[Graton, California USA]
The Cogenra Solar cogeneration system was found switched OFF two days after the commissioning celebration.
|From Sonoma Wine Company Cogenra Solar Installation|
“Cogenra Unveils Sonoma Wine Company Solar Cogeneration Installation” was the surprise announcement Friday morning. On Thursday, November 4, 2010, Derek Benham, founder and owner of the Sonoma Wine Company (SWC), and Cogenra Solar CEO Dr. Gilad Almogy were joined by former British Prime Minister Tony Blair and Khosla Ventures founder Vinod Khosla for a ceremony “to flip the switch on the 272-kilowatt (kW) installation, now supplying renewable heat and electricity to support the company’s winery operations.”
When I saw the announcement, I knew Graton would be on my weekend itinerary. After making the field trip up to Graton from the South Bay, I was disappointed to find the fifteen (15) Cogenra SunBase modules stowed like battle droids facing away from the sun as shown in the Picasa slideshow. The Bloomberg TV video “Khosla Sees Opportunity in Cogenra Hybrid Solar System” does show the system in operation as do photos at the Cogenra Solar Case Study webpage. Dr. Almogy answers questions about annual savings by the SWC, installation cost, and system payback with generalizations instead of the hard numbers Bloomberg TV interviewer Cris Valerio expected.
Am I unrealistic or naive to believe a system will be in near daily operation once commissioned? In his remarks at the event, Cogenra CEO Almogy said:
This is a very significant milestone for Cogenra as we bring our first project online in California’s wine country and toast to a bright future with solar cogeneration.
Similar statements were made by Dr. Almogy in subsequent press interviews. Just one day after his “Khosla on Hype and Opportunity in the Smart Grid” presentation at GreenBeat 2010, Mr. Khosla is found engaging in a bit of solar cogeneration Hype of his own.
Final interconnection, inspection, or performance testing could be to blame for the system not being online. Since the SWC Graton facility was closed on Saturday, and I expect it had limited hot water requirements, I began to consider other practical issues. Although the mid Concentration PhotoVoltaic (CPV) portion of the Cogenra system can leverage the least common denominator policy of net metering to match electricity generation and consumption over an annual period, the hot water generated must be used or stored on site. In periods of low hot water demand, can the CPV portion of the Cogenra Solar system operate in a closed loop fashion without pumping water out of the Preheat Tank? The Cogenra Solar Site Integration diagram does not indicate the existence of a closed loop CPV operation option though it may well be supported.
Parabolic Linear Fresnel Reflector
The Cogenra SunBase modules as installed at the SWC can be described as Parabolic Linear Fresnel Reflectors (PLFR) oriented lengthwise in a North to South direction and following the sun from east to west with single axis tracking. The narrow photovoltaic modules are mounted on two sides of the inverted triangle receiver facing the PLFR. I have not seen the SunBase modules in operation, but the inset Cogenra photo taken at the SWC site appears genuine and shows rather impressive even illumination of the PV modules by the PLFR. In fact, mirror image reflections of the PV modules can be seen when peering into the PLFR from the receiver direction. The PV modules are cooled by what Cogenra calls a glycol mixture circulated through a Preheat Tank to heat water and cool the glycol mixture for reuse.
Please note the 272 kW system capacity number is a very subjective performance rating that encompasses both solar electric and thermal capacity. Cogenra Solar has not released a datasheet on the SunBase modules or systems. The Cogenra SWC press release said:
The solar cogeneration installation employs 15 individual Cogenra SunBase™ modules to displace approximately 64,000 kilowatt-hours and 12,500 therms of natural gas annually. The solar thermal element will heat water to 165°F to sustainably fuel Sonoma Wine Company’s wine tank wash and wine barrel washing system.
Trial and error guesses with the National Renewable Energy Laboratory (NREL) PVWatts Viewer for the Graton, California location imply a standard photovoltaic solar DC (Direct Current) system capacity of about 48 kW will deliver just over 64000 kiloWatt-hours (kWh) of AC (Alternating Current) electricity annually.
The phrase “solar thermal element will heat water to 165°F” or 73.8 °C is the first mention of hot water temperature by Cogenra Solar. Silicon solar cell modules are specified at 25 °C STC (Standard Test Conditions) with 45 °C NOCT (Nominal Operating Cell Temperature) a more typical operating condition though modules have operating temperature limits extending from -40 °C to +85 °C.
Since silicon solar cell power output decreases at higher operating temperatures because of the negative temperature coefficient while also increasing module degradation rates, a thermodynamic tradeoff exists between solar electric power generation and heat extraction via module cooling with the glycol mixture. Efficient solar electric power generation dictates some 25 to 30 °C of the Cogenra’s quoted 73.8 °C must be obtained by direct solar heating of the glycol mixture.
Cogenra Solar has not discussed the solar thermal aspect of the system in any detail. How Solar Cogen Works states “Heat energy captured for solar hot water and to cool PV cells for optimal efficiency” and:
Cogenra has developed an extensive intellectual property portfolio covering its solar cogeneration technology. Cogenra Solar’s proprietary technology captures up to 80 percent of the sun’s delivered energy and produces five times the energy of traditional PV systems. To achieve these dramatic efficiency gains, Cogenra integrates advanced silicon PV cells, concentrating optics with single-axis tracking and an innovative thermal transfer system in a low-cost and scalable design.
Thus far, a lone Cogenra Solar patent from the extensive portfolio has been published under the old Skywatch Energy company name at the World Intellectual Property Organization (WIPO) as shown below and the United States Patent and Trademark Office (USPTO):
(WO 2010/099236) 1-DIMENSIONAL CONCENTRATED PHOTOVOLTAIC SYSTEMS
I asked SWC neighbor Maureen Lomasney, President and Founder of Art Honors Life | The Gallery at FUNERIA, about the celebration and the Cogenra Solar system. Other than Scotland Yard making their presence known securing the area for Mr. Blair’s visit, it does not sound as though many Graton residents were invited to the exclusive event.
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