The California Cleantech Open (CCTO), a yearly competition to identify some of the hottest new startups in green technology, has wrapped up its 2008 session with six winners, each in its own business sector. The six were chosen from 43 finalists, who were in turn drawn from a larger pool.

The CCTO has grown to be a significant event, in part because its sponsors read like a Who’s Who of good contacts to have (Google and the Department of Energy being two), and because each winner gets $100,000 in startup money, as well as, newly this year, membership in a San Jose city incubator called the Environmental Business Cluster and a year’s worth of business services.

Atop the various goodies, the winners — and some of the better runners-up — typically go on to get significant amounts of venture funding. Below are the winners:

Viridis Earth
This company looks like a case of “right time, right place”. As the story of energy efficiency, both at home and for businesses, catches on, there are a few key markets that get fingered for improvement. Typically the top three are lighting, heating and cooling. Lighting, of course, is a familar story; and now that many consumers have replaced their old incandescent bulbs with CFLs, they’re looking for the next big area for improvement. Often, that’s their air conditioning unit.

So Viridis Earth has devised a $350 retrofitting device for air conditioners that it says will pay for itself in a single season of use, in small commercial systems. The total efficiency gain is about 20 percent. That’s pretty good, and the price tag will make it easier to swallow than potentially more effective products like the Ice Bear, for which Ice Energy was just funded with a whopping $150 million.

Focal Point Energy
Of course, for every coin there’s a flip side. Focal Point Energy bills itself as a solar power company, but it’s actually in the business of providing heat, in particular process heat and steam for commercial applications. Focal Point’s basic idea is identical to solar thermal power plants: Focus lots of light on contained water using curved mirrors, until the water boils.

The genius is in the application. Instead of using bulky, expensive mirrors, Focal Point stretches a reflective membrane between steel frames. The result is a long trough that provides steam for about 10 hours a day. The troughs actually look similar to those made by Sopogy, another company that has impressed me, but Focal Point’s founder says his are cheaper per square foot, and light enough to mount on rooftops.

Power Assure
Another area in need of improvement are data centers, the buildings packed with computers that handle most of the Internet’s flow of information. But their owners have found it difficult to retrofit old facilities to be as efficient as they might like. Power Assure says it can make the average data center 50-80 percent more efficient.

Rather than a single product, this company is offering a platform service drawing from multiple other vendors — which is exactly what’s needed. There is a bewildering array of products on the market designed to handle dozens of tasks in the data center, making it difficult for the average administrator to find his way, as Cisco’s VP of green engineering pointed out in a VentureBeat interview.

ElectraDrive
The conventional wisdom says we won’t see many electric and hybrid electric vehicles on the road for three to five years, and even then their numbers will be limited. That’s because manufacturing capacity for new models of cars takes years to build out. So instead of making it new, asks ElectraDrive, why not just rip out the combustion engine and put in batteries?

Modifying old cars to run partially or completely on electric power is nothing new, of course. But ElectraDrive has engineered an adjustable mounting frame to put in place of the gas drive train in a relatively cheap process, which commercial fleets owned by companies or the government might be interested in. That makes the change cheaper, and allows a payback period of five years or so — provided gas prices don’t fall further.

BottleStone
BottleStone’s product is what it sounds like: Faux stone made with recycled bottles. The material is good for uses like building facades, countertops and outdoor furniture, and is priced competitively to granite. What the company is positioning itself to compete with, though, is concrete. BottleStone has three times the flexure of concrete, which is noted for its stiffness, and emits 42 percent less carbon when being made.

However, it wouldn’t be a good replacement for concrete in many applications. Try to put it in a roadway, for instance, and it likely wouldn’t survive. That, and you’d effectively be paying for a granite road.

Over the Moon Diapers
This company may not deserve to be at the very bottom of this list, but it’s difficult to get excited about used diapers. Those who aren’t raising a child (that includes me, thankfully) may not be aware that used diapers are a huge source of waste, with each rugrat going through 5,000 to 10,000 diapers before figuring out the toilet. That figures out to 27.4 billion diapers going to landfills in the United States alone, according to the Real Diaper Association.

Over the Moon Diapers wants to help out, of course. But this seems a bit more like a marketing than a technology play. After all, reusable cloth diapers have always been available.