Hi Everyone. I've been lurking on the site and learning, and really appreciate both the knowledge and friendly attitudes of people on the forum. My question today is about how to size and connect the wiring from the solar panels to the charge controller, which I'll get into in a moment. I think I have it right, but figured it made sense to ask the gurus here. Here's the overall system:
Totally off-grid, 200SF (10x20), insulated building (R51 ceiling, R19 walls, R21 floor) with a south-facing roof. We live in Maine (temps as low as about -20F but hasn't hit that for several years now) and I'm figuring only about 2.5-3 hours of sun per December day as theres a little bit of afternoon shade on the building, late in the day. Inverter charger will be a Victron Multiplus 24 volt, 3000KVA inverter-charger even though my load requirements are only about 1100 WH per day in winter, and perhaps 2200 WH per day in summer. I went with a larger inverter than I needed because I wanted enough excess capacity to run a coffee maker or some power tools now and then, and I may also use the building for another purpose one day. Battery will be 24V, either 100AH or 200 AH, which I'm still trying to figure out based on how often I want to fire up a generator (I'll probably post a second question about that, later).
I plan on installing four solar panels on the roof of this building, anywhere from 340-400W each, depending on the best deals and shipping/pickup locations I can find, and the vertical space limitations of the building. I really need to keep the panel size under about 70-72" long to fit it on the roof of this small building. For planning purposes, I've been using the upper end of specs for panels I'm interested in, which are (about):
35V VPM / 42V VOC
11A IMP / 12A Short Circuit
I'm planning to hook these up in a 2S2P configuration using 30A MC4 connectors at the panels and then running two wires (one positive, one negative) down to a 30A fuse or breaker (comments on which is better appreciated), then a marine cutoff switch, and then into the solar charge controller (will also be Victron). By my calculations, that should give me a max of 84Volts, 24 Amps INTO the charge controller. When I run the calculations through a solar charge controller calculator and account for a -20F temperature, it tells me that this could be a voltage as high as 105V. So.....
1) I'm thinking that a 150 volt, 60 amp charge controller should be fine. Correct?
2) I'm thinking that 14 AWG wire should be fine all the way down to the controller. Correct?
Thanks in advance for help, advice, and guidance.
Totally off-grid, 200SF (10x20), insulated building (R51 ceiling, R19 walls, R21 floor) with a south-facing roof. We live in Maine (temps as low as about -20F but hasn't hit that for several years now) and I'm figuring only about 2.5-3 hours of sun per December day as theres a little bit of afternoon shade on the building, late in the day. Inverter charger will be a Victron Multiplus 24 volt, 3000KVA inverter-charger even though my load requirements are only about 1100 WH per day in winter, and perhaps 2200 WH per day in summer. I went with a larger inverter than I needed because I wanted enough excess capacity to run a coffee maker or some power tools now and then, and I may also use the building for another purpose one day. Battery will be 24V, either 100AH or 200 AH, which I'm still trying to figure out based on how often I want to fire up a generator (I'll probably post a second question about that, later).
I plan on installing four solar panels on the roof of this building, anywhere from 340-400W each, depending on the best deals and shipping/pickup locations I can find, and the vertical space limitations of the building. I really need to keep the panel size under about 70-72" long to fit it on the roof of this small building. For planning purposes, I've been using the upper end of specs for panels I'm interested in, which are (about):
35V VPM / 42V VOC
11A IMP / 12A Short Circuit
I'm planning to hook these up in a 2S2P configuration using 30A MC4 connectors at the panels and then running two wires (one positive, one negative) down to a 30A fuse or breaker (comments on which is better appreciated), then a marine cutoff switch, and then into the solar charge controller (will also be Victron). By my calculations, that should give me a max of 84Volts, 24 Amps INTO the charge controller. When I run the calculations through a solar charge controller calculator and account for a -20F temperature, it tells me that this could be a voltage as high as 105V. So.....
1) I'm thinking that a 150 volt, 60 amp charge controller should be fine. Correct?
2) I'm thinking that 14 AWG wire should be fine all the way down to the controller. Correct?
Thanks in advance for help, advice, and guidance.