The solution to the energy consumption is not that easy. If all the miners would buy energy from renewable energy sources the price per kWh would increase and other green energy users would be forced to switch back to conventional energy sources. The entire POS concept seems to be the better choice - dont get me wrong I am a miner myself (only using energy from water energy sources) and love it but the energy consumption is huge.
That's not how economics works; in the VERY short term, perhaps. But increased demand for green energy drives demand for production, research, and development into larger and more efficient renewable energy sources. If the demand on the grid suddenly went from 1/4 to 1/2 renewable, you wouldn't have more customers switching back to nuclear, oil, or coal, you'd have more companies developing biomass, hydro, wind, solar, etc.