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Better Solar Energy Systems: More Heat, More Light Solar photovoltaic thermal energy systems, or PVTs, generate both heat and electricity, but __1__ now they havent been very good at the heat-generating part compared to a stand-alone solar thermal collector. Thats because they operate at low temperatures to cool crystalline silicon solar cells, which lets 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 it，s also a space problem：photovoltaic cells can take up all the space on the roof, leaving little room 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 panels are made with crystalline silicon，but you can also make solar cells out of amorphous silicon, __6__ known as thin-film silicon. 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 effect. | 
