Lost on Solar!

[QinReno]

Forgetting about the "rules", a typical 100W solar panel will put out around 5-6A maximum, meaning at maximum sun. So, assuming you drew 100AH from your battery bank, it would take around 16 hours of full sun to charge it back up. So, 200W of solar would take 1/2 that long for recharge.
- https://www.amazon.com/Renogy-Watts-Volts-Monocrystalline-Solar/dp/B009Z6CW7O
"optimum operating current (Imp): 5.29 Amps, short-circuit current Isc: 5.75 Amps".

And this is assuming you actually could get full sun for so long. In practice, it might take a "lot" longer than 16 hours, because of time of the year, cloudy days, sun angle, on and on. No one ever talks about sun angle, but if you mount the panels flat on the roof, you'll hardly ever get the full current output for very many hours.

If you have a frig that draws 60W, that's 5A @ 12V. If the frig runs half the time, that's 5A * 12hr = 60AH over the course of a day, and would require more than 8 hours of "full" sun every day to keep from depleting the battery, if having only 100W of solar. Not a chance. Even 200AH of batteries would drain over time. So, just to run your little frig, you should have at least 200W of solar.

(I think this is correct).

 

[frater secessus]

No one ever talks about sun angle, but if you mount the panels flat on the roof, you'll hardly ever get the full current output for very many hours.

=insolation#insolation]Insolation averages (in hours of Full Sun Equivalent) assume the panel is flat, so that math is straightforward.

Tilting the panel will increase yield in most cases but that math is not as simple.


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[frater secessus]

=insolation#insolation]Insolation averages (in hours of Full Sun Equivalent) assume the panel is flat, so that math is straightforward.

Tilting the panel will increase yield in most cases but that math is not as simple.


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Ugh, can't edit in phone. Was talking about insolation averages: http://rvwiki.mousetrap.net/doku.php?id=electrical:solar:output#insolation

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[QinReno]

If I interpret this table correctly, in Phoenix in summer, you'll get about 7 hours of full sunlight each day, but it drops down to 3 hours in winter. As you go north from there, the numbers drop quite a lot. Then of course, the sun angle changes a huge amount between summer and winter too.
- http://solarinsolation.org/wp-content/uploads/2012/01/Solar_insolation.jpg

Then on top of that, if the panel is not directly perpendicular to the angle of the sun, you'll not get full Amps out either. I just have a 100W panel and put it out in the daytime, and if it's not direct on to the sun, the output drops way down. So I'm thinking having panels mounted flat on the roof will hardly ever give full 100% output when you need it the most.

Which all goes back to the comments I made in post #21.

 

[frater secessus]

Then on top of that, if the panel is not directly perpendicular to the angle of the sun, you'll not get full Amps out either.

Not on top of that.  It's baked into FSE:  equivalent hours of 1000w/m2 perpendicular light, as when the panel was rated in the lab.

One still has to derate for cell temperature directly at the panel or indirectly based on ambient.

I'm thinking having panels mounted flat on the roof will hardly ever give full 100% output when you need it the most.

Agreed.  Solar panels, no matter their location or tilt, will never give 100% output when you most need it.  There isn't enough light to capture at those times.  This is why solar + something else works so well.