成本的热电池。分析了安装在带有 315 升储热水器的家庭住宅上的 3.6 kWp 光伏系统。结果表明，热水器的先进控制对于有效利用局部间歇性光伏发电至关重要。如果没有适当的控制，多余的光伏功率只能将储水式电热水器的电网能耗降低约13%。但是，通过适当的控制，储水式电热水器可以节省80%以上的外购电网电量。同样，使用热泵，通过利用多余的光伏电力，可以将购买的用于水加热的电网电力消耗减少近 90%。将多余的光伏电力用于水加热目的也可以显着减少光伏电力的出口，从而也有助于配电网络的电压和频率稳定。