New here and need saome good advice for off-grid

Re: New here and need saome good advice for off-grid

Welcome to the forum.

Some of those specifications seem a bit off. For instance "150 vdc 3000 w inverter 12/24/48". An inverter will have a fixed system Voltage of 12, 24, or 48 Volts DC. Its output will be 120 Volts AC or 240 Volts AC or 230 Volts AC for most applications outside North America.

4 x 180 Amp hour VRLA/AGM batteries of what Voltage? Again this comes back to what the actual system Voltage will be and how that relates to putting multiple batteries together.

I have never seen a 40 Amp MPPT charge controller and would be suspicious of one if I did. There are many "no name" controllers out there that claim to be MPPT but aren't really.

3 solar panels of 200 Watts is another matter. They could be "12 Volt" panels or "GT" panels. Here you need to get the numbers for Vmp, Voc, Imp, and Isc not just the wattage.

Maybe we're going at this the wrong way: could you tell us what you're trying to achieve and where?

Re: New here and need saome good advice for off-grid

Okay, an off-grid system is based on the batteries so let's look at the two choices proffered:

Four 180 Amp hour 12 Volt batteries configured for 360 Amp hours @ 24 Volts. This is two parallel strings of two in series. Using 25% depth of discharge you'd have about 2kW hours of power from these. You will probably find that to be on the low side for supplying your needs.

Two 300 Amp hour 12 Volt batteries in series would be 300 Amp hours @ 24 Volts. This will be even less power available; about 1.8kW hours.

For what it's worth, I have a 24 Volt system powering my off-grid cabin, including standard refrigerator, water pump, satellite Internet access, and lighting. It has 232 Amp hours of battery and 700 Watts of panel. It works fine in the Summer when there is lots of sun available. It would be impossible in Winter when our daylight hours shrink to 6. If I were to add more load I'd either have to run the generator more or increase the batteries and panels.

If you could push your battery bank size up to around 400 Amp hours you would be able to meet your 2.5kW hour goal (which is realistic). It is best not to do this with multiple parallel batteries if at all possible, as they can have problems keeping the current even between batteries during discharging and charging.

As for recharging them, you should try to size the array based on at least 10% peak charging current:
10% of 400 Amp hours = 40 Amps (@ 24 Volts). Factor in the average production derating of the panels (77% typically) and you'd have an array of (40*24/0.77) 1246 Watts. If using the 250 Watt panels that would be five, a number that's 'awkward' to work with for an array. If at all possible go up to six: three parallel strings of two in series. You will likely need two in series as panels of this size tend to have a Vmp around 30 which is too low for properly charging a 24 Volt system.

You should also be looking at a generator to supply power and charging when the sun doesn't shine enough. It always pays to have a back-up source.