Steve Blumenkranz
Primarily wind, solar and possibly thorium based nuclear. These are the most sustainable, the largest resources and the highest payback of the ones that can last. Hydropwer will still be there but is not as large a resource. Bio-fuels are possible contributor for high energy density liquid fuels with net zero CO2 impact if part of a properly designed production cycle but their effective solar to useful energy conversion efficiency is lower than photovoltaic solar. Significant low grade heat such as residential hot water and space heating can be done very well with thermal solar. Tidal power is a limited resource, has inadequate effective pressure head vs. hydro and a corrosive environment. Wave power and OTEC (ocean thermal engergy conversion) are losers based on low thermo-mechanical and capital cost efficiency and also hostile corrosion and physical environment. If we are still burning fossil fuels then we will be a much smaller population living a much harder life on higher ground. If we put the engineering effort into renewables we can be living well with a long horizon ahead of us.
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