Electricity is one of the main types of energy used in everyday life. Electricity is used in households, industry and increasingly in transport instead of traditional fuels. Changing other sources of energy to electricity allows reducing pollution and harmful effects on nature. In order to achieve the maximum ecological effect, it is very important how electricity is produced. In the European Union, about 40% of electricity is produced from renewable energy sources, and about half of this amount is produced in solar power plants. Photovoltaic power plants are popular all over the world and have recently become especially popular in Lithuania. It is useful to install photovoltaic power plants on the roofs of buildings, as it does not require a separate area. When installing solar power plants on pitched roofs, the photovoltaic modules are usually directed towards the sun according to the position of the roof of the building. In Lithuania, the optimal slope of the roof of the buildings on which the solar power plant is installed is about 35° and in the south direction. In other cases, the efficiency of the solar power plant decreases. This research examines two solar power plants installed next to each other with different tilt angles - the modules of power plant PP1 are tilted at an angle of 12°, and the modules of power plant PP2 are tilted at an angle of 35°. The research evaluates the amount of electricity produced by the power plants in one year. It was found that the efficiency of the PP2 power plant is about 7% higher in one year. The higher efficiency of the power plant is achieved due to the better positioning of the photovoltaic modules of the solar power plant.