NREL Solar Cell Efficiency Record

The improvement of some characteristics of human instruments and machines is not limited technologically, but fundamentally, by the very laws of physics. Even in theory, one cannot exceed a speed of 300,000 km/s, a light output of 683 lm/W, or the efficiency of a heat engine, established by Carnot’s theorem. And they approach similar limits asymptotically – the closer, the more difficult.

The efficiency of solar batteries is theoretically limited at the level of 66% (if we talk about photovoltaic semiconductors, without considering those that work in a fundamentally different way, for example, nanoantennas). And the last interest is submitted literally one per year:

  • 2009 (Spectrolab) – 41.6%;
  • 2011 (Solar Junction) – 43.5%;
  • 2013 (Sharp) – 44.4%;
  • 2014 (Fraunhofer ISE) – 46% (with focus on micro area).

And just this year, American scientists ( National Renewable Energy Laboratory , Golden, Colorado) surpassed the level of 47% – with 143 times the concentration of light.

The elementary cell of the battery contains 6 photoactive levels of various semiconductors, “tuned” to different wavelengths of light, which allows the most complete absorption of solar energy. In total, the new element consists of 140 layers, while having a thickness three times less than a human hair.

The cost of such a heterostructure still corresponds to its space application. But the use of lenses (and especially reflectors) that concentrate light from a large area on miniature chips can save the lion’s share of the semiconductor to convert the same amount of energy. This, of course, will make solar panels somewhat bulky, but much more mundane in price.

The second direction in the issue of further increasing the efficiency (and, consequently, reducing the cost of the energy received) of multilayer photovoltaic cells, according to John Gage, a leading specialist in the NREL high-efficiency crystalline photovoltaic group, is to reduce the internal resistance of the battery, which inevitably increases with an increase in the number of series-connected layers. This will make it possible to overcome the 50% efficiency threshold in the near future.

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