It is expected that European biogas production will double by 2030 and quadruple by 2050. There are currently more than 18,943 biogas plants operating in Europe. With the emergence of biogas upgrading technologies, biogas is upgraded into biomethane with carbon dioxide as a byproduct. A common practice in biomethane plants is to release carbon dioxide (CO2) into the atmosphere instead of utilizing it as an input for greenhouses or algal farming. In this study, the unutilized 1,900,000 m3/y carbon dioxide from the biogas plant in Bruck an der Leitha (Austria) will be used for greenhouse crop farming. This study aims to determine the number of hectares of greenhouses that can be enriched with this CO2. An optimal greenhouse enriched with CO2 will be designed for the production of local crops to reduce the biogas plant carbon dioxide emissions. The daily daylight, solar radiation, crops carbon dioxide uptake rate and the 5,200 m3 of carbon dioxide daily available were utilized to calculate the optimal greenhouse areas with and without onsite CO2 storage for completely closed greenhouses and partially opened greenhouses with double polyethylene walls and standard glass walls.