"Obviously when you're looking at absorbing visible light and it's transparent, it's not as efficient as an opaque panel," Conklin said.
When it comes to solar windows, however, efficiency matters less than transparency, Conklin said.
Photo by G.L. Kohuth Yimu Zhao, a doctoral student in chemical engineering and materials science at Michigan State University, and Richard Lunt, assistant professor of chemical engineering and materials science, run a test in Lunt’s lab. Lunt and his team have developed a new material that can be placed over windows and create solar energy.
"When you're looking at transparent or clear photovoltaics, it's not necessarily a function of power conversion efficiency as it is about using the vast amount of space available for that tech," Conklin said. "We're making use of the space that right now is not available for solar energy production. Passive windows are turned into active energy generating windows."
In other words, transparent solar PV is about not wasting perfectly good real estate in order to supplement a building's power requirements.
The solar window technologies utilize varying methods of transmitting the energy that the PVs produce to a building's internal power infrastructure.
Solaria, for example, hides its wiring in the window's frame, and the connectors are wired into a newly constructed building's electrical conduits. Those conduits lead to a central power inverter, which converts the solar windows direct current to alternating current that's usable in the electric grid.
SolarWindow's technology can come with micro DC-to-AC power inverters, allowing the electricity to be used only in one room with a solar window. Alternately, it can be connected to a distributed microgrid inverter to power a single floor of a building or to a central inverter from which the entire building can draw power.
Solaria is already piloting its windows in "a few" buildings and it is working on the first large-scale commercial projects in California and Europe, according to Sharma. Sharma did not disclose the projects.
Solaria has also partnered with Tokyo-based Asahi Glass Co., a global glass manufacturer. Sharma said Asahi intends to sell both windows and a bamboo shade called Sudare with embedded solar cells from Solaria.
"So we're enabling different glass and curtain wall providers in North America, Europe and Asia to provide products," Sharma said.
Solar windows will cost about 40% more than conventional windows, but the ROI is achievable in under a year and there's big demand even though products have yet to ship, the manufacturers say.
"It's actually very viable and will be even more viable as we approach our product launch," Conklin said. "It's in very high demand because right now skyscrapers... don't have a good way of offsetting energy through renewable energy generation."
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