The issue of photovoltaic cells usage for hot tap water heating in a household has been presented. There has been built a research point, which was situated on a single-family house in the country. The aim of the research was obtaining maximum performance characteristics of the system for hot tap water heating based on photovoltaic cells. It was carried out during summer solstice because of the most favourable relationship of day versus night, from the point of view of efficiency. Results collected from the research enabled to obtain a lot of exploitation characteristics describing the system. There have been presented exemplary time courses of action of generated power and selected working parameters. Maximum energy performance of the system has been determined. Further research should enable to define minimum hot water tank capacity as a buffer of energy and minimum number of panels that constitute a heating water battery, in order to fulfil requirements included in the Ordinance of the Minister of Infrastructure dated 14th January 2002, related to defining average norms of water consumption (Journal of Law 8/02 item70).