Off-Grid Shed Panel upgrade options

[SPFycool]

Hey guys. I've been using a small-scale off-grid system in my detached shed for a couple years now. Just a tiny 30w panel and a single 12V SLA battery (power wheelchair type) with a cheap Amazon PWM controller. I'm done playing around with a toy system and want to actually do something other than power a couple lights and charge a phone, etc.

I reached out to a local solar installer to see what kind of "misfit" panels they had they would be willing to sell for cheap. Here are the choices I have, all for $150/ea

1x Solarworld SW285 Mono (285 watt) - Used briefly, but in excellent condition.
1x Unknown brand 285 watt - Brand new
2x LG Mono black 365 Watt - Panels are new, but frames are detaching from the panels.

All the panels are the same size dimensionally, so it's just a matter of picking which one would be best.

Obviously the LG's make the most power, but I worry about the frame detaching. I could probably use some sort of resin to reattach the frames and reinforce them to some degree.

I was originally looking for around the 300w range, but if I take both LG's I may see if I can grab them for $275 total or something. $0.40/watt is a damn good deal!

I'll also need to plan the rest of the system once I pick the panels. Usage case for this would be to run some small power tools (palm sanders, mini saw's, charge cordless tools), lights, fans, stereo. More wattage the better. 700+watts from the LG's would allow a decent (24V?) battery bank with a nice MPPT controller.

Any thoughts?

[Mike90250]

I'd skip any panel with visible problems, that leaves just the

1x Solarworld SW285 Mono (285 watt) - Used briefly, but in excellent condition.

Find out what it's voltage s are Voc, Vmp and you will need a MPPT controller to charge your battery,

[SPFycool]

Find out what it's voltage s are Voc, Vmp and you will need a MPPT controller to charge your battery,

I believe they are all grid-tie ~36V panels outputting between 19-26amps max. I can gather more info info on them, just forgot to take pictures of the spec label on the back when I inspected them.

Also, the LG panels themselves were in pristine condition aside from the glue holding the frames in place. The guy said it was a MFG defect that does not appear to be affecting performance of the panels.

I didn't realize how many more MPPT controllers are on the market now. I'll probably need some help eventually selecting one along with a 24V battery bank.

[SPFycool]

Hey guy, just wanted to post an update with some additional questions on this project.

I ended up going with the 2xLG panels. I inspected them further and the panels themselves were in pristine condition and never even used. The only tiny flaw was with the aluminum mount on the outside of the panels. There is a tiny bit of play in a couple spots. A bead of adhesive/caulk should seal them up nicely.

The model of the panels are LG365Q1C-A5

Specs:
Maximum Power (Pmax) = 365
MPP voltage (Vmpp) = 36.7
MPP current (Impp) = 9.95
Open circuit voltage (Voc) = 42.8
Short circuit current (Isc) = 10.8
Module efficiency (%) = 21.1

Got them for about $0.40/w

I haven't hooked the panels up to test yet as I need to completely rewire my shed first.

I've already purchased an EPever 40A MPPT controller and am using it with my current setup just to test it out. If my calculations are correct, the controller will be charging the 24V batteries at 30A max, so I should be fine I don't plan on adding more panels in the future, mostly because I really won't physically be able to on the roof of the shed.

Next question is in regards to cabling and fusing. I've heard conflicting information in regards to fusing on the PV input on the controller. I have a small inline fuse on my current setup on the input side, but not sure its needed for the new setup.

Also, i'm aiming to run 12AWG to the controller. Only need roughly 15ft, so losses should be minimal (<1%) with the ~70V PV input.

Still haven't settled on batteries or an inverter yet. I definitely want to go with 24V over 12V though. Budget for batteries is around $400. Trojan has a few 12V RV batteries in the 100-150Ah range that may suite me. 4x6V golf cart batteries are bit outside my budget, but I did contact a local Trojan dealer that is also a Golf cart dealer to see what they have.

Any other suggestions?

[littleharbor]

Look at Costco for their Golf Cart batteries. Last I checked they were about $86.00 a piece. Of course you likely have core charge or exchange cores if you have.

[SPFycool]

Look at Costco for their Golf Cart batteries. Last I checked they were about $86.00 a piece. Of course you likely have core charge or exchange cores if you have.

Interesting! I'll have to check that out. Thanks!

I haven't really looked very deeply into Golf cart batteries as the cost for 4x6V seemed to be coming out to $600+. Looking at some reviews of the Costco batteries, they seem to only be rated for 300 cycles at 50%, but I haven't found any data sheets. I also see references to "Trojan Pacer" batteries that got for around $90 that look to have better cycle ratings. Don't see these listed on Trojan's site, so they must be rebadged/reduced cost models or something? I'll check out what the have locally, though the closest Costco is roughly an hour drive.

I do have a couple old 12V batteries that I could use as core exchanges to save that expense.

As far as my cycle usage on the batteries. I won't be using them every day and most likely only using 15-25% D.O.D or roughly 500-800Wh when I am using them. Also plan to store inside over the Winters. Just trying to keep the cost down as I know I won't be using the system very heavily, but would like enough juice when I do to maybe run a 12AMP saw for a few minutes at a time. The 700+ watts peak PV should have no problem keeping the batteries topped up. I actually worry I may have too much PV wattage for a relatively small battery pack. I sized it with the intent on going Lithium in the future. Another reason I am trying to keep this initial battery cost down a bit.

[littleharbor]

If you can come up with a graph with cycle vs. DOD you should see much better cycle life at 20- 25% DOD If you have to regularly discharge to 50% DOD you should be using larger batteries. Your intermittent usage sounds like it should give you many years of service from the golf cart batteries, especially if charging parameters are set up correctly and you regularly check the SOC with a hydrometer. These batteries are around 210 amp hours so @ 24 volts you need 20 to 25 amps of charging power from your CC

[SPFycool]

I did a quick check at a local BJ's Wholesale (no Costco's local to me) to see what they had in stock. Found a bunch of Interstate XGC2 6V 210Ah Golf Cart batteries for $93.99/ea. Can't find the exact model on Interstate's site, but I found this which seems to match very closely to the specs. https://www.interstatebatteries.com/products/pf-gc2-utl?productLine=golf-car&subcategoryKey=&ignorecategoryid=true

The 6-month free replacement does sound appealing as I should have a decent understanding of the performance of the batteries by then and replace any duds.

It would solve my concern about too high charge current on a smaller battery and fits in the budget. My controller should be outputting up to 30 amps in full sunlight, so I should have no problem keeping them healthy. Pretty much an ideal situation in fact!

I guess I didn't want to gamble on possible low quality batteries, but then again it's not like i'm depending on them for daily living. Just a small workshop to run tools, lights and a small water pump to irrigate some raised garden beds. I may just grab them!

Thanks for the advice littleharbor!

[littleharbor]

You're welcome. Like to hear how it works out for you down the road.

[SPFycool]

Getting closer to pulling the trigger on batteries. Leaning towards the 4x6V golf cart battery config. Now i'm also shopping for wiring and fuses/breakers to protect the system.

Question 1: I'd like a quick disconnect for the PV input to the controller. My panels have an MPP current rating of 9.95A. 10A wouldn't provide much wiggle room, but would be very quick to disconnect in the event of an issue. Should I go with 10A or 20A? I was hoping to find something like a 12A, but it doesn't seem very common.

I'd like to use something like THIS

Also, plan to use a 40A version of the above between the controller and batteries.

Question 2: For series-connected batteries, is it necessary to have fuse blocks between batteries, or just between the controller and load (inverter)?