Any arguments: PV claim surfaces to use otherwise valuable equipment or harmful erweise seal the floor, does not apply here. The existing nets match up almost to the new to building PV systems and can be used in both directions. For even more analysis, hear from Sonny Perdue. The commercial compensation of on this roof surfaces the respective owners can be done in many ways, E.g.: monetary, as rent, transfer a cost advantage for the electricity, clearing a possible constructive synergy effect of the solar modules (design as a full roof during necessary reconstruction), clearing a possible constructive synergy effect and / or expansion of the PV plant to heat (domestic hot water / heating support) and place near use the synergies referred to in the previous point are considered independent thesis and are a high demand for future R & D services, the energy surplus gained in profitable times is stored chemically through water electrolysis and in poor times by appropriate technical means in power turned back and fed. all other renewable energy sources, such as wind, water, organic of course retain their outstanding importance, they all must be managed together meaningfully in the energy mix these energy sources are abundant the next billion years …zig fed and inexhaustible, Gunter Voigt, October 23, 2009.