Combined heat and power (CHP) is used to generate electricity and provide heat as a waste product. An energy efficiency of over 90% is predicted by the vendor. The electricity-generating engine is fueled primarily by gas. The issue: larger biogas-plants are mostly in massive buildings at a distance of more than 500 meters to the nearest residential area. Smaller plants move ever closer to the vulnerable housing and are housed in part only thirty meters away. Micro-CHP will be even in the basement of homes, schools, hotels and commercial facilities.