Renewable energy, however defined, is widely seen as a sustainable and socially responsible (and, if the investing is done right, very profitable) addition to one's portfolio.
Indeed, such entities as the Institute for Energy Economics and Financial Analysis, an Ohio based research-and-analysis shop, exist to show that renewables are the asset class of the near future and that the wise and nimble will climb aboard.
Further, there are now a lot of ways to play this conviction with listed equities. From Nasdaq, one could look to Ballard Power Systems (BLDP), Canadian Solar (CSIQ), Enphase Energy