Organic Valley, the co-op that brought sustainable farming to the dairy industry, has adopted the latest twist in solar technology: windows with embedded with solar cells that generate electricity and save energy by boosting the benefits of daylighting.
Twenty windows at Organic Valley's headquarters in La Farge, Wisc., feature the unique product Pythagoras Solar of San Mateo, Calif., calls photovoltaic glass units.
The windows are latticed with solar cells that are embedded between two panes of glass, making the window look as though a set of open venetian blinds were built into it.
There's a picture of a window in Organic Valley's office building, to the right, and another photo, below, shows how the windows look from the outside.
The built-in grid in the windows captures direct sunlight to generate electricity while also diffusing the rays so building occupants get the benefits of the light, as well as the advantages of a curtain wall that helps insulate the interior, making it cooler during hot weather and warmer during cold spells. As a result, the windows provide green power while also reducing the amount of energy a building uses for heating and cooling.
Building-integrated photovoltaics, which enable a structure to become a power source and not just a consumer of energy, have been around since the 1990s -- but optimization of their technical capabilities and commercial viability is relatively recent. [For example, here is a Q&A with Dow about its development and release of solar roofing tiles.]
Pythagoras Solar's product, the first designed to provide high power density and energy efficiency via enhanced daylighting, won a $100,000 grant in GE's ecomagination Innovation Challenge last year.
The window's capabilities appealed to Organic Valley, according to Cecil Wright, the firm's vice president of sustainability and local operations. I recently asked how the company came to choose solar windows over other technologies such as dynamic glass, which electronically and automatically tints and clears to manage sunlight and heat gain, window film and roof-mounted solar.
"Our solar portfolio includes trackers, rooftop PV and solar thermal," Wright said via email. "We felt that the windows, being BIPV, fit well with those other projects."
Dynamic glass offers the daylighting and occupancy comfort the firm was seeking, he said, "but Pythagoras goes to the next level ... we were drawn to the building integration of the Pythagoras windows. By adopting these innovative windows, we are also helping to pave the way for this technology, which has the merit to become a standard in the design and construction of net zero energy buildings."
Pythagoras says its product provides four times the power density of existing BIPV technologies. When I asked how that compares to rooftop PV for power generation and cost benefits, here's what Udi Paret, vice president of business development and marketing said:
"Energy generation wise, the PVGU would be equivalent to standard rooftop PV panels when mounted in the same orientation, achieving up to 14 percent module efficiency," Paret responded in an email. "However, unlike rooftop panels, the PVGU is designed as a building material, part of the building skin and being marketed into the building and construction value chain, not the PV one."
As to how the cumulative benefits of the company's BIPV compare to that of "traditional" PV, Paret wrote: "They really don't. The PVGU is the industry's first to simultaneously deliver energy efficiency benefits, high power density and optimized daylighting -- resulting in attractive economics, typically 3-5 years ROI [return on investment] and around 20 percent IRR [internal rate of return]."
Organic Valley's 160 square feet of PVGU delivered a 49.68 kg CO2 reduction last month, said Wright. And the greatest reduction thus far occurred in October, the first month of the system's operation, when 54.74 kg of carbon emissions were avoided. Energy wise, he said, "we are seeing an average energy production over 3 kwh per day, with some days producing over 6 kwh per day."
Here's a diagram of how the Pythagoras technology works:
Top photo courtesy of Organic Valley. Other photos courtesy of Organic Valley and Pythagoras Solar. Diagram courtesy of Pythagoras.