Nature reporters Quirin Schiermeier et al. summarize the prospects for electricity produced with minimal carbon emissions by the leading candidates in alternative energy: hydro, fission, biomass, wind, geothermal, solar, and tidal and wave. In the authors’ estimation, the likely most productive sources, ones which could be built up in the coming decades to a terawatt of generating capacity each, are hydropower, nuclear fission (if the political climate changes), and wind. They are less sanguine about solar power:
In the middle to long run, the size of the resource and the potential for further technological development make it hard not to see solar power as the most promising carbon-free technology. But without significantly enhanced storage options it cannot solve the problem in its entirety.
For comparison purposes, on the consumption side, 18,000 TW-hours of electricity (about 40% of total energy use) were generated in 2005, which works out to an average constant comsumption of 2 TW. Actual worldwide generating capacity is higher, because no plant works flat out 24/7/365.