Working with what I have (shade, distance, old panels)

[roanbox]

I recently bought a cabin. It's off grid. It came with some equipment that the former owner was planning on using. It's a puzzle for me. Here's what I have to work with:

8 75 watt Siemens SP75 panels.
Xantrex c40 charge controller
24 volt battery bank
xantrex prowatt 800 watt /24 volt
some 10 AWG wire

I've mounted the panels in the only really good place there is, which is about 90 feet from the cabin. Everything else gets shade (trees, in a valley, etc.) The siemens panels are either 6 or 12 volt. I could wire them to be 24 volt, but it seems that at 24 volts with 10 awg wire, i could only go 17 feet. To go 90 feet with 24 volts, I would need 1/0 wire? Not going to happen.

I see two options.

1. Build a little hut for the batteries and charge controller and inverter near the solar panels, and then run 120volt AC wire to the cabin. The cabin, by the way, is not wired in any way for electrical. AND, the inverter is set up for a regular household AC plug. I don't think it would be wise to use a 100' extension cord in a permanent way running to the cabin. In this case, I would need to somehow convert the AC plug into something I could run underground. Is this possible?

2. Change some of the equipment. For example, if I changed the charge controller to one that could handle higher volts, and then adapt that to the 24 volt battery bank, I could run a higher voltage from the solar panels and get more distance with the 10 awg wire.

I am all ears.

[johngalt]

My panels are 12v 145 watt panels. I have 2 strings of 5 producing about 110 volts at 8 amps max. I used 10 AWG solar grade wire to run about 90 feet from the shed to the utility closet in the house. I have two circuits each with a 15 amp breakers combining them both at the panel. I've seen little to no voltage loss using that gauge, at that distance, for that voltage. At the breaker panel to the charger I use a much larger gauge because the circuits are combined for higher amps. I am using about 24 inches of #4 from the breaker box to the charge controller and the same from the CC to the batteries and the same from the batteries to the inverter although the inverter specs say I only need 10 awg from a 48 volt battery bank.

I would configure the panels in series to get 36 to 48 volts per string using a MPPT controller. This should insure you have more than enough volts/amps to keep the 24 volt controller well fed for longer periods during the day.

You will need to check your controller specs to see what it can handle.

This is just a rough SWAG as I have no idea about your panel specs or your controller specs.

I also used those dual post fuse connectors from Blue Sea. They were the perfect solution to my setup. The charger goes to one post and the inverter connects to the other.

[roanbox]

Good.

That's pretty much what I'll do. Here's my setup, now, in progress, thanks to Real Goods (awesome place).

still using the existing 8 Siemens sp75 panels - wired 10awg in two strings of 4 panel series to midnight solar combiner box, 15a breakers, then tristar mppt charge controller.

i got a couple of kyocera 205watt panels that I will add to the same combiner box (split bus) and to a separate sunsaver mppt charge controller.

then to disconnect, then 24v battery bank, then disconnect, then to outback magnum 1000 watt sine inverter. all should work well like this.

I'm sure there will still be some head scratching, but I think I get the picture now. MPPT is the way to go. And looking at the Kyocera panels, they're huge. My older siemens panels aren't so lightweight after all. They're about half the size. 75 watt vs 205 watt.

[roanbox]

distance

and yes, the distance between the combiner box and mppt charge controller shouldn't be an issue whatsoever.

the price for 8 gauge was not terribly different from 10 gauge.