On a cost-per-BTU basis, taking into account upfront CAPEX, cost-of-capital, present-value discounted cash flow analysis (PV10, for example), storage, processing, transport, and end-use thermodynamics, there are no known energy sources in 2009 that are cost-competitive with hydrocarbons.
Which probably explains why such insanely large amounts of cash are flowing to K-Street for Waxman Markey.
The only applications where using something other than hydrocarbons makes business sense, is in applications where the cost of energy is not important.
For instance, telecommunications satellites. Or, closer to home, energizer batteries at the grocery store. A single D-cell lead-acid battery has an energy cost of $500,000 per kilowatt-hour. However, no one thinks of it in those terms -- cost-of-energy is not an important factor for this niche.
Thinking of "renewable energy" sources as a replacement for hydrocarbons is a huge mistake. Hydrocarbons are used in large-scale applications where cost is the only metric that matters. And on that metric, it is impossible to compete with hydrocarbons.
The best bet for "clean tech" is to target niche applications that are underserved by hydrocarbons. Clearly, you're not going to use an internal combusion engine to power your laptop. Rather, you're going to shell out hundreds of dollars for a lithium ion battery -- and then charge that battery from the grid, which is likely to be powered by coal or natural-gas power plants.
To take a page from the enterprise software world, the problem with "clean tech" and "green tech" startups is that they are trying to make a "value" sale in a cost-driven market. That never works.
Unless, of course, you can get the federal government to tax the low-cost producers to death.