Instead of promoting one technology or another, it seems to me that it would be better to first try to reduce the existing promotion of bad technologies. After all, if we didn't have such huge subsidies for gas and oil, then alternative energy technologies would be better able to compete. If you promote a technology there are lots of risks:

• You get into a "subsidy war" where one side is dumping state money into (say) fossil oil and the other side into (say) biofuels.

• You take a big chance on choosing the wrong technology. Electric cars had a huge government subsidy and went nowhere (for a range of reasons), but hybrid cars had no subsidy (at least initially) and there have been almost 1,000,000 sold in the U.S.

• Distortions in your local electoral system are magnified. There's huge support for Ethanol fuel in the midwestern corn (maize) states of the U.S. because, duh, the senators want to get re-elected. It has nothing to do with whether it's a good idea, though.

• You hold back development of other possibilities. How can someone concentrate on developing a better battery, for example, if all the government money is going to diesel or biofuel technology?

As has been discussed here in the past, governments should apply taxes that capture the social cost, and should do so at the point in the process where the tax least distorts the market. That's at the well, in the case of oil, or at the refinery depending on exactly how you do it...