Any tips on my setup?

[Wrybread]

> Since you ask for comments - a general one: Learning more about the solar resource and it's potential and limitations might serve you well before you go much further.

That's what I'm doing by posting here and reading the various threads. But that said, I've been installing solar systems on my RVs and off-grid living situations for coming on 20 years. I'm not new to it.

I fully know that I'm pushing it a bit with the possibility of installing 3 panels of this size. And I'm not necessarily going to do it, but I'm wondering what the disadvantage of installing a 3rd panel that's default covered (i.e. not in use).

[J.P.M.]

There's a bunch of places in the forum I found the .77% multiplier. In this post for example:

https://www.solarpaneltalk.com/forum...too-much-solar

Are you saying you think panels output 100% of their rated power?





Thanks, that's a useful stat.




I'd say I didn't "screw myself" with anything, if I just installed 2 of them it wouldn't be the end of the world. But I'd really like that 3rd panel for cloudy days.

Does anyone have any comment on the plan to install the 3rd panel in a sometimes cover place, and uncover it on cloudy days? Is there a disadvantage other than the hassle?

Since you ask for comments - a general one: Learning more about the solar resource and it's potential and limitations might serve you well before you go much further.

[Wrybread]

> You would still have to .... use over current protection for each in a combiner box

Could someone possibly post a link to something that would work for that?

Or some more details?

[Wrybread]

False. Where are you getting this stuff?

There's a bunch of places in the forum I found the .77% multiplier. In this post for example:

https://www.solarpaneltalk.com/forum...too-much-solar

Are you saying you think panels output 100% of their rated power?

PV Watts. It reduces you Insolation around 15%

Thanks, that's a useful stat.

Output. Amps = Panel Wattage / Battery voltage. 900 watts / 12 volts = 75 Amps

You screwed yourself using Prime Numbers as it only leaves you with 2 options of configuring your panels of either all in series or all in parallel. You can get away with 3 panels if your controller Voc input is high enough to allow you to wire al panels in series. Your Controller wil not allow that forcing you to wire them in all in parallel loosing the some of the advantages of a MPPT Controller. NO 12 AWG is not large enough. .

I'd say I didn't "screw myself" with anything, if I just installed 2 of them it wouldn't be the end of the world. But I'd really like that 3rd panel for cloudy days.

Does anyone have any comment on the plan to install the 3rd panel in a sometimes cover place, and uncover it on cloudy days? Is there a disadvantage other than the hassle?

[Sunking]

- from reading this forum, I see that these 900 watts of solar panels are more like 693 watts (900 * .77).

False. Where are you getting this stuff?

- my panels are all permanently flat mounted, so their output is probably a lot less than that. Is there some formula for determining the output of a flat mounted solar panel? I'm in Northern California (latitude 38) if that's a factor.

PV Watts. It reduces you Insolation around 15%

I've read conflicting reports of what that amp rating means, but I think it means a maximum of 40 amps on either the PV or battery side?

Output. Amps = Panel Wattage / Battery voltage. 900 watts / 12 volts = 75 Amps

- since I'm connecting 3 solar panels, I can't wire them in series, correct? If so, 693 watts / 36 volts = 20 amps. Is 12 gauge wire sufficient for that?

You screwed yourself using Prime Numbers as it only leaves you with 2 options of configuring your panels of either all in series or all in parallel. You can get away with 3 panels if your controller Voc input is high enough to allow you to wire al panels in series. Your Controller wil not allow that forcing you to wire them in all in parallel loosing the some of the advantages of a MPPT Controller. NO 12 AWG is not large enough. .

- If I got a full 693 watts output from my charge controller, that would be 50 amps @ 14 volts. Should I worry about going that high? I'm thinking I'm not likely to get that much power from flat mounted solar panels, am I right?

Nope not even close. You need a 80 amp controller.

if I got a full 693 watts of output, I believe that would be a C8 charging rate (5400 watt hours / 693 watts = 7.7).

Right answer wrong units. Amp Hours, not Watt Hours.

So here is your tip: Get yourself a 80 Amp Charge Controller that wil allow you to wire your 3 panels in series.

[SunEagle]

The big issue I see is that 40Amp CC. It will limit you to about 500 watts max of pv at one time no matter how you wire them.

But maybe if you face them at different compass angles you could "cheat" and get some output from each 300w all day long. You would still have to wire them in parallel and use over current protection for each in a combiner box but at least you could get something out of all 3.

[Mike90250]

Quality MPPT charge controllers limit their output to the rated amps, so it's own limiter will kick it at 40A all by itself
It's good to avoid parallel panels, because you need combiner boxes and circuit protection. But on a RV, it's likely you will have shade issues somewhere on the roof, so you have to go parallel, and use Combiner Box and circuit breakers.

[Wrybread]

I'm setting up the solar on my new-to-me 24 foot Class C RV. I've been running a single 300 watt / 36 volt solar panel through a Tracer 40 amp MPPT charge controller, and things have been running great.

I just got a great deal on two additional 300 watt solar panels (same voltage and specs), and I have room for them on my roof, so I was thinking about mounting all three panels. A few questions:

- from reading this forum, I see that these 900 watts of solar panels are more like 693 watts (900 * .77).

- my panels are all permanently flat mounted, so their output is probably a lot less than that. Is there some formula for determining the output of a flat mounted solar panel? I'm in Northern California (latitude 38) if that's a factor.

- my battery bank is 4 Trojan T105s wired for 12 volt. From reading this forum, I gather that's 450 amp hours, which is 5400 watt hours.

- my charge controller is the Tracer 40 amp. I've read conflicting reports of what that amp rating means, but I think it means a maximum of 40 amps on either the PV or battery side?

- since I'm connecting 3 solar panels, I can't wire them in series, correct? If so, 693 watts / 36 volts = 20 amps. Is 12 gauge wire sufficient for that?

- If I got a full 693 watts output from my charge controller, that would be 50 amps @ 14 volts. Should I worry about going that high? I'm thinking I'm not likely to get that much power from flat mounted solar panels, am I right?

- if I got a full 693 watts of output, I believe that would be a C8 charging rate (5400 watt hours / 693 watts = 7.7).

- one thing I'm thinking, is that if my output gets near 40 amps, I can simply cover one of the panels. Since they'd be wired in parallel there's no down side to that, correct?

Thanks for any help.