In the 1939 film classic Mr. Smith Goes to Washington, Jimmy Stewart plays Jefferson Smith, a young idealistic senator forced to do battle against his corrupt political peers. It's a tough fight, but Smith ultimately wins the day, thanks to the support of a believing public and the strength of his convictions.

I was reminded of the movie this past week, when I learned that the Solar Energy Industry Association, whose members include BP's (NYSE:BP) BP Solar, SunPower (NASDAQ:SPWR), Kyocera (NYSE:KYO), General Electric (NYSE:GE), and scores of other smaller solar manufacturers, distributors, contractors, and installers, had established a political action committee.

In the past election cycle, the group doled out a trifling $10,500 to 19 members of the House and Senate. The donations, split almost evenly between Republicans and Democrats, amounted to an average contribution of just more than $500.

By Washington standards, that's chump change. Compare it with the nearly $8 million the oil and gas industry and its member companies -- such as ExxonMobil (NYSE:XOM), Chevron (NYSE:CVX), and Halliburton (NYSE:HAL) -- contributed to politicians' coffers in the 2006.

But last week, two House members nonetheless introduced H.R. 6, the "American Energy Independence" bill. Among other things, the bill seeks to extend the 30% business credit for solar-cell (and fuel-cell) systems purchased for residential and business applications, and to create an accelerated depreciation period for all solar equipment.

On one hand, the bill's prospects for victory might appear bleak, given the solar industry's relative weakness against the more established oil and gas lobby. However, like Mr. Smith, the solar industry has something besides money on its side: the public's growing support.

I believe that counts for a lot and that the bill will enjoy a happy ending by being signed into law. If so, it'd be important for investors of solar energy companies, because its passage -- especially the extension of the 30% tax credit -- could be a notable boon to the sales and revenues of many solar companies.

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Fool contributor Jack Uldrich believes sunshine is the best disinfectant -- and that Washington, D.C. (currently snowy and overcast) needs all the sun it can get. He does not own stock in any of the companies mentioned in this article. The Fool has a strict disclosure policy.