Maintaining battery bank without solar

TorontoTim

Like some do, I'm considering starting my solar adventure with just a battery bank, to be charged by my generator.

So - if I end up going that route, it will be a bank of 4 S-550 Rolls batteries in 24v. This is a vacation property, but we'll be there for 1-2 weeks at a time with 1-2 weeks perhaps between visits during the spring and summer.

How long can I leave the battery bank between running the generator if I'm not using any power? Should I even consider this setup, or should I invest in at least a minimal PV panel/charge controller setup to maintain the batteries, keep them topped up between uses etc.?

I'm trying to stick to a bit of a budget, as we just bought the property last fall. While I could go with a smaller 12v system including 2 panels and 2 batteries, for a few hundred less I can go with a 4 battery bank setup and charger instead. I think I need the larger bank in the long run, and would definitely plan on adding a 4 panel array in the future - likely next spring.

So - for the spring/summer/fall, can I leave the batteries for a couple weeks at a time between charges (no load - disconnect the inverter)? And then for the winter, even with panels they'd be covered in 10 inches of snow by late November. Can I leave the batteries in the frozen wilds all winter or am I better off packing them up and bringing them to the city for the season and keeping them indoors / perhaps charging off the grid all winter?

Clearly people with large setups don't haul their batteries around every season, but with only 4 batteries I can manage that if it's worthwhile or necessary.

Cariboocoot

Re: Maintaining battery bank without solar

What you're wondering about is called the self-discharge rate. For new, well-treated batteries it is not very high. As they age or if they are not treated well that will accelerate. Since you don't want them to sit below 75% SOC for more than 3 days you actually have quite a bit of time you can leave them for if they are fully charged when you go.

A few weeks without charge won't be a problem. Months on the other hand would be.

Winter is another issue. For one thing the cold temps slow down the chemical reaction, buying you time. But they must be kept charged because discharged batteries could freeze and burst. Panels can be tilted vertical to keep snow off and still provide enough current to maintain batteries.

You could take them home with you in Winter, or you could arrange for a very small amount of solar to maintain them when you're not there. You would only need about 4 Amps maximum for those S550 batteries, which would be 140 Watts. The problem there is that a 140 Watt panel is typically "12 Volt" and won't charge a 24 Volt system (Vmp at 17.7 is too low obviously). But a couple of smaller panels in series would do the job.

mike95490

Re: Maintaining battery bank without solar

Cariboocoot wrote: »

....
You could take them home with you in Winter, or you could arrange for a very small amount of solar to maintain them when you're not there. You would only need about 4 Amps maximum for those S550 batteries, which would be 140 Watts. The problem there is that a 140 Watt panel is typically "12 Volt" and won't charge a 24 Volt system (Vmp at 17.7 is too low obviously). But a couple of smaller panels in series would do the job.

You are likely to find that a 140watt panel will cost you as much as a larger "grid tie" 200w 40V panel, and then you can use a small MPPT controller $220 to charge your 24v bank from. And you won't be needing to worry about "borderline" charging, except when bad weather buries your panels under 20' of snow.
230W @ $237