Have you ever seen one of those massive skyscrapers with silvered windows? They’re beautiful, right? They are also pretty wasteful. They’re made to be so reflective because the designers of the buildings don’t want to turn them into greenhouses, cooking the occupants.
If that seems like a waste of good solar power, then you’d be right. However, it’s not practical or affordable to cover the entire outside of the building in solar panels, at least not if we’re thinking about traditional solar panels that consist of complex electronics.
The Winner is the Thinner
If you’ve read my article on the three main types of solar cell then you will know the newest product is a thin-film solar panel. This panel technology works completely different than more traditional solar cells. To make a thin-film cell you have to spray thin layers of photovoltaic materials onto a substrate such as glass – specifically amorphous silicon, cadmium telluride, or copper indium gallium diselenide (CIGS). Each of these materials has different things that make them good. The silicon option is out because it’s too inefficient. The cadmium option is viable from a power viewpoint, but cadmium is very toxic. Like, really toxic.
That leaves CIGS, which is the most power-efficient material of the bunch. Unfortunately, there’s a big spectrum of manufacturing qualities. Since this type of thin-film panel consists of four alloy combinations, it means it’s easy to get the mix wrong or for impurities to get in.
Making a Solar Window
To solarize a window with thin-film technology, you actually spray the material onto the glass surface. That doesn’t mean that you can take a spray can and convert the existing windows in your building to solar. It means that normal glass windows are converted in a clean and controlled factory.
How Well Do They Work?
These solar windows are very much still in the early stages of their development, as is the entire thin-film industry. They aren’t really a commercially-viable product by any means. Of all the solar technologies that are currently practical, these panels are the least efficient. For one thing, you can still see through solar windows. Which means plenty of light is passing through without being converted. It’s really a comparative situation. Normal windows let almost all the light through, which is a useful attribute in a window. By putting the solar film on them you can make some power using a portion of the light, but the rest of the light isn’t exactly wasted as it is with other solar technologies. That light still does the job of illuminating the interior of the building and letting people see the outside.
Since they are so inefficient, you need a lot of these panels in order to get any sort of usable power from them. Most people don’t have a ton of windows in their houses, but skyscrapers and other buildings that have mostly glass as their exterior provide enough surface area to make it worthwhile.
Don’t forget that this technology is still heading for its peak. People are working hard on improving thin-film technology. Since this technology is going to be used on massive surfaces, even a small improvement in efficiency will make a large absolute difference in power production.
Where Can We Get Them?
Well, right now you really can’t get them anywhere, at least not easily. Only a handful of companies are making solar windows. Japan and China are major players and some US and UK labs are also working on ways to make these windows more attractive from a cost and performance perspective. While there were promises that solar windows might come to the mainstream market around 2016, as of 2018 they still aren’t ready. For now it’s an interesting development for the future of solar, but for anyone who wants practical solar energy today, it’s not of particular interest.