TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The method involves a) seeding the hydroponic biomass system with seeds for the production of biomass crop; b) allowing the seeds to germinate and grow into the biomass crop; c) feeding the biomass crop to the anaerobic digester as feed stock; d) allowing the anaerobic digester to digest the biomass crop and generate carbon dioxide, biofuel gas and nutrient containing digestate; e) re-seeding the hydroponic biomass system with seeds for the production of new biomass crop; f) introducing nutrient digestate and carbon dioxide, generated by the anaerobic digester, to the reseeded hydroponic system; g) harvesting the biofuel gas from the anaerobic digester; and h) repeating the steps (c) through (g). In the method, biofuel gas producing unit comprises at least one anaerobic digester and at least one hydroponic system are vertically stacked and interconnected to produce biofuel gas, where the hydroponic system is situated above the anaerobic digestor and the hydroponic system is tilted to cause the biomass crop in it to slide into the anaerobic digester with a gravity feed. The heat is generated in the anaerobic digester in an exothermic reaction during digestion of the biomass crop and the generated heat is channeled to the hydroponic system, where the generated digestate, carbon dioxide and heat are pumped from the anaerobic digester to the hydroponic system. The biomass crop growth rate is matched to the rate of digestion. The organically digestable and water resistant trays are used as supports for the biomass crop, with the trays being fed with the biomass crop into the anaerobic digestor and digested together with the biomass crop and the trays are replaced in the hydroponic system prior to the step of subsequent seeding. Preferred Components: The biomass crop is comprised of perennial grass (preferably barley grass).    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Device: The at least one anaerobic digester and the at least one hydroponic system is connected with at least one respective conduit through which heat generated by the anaerobic digester is provided to the at least one hydroponic system. The hydroponic system is stacked above at least one anaerobic digester with the device further including at least one respective member which tilts the hydroponic system to cause the biomass crop in the at least one hydroponic system to flow by gravity feed to the anaerobic digester. The device is provided with at least one pump to accelerate the flow of carbon dioxide and digestate from the anaerobic digester to the hydroponic system. In the device, organically digestable and water resistant trays are used as supports for the biomass crop in the hydroponic system, with the trays being adapted to be fed with the biomass crop into the at least one anaerobic digester and digested in it. EXAMPLE - No suitable example given.