1. Variation of average sunshine with latitude and with time of year.
Variation of average sunshine with latitude and with time of year. (a) Average power of sunshine falling on a horizontal surface in selected locations in Europe, North America and Africa. These averages are whole-year averages over day and night. (b) Average solar intensity in London and Edinburgh as a function of time of year. (Average powers per unit area are sometimes measured in other units, for example kWh per year per square metre; for the reader who prefers those units, the following equivalence may be useful: 1 W=8.766 kWh per year.) Sources: NASA's Surface meteorology and Solar Energy (eosweb.larc.nasa.gov; solar-insolation-levels/lightbucket.wordpress.com/2008/02/24/insolation-and-a-solar-panels-true-power-output/.) (Online version in colour.)‏
MacKay D J C Phil. Trans. R. Soc. A 2013;371:
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