I'm ready to buy a couple more panels and a new combiner box, breaker box, charge controller and breakers. Here's what I have designed and would like a 2nd pair of eyes to look at my calcs to see if I'm in good shape.
PV array = (3) PowerUp BSP 20. I currently have (1) and am adding (2) more to the system
BSP 20 specifications
Maximum Power (Pmax) 20W
Voltage at Pmax (Vmp) 17.3V
Current at Pmax (Imp) 1.20A
Short-circuit current (Isc) 1.30A
Open-circuit voltage (Voc) 21.7V
Combiner Box
Midnite Solar MNPV6 Combiner Box
Breaker Box
Square D QO24L70RB Square D QO Load Center
Charge Controller
Xantrex C35 35A, 12/24V PWM Charge Controller
These panels come with 15.5’ of #18 AWG cable pre-attached, so I will be using it to go to the combiner box box. It seems sized correctly for the Isc of 1.3 x 156% = 2.028amps per panel. OR do I need something other than #18awg? I cannot find #18awg in the NEC wire table for 12v systems. I don’t plan on using the entire 15’-6” of cable and will probably end up cutting it down to about 10’-0” in length to get to the combiner box.
I am going to wire them individully into a Midnite Solar MNPV6 Combiner Box and then send the “paralled” combined output to the charge controller. This will give me 60watts at 12vdc nominal. Each panal will go to a 10amp breaker? Again, I cannot find #18awg in the NEC wire table, so I’m assuming that #18awg cannot carry more than 10amps?
The combined wire I will use from the Midnite Solar MNPV6 Combiner Box will be rated for the total Isc of 1.3amps x 3 x 156% = 6.084amps. the wire run length from the combiner box to the breaker panel before the charge controller will be approx 10’-0”. So I will use #8awg for the run from the combiner box to the breaker box. I will use a 40amp breaker in the breaker box before the charge controller.
The last run of wire is from the breaker box to the charge controller. I’ll upgrade my charge controller from a Sunwise Sunguard to Xantrex C35 35A, 12/24V PWM Charge Controller. The wire from the breaker box to the charge controller will only need to go about 6’-0” at the most so I will again use #8awg from the breaker box to the charge contoller. Allowing for expansion in the future.
My plan is to eventually add a couple more BSP20 panels, so I end up with 5 panels. The #8awg should handle the upgrade to (5) panels in the future as well as the rest of the system.
Thoughts? Comments? Suggestions? Please...
Thanks so much for all the great info I have learned so far through this forum.
James
