What the government (the public) should subsidize in our society is a pretty fundamental expression of our values I suppose.  We should ask this question honestly in a broader sense.

We seem to value mobility, in fact we have become dependent on being mobile in order to survive - in this way we are like the nomadic people, except that we return to the same bed every night.  Is it possible that we will every come back to seeing the value in living in place, without he need for so much mobility?  If that happened, I think then the questions over what the public should subsidize would change quite a bit.  

Did the "free market" build our road network? I always found the case of Thomas Paine Bridge Designer, not revolutionist writer, to be very instructive.

In 1979, Denmark implemented a subsidy equal to 30% of wind turbine investment costs. This spurred much investment and led to the initial deployment of 200-300 machines a year. These subsidies were phased out for wind power in 1989, after they helped increase the reliability and decrease the price of turbines. Until 1999, the government provided direct grants for each kWh turbine owners sold to the grid. Now Denmark has about 15 subsidy programs for both energy production and consumption. The largest subsidy is a production subsidy per kWh for electricity generated from renewable energy resources. The majority of the subsidy schemes "are directed primarily at converting central and electric heating systems to district heathing and to expanding and renovating the existing district heating network" (Renewable Energy Policy Project)

http://www.geni.org/globalenergy/policy/renewableenergy/subsidies/wind/denmark/index.shtml

Unfortunately I could not find a source for the exact amounts envolved but I could guess they are in the billions.

http://www.aweo.org/ProblemWithWind.html

Despite their being cited as the shining example of what can be accomplished with wind power, the Danish government has cancelled plans for three offshore wind farms planned for 2008 and has scheduled the withdrawal of subsidies from existing sites. Development of onshore wind plants in Denmark has effectively stopped. Because Danish companies dominate the wind industry, however, the government is under pressure to continue their support. Spain began withdrawing subsidies in 2002. Germany reduced the tax breaks to wind power, and domestic construction drastically slowed in 2004. Switzerland also is cutting subsidies as too expensive for the lack of significant benefit. The Netherlands decommissioned 90 turbines in 2004. Many Japanese utilities severely limit the amount of wind-generated power they buy, because of the instability they cause. For the same reason, Ireland in December 2003 halted all new wind-power connections to the national grid. In early 2005, they were considering ending state support. In 2005, Spanish utilities began refusing new wind power connections. In 2004, Australia reduced the level of renewable energy that utilities are required to buy, dramatically slowing wind-project applications. On August 31, 2004, Bloomberg News reported that "the unstable flow of wind power in their networks" has forced German utilities to buy more expensive energy, requiring them to raise prices for the consumer.

And another one:

http://www.countryguardian.net/denmark.htm

More specifically, Krogsgaard (2001a) claims that Danish electricity consumers annually pay more than DKK 10 billion (including VAT) in excess of what they would if the country only operated its central power stations, said to be amongst the most modern and least polluting in the world. Other estimates put the annual total Danish climate input cost at DKK 15 billion (From, 2001e). About DKK 2.5 billion of subsidies is paid to private owners of turbines (excluding VAT); and a further very large subsidy is paid to combined heat and power (CHP) plants, many of which (e.g. open field plants) are facing serious economical problems.