Any tips on my setup?

[Sunking]

Hmm, interesting, could be. What do you think the multiplier would be when using MPPT?

What multiplier? There is no multiplier and causing you to make poor decisions and opinions based on Junk Science.

MPPT Output Current = Panel Wattage / Battery Voltage.

Your 40 amp MPPT Charger maximum Input is 520 watts. Its maximum Voc Input = 92 Volts. Read the manual.

Your Controller is incompatible with your panels unless you are just using 1 panel. With 2 panels you are screwed twice over. You cannot wire them in series because you will exceed the maximum Voc input. 3rd panel is out of the question, and screws you a third time. 3 is a prime number which means you only have 2 possible panel configurations of all in series or all in parallel. Something expensive happens when you put 3 or more panels in parallel. It requires you to use fuses, 3 times the amount of much larger more expensive wire.

With either 2 or 3 of those panels you need a MPPT Controller with at least 150 Voc input. Either a 60 amp controller using two panels, or 80 amps with 3 panels and a 200 Voc input. Then you get to wire all the panels in series with small wire and just one set. You pinching pennies is going to cost you a fortune. Your way no matter what you do is a 500 watt system at best from 900 watts of panels.

[Wrybread]

What multiplier? There is no multiplier and causing you to make poor decisions and opinions based on Junk Science.

As I explained a few times, by "multiplier" I'm referring to predicting an estimate of actual PV output versus stated ratings. Thanks to this website I can see what I was looking for is the PTC rating, which I can look up here:

http://gosolarcalifornia.com/equipment/pv_modules.php

And I can look up how it varies throughout the year in any given region here:

http://pvwatts.nrel.gov/pvwatts.php

Furthermore my panels are flat mounted, so the multiplier (or percentage of their output if you prefer) is going to be even less.

MPPT Output Current = Panel Wattage / Battery Voltage.

Your 40 amp MPPT Charger maximum Input is 520 watts. Its maximum Voc Input = 92 Volts. Read the manual.

Your Controller is incompatible with your panels unless you are just using 1 panel. With 2 panels you are screwed twice over. You cannot wire them in series because you will exceed the maximum Voc input. 3rd panel is out of the question, and screws you a third time. 3 is a prime number which means you only have 2 possible panel configurations of all in series or all in parallel. Something expensive happens when you put 3 or more panels in parallel. It requires you to use fuses, 3 times the amount of much larger more expensive wire.

Where are you getting your info from? Here's the manual:

http://www.aasolar.co.nz/Instructions%20-%20A%20Series.pdf

It clearly says the maximum Voc input is 100 volts. But even if it was 92 volts, that's still perfect for two panels in series (each of which is 46 volts open circuit). But since its the roof of an RV and there's shade issues, I'll probably go with parallel wiring anyway.

And for the 3 panels, the plan I'm half considering at the moment is to only expose (or connect) the 3rd panel (all of which are wired in parallel) when its cloudy. So it's essentially two 300 watt panels flat mounted, wired in parallel. Or I might just go with the 2 panels and keep the 3rd panel for another project. Seems a shame though, since here on the Northern California coast it's cloudy for weeks at a time, especially in summer and winter, and it would be nice to have a way to occasionally boost the power when needed.

Thinking out loud now, but like most modern MPPT charge controllers, my controller outputs its data through a serial interface. There's no reason a Raspberry Pi or similar couldn't trip a relay that connects and disconnects a 3rd panel depending on the current charge conditions. Or I can just manually flip a switch of course.

[Wrybread]

Hmm, what happened to the reply I posted?

[sensij]

> Use PVWatts

Thanks, very interesting. You're talking about this website, right?

http://pvwatts.nrel.gov/

Yes, that is the one. A very good grid tie system can be represented reasonably well with "premium" panels and an 8% loss factor. For off grid panels, I would use those same assumptions to set an upper estimate to the DC production you might see. You can apply the efficiency curve from the charge controller manual to calculate how much of that is lost converting down to the battery voltage.

