Going green doesn't just mean using clean energyanymore. In the case of solar power, for example, it means solar investors are putting greenbacks in their pockets as well.

With all three U.S. presidential contenders on record as favoring some sort of cap-and-trade restrictions on carbon emissions, many in the alternative energy industry are eyeing the day when solar electrical generation can compete against fossil fuels on a kilowatt-per-hour basis. Combined with some state initiatives that mandate solar electric production, companies in the solar electric industry are enjoying sunshine times both in sales and stock price.

Take, for example, First Solar, Inc. (NASDAQ: FSLR).

First Solar "manufactures solar modules," says the company, "with an advanced thin film semiconductor process that significantly lowers solar electricity costs." Revenues for the fiscal year 2007 for FSLR were $504 million, up from $135 million in the previous year. That's a 373% sales increase.

And the stock price is following suit. After opening up at a price of $24.50 during its initial offering on November 17, 2006, the company's common stock is now trading at $301.37 as of April 22, 2008.

While the company is comfortably profitable, much of what is driving valuations industrywide are the mandates of some Southwestern states that are requiring some portion of their states' electrical generation to come from solar sources, says the technology publication Wired. As case in point, First Solar's stock trades at a dot-com-like 148 times its 2007 earnings.

"In the near term," writes Alexis Madrigal of Wired, "these deals are being driven by southwestern states' laws, which have built solar requirements into their renewable energy dictums. Nevada, Arizona, New Mexico and Colorado all require between 15 and 20 percent of their power to come from solar sources."

Without these state mandates, solar power might still remain an interesting, but uneconomical alternative to all but the most dedicated environmentalists.

That's because the price per kilowatt hour for solar power electrical generation at the largest scale still hovers around $.21 per kilowatt hour, according to the website Solarbuzz.com. Old-fashioned coal-fired electrical generation only cost an average of $.0821 to $.1648 per kilowatt hour in 2007 depending on region, according to figures compiled by the Energy Information Administration. And competing alternative energy sources - like wind energy - are lower cost in most regions than solar, too. Solar's costs have to still come down substantially for a long-term boom to take hold.

But so far, the initial enthusiasm is driving significant growth in the industry. First Solar isn't the only solar energy company going gangbusters, either.