Check out the Stern Report, summary here: http://news.bbc.co.uk/1/hi/business/6098362.stm

Since the opportunity cost of doing nothing is at least 1% of GDP, you can spend up to that doing something to mitigate that cost.

I see no problem in selling C02 permits to internalise the externalities of the energy market.

A feed-in subsidy for electricity generation, like the Germans, would help the solar markets achieve economies of scale and technological progress more quickly.

Substitution of oil, gas, and coal use for power generation by solar, wind, and reduced consumption (by conservation measures), reducing our dependency on scarce imports is a plus.