NOVELTY - The system comprises a biogas purifier comprising methane as a fuel, an air-conditioning and heating equipment for air-cooling and heating a crop cultivation facility, an anaerobic digestion plant, a liquefied fertilizer production facility, and a separator for separating solid from liquid contents from a slurry generated in the anaerobic digestion plant. The biogas purifier supplies refined methane and carbon dioxide to the crop cultivation facility. The anaerobic digestion plant is connected with an apparatus comprising a seed by-product, livestock excretions and by-product of food waste.    USE - The system is useful for generating renewable energy (claimed).    ADVANTAGE - The system is capable of eco-friendly generating the renewable energy without secondary pollution and air pollution.    DETAILED DESCRIPTION - The system comprises a biogas purifier comprising methane as a fuel, an air-conditioning and heating equipment for air-cooling and heating a crop cultivation facility, an anaerobic digestion plant, a liquefied fertilizer production facility, and a separator for separating solid from liquid contents from a slurry generated in the anaerobic digestion plant. The biogas purifier supplies refined methane and carbon dioxide to the crop cultivation facility. The anaerobic digestion plant is connected with an apparatus comprising a seed by-product, livestock excretions and by-product of food waste. A regulating unit controls: an amount of the liquefied fertilizer and carbon dioxide supplied to the crop cultivation facility. An air conditioning system is connected with the air-conditioning and heating equipment to control cooling rate or heating rate in the crop cultivation facility. A sensor is configured for measuring carbon dioxide concentration and gas concentration in the crop cultivation facility. A control unit maintains constant concentration in the crop cultivation facility. A luminance sensor: blocks the supply of carbon dioxide into the crop cultivation facility if luminance sensor confirms a roughness signal due to sunrise; and allows the supply of carbon dioxide into the crop cultivation facility if luminance sensor does not confirm the roughness signal due to sunset. A seed by-product pulverizing unit supplies the pulverized seed by-product to a food waste by-product processing system and a livestock excretion processing system. The processed mixture from the seed by-product pulverizing unit, the food waste by-product processing system and the livestock excretion processing system is fed to the anaerobic digestion plant.