Installing photovoltaic solar cells is a great way to easily tap into an environmentally sustainable energy source, and in sunnier parts of the world it’s even feasible to use them to actually make money by selling power back to the grid as part of a smart grid installation. But according to new research by the University of California at San Diego, there’s a massive payoff just by having the things on your roof: They act to insulate your home from heat, and actually lower your air-conditioning bills.

The research team from the engineering department used thermal imaging cameras to look at the heat radiation signature from building roofs and structures on top of them. The result was simple, but starkly interesting: Beneath a solar panel, a building’s ceiling structure was 5 degrees Fahrenheit cooler than under a section of roof that was exposed directly to the sun.

This lowers cooling costs in the building during the daytime, resulting in a roughly 5% discount on the solar panel’s price over their lifetime. The environmental payoff is also interesting, because the cooling effect means the solar PV panels are, in effect, selling 5% more electricity back to the grid than they’re actually producing by converting sunlight.

One building studied had a 38% reduction in the amount of solar heat hitting the building roof–indicating that they’re even greater savings than 5% possible, because bigger panels provide more shading effect, and angled ones that have an air pocket trapped beneath them are the most efficient. Interestingly enough, the benefits even continue to the nighttime, where the solar panels act to actually boost roof insulation, and prevent precious heat escaping.

There is a downside, of course. In winter, the panels prevent warming solar energy heating the building–but the San Diego team thinks this is canceled by the fact that the panels also keep heat in at night. They’re busy honing a mathematical model that may help homeowners work out the full payoff of installing different solar PV panel configurations. And more useful than this, perhaps, is that in an era of multi-billion-dollar experiments, this case proves that simple straight-thinking science can still turn up valuable data.

[Image: Flickr user steevithak]