The tantalizing idea behind solar windows is that the vertical surfaces on the outside of just about any building could unobtrusively generate electricity.
But first, researchers and companies need to figure out how to take this product from the lab to the factory.
Along those lines, University of Michigan researchers have published the results of their work on a process to manufacture windows that can be large—up to two meters by two meters—and efficient in terms of electricity production.
“You see a lot of these glass and steel buildings around which are just walls of windows,” said Stephen Forrest, an electrical engineering professor at Michigan and co-author of the study. “Why not turn that excess energy (from sunlight) into electricity to help power the home or the building?”
Most solar panels use silicon as the material that receives solar energy, but solar windows need something different because silicon isn’t transparent. An alternative is to use dye-like compounds, similar on a molecular level to the dyes used in clothing.
Nearly all solar windows are semi-transparent, with a tint that can come in a variety of colors. From a distance, they may look like any tinted window, but up close you can see the clear lines separating the strips of solar material.
The Michigan team, whose work appeared this month in the journal Joule, has come up with a process of making solar cells from dye-like materials, which are connected to lines of metal so small they are invisible to the eye. The researchers designed the process to be able to work in a factory, as opposed to just in a lab.
The solar cell shown in the journal article is small enough to hold in your hand, but the process allows for construction on a much larger scale.
The window has an efficiency of 7 percent, which is the share of solar radiation that gets converted to electricity. This is less than the 10 percent that the team views as easily within reach with the technology, and also less than the 15 percent that is a starting point for most new silicon-based systems.
But developers of solar windows aren’t necessarily competing with the efficiency of silicon solar panels. While some buildings can have solar on their rooftops, a buyer of solar windows may be looking for the opportunity to generate electricity from windows, in addition to rooftop solar.
Like most emerging clean energy technologies, much of the work on solar windows is to increase efficiency and reduce costs to the point that the product makes sense to a prospective buyer.
Forrest and his colleagues have previously written that a solar window can be built and installed for about double the cost of a conventional window, and the income from generating electricity would pay for the difference in cost in two to six years, depending on factors like the level of sun exposure.
The University of Michigan is seeking a patent on the technology and also is looking for partners to take the next steps in producing and selling the windows.
Among the companies working in this space is NEXT Energy Technologies of California, which is developing its window product and building prototypes.
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