The energy production portfolio of our world contains more and more renewable energies. The energy production of renewables – like solar panels – is not calculable and not consistent. This stochastic power availability is an increasing issue referring to the stability of the energy system. This instability is due to generation and consumption non-simultaneity. The spread of renewables is also huge in household sized small power plant segment and the generation is becoming more decentralized. At present the main power grid is used as energy storage system. In the case of solar plants, the daytime generated energy is feed into the grid, while the morning and evening peak consumption is covered from the power grid. Until relatively low number of household sized small power plants is in use, the stability issues can be controlled by the system operators. However in the future with the increasing spread of small solar power plants the stability issues could not be solved without the use of energy storage systems. In my dissertation I make a suggestion to install a household sized small solar power plant and a battery energy storage system to a four-flat condominium. This dissertation contains an estimation of the building’s energy consumption, scaling of the solar power plant, a statement of battery technologies, scaling of the chosen battery system and simple economic calculations on the aforementioned systems.