24 volt system panel wiring

Re: 24 volt swsyem panel wiring

cliff4079 wrote: »

Should I wire these in 2 sets of two in series then parallel or just parallel all 4 of them together? My previous panel selection would have been the 2 sets of 2 to get the voltage up but the voltage is a bit higher on these so I'm not sure.

This will be for charging a 24v system with a Midnite KID controller.

The kid will be slightly more efficient (probably) with 4 in parallel. With 2x2, you will not need a combiner (fuse/breaker per string) and you can uses smaller gauge cables (much less copper expense--especially if you have to send the array power some distance).

Overall--It is probably a wash--But I would go with 2x2 and possibly an on/off switch (or DIN Rail breaker from Midnite) in the solar panel input so you shut down the controller for service.

Some people use the combiner so they can shut down one panel string at a time to debug low production problems (turn off a string, and the power output remains the same, you found the problem location). Off course, if you buy an AC/DC Current Clamp DMM (like this one from Sears), you can simply measure the panel string current (and other currents) directly.

Also, if either would work is one way more efficient than the other? My thought would be 2 sets of 2 in series/parallel would possibly provide better low light charging because of the constantly higher voltage on the PV side of the system even not in full sun and the MPPT controller would just create more amperage as voltage/light increases? Let me know if I am was off base here, I'm still new and learning.

You will not gain any power output from 2x2 array in low light--Panels output near Vmp as soon as you get weak direct sun (early morning/late evening) on the panels. At that point, the current is proportional to the amount of sun hitting the panel. If there is not enough light to hit (near) Vmp--Then there is virtually zero current available too.

If you have shading issues--A 1sx4p array may give you more power... 1 shaded panel, 25% array power reduction.

On a 2x2 array, 1 panel shaded gives you a 50% power reduction (entire string output is zeroed out by shade/drop in Vmp-shaded vs unshaded Vmp.

All in all--I probably would go with the 2x2 setup (less copper, less connections, no combiner box, get the DC Current Clamp DMM). But either configuration is fine.

Note that 4 panels is somewhat large for the Kid on a 24 volt system, about 33 amps typical maximum solar output will be clamped to 30 amp by kids... If you ever plan on adding more solar, you might want to think about a single Classic 150 vs a pair of Kids.

4x 310 Watt panels * 0.77 panel+controller derating * 1/29 volts charging = 32.9 amps "typical" maximum current

Will not hurt the Kid--Most MPPT controllers are designed to safely/reliably limit maximum output current.

-Bill

Re: 24 volt swsyem panel wiring

What do you mean by 4x1? 4 parallel by 1 series (just to be clear).

8 awg @ 20 feet and 8.42 amps?

Generic voltage drop calculator: 0.3 Volt drop per string

You could probably get away with 14 AWG wire too at 1 volt drop too.

From the combiner to the controller, you are looking at ~33+ amps -- So you will need some heavier gauge wire there.

If you are going to add panels to the array later--I would really look at 2 panel in series. Will make the wiring 1/2 as many runs (and breakers in the combiner box)--And much less copper too (1/4 or le$$ copper).

-Bill

Re: 24 volt system panel wiring

No worry, just trying to be exact/clear.

You could get a higher voltage Classic controller and do 4 panels on series.

System sounds fine. Check village drop /maximum current with calculator and NEC.

-Bill