Recyclable diapers, a stone-looking building material made with 80 percent of recycled glass and a device to cut an air conditioning's energy use by 20 percent are among the winners of the 2008 California Cleantech Open.

The private nonprofit California Cleantech Open announced the winners from six categories during a ceremony in San Francisco Thursday night. The business plan competition chose the winners from among 43 finalists, companies that went through a series of workshops before pitching their ideas to a panel of judges.

The winning companies get $50,000 in cash and $50,000 in services to help them launch their businesses. The competition inaugurated in 2006.

San Jose Mayor Chuck Reed took the stage to pitch his city as a place to incubate tech companies. He said the city will sponsor an award that offers a one-year free rent to the winner.

Steve Vassallo, principal of Foundation Capital and David Rodgers, the deputy assistant secretary of energy efficiency at the U.S. Department of Energy gave pep talks about the value of developing greentech and the need to continue to invest in them even during the economic downturn.

Here is a list of winners:

Green Building

  • Air and Water: Over the Moon Diapers: The San Francisco company develops diapers made with mostly recycled materials and strong enough for industrial washing.
  • Energy Efficiency: Viridis Earth: The company has engineered a $350 device that cuts energy use in residential air conditioners.
  • Green Building: BottleStone: The Los Altos Hills, Calif. company has created a building material with a ceramic stone surface and made with 80 percent recycled glass.
  • Renewables: Focal Point Energy: The San Jose, Calif. company has asolarconcentrator that uses the sun's heat instead of light to generate electricity.
  • Smart Power: Power Assure: The Santa Clara, Calif. company has developed a software for data centers to manage power use and conserve energy.
  • Transportation: ElectraDrive: The San Francisco company converts gasoline vehicles into electric rides by replacing the drive trains. 
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