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--- opinion:frater_secessus:solar_harvest [2020/09/24 14:13]
frater_secessus [observations]
+++ opinion:frater_secessus:solar_harvest [2023/02/17 15:20] (current)
frater_secessus [correlation with available direct light]
@@ Line 17: / Line 17: @@
 ===== observations =====
-Overpaneled configurations (relatively high panel watt to batter Ah ratio) tend have two main features:
+Overpaneled configurations (relatively high panel watt to battery Ah ratio) tend have two main features:
   - improved charging in adverse conditions
   - //apparent// low output in normal conditions  - this occurs because the batteries are typically in Absorption with battery charging demand dropping by solar noon;  there is rarely an opportunity to [[http://bdp.mousetrap.net/index.php/2020/07/17/mythtesting-higher-voltage-for-additional-yield-in-the-mornings/|demonstrate full output]].
-Note that overpaneled systems are typically only making
   * full sun normal
-    * 305w, 54% of rated, 4
+    * 305w, 54% of rated
   * bright sun through thin / cirrus clouds, shadows thrown
     * 312w at 11am, sea level.  55% of rated, 67% of theoretical.
@@ Line 38: / Line 37: @@
       * thunderstorms, typically 10W, less than 2% of rated.
+===== correlation with available direct light =====
-===== ununsual scenarios =====
+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
+  -  derive cosine of the above; this is the percentage of direct sunlight landing on a flat surface
+  -  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.))
+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
-    * exceptionally high yield, 90% of rated
-        * [[http://img.mousetrap.net/2020/Screenshot_20200222-114332.jpg|519w at in February in Quartzsite @ noon]], ~500' elevation.  91% of rated, 114% of theoretical.  I've seen 500w+ rarely, maybe 3x in two years off grid so far.
-      * wildfire smoke - [[http://img.mousetrap.net/2020/Screenshot_20200908-122938.jpg|8.98W at noon]], sea level.  1.5% of rated, 1.9% of theoretical during September 2020 wildfires in Oregon.
+===== ununsual scenarios =====
+    * exceptionally high yield, 90% of rated
+        * [[http://img.mousetrap.net/2020/Screenshot_20200222-114332.jpg|519w at in February in Quartzsite @ noon]], ~500' elevation.  91% of rated, 114% of theoretical.  I've seen 500w+ out of 570w rarely, maybe 3x in two years off grid so far.((before I increased array to 750w))
+    * wildfire smoke - [[http://img.mousetrap.net/2020/Screenshot_20200908-122938.jpg|8.98W at noon]], sea level.  1.5% of rated, 1.9% of theoretical during September 2020 wildfires in Oregon.

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