US energy subsidies: measuring apples to apples?

Whenever discussing federal energy subsidies, I typically think of the ethanol industry. But lately I find myself wondering about how to accurately compare subsidies and tax credits across fuel types.

This question stems from recent publicity about extensions for production tax credits (PTC) for wind power. The US Energy Information Administration reports PTC significantly encouraged wind capacity growth.

During 1999-2007, wind power was the only primary energy source for which production increased each year, EIA said. Wind producers received an estimated $666 million in PTC during fiscal year 2007. This was distributed over 27.7 million Mw-hr.

EIA reports the US government spent an estimated $16.6 billion in energy subsidies and support programs during 2007. Only $4.9 billion of that went toward renewable energy. Certain fossil fuels also were heavily subsidized.

I have yet to find any cost comparisons per btu between various types of subsidized fuels.