Indicating growth graphs for the wind, solar, biodiesel and ethanol industries -- all of which are rising at dizzying rates -- New Energy Fund Managing Partner Mark Townsend Cox said: "It's the light in the life of an investor when the charts are all looking like this."

Investment banker Riaz Ladhabhoy, Deutsche Bank's vice president of technology investment banking, described the graphs as going "up and to the right in a massive way."

There are about 60 quoted solar companies on the market now, a big jump from the 30 or so last year and the five the year before, Cox told United Press International.

"That looks bubble-like," he said. Stock prices for solar companies are also rising in "Microsoft-ish" fashion -- Solar World traded at 12 euros last year and is up to 140 euros this year, Cox said. But, he stressed, the market really isn't a bubble.

"Sixty percent of the group (of quoted companies) is profitable (and) a large chunk of the others are getting toward that point," Cox said.

The difference between solar, which seems too good to be true, and the dot-com boom, which was a bona fide bubble, lies in the fundamentals, Cox said.

"There's nothing so abstract as a 'killer ap,'" he said, referring to the computer and Internet applications that constituted dot-com's main product.

Solar, on the other hand, is a tangible product that is hardly new and is proven to work.

Photovoltaics have been around since the earliest days of the space program, and the technology may even be over-engineered for terrestrial use, solar experts say.

The key in understanding the market's stability and potential for growth, according to Cox, is to look at the economy from a "holistic" perspective.

When investors consider the cost of nuclear energy's damage to the environment, or the number of cancer patients that pollution creates, or the high incidence of respiratory disease, fossil fuel-driven energy starts to look more and more costly, Cox said.

"The costs are more than the community can bear," he stressed.

But like all investors, Cox is aware of the importance of the bottom line, and he says solar delivers on that front.

"I'm looking for companies that are profitable, or are reducing their losses; companies that have a growing top line, great management ... it's no different from other investors," he said.

Increasingly, companies whose focus is something other than solar are entering the solar market, an engineer in the solar industry told UPI.

"Companies like (oil giants) BP and Shell may be doing it to improve their image, but companies like General Electric and Dupont have nothing to (prove) -- they just see the potential to make money," he said.

Of course, it could go wrong. One highly placed expert in the solar industry told UPI that he fears "bad actors" will enter the market, and purposely or not, will "produce products that don't live up to their warranties."

That would give the entire industry a bad name, and could scare investors away, the expert said.

"The industry needs certification," Rhone Resch, the president of the Solar Energy Industries Association, told UPI.

He called this certification and product rating process "critical" for the industry, whether the program be national or international, voluntary or mandatory.

Resch cited examples of substandard products sold in Africa, and stressed that "all of solar has to be overly responsible."

The problem of image points to a fundamental component of public company valuation, New Energy Fund's Cox said -- investor and public sentiment.

"Sentiment could be harmed" by a view that the solar market looks ready to burst, Cox said. But if the market continues, every fiscal quarter, to perform and to deliver good products and profits, "it would blow snot in the face of the sentiment guys."