What to do with mothballed equipment?

[Intheswamp]

Back in 2001 I started building a small cabin down in the swamp. I had a builder doing the work and I ended up getting ripped off bigtime. The cabin sits down in the swamp without windows or doors, etc.,. Lessons sometimes are learned very hard...this was my first (and only) large building project. Regardless... The proposed cabin is way off the grid so during that time I bought four Shell SQ140 140w/24v panels and a 24-volt Trace "power panel". All of this is still sitting new in the box and crate. I only opened the crate once to retrieve the manual for the Power Panel and now can't seem to find it (it's gotta be here somewhere!). To be honest, I'm not even sure what all is included in the "power panel". SW4024 sounds familiar and it has an automatic generator transfer switch, but that's about all I remember. The equipment is stored and I need to pull it out and see exactly what I have, but that may be a week or two away before I'm able to get to them

What I'm trying to figure out is, is how to utilize the solar panels in the best way. Finances are limited but what I want to do is to set up a 225Ah or 450Ah 24-volt battery bank for running household essentials...lights, fans, small television, phone charging, maybe power a computer/modem/router. I'm planning on running our generator periodically for powering our refrigerators, auxiliary battery charging, and other heavy tasks.

I know I need to crack the crate open and see what exactly is included in the power panel but I know technology has changed since 2003 (when I bought this equipment). I'm considering going with an MPPT controller as I figure if the controller included with the power panel (if one is even included with it) would most likely be PWM and I'd like to eek out as much power as possible. Back in 2003 there wasn't nearly as much info available as there are now and panels were definitely higher priced back then, thus my basically 560 watts in four panels...but, they're paid for. ?

I've been looking at the specs on these panels, which I've attached in a jpeg, and it appears, in my feeble mind, that the voltage will be too high to run in a single string to most charge controllers. The STC states a Voc of 42.8v so, from what I understand, four of those in series would (literally) blow up a 150v SCC. I'm in south Alabama and temperatures in the winter are all over the place...from the 80F's down into the 20F's....the day after the cold nights we often see the daytime temps stay in the 40-50F range, and sometimes in the upper 30's. From this data, I'm thinking the option for these four panels would to do a 2p2s...I think I wrote that correct....parallel two pairs of panels and then wire the pairs in series. That would keep the voltage below most SCC limits...I think. The drawback that I see is that pv wire size will need to be larger for the lower voltage...and I'm not even sure what length I'm talking about yet.

So, at least in regards to panel wiring, am I on the correct path? Any thoughts about this mothballed equipment is appreciated. As for the old cabin, I haven't ruled out doing some more work on it and installing the pv system down there...got lots of work to do to get that going, but I've got a couple of guys interested in helping, so who knows?

I'm stumbling around here, but willing and needing to learn more...lots more.

Thanks for your feedback!
Ed

 

[rmaddy]

You didn't include an image of the panel specs.

If you have a 150V MPPT SCC then you are correct that you can't put your panels in 4S. 2S2P would be a good choice. Two in series. The other two in series. Those two strings in parallel. That's simpler than 2P2S since you only need one pair of Y connectors instead of two.

Depending on the exact temperature coefficient for Voc of your panels (somewhere near -0.3%/ºC) and the likely coldest temperature you could ever see, you might be able to use a 100V MPPT SCC with the panels in 2S2P.

 

[Intheswamp]

Sorry about the missing data! Here's the info on the panels that I'm pretty sure I have. Before spending any $$$ I'll definitely verify what I've actually got. Good deal on the 2S2P...I need to keep things as simple as possible. Thanks for the feedback!