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Due to the climate changes in the world, countries need to work more towards more energy- efficient solutions and expand their use towards renewable energy sources. Using solar cells, it can contribute to a bigger part of the total energy production in the world. ETC Bygg has chosen to build passive wooden apartment buildings to reduce emissions from new constructions. Thanks to the energy savings achieved with good insulation, heat exchange, solar panels, and hot water recycling, ETC Bygg’s buildings can be seen as climate positive. A climate positive building means that the building goes beyond just achieving net zero carbon dioxide emissions to create an environmental benefit by removing additional carbon dioxide from the atmosphere. The buildings are located in Västerås, Sweden and have a total living area of 1765.8 m2 divided into 30 apartments, 15 in each building. The total roof area is 338 m2, where the entire area has been used for solar cells, which means that a total of 218 solar cell modules with a rated power of 405 W per panel can be installed. Since the roof is located on both the east, west and horizontal sides, solar radiation can be used regardless of the position of the sun during the day. This work answered questions that arise when installing a photovoltaic system in an apartment building, what the economic conditions for solar cells in an apartment building look like, its solar production and the general conditions such as slope and geographical position. With the help of solar cells, the goal is to produce as much energy as possible, to supply the apartment buildings with electricity. In this work, simulations and calculations were made for both solar production and on the economic aspects of a photovoltaic plant. With the help of the PVGIS program, the total solar production was calculated from the system, then this result was compared with the theoretical calculations from ETC Bygg regarding the building's estimated energy needs of 57,300 kWh per year. The installed peak power at the photovoltaic system was calculated to 88.3 kWp. Total annual solar production was estimated at 64,715 kWh without optimized slope. With optimal slope, the total annual solar production was 70,122 kWh, which is an increase of 8%. After this comparison, the results showed that the photovoltaic plant produces more than enough solar energy during the summer but not during the winter. During the summer, it’s then possible to sell the surplus electricity back to the grid. The levelized cost of electricity was estimated at 0.85 SEK/kWh and the payoff period was estimated to be between 9-14 years depending on the ROT deduction, tax reduction and investment subsidies. For all cases, positive net present values were obtained. Further, a sensitivity analysis was made to evaluate the most significant factors of the economic calculation.