Cogenra Mixes Solar PV and Hot Water


Khosla Ventures-backed Cogenra Solar made big news this month when it celebrated the unveiling of an impressive 272-kW solar cogeneration installation at Sonoma Wine Company in Graton, California.  Former British Prime Minister Tony Blair attended the event to flip the switch on 15 Cogenra SunBase modules that generate both electricity and hot water for the winery.

Cogenra-solar-sonoma-wine Cogenra-solar-sonoma-wine2

The Cogenra system includes advanced silicon PV cells, concentrating optics, single-axis solar tracking, and a thermal transfer system.  The process of generating electricity is relatively straightforward.  Solar rays reflect off parabolic mirrors toward two strips of solar PV cells, generating power that’s fed into the grid.

The process of generating hot water is a little more complicated.  An aluminum pipe behind each PV strip contains glycol and absorbs heat from the solar PV strip to optimize electricity yield.  As the glycol warms, it is transferred to a preheat tank where the glycol heats water.  After that, heated water flows to the boiler for final heating.


At Sonoma Wine Company, the 15-module installation will produce 50 kW of electricity and 222 kW of thermal energy, which should equate to about a 10% of total electricity and a 45-50% reduction in natural gas for water heating, according to Technology Review.

Cogenra Solar engineered and financed the installation under a Heat & Power Purchase Agreement over 15 years.  Pursuant to the HPPA, Sonoma Wine Company will purchase electricity and thermal energy for a guaranteed rate throughout the term.

Vinod Khosla told Forbes in an interview that Cogenra Solar’s solution “is more effective than almost anything you’ve heard of in solar.”  Perhaps that’s due in part to the fact that the solar cogen system qualifies for both solar electric and solar hot water incentives.

Credits: Cogenra Solar.

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  • MrSteve007

    I’m very curious about their PV warranty. I have yet to see a concentrating PV array that hasn’t severely degraded the PV element within 5-8 years, from excess heat. Their hotwater element can cool it, but you’re still talking about extreme (300+ degree) heat loads on the surface, when a normal PV panel experiences ~180 degree operational temperatures.

    From you link: “The company has not released an estimate for the cost-per-watt of its electricity . . .”

    That’s always a bad sign for any hope of affordable.

  • Sep

    Thank you for the amazing and great articles. Good luck.

  • Cal Solar Eng

    This technology is impressive and only getting better, but we need to see systems installed before they will benefit anyone.

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