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  3. Better Solar Energy Systems: More Heat, More Light Solar photovoltaic thermal energy systems, or PVTs, generate both heat an

Better Solar Energy Systems: More Heat, More Light Solar photovoltaic thermal energy systems, or PVTs, generate both heat an

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问题                 Better Solar Energy Systems: More Heat, More Light
    Solar photovoltaic thermal energy systems, or PVTs, generate both heat and electricity, but【C1】______now they haven’t been very good at the heat-generating part compared to a stand-alone solar thermal collector. That’s because they operate at low temperatures to cool crystalline silicon solar cells,【C2】______lets the silicon generate more electricity but isn’t a very efficient way to gather heat.
    That’s a problem of economics. Good solar hot-water systems can harvest much more energy than a solar-electric system at a substantially lower【C3】______. And it’s also a space problem: photovoltaic cells can【C4】______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【C5】______in the form of a better PVT made with a different kind of silicon.
    Most solar panels are made with crystalline silicon, but you can also make solar cells out of amorphous silicon, commonly known【C6】______thin-film silicon. They don’t create as much electricity, but they are lighter, flexible, and cheaper. And, because they【C7】______much less silicon, they have a greener footprint.【C8】______, thin-film silicon solar cells are vulnerable to some bad-news physics in the form of the Staebler-Wronski effect.
    "That means that their efficiency drops when you【C9】______them to light—pretty much the worst possible effect for a solar cell," Pearce explains, which is one of the【C10】______thin-film solar panels make up only a small fraction of the market.
    However, Pearce and his team found a【C11】______to engineer around the Staebler-Wronski effect by incorporating thin-film silicon in a new【C12】______of PVT. You don’t have to cool down thin-film silicon to make it work. In fact, Pearce’s group discovered that by heating it to solar-thermal operating temperatures, near the boiling【C13】______of water, they could make thicker cells that largely【C14】______the Staebler-Wronski effect. When they applied the thin-film silicon directly to a solar thermal energy collector, they also found that by baking the cell once a day, they【C15】______the solar cell’s electrical efficiency by over 10 percent.
【C1】
选项 A、unless
B、until
C、when
D、if
答案B
解析 句意为：与太阳热能单机集热器相比，______传统太阳能光伏热能系统在转换热能方面效率一直不是很高。四个选项：unless“除非，如果不”；until“在…以前；直到…时”；when“当…时”；if“如果；即使”。
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