Renewable energies, and among them solar photovoltaics, are becoming more important in the last years due to the lack of fossil fuels and the environmental impact of them. PV installed capacity is increasing over and over in some countries and the prices of the installation are decreasing while the prices of the electricity are predicted to increase. Electricity use in buildings account for an important part of all electricity use in the world. This two facts make the PV installation in the rooftops of buildings a good opportunity to reduce the purchase of electricity from the grid.   The aim of the thesis is to analyze the profitability and the environmental impact (when using a hot water accumulator) of a PV system with different storage systems placed in the rooftop of two dwellings located in Gävle (Sweden). The storage systems can be either batteries or hot water accumulators. The purpose of the storage system is to increase the self-consumption rate of the PV system and to save the highest amount of money possible. It is also studied the difference of installing PbA and Li-ion batteries, and the reliability of the data used in the simulation of the alternative systems with the help of the software PVsyst.   Results show that the profitability of the proposed three alternative PV systems with storage is not higher than the PV system without storage. The reason for this has been found in the low prices of electricity and DH nowadays. Moreover, the impact of decreasing the heating demand from DH network does not benefit the environment, because the electricity has to be produced in power plants that produce more pollutants. It can be said also that the data obtained in PVsyst has been determined reliable and that the difference between the two types of batteries is not conclusive.   It can be concluded that if the cost of the PV systems or the batteries would decrease, the profitability will be higher. Furthermore, the increase in the price of electricity, DH or governmental subsidies would improve the results.

Master´s thesis is focusing on zero energy building with technical equipment. The building was built in 70. decade of last century. It has been using for sport and cultular events until these days. Restaurant was connected to sport hall. First part is focusing on zero energy building and technical equipment, their using, combination and optimal connecting in systém. Second part solving how many fotovoltaic panels must be in the system to reching economic advantage. In third part is solving how to connecting fotovoltaic panels to the system.