Solar cell efficiency
Solar cell efficiency refers to the portion of energy in the form of sunlight that can be converted via photovoltaics into electricity.
The efficiency of the solar cells used in a photovoltaic system, in combination with latitude and climate, determines the annual energy output of the system. For example, a solar panel with 20% efficiency and an area of 1 m2 will produce 200 W at Standard Test Conditions, but it can produce more when the sun is high in the sky and will produce less in cloudy conditions and when the sun is low in the sky. In central Colorado, which receives annual insolation of 5.5 kWh/m2/day, such a panel can be expected to produce 440 kWh of energy per year. However, in Michigan, which receives only 3.8 kWh/m2/day, annual energy yield will drop to 280 kWh for the same panel. At more northerly European latitudes, yields are significantly lower: 175 kWh annual energy yield in southern England.
Several factors affect a cell's conversion efficiency value, including its reflectance efficiency, thermodynamic efficiency, charge carrier separation efficiency, and conduction efficiency values. Because these parameters can be difficult to measure directly, other parameters are measured instead, including quantum efficiency, VOC ratio, and fill factor. Reflectance losses are accounted for by the quantum efficiency value, as they affect "external quantum efficiency." Recombination losses are accounted for by the quantum efficiency, VOC ratio, and fill factor values. Resistive losses are predominantly accounted for by the fill factor value, but also contribute to the quantum efficiency and VOC ratio values.
As of December 2014, the world record for solar cell efficiency at 46% was achieved by using multi-junction concentrator solar cells, developed from collaboration efforts of Soitec, CEA-Leti, France together with Fraunhofer ISE, Germany.
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