Preparation - Pacific Crossing Notes: A Sailor's Guide to the Coconut Milk Run - page 50

Post Script: Sun Altitude and Solar Power
As mentioned earlier, any deviation of the sun's position from directly overhead will re-
duce its power input to your solar panels in two ways:
1. As the sun drops from its zenith to the horizon, a given cross-section of a solar
light beam will be spread over a larger area as the light hits at an increasingly lower
angle.Forexample, atasunaltitude of60°abovethehorizon,thiseffectreducesthe
power produced by your solar panels by approximately 15% vis-à-vis their output
with the sun directly overhead. With the sun at an altitude of 30° above the hori-
zon the output will be reduced by 50%, and at 15° by about 75%. Figure A1 shows
how a given quantity of incoming light is “diluted” over a greater surface area as
the sun's altitude drops.