overpaneling for challenging solar conditions

[found this early July post in my Drafts folder]

I forgot to add something about the weekend among the Douglas Firs.

When camping in wide open spaces like the BLM land around me, my overpaneled solar configuration is overkill.  I run all kinds of things with minimal oversight.

But when camping in a small clearing in a forest the configuration is merely adequate; there is no meaningful surplus of power.  Back to reality!

  • In the morning there is very little power coming through the tree trunks, usually less than 75w.

  • In late morning the sun is only partially blocked by the forest canopy.  100-200w depending how how much the sun is blocked.

  • at solar noon (assuming we haven’t achieved Absorption voltage yet) and no canopy in the way the system pulls 300-350w for maybe an hour. After that the narrow view of the sun was affected by canopy again.    It peaked in the low 430w range briefly  one of those days but the it may have been cloud-edge effect as it was partly cloudy.

  • the process reversed as the sun went down.

I was able to finish Absorption on those days, mainly because it was ~70F and I didn’t have to run the evaporative cooler.  The maxxfan on thermostat also slowed down to the lowest setting and sometimes shut down.  At normal ELP altitudes (~4000ft) in the summer the maxxfan and evap run full blast all night.  Together they and the other fulltime loads (pvr, router, refrigerator) pull about 100w.

[on a more recent weekend up there it was full overcast for the whole time and rained lightly several times each day.  I maxxed at about 200W when overcast and about 125w when dark overcast.  This was not enough to attain Vabs, much less complete the ~3hr duration I prefer.

Completing Absorption after each cycle is generally the goal, although there is some evidence that completing it 2x/week or so is enough to stave off capacity “walk-down”.  Folks who find themselves unable to complete Absorption regularly would likely be better off with a lithium or carbon-foam chemistry.

Digression:  I intend to milk my golf cart bank until 2024 when I retire.  At that point I’ll likely build a bare-cell LFP 100Ah bank.

[The situation was even more dire on a later weekend