What about massive sulfuric acid/vanadium based redox cells? those are rechargable with sulfuric acid addition, and we have access to plentiful sulfuric, sulfuric di- and trioxide, from volcanic fumaroles etc.
I am given to favouring a combined approach, including tidal generators, river-mouth redox devices, wind and solar farms, with lenses focused on the solar cells, and using cell material that can take infra-red, in the near IR range.