If you followed the buzz around the State of the Union address, you may be wondering how to make money investing in alternative energy. After all, when even this president starts talking about "global climate change," you have to assume the issue has legs.

The new Democrat majority in Congress is already pushing ahead with ideas of its own. And alternative energy ought to be a slam dunk for America. Even those politicians who are still skeptical about global warming agree we need to cut our dependence on oil. After all, some of the money we spend on it is helping finance our enemies, from Al-Qaeda to Iran. And nobody, on either side of the aisle, can ignore the economic cost of oil prices at $50 a barrel or more.

So where should you put your money?

Hours after the president's speech, I talked to one of the most experienced professional investors in the field. Jack Robinson is the founder and president of Winslow Asset Management in Boston, which has been investing in green energy since 1983. Its ( WGGFX) Winslow Green Growth Fund has a third of its money in the sector and has a terrific record.

The first thing to note is that Robinson's warning investors away from the most popular and obvious companies -- such as those involved in corn ethanol and solar technology. They're overhyped and too risky, he says. "Everybody and their brother and their mother is going into the ethanol business," he says. "It's like a gold rush. It's scary. We are not involved in that space, and we continue to avoid it."

Among the problems, he says, is that corn is a pretty inefficient way of making ethanol. And there are a lot of logistics involved in getting it from where the corn grows to where the fuel is needed. "A lot of people rushing into the ethanol 'space' haven't thought it through," he says.

Solar power has a different problem. Eventually, it's going to be one of our major energy sources, Robinson predicts. "But it's not yet economic, and I think a lot of the valuations in this space have been inflated. You need to be careful there."

The really big problem right now, he argues, is that the essential ingredient for solar paneling is silicon. And there is a worldwide shortage of silicon. That means some of these companies can't get access to the silicon they need to grow the business. The rest will have to pay up for it. And that will make their products even less economical.

So where is Robinson putting his investors' money? His biggest tip is geothermal energy. It doesn't sound sexy, but it has three big advantages. First, it already makes economic sense, even if oil falls to $40 a barrel. Second, there are some great plays right here in the U.S. And third, hardly anyone is talking about it on Wall Street, so those stocks look pretty cheap.

Among Robinson's favorites is WFI Industries . It's listed in Toronto but is based in Fort Wayne, Ind. "Nobody really knows about it in the States, but it's approaching a $100 million run rate in sales, and it's growing like crazy," Robinson says.

WFI, which stands for Water Furnace Industries, makes systems you can install in your home that will heat it using underground energy. You may only have to go down about five feet to tap the Earth's power. A typical system might cost about $12,000 to install.

WFI stock is C$25.00. While some estimates suggest that that's around 35 times the company's likely earnings for 2007, Robinson believes the company will do better than that. He puts the price/earnings ratio down in the 20s. That's pretty cheap for a fast-growing company. At these levels, there's even a 2.3% dividend yield.

Another stock he's following is US Geothermal ( UGTH). (Note: This is a speculative stock that trades over the counter.) The company is working geothermal energy from the other end -- building big power plants to harness underground energy and then selling that energy into the grid.

The first plant, in Idaho, is under construction and will open by the end of this year, Robinson says. Although it will start by producing 20 megawatts, he believes that could go as high as 200 megawatts in time.

The stock is at $1.40. There are no earnings as yet, which of course makes it risky. But Robinson says the company has the capital it needs to get the first plant up and running. "It's a very small company -- nobody knows about it," he says. The market value is barely $60 million.

Away from geothermal energy, Robinson has also got big bets on three other alternative energy companies. FuelTech ( FTEK) has a technology that helps coal power stations save money and emissions by cutting down on the "slag" or residue buildup in the furnaces.

Sound dull? Right now that residue is a big problem. Power stations have to shut down every so often and dynamite out this residue. That involves heavy costs, including downtime.

FuelTech uses technology and chemicals, including additives to the coal, to avoid the problem. The company already has contracts with 30 power stations, and it's growing fast. "They have about 2.5% of the market and no competition," says Robinson. The stock is currently $25.70. By some estimates, that looks as high as 60 times forecast 2007 earnings -- though, as with WFI, Winslow believes earnings will be a lot better than that.

Then there's Nova Biosource Fuel ( NVBF), based in Houston, which can convert fat renderings into biodiesel. Robinson's not kidding: He says the company could turn the leftover fats from a McDonald's fryer into pretty clean fuel, saving costs, waste and emissions.

Once again, this is a speculative stock that trades over the counter. It's currently just $2.37. As they say on Wall Street, at least you know your downside.

The chief executive, 69-year-old Kenneth Hern, is an oil industry veteran: He's a former executive at Texaco (now part of Chevron ( CVX)). And the company last month raised $47 million. It's busy building relationships with suppliers and customers.

A fifth company Robinson likes is Covanta ( CVA), which is the market leader at turning trash into energy. It's already a big business, but the company got saddled with too much debt and is currently going through a huge recapitalization.

Most of these are, admittedly, risky or speculative stocks. They're like Tabasco -- add them to your portfolio sparingly.

Winslow Green is about more than energy. It invests across the "socially responsible" field. But it has trounced the wider stock market since it was launched five years ago, and it's not a bad way to go. Stay tuned to see if the company launches a focused green energy fund.

Robinson warns those rushing blindly into alternative energy investments that "just because a company is green doesn't mean it's a good investment. Everything else needs to be there -- you need a sustainable business plan, you need the management, you need the capital, and you need a market."

It's a year since President Bush first raised the curtain on this industry in his previous State of the Union address. The ethanol business saw a brief stock market bubble in the spring, and then a bust. But if you look at the big picture on the environment, the economy and national security, this issue is not going away.

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