Help me finalize my off grid system please

[hammick]

I am going to call Crown and tell them the situation and see what my options are. Maybe eight fresh ones shipped from the factory.

[sensij]

I am having a little problem following your logic or arithmetic here.
six 285W panels will produce (at STC) 1710 W. If you assume that the MPPT CC is 100% efficient you do get ~35A.
I guess your normal estimate, factoring in CC efficiency and panel power drop at real temperatures, is about 70%. That seems a little low to me, but you have a lot more real world experience.

I ran the numbers in this followup post. At 59 V bulk charging, 1710 W / 59 V = 29 A, which would be the charge current at STC and 100% efficiency. Yes, battery voltage will be somewhat less than that at the start of charging, but start of charging is typically in the morning, when the sun is not hitting the array directly and peak power is not available. By the time you get the sun overhead, hopefully the voltage has risen close to the bulk value and adsorb is starting (if thinking about it as a 3-stage charge).

86% of STC panel output + 95% MPPT efficiency gets you to 25 A. Reality is more complicated than that, and I used PVWatts to model what actual power would be available from the array, given the OP's location and his description of the array orientation, and assuming the panels + charge controller would function as efficiently as panels + a grid-tie inverter, which is where my real world experience is.

Too often, when we talk in design rules of thumb we treat PV power as this steady thing, but in reality, the max current is available for only a short time each day, and mostly it is less. I tried to present that in the histogram in the other post.

As discussed somewhat in the max smoke thread, it is much harder to overcharge a battery using PV than it is to undercharge it, and from all of the experience shared in the forum, it seems to me that sound advice would steer towards the overcharging direction, and away from undercharging.

[inetdog]

This wasn't great advice. Those 6 x 285 W panels will never produce 35 A, more like 25 A at best once you look at real world ratings and efficiency. They would have been reasonably well matched to a 208 Ah battery (C/8 max amperage).

I am having a little problem following your logic or arithmetic here.
six 285W panels will produce (at STC) 1710 W. If you assume that the MPPT CC is 100% efficient you do get ~35A.
I guess your normal estimate, factoring in CC efficiency and panel power drop at real temperatures, is about 70%. That seems a little low to me, but you have a lot more real world experience.

[sensij]

I bought all six that they had and two more are coming from the warehouse for me to pick up Saturday. The warehouse batteries have July stickers.

Looking for more opinions on this. I am very familiar with stratified batteries and battery maintenance but they have probably only been below 80% for a couple months. Surely a good equalization will bring them back to 100%. Do the battery warehouses maintenance charge their batteries?

These are heavy mothers and I'm not looking forward to returning them.

Thanks.

I haven't gone through your posts to see where you've worked out the load these batteries need to serve, but at the beginning of the thread, you were ready to go with a 208 Ah battery. Perhaps even if the 330 Ah battery has lost some capacity, it will still be sufficient for your needs, and bought at a price that made it worthwhile.

[Mike90250]

The magic happens between 80 -75% . After a week, it's hardened, and not removable. At least that's the "rule of thumb" I've heard and obey. Maybe you will get lucky. But 60% for a month, is way down in the bad zone.
Good Luck.

[hammick]

That sucks, Below 75-80%, the sulfates harden and it's nearly impossible to restore to solution. So I would say they have lost capacity. Piss poor battery shop that does not do a monthly freshen charge on them. They sold you damaged batteries, and you should be able to take them back. The way to do it is go there TOMORROW, with the same meter, and firmly ask to check the rest of the batch they have on the shelf. If their stock on the shelf reads low with both your meter and theirs, it's time to ask for a partial refund.

I bought all six that they had and two more are coming from the warehouse for me to pick up Saturday. The warehouse batteries have July stickers.

Looking for more opinions on this. I am very familiar with stratified batteries and battery maintenance but they have probably only been below 80% for a couple months. Surely a good equalization will bring them back to 100%. Do the battery warehouses maintenance charge their batteries?

These are heavy mothers and I'm not looking forward to returning them.

Thanks.

[Mike90250]

..All of the Crowns are June 2015 manufacture with resting voltages of 6.15 or 6.16 volts. Once is at 6.13 volts. Any worries about getting them at about 60% SOC?

That sucks, Below 75-80%, the sulfates harden and it's nearly impossible to restore to solution. So I would say they have lost capacity. Piss poor battery shop that does not do a monthly freshen charge on them. They sold you damaged batteries, and you should be able to take them back. The way to do it is go there TOMORROW, with the same meter, and firmly ask to check the rest of the batch they have on the shelf. If their stock on the shelf reads low with both your meter and theirs, it's time to ask for a partial refund.

