= Solar Energy Intercepted by the Earth =
=== S1.7e17 ===
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The average optical energy flux ( UV, visible, Infrared, with a blackbody spectrum around 5778K ) reaching the Earth at 1AU (149.6e9 meters from the sun ) is 1366 W/m² in space, varying from [[https://en.wikipedia.org/wiki/Solar_cycle#/media/File:Solar-cycle-data.png | 1365.5 to 1366.5 W/m² ]] over the 11 year solar cycle.  The mean (average) radius of the Warth is [[  https://en.wikipedia.org/wiki/Earth | R = 6371.0 km ]], so the area facing the sun is πR² or 1.275e14 m².   Multiplied by the 1366 W/m² flux, that's 1.742e17 W or 174 petawatts.