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There's probably not much you can do about shading other than plan for some loss of output. I have a treed ridge to the south that means basically no sun from early Dec to early Jan., so had to install a couple of winter float arrays to maintain batteries when I'm away, and have to run a generator if I'm there.
Likewise, you can't change the weather. We've had weeks of temps <0°F, which is pretty normal for this time of year here. DC shouldn't be nearly as extreme, so you may be able to get away with charging cold. The problem is apparently lithium plating of anodes charging cold, which is permanent damage. The battery should generate a bit of heat when charging, which may mitigate the issue to some degree. Locating the battery out of the wind, or even insulating it may help.
Lead acid can be charged at much colder temps, and won't freeze until very cold (-70ish) fully charged. In this application though, I'd be concerned that a partly discharged battery might sit overnight in temps cold enough to freeze it in the discharged state. Charging a frozen lead acid battery is potentially dangerous.1
> @westbranch said:
> I see one major calculation error, you did not use the standard , 50%, derating for the amount of power you can draw from the battery. Going below is the fastest way of killing any battery.
Being a LifePO4 battery, the charge/discharge profile is a bit different, generally kept between ~10% and ~90% is recommended, vs ~50 to 100% for lead acid. Lithiums are apparently happiest sitting in a 50% or so SOC, whereas a LA battery won't be happy at all sitting at 50% for long periods.
One possible issue with using lithium in this application though is they don't like being charged in freezing temps. Discharging is okay, but they should be warmed to 0°C to charge. The battery may have self-protection to prevent low temp charging, or possibly even some sort of internal preheat, which may be a factor in current performance issues?1
My cistern normally supplies low pressure only to toilets etc which use lots of water, but don't need much pressure to fill. If need be, I can fill pressure tanks from cistern using the small 12vdc marine pump, but putting the toilets on the cistern cut the high pressure usage enough that it's not really needed.
Assuming a fair bit of the 500' well depth is fresh air, you should be able to save a fair bit of power by pumping to a cistern when the sun shines. In my case, separating out low-pressure / high volume uses works well, but the MIL thing may make just having a small pump fill the pressure tanks a better choice for you.1
At $35k, you're just about at a point I would have connected to grid.
Before deciding, I'd recommend really thinking hard about whether you want to run your own grid. Cost aside, there's a lot to be said for just flipping a switch, and being pretty sure it will work. Going off grid means you ARE the grid, with all the responsibility for making stuff go that goes with that.
Off-grid is a different lifestyle, and not for everyone. It CAN be rewarding, but at $35k for grid, I don't think $ would be my first consideration. Lots of folks here can help you put together a usable system, but only you can determine if off-grid is really right for you. I'd focus on the lifesyle aspect first.1
For cost modelling small scale solar pv reasonable replacement cycle time numbers to use would be; 5yrs for batteries, 10yrs for electronics, and 25yrs for pv, racking, wire, etc.
There are very few places where battery-based solar will come close to or below grid price, even in the long term. In order to make sense long term, you would have to make some really big assumptions about the path of future grid rates.1