building a system

[Steve Booth]

Our family has been running off grid for the most part for over a year and are in the process of building a new home. We have a large family of 8 in the house and large shop to supply. Currently we have 42/ 220 watt panels hooked to 8 banks of 100 ah GM batterys. This seems to be enough to supply us now so long as it is sunny for some of the day we hit float no problem. I have purchased a bunch of panels as I could afford them and we need a couple more to make 36 / 285's we have been running schnieder elec xw 5548 I am looking at the xw7248, any familiar with this inverter?

I am wondering what is your thoughts on battery's for this set up, with what I have now 800ah it will not give me 3 days of storage I figure I need at least 3 times the ah of storage. I will have a separate power shed from the house or garage so the battery's can be vented and will not affect our living space. initially I was looking at the salt water batts but they have seemed to go under. would you recommend 2v cells 6v cells ?
Thanks for any advice just a hillbilly trying to learn

[Rob Beckers]

Hi Steve,

That's a pretty large off-grid system!

First, I'd suggest having a look at an article I write about batteries. Maybe you already know all of it, if not it could be helpful: https://www.solacity.com/lead-acid-battery-care/

The Schneider XW series inverters are very good! A bit pricey for my taste (I tend to spec Magnum/Sensata (http://www.magnum-dimensions.com/) for most of my off-grid customers, due to the better-bang-for-the-buck ratio).

The basis for battery bank sizing is energy use. If you have a good idea of how many kWh's (or Ah) you need per average day in summer and winter that would be very helpful. Standard off-grid sizing is to have 3 days of energy in the batteries, so after that time (with nothing coming in) they are down to 50% state-of-charge (SOC). This isn't he be-all end-all of sizing, but it has shown to work well for most, in particular when it comes to winter.

Battery Voltage is irrelevant. The only reason that some are 6V and others 2V is size and weight. There's a point where a 12V battery gets just too heavy to haul around manually, that's when 6V batteries come into play. Same when 6V gets too heavy (a 450Ah 6V battery is 125 lbs!), then it's down to 4V or 2V cells. At the end of the day it makes no difference to the number of cells.

Aquion, the salt-water battery maker, went indeed belly-up. Theirs was just too expensive, and they never managed to get out of startup mode, where as a company they're burning money. When it comes to affordability regular lead-acid is still king.

So, you have a total of 42x 220W plus 36x 285W in panels? That's 19,500 Watt in solar PV! Where abouts are you located? That'd give me an idea of energy yield out of that much solar.

-RoB-