[mapmaker]

Any worries about getting them at about 60% SOC?

Yes. Get them charged ASAP. Time is of the essence. The batteries are getting on 4 months old.

I would like to equalize these before putting them in my system. It may be Thanksgiving before I can install them. All I have available right now is a manual charger that will do 50a charge at 6 volt. Shall I just leave it charging for an hour or so after amps taper to 0?

I do have a CTEK 4.3a charger that has an equalization mode. I could put two batteries in series and use it but it would take forever to equalize all the batteries.

I don't know what a 'manual charger' is. I don't know the particulars of the CTEK, except that it is apparently a 12 volt charger. Use it to charge the batteries 2 at a time... do not try to charge or EQ them while they are in parallel. By the way, do NOT equalize the batteries until after they are charged up.

While charging, monitor the voltage (and the current if you have a shunt or DC clamp ammeter) while charging to see what that charger can do.

--mapmaker

[hammick]

I ended up buying the Crown CR330 batteries. Saved a bunch of money and hopefully will charge better with my proposed equipment.

All of the Crowns are June 2015 manufacture with resting voltages of 6.15 or 6.16 volts. One is at 6.13 volts. Any worries about getting them at about 60% SOC?

I would like to equalize these before putting them in my system. It may be Thanksgiving before I can install them. All I have available right now is a manual charger that will do 50a charge at 6 volt. Shall I just leave it charging for an hour or so after amps taper to 0?

I do have a CTEK 4.3a charger that has an equalization mode. I could put two batteries in series and use it but it would take forever to equalize all the batteries.

[sensij]

In cold, clear conditions you actually can produce STC outputs for a sustained period.

This is only true for panels that are mounted relatively normal to the angle of the sun. On a 4-12 roof (18 deg tilt), hitting STC is unlikely, except for some rare edge-of-cloud effects. Even high albedo from snow cover won't help much at that tilt, since the sun angle in winter (when it is cold) is very low. The panels would need to be mounted much more steeply to approach STC. See the PVWatts hourly output, which accounts for temperature. It doesn't account much for albedo, but again, in this situation, that isn't going to be much help.

[mapmaker]

35A is going to be too much into those batteries. If you want to use all those panels then buy L16 batteries, if you want to use the GC batteries then drop some panels.

This wasn't great advice. Those 6 x 285 W panels will never produce 35 A, more like 25 A at best once you look at real world ratings and efficiency. They would have been reasonably well matched to a 208 Ah battery (C/8 max amperage).

I think you're both right. In hot climates sensij is correct, NOCT will be lower than STC. The OP is in Montana. In cold, clear conditions you actually can produce STC outputs for a sustained period.

As has been mentioned, most name brand MPPT controllers can limit their output.

--mapmaker

[sensij]

This wasn't great advice. Those 6 x 285 W panels will never produce 35 A, more like 25 A at best once you look at real world ratings and efficiency. They would have been reasonably well matched to a 208 Ah battery (C/8 max amperage).

Further supporting this, here is what the PVWatts model would show for this system, annually, assuming 59 V charging as per the battery data sheet. Average monthly sun-hours range from 1.9 to 7.1 (4.6 average).

Hammick.GIF

C/8 for 208 Ah is 26 A, you would probably never see charge current in excess of that (data from PVWatts hourly output).

Hammick2.GIF

[Raul]

My 2 pennies worth; I have hands on experience with the similar setup. I totally agree with the above post. If you see 25a is good. Don't forget the clouds and rain that a smaller array would not cut it . I over paneled (I thought ) but in reality you will get about 80% of rated power.
Also to consider is your inverter / well pump. It will surge and that first one at 4kw will not be enough if you run other loads and pump.
Mike did a good observation and pointed to you in the first post about comparing the price for the next one up. I would go for the 6kw one as I know if the pump is running and the fridge wants to start your inverter will sound like a welding transformer if is not big enough.
First bank I also would recommend the cheapest.

I hope this post does not disappear as many have.

[sensij]

35A is going to be too much into those batteries. If you want to use all those panels then buy L16 batteries, if you want to use the GC batteries then drop some panels.

This wasn't great advice. Those 6 x 285 W panels will never produce 35 A, more like 25 A at best once you look at real world ratings and efficiency. They would have been reasonably well matched to a 208 Ah battery (C/8 max amperage).

[mapmaker]

There is the issue of when the water / electrolyte heats up and overflows the vents.

That's why I add water as soon as I get to float... by then the batteries are charged up and warmed up and there's still enough time in the day to stir up the electrolyte with another hour of absorb or EQ.

I've never had an overflow. Disclaimer: I do have tall water miser caps, but even if I didn't, I don't think I would overflow.

--mapmaker