Storing excess solar power in hot-water tanks on household level as power-to-heat system

Abstract

With installed solar power increasing rapidly in the Netherlands, interest in technologies that allow for the storage and usage of excess solar energy is growing as well. A new technology that serves this purpose is the Water Battery of the company Solyx Energy. This set-up utilises surpluses of solar energy to heat tap water for showering and cleaning, thereby lowering gas use and leading to both monetary savings and reduction in CO2 emissions. The goal of this research was to create a model to analyse the effectiveness of the Water Battery in lowering energy costs for different types of households, especially with the planned termination of the netting system in the Netherlands. To accomplish this, the model simulates the average daily energy production and energy use per month of a household based on the household size and installed solar power. Based on these data, calculations were performed for the yearly savings in energy costs by utilising the Water Battery. The model also performs this function for similar technologies, such as a home battery, a heatpump boiler, and a solar boiler. A multi-criteria analysis (MCA) was conducted in order to compare the benefits and drawbacks of all options. The results show that for households with limited installed solar power (for example 3 kWp), the Water Battery has little benefit while the present netting system is in place, but the benefits become greater as the netting system is gradually terminated. The early benefits can be increased for such households by utilising smaller water storage containers, although this limits savings when netting is no longer an option. For households with higher installed power, the Water Battery immediately leads to savings in energy costs. When comparing the technologies, the Water Battery and the heat-pump boiler score highest in the MCA. The heat-pump boiler is the most effective at lowering gas use and energy costs, while the Water Battery has lower initial costs and allows use of more excess solar energy. This means that the Water Battery is a good choice for households that want a simple way to make better use of their solar energy production. While less effective overall than a heat-pump boiler, the Water Battery does allow for an easier bottoms-up transition towards sustainability.