One thing to understand about PVWatts is that it is calculating hourly averages. Instantaneous power spikes of a few seconds to minutes are possible, especially with reflections from the edges of clouds. As long as your charge controller is operating properly, it will handle it. 3 panels in parallel meet the Voc and Isc requirements for the Tracer 4210RN, and it will let you know if it sees values outside of its limits. Despite Sunking's misgivings, the 40 A CC ought to work, although you'll be leaving energy on the table relative to what you'd produce with a 60 A CC.

You would probably be better off with a 4th panel and moving to a 24 V setup... the panels, CC, and batteries would support it, but you'll have to see if your inverter is compatible. You'd have to keep an eye on the charge rate through, maybe cover part of the panels equally on both strings during the times of the year in which you'd be hitting the batteries too hard.

[Wrybread]

I posted a reply here but it said "unapproved", and then it was deleted. Mod, what's up?

[SunEagle]

Hmm, what happened to the reply I posted?

It had some weblinks that our software sent it to review for approval and made it unviewable until a MOD said it was ok.

[Wrybread]

> It had some weblinks that our software sent it to review for approval and made it unviewable until a MOD said it was ok.

Aha, makes sense, thanks.

[J.P.M.]

One thing to understand about PVWatts is that it is calculating hourly averages.

PVWatts does not calculate hourly averages.

[sensij]

PVWatts does not calculate hourly averages.

OK, more formally, it is approximating the hourly output by using the angle of incidence based on he solar position at the midpoint of each hour (xx:30),combined with irradiance data in the selected TMY file. The point being, the hourly production it models will not reflect real world observed values over shorter periods of time, even if the environmental and equipment assumptions are perfectly matched to real world conditions.

[Wrybread]

Thanks Sensij, great info. And man, tough crowd on this website. An odd amount of bickering over semantics.

[J.P.M.]

Thanks Sensij, great info. And man, tough crowd on this website. An odd amount of bickering over semantics.

It may seem like semantics to the uninformed, but it isn't. It's the way the model works.

Saying it calculates averages is simply incorrect, as a quick read of the help screens will enlighten. Saying so may lead others who are unfamiliar with what they're doing to incorrect assumptions/conclusions, and result in perhaps costly errors based on the incorrect information.

Take what you want of the above. Scrap the rest.

[J.P.M.]

OK, more formally, it is approximating the hourly output by using the angle of incidence based on he solar position at the midpoint of each hour (xx:30),combined with irradiance data in the selected TMY file. The point being, the hourly production it models will not reflect real world observed values over shorter periods of time, even if the environmental and equipment assumptions are perfectly matched to real world conditions.

Close enough. Thank you for the correction.

[Sunking]

Where are you getting your info from? Here's the manual:

From the manual, page 10. You might try using the USA Model, not New Zealand's.

http://www.aasolar.co.nz/Instruction...A%20Series.pdf

It clearly says the maximum Voc input is 100 volts. But even if it was 92 volts, that's still perfect for two panels in series (each of which is 46 volts open circuit).

Wrong. does not matter if the Controller Voc is 92 or 100 volts, you cannot use two panels in series. The panel spec is at 75 degrees. You have not applied any temperature correction factor of 1.25. That means if the panel spec Voc = 46 volts is adjusted to 46 volts x 1.25 = 57.5 volts.

As for shade, no problem, you have NO POWER to worry about.

[Wrybread]

Two 46 volt solar panels in series is 92 volts. Are you seriously saying that's not the case?

But anyway, as I said about 10 times, I'm wiring them in parallel.

> As for shade, no problem, you have NO POWER to worry about.

Sorry to be the one to have to tell you this, but you're not making any sense.

[sensij]

Voc varies with temperature. You'll see a temperature coefficient on the panel's datasheet... typically around -0.3%/K, or -0.14 V/K. If the panels are 46 Voc at STC (25 deg C), it needs to be adjusted for the minimum temperature they'll see. Minimum design temp for Stockton is -3 deg C (see link below), so that would be a 3.92 V increase, raising the 46 Voc panel to 49.92 V. Two panels in series just barely clears the 100 Voc limit for the Tracer charge controller.

http://www.solarabcs.org/about/publi...map/index.html

However, if the Voc is really that high, forget what I said about needing a 4th panel. You could support a 24 V battery with the three panels in parallel, more efficient overall and less expensive wiring.