Not long ago there was a dumb idea going around: photovoltaic roadways. It was almost impossibly stupid, ignoring the fact that roads need to carry almost unlimited loads, need to be recycled every few years and are often shaded or covered with snow or dirt. Nevertheless, it got $2.2 million from probably well-meaning people on the crowdfunding website IndieGoGo.
There’s a new only slightly less dumb idea going around: photovoltaic building windows. It ignores that almost no windows face the sun directly, for good reason. Unless you are in a truly frigid climate, building windows that directly face the sun waste energy by overheating the space, requiring cooling or (often mechanical) ventilation. In the article at that link, the inventor fantasizes about using a PV film instead of current energy efficiency films on skyscrapers. Builders will have to justify any additional cost for the films and all the wiring through the building to collect all this energy. Adding to the cost is any reduction in operating efficiency of the building — if the PV film is any worse than the fancy efficiency films it displaces, you need to count in the increased energy consumption for the building and the need for bigger chillers, ducts and cool water piping. This starts to look like an awful expensive way to produce a tiny amount of electricity.
If you really want to reduce a building’s net energy consumption, one of the best things is to shade the windows so you get daylight without direct blast of solar gain, at least not in summer. PV windows won’t work if they are shaded.
Both of these clever PV ideas are based on a faulty premise: that the lack of solar power generation is for lack of places to put solar panels. There are plenty of places to put solar panels. If solar panels aren’t being installed in your town, it is probably because the level of insolation is too low to justify it, utility rate structures make it uneconomical, or other energy sources in your area are much cheaper. None of these are affected by clever inventions like solar roads or windows. You need to go back to boring old utility rate regulation, carbon taxes, and the weather.
These newfangled ideas obstinately forget all the lessons from decades past about negawatts. This is the idea that generation is no better, and often worse, than conservation. If you want to overall reduce the amount of fossil fuels being used for energy, you should probably drive less on any kind of road, with or without embedded PV cells. You should shade windows, especially in summer. And yes, you should build more PV installations — at the exact angles best suited to capturing peak solar radiation, in locations with minimal cloud and shade. In other words, make good use of roads and windows. Don’t try to cover over wasteful construction with a coat of PV film.