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Solar photovoltaic thermal energy systems1, or PVTs, generate both heat and electricity, but l now they2 havent been very good at the heat-generating part compared to a stand-alone3 solar thermal collector. Thats because they operate at low temperatures to cool crystalline silicon solar cells4, which5 1ets the silicon generate more 2 but isnt a very efficient way to gather heat. Thats a problem of 3 Good solar hot-water systems can harvest much more energy than a solar-electric system at a substantially lower 4 . And its also a space problem：photovoltaic cells can take up all the space on the roof, leaving little room6 for thermal applications. In a pair of studies, Joshua Pearce, an associate professor of materials science and engineering, has devised a 5 in the form of a better PVT made with a different kind of silicon. His research collaborators are Kunal Girotra from ThinSilicon in California and Michael Pathak and Stephen Harrison from Queens University, Canada. Most solar panels7 are made with crystalline silicon, but you can also make solar cells out of amorphous silicon8, 6 known as thin-film silicon9. They dont create as much electricity, but they are lighter, flexible, and cheaper. And, because they 7 much less silicon, they have a greener footprint. Unfortunately, thin-film silicon solar cells are 8 to some bad-news physics in the form of the Staebler-Wronski effect10. | 
