Bought a cabin with off-grid solar and now looking for some help

[mc89]

I just bought a cabin that has a off grid solar power system installed. The owner said the batteries are 8 years old and I don't think the charger that is used to charge from the generator is working.

My next step is to troubleshoot to determine if I need to replace the charger and monitor the batteries to see if they need to be replaced. If the batteries need replacing I am considering using 8 MotoMaster GC2 which are made by Deka.

I'm looking for some advice on whether I should replace the current components or upgrade them to something different. Also, any tips on how to maintain the system would be greatly appreciated.

Some info on the current set up:

I am located in a fairly cloudy area in Canada and the system mainly has to power lighting, well pump, refrigerator, TV, and computer.

Panels - 4 x 180 watt

Mppt - Tristar TS-MPPT-60

Inverter - Xantrex DR

Transfer Switch - IOTA ITS 30

Charger - IOTA DLS 27-35

Batteries - 12 x Interstate GC2-XHD-UTL 232 Ah

[Mike90250]

Realistically, you can only expect 80% power from your panels, so a solar noon harvest of 576 watts would be reasonable.

That gives a charging amps of 24A, so your max battery size is about 250ah - 300ah. Larger than that size bank, and the batteries will suffer from not enough charge to bubble the electrolyte to prevent stratification.. Even if you only use a little bit of power, and let the PV top the cells off daily, larger than 300A will stratify and die sooner than expected.

I'll re-post a battery wh chart I made up a couple years ago. Batteries need about 10-15% of their rated capacity charge rate to stay healthy.

Generally, systems are sized for your loads, and you choose an inverter rated 130% of your average peak load. Then daily wh sets the bank size, finally your location sets the size of the PV array required to keep the batteries healthy.


battery compare.jpg

[mc89]

Is this the same whether the system is being used on a full time basis vs part time? I plan on using it 2 days a week for most of the year and for a full week once or twice a year. I assume when I am there for longer than a few days I will have to charge using the genset much more frequently.

I was considering changing the battery bank out to be about 1800 Ah at 24 volts and upgrading the panels to 4 x 320 watts so at 80 percent they would put out about 1000 watts at solar noon.

This is still well under the recommendations in your chart but I was wondering if it would make sense for part time use?

Thanks for the response, I've been reading up on this stuff any chance I get but I am struggling to make sense of it all.

[Mike90250]

Creating a large battery bank and a small solar array was "in" in the 70's but the batteries were always dieing. When batteries are discharged below about 80% for more than 24 hours, they start to sulfate. if it takes your small PV array 3 days to recharge, you loose a couple % of capacity to sulfation each time, effectively "walking down" your bank capacity 2% each week. If you run your genset a bit on the morning when you leave, you can charge batteries, make coffee and run the microwave. Even an hour of generator charging will help a lot