backchannel: Why don’t we get more from 800w of panel?

From this thread on which I’ve really been enjoying lately. Lots of good discussions there, many clueful and experienced posters.

First off, this is OP’s (original poster, the originator of the thread) first post. This often ends up in a “walk-off” (my term, no response to comments or questions, and never heard from again). So don’t get your hopes up.

We have 8 100 watt solar panels mount on top of our travel trailer. We have an e-pever mppt solar controller and a Victron BMV 712, and 2 Battleborn 100 ah batteries > >

8x100w is the most expensive way to get it done, but their roof tetris might have dictated it.

It would be useful if they told us the rating of the controller, but such are the ways of the 1-post OP.

We installed 8 panels with the expectation of being able to take in between 400 - 800 watts. We have never seen above 400 watts, and we usually only see around 150 watts on a sunny day, and much lower on slightly cloudy days. > >

OP was half-right; 400w is quite doable and 800w is highly unlikely for various reasons, not the least of which being he is posting in the dead of winter when the sun is low in the sky. . Even if the controller is adequately sized (most people would go 60A, I’d likely do 50A) there is so much panel (800w:200Ah) that the bank is likely getting charged before solar noon when Big Numbers might otherwise be seen. The way to test the system is to disconnect the panels until solar noon then let them rip.

150w on a sunny day means nothing if we don’t know the bank’s state of charge and loads applied to the system; solar doesn’t make power until it is demanded. 150w of demand == 150w of solar power (assuming the solar config can meet the demand).

Because of the overpaneling (and assuming appropriate controller sizing) I’d expect something like

  • 400-450w harvest under clear skies unless big loads are applied
  • ~200w -300w under bright overcast
  • ~125w under overcast
  • ~75w under dark overcast or rain
  • maybe 700w max under rare/heroic conditions

Starting to see why I’d put a 50A controller on there? 50A at 12v = 600w. 50A at 14.2v = 710w. A 50A would likely never max out and have to clip.

You will be shocked, SHOCKED, to learn OP never answered any questions, responded to comments, or ever posted again (as of this writing). Starting to see why folks pick the people they think can be helped?