If we take 6000 K for the temperature of the sun and 300 K for ambient conditions on earth, this comes to 95%. If one has a source of heat at temperature T s and cooler heat sink at temperature T c, the maximum theoretically possible value for the ratio of work (or electric power) obtained to heat supplied is 1- T c/ T s, given by a Carnot heat engine. This efficiency limit of ~34% can be exceeded by multijunction solar cells. This calculated curve uses actual solar spectrum data, and therefore the curve is wiggly from IR absorption bands in the atmosphere. The Shockley–Queisser limit for the efficiency of a single-junction solar cell under unconcentrated sunlight at 273 K. Thermodynamic-efficiency limit and infinite-stack limit See Shockley–Queisser limit for more detail. The factors affecting energy conversion efficiency were expounded in a landmark paper by William Shockley and Hans Queisser in 1961. Factors affecting energy conversion efficiency In 2019, the world record for solar cell efficiency at 47.1% was achieved by using multi-junction concentrator solar cells, developed at National Renewable Energy Laboratory, Golden, Colorado, USA. Resistive losses are predominantly accounted for by the fill factor value, but also contribute to the quantum efficiency and V OC ratio values. Recombination losses are accounted for by the quantum efficiency, V OC ratio, and fill factor values. Reflectance losses are accounted for by the quantum efficiency value, as they affect "external quantum efficiency". Because these parameters can be difficult to measure directly, other parameters are measured instead, including quantum efficiency, open-circuit voltage (V OC) ratio, and § Fill factor. Several factors affect a cell's conversion efficiency, including its reflectance, thermodynamic efficiency, charge carrier separation efficiency, charge carrier collection efficiency and conduction efficiency values. The absorption and collection efficiencies of a solar cell depend on the design of transparent conductors and active layer thickness. Light transmits through transparent conducting electrode creating electron hole pairs, which are collected by both the electrodes. Schematic of charge collection by solar cells. At more northerly European latitudes, yields are significantly lower: 175 kWh annual energy yield in southern England under the same conditions. However, in Michigan, which receives only 1400 kWh/m 2/year, annual energy yield will drop to 280 kWh for the same panel. In a high-yield solar area like central Colorado, which receives annual insolation of 2000 kWh/m 2/year, a panel can be expected to produce 400 kWh of energy per year. The global regions that have high radiation levels throughout the year are the middle east, Northern Chile, Australia, China, and Southwestern USA. These two variables can vary greatly between each country. Two location dependant factors that affect solar PV efficiency are the dispersion and intensity of solar radiation. A solar panel can produce more when the sun is high in the sky and will produce less in cloudy conditions or when the sun is low in the sky, usually the sun is lower in the sky in the winter. Usually solar panels are exposed to sunlight for longer than this in a given day, but the solar irradiance is less than 1000 W/m 2 for most of the day. For example, a solar panel with 20% efficiency and an area of 1 m 2 will produce 200 kWh/yr at Standard Test Conditions if exposed to the Standard Test Condition solar irradiance value of 1000 W/m 2 for 2.74 hours a day. 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. Solar-cell efficiency refers to the portion of energy in the form of sunlight that can be converted via photovoltaics into electricity by the solar cell. Reported timeline of research solar cell energy conversion efficiencies since 1976 ( National Renewable Energy Laboratory)
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |