Better Solar Energy Systems: More Heat, More Light

Solar photovoltaic thermal energy systems, or PVTs, generate both heat and electricity, but 51 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, which 1ets the silicon generate more 52 but isn't a very efficient way to gather heat.

That's a problem of 53_. Good solar hot-water systems can harvest much more energy than a solar-electric system at a substantially lower 54 . 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 55 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 Queen's University, Canada.

Most solar panels are made with crystalline silicon, but you can also make solar cells out of amorphous silicon, 56 known as thin-film silicon. They don't create as much electricity, but they are lighter, flexible, and cheaper. And, because they 57 much less silicon, they have a greener footprint. Unfortunately, thin-film silicon solar cells are 58 to some bad-news physics in the form of the Staebler-Wronski effect.

"That means that their efficiency 59 when you expose them to light-pretty much the worst possible effect for a solar cell," Pearce explains, which is one of the 60 thin-film solar panels make up only a small fraction of the market.

However, Pearce and his team found a way to engineer around the Staebler-Wronski effect by incorporating thin-film silicon in a new 61 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 62 of water, they could make thicker cells that largely.

63 the Staebler-Wronski effect. When they applied the thin-film silicon directly to a solar thermal energy 64 , they also found that by baking the cell once a day, they 65 the solar cell's electrical efficiency by over 10 percent.

練習(xí)：

51. A unless B when C if D until

52. A electricity B magnetism C ultraviolet D radioactivity

53. A dynamics B geology C economics D biology

54. A reward B cost C bill D pay

55. A decision B solution C suggestion D qualification

56. A roughly B probably C commonly D specially

57. A retrieve B merge C exchange D require

58. A vulnerable B necessary C important D renewable

59 . A works B counts C rises D drops

60. A restrictions B advances C reasons D strengths

61. A size B shape C type D brand

62. A area B point C place D extent

63. A overcame B promoted C improved D postponed

64. A transformer B adaptor C transmitter D collector

65. A boosted B defined C wasted D lower

答案：DACBB CDADC CBADA

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