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--- opinion:frater_secessus:solar_harvest [2023/02/17 15:17]
frater_secessus [observations]
+++ opinion:frater_secessus:solar_harvest [2023/02/17 15:20] (current)
frater_secessus [correlation with available direct light]
@@ Line 41: / Line 41: @@
 This is harder to grasp and compute, but increases accuracy by factoring in location, time, etc.((It cannot account for //indirect// light by refraction, reflection,etc. The contribution of indirect light is considered to be +15% in clear skies.))
-.  find solar zenith angle with app or calculator
+  -  find solar zenith angle with app or calculator
-.  derive cosine of the above; this is the percentage of direct sunlight landing on a flat surface
+  -  derive cosine of the above; this is the percentage of direct sunlight landing on a flat surface
-.  multiply this value by panel wattage
+  -  multiply this value by panel wattage
-.  the result is the theoretical direct light available at that time/place under clear skies.((since MPPT-based system losses typically are -15% and indirect lighting is +15%, an MPPT-based system might make this direct-light power level under clear skies.))
+  - the result is the theoretical direct light available at that time/place under clear skies.((since MPPT-based system losses typically are -15% and indirect lighting is +15%, an MPPT-based system might make this direct-light power level under clear skies.))
+I have observed the following cosine-based direct light percentages:
+  * clear skies:   98% of theoretical direct sun
+  * bright overcast skies (shadows thrown):  82% of theoretical direct sun
+  * overcast: 58% of theoretical direct sun

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