Interest in alternative energy such as wind, geothermal, and solar is spreading beyond so-called "fringe" environmentalists and "tree huggers" to the business world. If there is any doubt, consider this: U.S. clean energy venture capital investments totaled $2.7 billion in 2007, a 70% increase over 2006. Worldwide investments in clean energy totaled $148 billion, a 60% increase over 2006. Alternative energy is going mainstream.

That's according a "2008 Clean Energy Trends" report by Clean Edge. According to their findings, growth in four key clean energy technology markets grew 40% from 2006, reaching $77 billion in 2007. They expect growth to exceed 300% over the next decade, reaching $254 billion.

You've probably heard all the candidates talking about "green-collar jobs." This isn't just election year rhetoric.

For example, an op-ed column in today's Nashville Tennessean says that Tennessee could gain $307 million in solar energy investments and hundreds of new jobs by the year 2015. The Solar Energy Industries Association (SEIA) says there are already more than 50 solar power related businesses in the state, including the Sharp Electronics solar panel manufacturing facility in Memphis which employs more than 200 workers and which, according to Sharp Electronics, has shipped more than 200 MW of solar array modules since 2002.

The Tennessean column urges support of HR5351, the Renewable Energy and Energy Conservation Tax Act recently passed by the House and now being considered in the Senate. This bill extends commercial solar power investment tax credits, which are set to expire at the end of 2008, for eight years. It also extends residential tax credits for one year and removes the $2,000 cap.

According to the SEIA, the U.S. could lose 116,000 jobs and $19 billion in solar and wind power investments if the tax credits aren't extended.

Some might argue that this amounts to corporate welfare for the clean-energy industry. It should be noted, however, that coal, nuclear, and hydro power are all heavily subsidized by taxpayers, directly in terms of capital construction costs, infrastructure, and government regulation, and indirectly in terms of the environmental costs. Also, the amounts involved are a fraction of what we already spend on "traditional" power generation, with the potential for huge long term environmental and economic benefits.

For example, the Clean Energy Trends report estimates the per-gigawatt construction costs for a typical nuclear plant at $2 to $6 billion (not to mention taking years to get online due to regulatory hurdles), versus $1.4 to $1.8 billion for wind, or $1.6 billion for geothermal. Solar is still more expensive at $5 to $10 billion (but in the same ballpark as nuclear), and unfortunately coal is still the cheapest (not counting the environmental costs) at $750 million to $1.4 billion.

But, as clean energy R&D investment increases and manufacturers ramp up production, costs are expected to come down and efficiencies are expected to go up, so federal support in terms of tax credits and R&D funding makes sense.

Both Clinton and Obama voted for the 2007 Clean Energy Bill. McCain abstained. That bill proposed these and other clean-energy incentives and would have paid for them by eliminating tax breaks for oil companies, shifting incentives away from polluters to clean energy producers.

These provisions were dropped from the Clean Energy Bill as passed, but are now back as part of HR5351. It will be interesting to see how our three presidential candidates act on these proposals in relation to their day jobs in the U.S. Senate.