Help me finalize my off grid system please

[hammick]

My off grid barn has six 285w Solar World panels facing due South on a 4/12 roof pitch. They are in two strings of three and installer estimates 6 kwhs per day. I plan to do the rest of the install myself (equipment below) and my main question has to do with battery size.

Two biggest loads will be an energy star rated 11.5 cubic foot refrigerator that uses .852 kilowatt hours per day. Also a 3/4 hours 230v well pump that pulls 8.4 amps and has a power factor of 1.0 I estimate that it will run for a total of 10 - 15 minutes per day (maybe less as we have a big pressure tank fills pretty quickly). Other loads will be typical household. Living quarters is only 480 sq feet and all lights will be led. We will have a small microwave, garbage disposal and TV. We are used to boondocking with our camper that has solar and know how to conserve battery power. Heat will be wood burning stove and no AC. Very dry climate so I am skipping the bathroom fan.

Looking for opinions on this system. The panels are on my roof and wired to combiner box with breakers and surge protection. Thanks.

[Mike90250]

Welcome.
First, check the price difference between the xw4048 and the xw6048 if it's small enough, AND you can tolerate the slight increase of the tare load wattage, might consider it.

You NEED some control/monitor box for the XW system, either the SCP or the Combox. I have both and greatly prefer the Combox, even though it's pricey, it provides a web interface, more programming than the SCP, datalogging options and even firmware update capability. To connect your genset, and program it to be properly loaded, you need to program the integral charger in the inverter. (Generator connects to AC2)

You will really want an E-Panel, which is a fancy wiring box, that ties all the AC & DC wires, AC & DC breakers and charge controller breakers. Midnight Solar has a very nice one for the XW

http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=41&productCatName=E-Panel%20-%20Schneider%20Electric%20%20XW

DC rated breakers are much better for testing than fuses, and cost about the same as the big high amp DC fuses.

You need a hydrometer and a stock of distilled water

Wintertime, before you leave the cabin, do a couple full charges of the batteries, an EQ cycle, and then top off the water, and disconnect loads. Disable auto EQ and you can set Absorb Timer to a low value, and the batteries should be fine.

The battery bank is a bit undersized, and may have some issues if the sun hits the panels hard at sunrise, and you may exceed the suggested max charge rate for them (30A) Just something to be aware of, a short burst won't be too bad, but for a long time, it may heat the batteries too much. Also, with a small battery, if it is low (like in the AM) and the pump kicks on, you may get a Low Battery disconnect from the inverter, depending on how much of a starting surge the motor actually takes.

I'm attaching a well pump motor spec table, unless you are using an electronic controlled $2,000 pump, you will NOT see a 1.0 PF on any motor. 3 wire motors (external starting cap in a control box) have much lower starting surge than 2 wire pumps with their tiny cap buried in the motor case. Consider that if you have not bought the pump yet.

Welcome to the club and Have Fun.
WellPumpMotorSpecs.jpg

[mapmaker]

Wintertime, before you leave the cabin, do a couple full charges of the batteries, an EQ cycle, and then top off the water, and disconnect loads. Disable auto EQ and you can set Absorb Timer to a low value, and the batteries should be fine.

Good advice from Mike... but one thing I would do different is to add the water before the EQ. The water you add will stay at the top of the cell (stratification). I fully charge the battery before I add water, but after I add the water I like to do an EQ or long absorb to stir up the newly added water.

--mapmaker

[hammick]

Thanks for the info guys. I forgot to mention I will also be buying the Conext DC panel for the inverter and two of the 60a DC rated breakers for the charge controller.

I plan to install a 125 amp AC panel close to the inverter where my Ufer ground comes out of the sill plate (I will bond ground and neutral in this panel). What is the benefit of going with the Midnight solar AC/DC E-panel? My two solar panel breakers are installed in an Outback combiner box already with the surge protection. My installer was able to put the combiner box inside using a compression fitting and conduit. I can easily reach the box and breakers with a 10' ladder.

I just got a quote on Trojan L-16s for $340 each.

Keep the advice coming. I plan to decide and purchase next week. Thanks.

[thastinger]

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.

[hammick]

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.

I have decided on the L16P 420ah batteries. Thanks for the heads up on too much amps for GC2 batteries. Just thinking out loud though can't the XW60MPPT (and most higher end MPPT controllers) be configured for lower amps if I did choose to use GC2?

[thastinger]

I have decided on the L16P 420ah batteries. Thanks for the heads up on too much amps for GC2 batteries. Just thinking out loud though can't the XW60MPPT (and most higher end MPPT controllers) be configured for lower amps if I did choose to use GC2?

I don't know about all the other CC but I know on mine(midnite 200), I can change/limit voltages and times for phases of the charge cycle etc but I've never seen any setting to limit inrush amps to the battery bank during the bulk phase. The CC does perform this function on its own as the charge cycle nears the end but I'm not sure if the amps could be limited in a scenario where the battery bank was at a 70% SOC and the sun was bright at 11AM.

[hammick]

I checked the manual on the XW60MPPT and the ah of the battery bank can be configured anywhere from 50ah to 2000ah and the charging amps range from 6a to 60a depending on the size of the bank selected.

[thastinger]

Oh ok, that is good to know. I wonder (just outloud) how the CC "senses" the internal resistance of the battery bank. I'll have to look mine up as I recall that I could tell it the voltage of the bank but I don't recall being able to program the capacity. Its been almost 3 years now since I set mine up so I'll check again because that would be a nice feature to have.

[Mike90250]

.... I fully charge the battery before I add water, but after I add the water I like to do an EQ or long absorb to stir up the newly added water.--mapmaker

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

But insuring the water mixes into the electrolyte is important too.

[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

[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).

[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]

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

[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