Making a parts list for new 24V system with used Santan panels

[jkb458]

I should be receiving my 250W used Santan panels this week. I haven’t ordered anything else yet. I initially planned to use a LV2424 all-in-one, but they keep going out of stock…and I can see some benefits of just building a 24V system.

I’ll list the main parts I’m planning to use, based on Will’s 24V blueprint. If anyone sees any issues, or has other suggestions, I welcome the input! I’ve never done anything solar before, but my husband and I built our own house. Surely, we can do this.

(12) 250W Santan T-Series used panels. Wired 3S4P.

(2) Epever Tracer BN 40A with MT50

Giandel 24V 3000W Inverter

(2) Ampere Time 24V 100 Ah batteries

I think I’ll need 12 pairs of the MC4 connectors. After wiring in 3S4P, should I tie them together with pigtail connectors before going to the SCC, or should I be using a combiner box? I have read A LOT on this forum, but I want to make sure I’m ordering what I need.

Thanks!!

 

[MisterSandals]

(12) 250W Santan T-Series used panels. Wired 3S4P.

Your SCC must allow max input voltage a bit over 3x the panel Voc to allow for temperature induced voltage increase.

12 x 250W = 3000W
3000W / 25.6V = 117A available for charging. A single BN 40A will leave about 80A on the table.

You could split your array into 3 parts. 4 panels east-isn (1000W / 25.6V = 39A), parallel with 4 panels south (39A) and parallel with 4 panels west (39A).

This will maximize your limited 40A charging capability. Your charging will start early with your east array and finish late with your west array.

If you want all your panels (needlessly) to face the same direction, you should get close to 120A of SCC charging capacity.

 

[rmaddy]

The panels should already have an MC4 connector on each wire so you should not need 12 pairs of MC4 connectors.

With 3S4P you need a combiner box and each of the 4 strings should be fused. You might need 4 pairs of MC4 connectors to connect each string to the combiner box.

Post the actual specs of your panels and the charge controller.

 

[jkb458]

I was planning to use 2 of the 40A controllers (see my OP). I had hoped it would work well to put 6 panels facing east and 6 facing west, then run 3S2P to each scc. I could probably only face south by tilting some of them. I wondered if it might be a waste of money to buy a higher amp scc, because it seems unlikely that the used panels will produce anywhere near 3000W.

 

[rmaddy]

OK, then 3S2P per SCC doesn't require a combiner box. You need a pair of Y connectors to connect the two strings together. Then a second pair of Y connectors for the other set of 3S2P.

 

[jkb458]

Panels:
250W
VOC 37.6V
VMP 30.3V
ISC 8.85A
Max Pwr Cur 8.27A

Charge Controller (using 2 of these)

40A MPPT Charge Controller Nominal System Voltage: 12V, 24V
Rated Charge Current: 40A
Rated Load Current: 20A
Max PV Open Circuit Voltage: 150V / 138V
Max PV Input Power: 520W (12v battery) / 1040W (24v battery)

 

[rmaddy]

Why are there two values for max PV Voc? Your panels in 3S should be OK even if the limit is 138V. You'd have to get the panels down to about -50ºC (-58ºF) to exceed 138V.

But you are planning 1500W per SCC and you have a limit of 1040W with your 24V system. Given that they are used you probably won't see 1500W but you should get over 1040W. I don't know if you can over panel that SCC.

You are also losing a lot of current with this combination of panels and SCC. If new, those panels in 3S2P could potentially result in about 70A charge current to the battery but the SCC will limit it to 40A.

 

[jkb458]

OK, then 3S2P per SCC doesn't require a combiner box. You need a pair of Y connectors to connect the two strings together. Then a second pair of Y connectors for the other set of 3S2P.

Why are there two values for max PV Voc? Your panels in 3S should be OK even if the limit is 138V. You'd have to get the panels down to about -50ºC (-58ºF) to exceed 138V.

But you are planning 1500W per SCC and you have a limit of 1040W with your 24V system. Given that they are used you probably won't see 1500W but you should get over 1040W. I don't know if you can over panel that SCC.

You are also losing a lot of current with this combination of panels and SCC. If new, those panels in 3S2P could potentially result in about 70A charge current to the battery but the SCC will limit it to 40A.

Two values for max PV Voc: The product states 150V (138V @ 77 degrees F) I don't understand the range.
So, I would be better off to just use a single charge controller? 80A? 100A?

 

[rmaddy]

You need two SCC that support closer to 70A each to take full advantage of the panels. But again that assumes new panels. Maybe two that support a bit less would be fine but 40A probably means giving up a lot of potential.

 

[jkb458]

You need two SCC that support closer to 70A each to take full advantage of the panels. But again that assumes new panels. Maybe two that support a bit less would be fine but 40A probably means giving up a lot of potential.

I appreciate the help. I may just not use all 12 panels. It's getting pricey to try to use all of them. That leaves me some spares in the event of damage or failure. Thanks again!