Solar power to keep batteries charges during storage??

[bayou-techie]

I've been full-timing it for the last few years and been able to keep the batteries charged pretty well while I was loving in it. However, now it's going to be in storage from time to time (ok, MOST of the time) and I'm concerned the batteries will drain when sitting. I have installed a battery disconnect but, since leaving it for a week (while traveling for business) at a time, the batteries would tend to drain and I'd have issues starting it.


So, I decided to ask the experts...


I have 10 (6V) golf cart batteries for house batteries connected to make 5 (12V).



My question is, how much power do I need from a solar panel just to keep the batteries charged? I'm counting on the fact that the batteries will be at a full charge when I return it to storage so I don't expect I'll have any need to use a BULK charge mode.


I'm sure there is additional information needed so, feel free to ask...


Thanks in advance...

[kunzelj]

My four 100W solar panels connected to a MPPT Victron solar charge controllers will easily keep the batteries at full charge if the master switch is disconnected. It depends so much on how much sun you get, but just to maintain 12.6V with very little load... won't take much.

[NoGas]

Batt Master OFF - not much given sufficient sunny hours & no shading of the panel. An unconnected batt naturally discharges over time at about 4% of its total pack capacity per week. You do the math and then figure enough solar panel size to replace that plus a fudge factor for clouds and reduced hours of sunlight in the winter. Batt Master ON - you’d need to figure your phantom draw and replace that plus the watts you come up with above. Again, either way you need to match the panel size using their worst case reduced winter output minus that fudge factor. Batts LIKE being charged through all 3 phases (Bulk, Absorbtion and Float) and then resting (automatically happens at night) - EVERY DAY. So get a solar charge controller that can do this, even a cheap one will work.

[DW SD]

One commercial type solar panel might be WAY more than enough. I think self discharge rate is more like 1% / week. That would be only 10 amphours per week. Or 140Watt hours. That’s with no losses of course which is a little unrealistic. Still even a small 100 watt panel would achieve with good sun exposure, say a few hours per day(or less).

AND
It would need to be wired in a way that the charge controller is still connected but 12V loads turned off which will require a bit of thought and also how you will connect and mount the panel.

But... I’d first ask for you to comment on your goals:
1. Are you looking for a setup where the panel and charge controller is mounted permanently?

2. One other thing to consider is if you’d want to have enough charging to park with a depleted battery and have the solar setup, restore charge within a certain timeframe. If so, then You might want to oversize. You can buy a commercial grade 300W panel from a solar supply wholesaler for around $220 in San Diego area. And an inexpensive mppt charge controller on amazon for another $120 or so.

Van and I have permanently mounted systems that will maintain batteries, with decent sun exposure while off grid camping (no or limited generator use).

While any product recommendation is premature without knowing your goals, here is an example of a good brand that doesn’t cost much.
Victron SmartSolar Charge Controller with Built-In Bluetooth – MPPT 75/15 – 75 Volts, 15 Amps https://www.amazon.com/dp/B075NQQRPD...sms_tai_duWWBb...