Hello everyone, happy new year. I'm looking for some advice. Here's my situation.
I currently have thirty-eight 185w Suntech panels in a grid-tie setup using Enphase microinverters. The system has worked well for me so far. I generate 23Kwh/day on average, although here in PA the output varies considerably depending on the weather and season. Lately I've been thinking about how I could make use of my panels during a long term grid outage (aka SHTF). I have a Honda EU2000i to handle any short term grid outages.
My goal is to have the proper equipment on hand to manually convert my grid-tie system to a light use off-grid system in response to a serious extended outage. I'd like to be able to run my household size fridge, microwave, toaster, and some electronics (not concurrently) during daylight hours, and just a CFL bulb or two at night. I understand that I'd need the following things:
1.) MPPT style charge controller
4.) Wire, connectors, breaker/fuses
For the charge controller, I'm looking at the OutBack FM80. It seems like a quality piece that provides a lot of flexibility. Items #2 through #4 are where I'm in need of advice.
Because I'm only planning to convert my system to off-grid in the (unlikely?) event of a long term grid outage, I'm not too keen on spending huge sums of money on lots of batteries that will just sit around degrading or on $2,000 inverter that I may never use. This has me leaning more toward a simpler 12v system. At the moment I'm considering just a single Concorde AGM 108Ah at $300, or maybe even just stealing the 12v batteries from our family cars. Anyhow, this also means a 12v inverter. I'm considering the Xantrex SW2000. It seems okay for $350 and I like that a decent 12v inverter is good to have around anyhow. So for not much money ($600 controller, $350 inverter, possibly $300 battery), I could have the main components on hand to go off-grid during a long grid outage.
The downside of this cheap configuration (aside from the obvious fact that it's small) is that I don't think it will really allow me to leverage the thirty eight 185w panels that I have installed. If I understand correctly, with the Outback FM80 I'll be limited to 1250 watts with a 12v battery system. Does this mean that I'm limited to feeding a maximum of 1250 watts to the FM80 from the panels? Could I wire more (or even all?) of my panels to the FM80 so that I'm practically guaranteed 1250w of constant power delivery even on a cloudy day, since I have all these extra panels to spare? I think this is really the question that I'm most interested in.
My original thought was to wire 3 panels in series (185w x3 @ 105v), and then run two of those in parallel to deliver 1110w @ 105v to the charge controller. Of course, that is on a perfect day - and not even then. Most of the time it would be producing substantially less than 1110w. I supposed that I could manually keep an eye on the weather conditions and connect more panels to the controller only on a cloudy day. But that seems dangerous. What if the sun suddenly pops through the clouds for a minute? Will the charge controller just ignore the excess power delivery? Will it simply trip the 80 amp DC breaker on the battery side of the controller? Do I need a breaker on the PV side of the controller to protect against this? Is this simply a stupid idea?
I have considered the 'big budget' alternative - which would include a couple thousand dollars in a 48v battery bank and an Outback FX3048T 48v inverter, but I'm having trouble justifying the expense for an unlikely scenario. However that would allow me to legitimately feed in 5000 watts from the panels per the Outback FM80 specs.
Lastly, regarding wiring, what is the acceptable gauge wire to run from the 3 panels in series to the charge controller over 75 feet? What about from the charge controller to the battery and inverter? I've seen recommendations for 3/0 or even 4/0 for 12v @ 2000w, but it seems like the Outback charge controller only accepts #2, so I'm confused about that.