Building a 48v system for my off-grid workshop

[HPaulPayne]

I have a battery bank consisting of 24 12v 120ah AGM batteries series-parallel wired for 48v and 34,560wh total (17,280wh at 50% DOD // 8,640wh at 25% DOD).
Will soon have the Aims PICOGLF10KW48V240VS 10,000w 48v split-phase inverter-charger. Using Outback Flexmax 80 charge controllers.

The solar panels are Jinko JKM400M-72HL-V 400w mono half-cut PERC modules.

I am located in Montana and completely off-grid. My question is the following: Since 10 of the 400w panels should (theoretically, but not in reality) provide 4kwh of power per hour under the best/optimal conditions, should I install one bank of 10 panels or two? What are the opinions of the users here?

Other information: Latitude is approximately 45 degrees. Winter sun-hours is are not very good.

Thanks in advance.
Paul

 

[snoobler]

4S6P is a massive bank and balancing the current between each string is a major challenge. You should be monitoring the individual 12V batteries because it doesn't take much to drive one in outlier territory and kill it quick.

With your AGM batteries, using typical charge specifications, You need 3500-7000W of solar to keep your batteries happy. You can overshoot that a little due to the fact that you almost never get peak output. 8000W would be fine.

If you're asking if you should get 4000W or 8000W of solar, the answer is 8000W.

 

[HPaulPayne]

4S6P is a massive bank and balancing the current between each string is a major challenge. You should be monitoring the individual 12V batteries because it doesn't take much to drive one in outlier territory and kill it quick.

With your AGM batteries, using typical charge specifications, You need 3500-7000W of solar to keep your batteries happy. You can overshoot that a little due to the fact that you almost never get peak output. 8000W would be fine.

If you're asking if you should get 4000W or 8000W of solar, the answer is 8000W.

Yes. That is what I was asking.

Thank you.
Paul

 

[snoobler]

Yes. That is what I was asking.

Thank you.
Paul

To clarify, the answer is 8000W because it's more than 4000W.

Truly, it should be dictated by your energy needs as your solar provides your maximum sustainable energy use.

 

[HPaulPayne]

To clarify, the answer is 8000W because it's more than 4000W.

Truly, it should be dictated by your energy needs as your solar provides your maximum sustainable energy use.

I have all of the normal things that you would find in a workshop, and a little bit more. And then, a few things that you wouldn't often expect to see.

My air compressor (80-gallon tank) is 220v/10hp. The table saw, band saw, drill press, etc. are all 110v. But the commercial bullet casting machine is 220v and draws about 5kw when running at full load.

I also want to supplement the power to the small apartment that is connected to the shop. I will use "shop power" to run the mini-split, cell phone booster, large freezer, and microwave oven circuits. The rest of the power for the apartment already comes from the same (12v / 4kw) solar/wind system that powers my well water system and RV hookup.

Thanks again.
Paul

 

[snoobler]

Once I got to bullet casting, I stopped reading... had to google. Sweet.

Recently got back into shooting/reloading, and holy moly. I wasn't paying attention. Fortunately, I found a fair amount of reloading supplies squirrelled away to take the sting out.

Sounds like you're probably covered. You have a lot of high surge items, but the ratings of that new inverter should be able to handle it unless you turn every motor on simultaneously.

 

[GXMnow]

That 10 HP air compressor is going to be on the edge to get started. Check the plate on the motor for the LRA (locked rotor amps) and see if the inverter can take that for a few seconds. You may need to get a soft starter to reduce the surge. My A/C compressor only runs at 14 amps at 240 volts for 3,360 VA and the locked rotor current it 105 amps. You can hear the wires buzz in the conduit when it fires up. I have that on grid power.

 

[HPaulPayne]

That 10 HP air compressor is going to be on the edge to get started. Check the plate on the motor for the LRA (locked rotor amps) and see if the inverter can take that for a few seconds. You may need to get a soft starter to reduce the surge. My A/C compressor only runs at 14 amps at 240 volts for 3,360 VA and the locked rotor current it 105 amps. You can hear the wires buzz in the conduit when it fires up. I have that on grid power.

That is good advice and I will do so. Aims claims that their inverter/charger will sustain a load of "30,000 watts of surge (for up to 20 seconds)." I am hoping that this will be enough. If not, I will make the appropriate adjustments.

Thank you.
Paul

 

[Supervstech]

600Ah lead will need

4S6P is a massive bank and balancing the current between each string is a major challenge. You should be monitoring the individual 12V batteries because it doesn't take much to drive one in outlier territory and kill it quick.

With your AGM batteries, using typical charge specifications, You need 3500-7000W of solar to keep your batteries happy. You can overshoot that a little due to the fact that you almost never get peak output. 8000W would be fine.

If you're asking if you should get 4000W or 8000W of solar, the answer is 8000W.

how is this accomplished? Are there 12V lead acid BMS systems out there? Is there a wiring method to accommodate monitoring of the 12v “cells” would there be a better orientation for the 12V batteries to help with keeping them balanced better?
Like, set the 6P banks together on bussbars, and series them after, or vice,versa?

 

[Hedges]

That 10 HP air compressor is going to be on the edge to get started. Check the plate on the motor for the LRA (locked rotor amps) and see if the inverter can take that for a few seconds. You may need to get a soft starter to reduce the surge. My A/C compressor only runs at 14 amps at 240 volts for 3,360 VA and the locked rotor current it 105 amps. You can hear the wires buzz in the conduit when it fires up. I have that on grid power.

That is good advice and I will do so. Aims claims that their inverter/charger will sustain a load of "30,000 watts of surge (for up to 20 seconds)." I am hoping that this will be enough. If not, I will make the appropriate adjustments.

Thank you.
Paul

I expect starting surge of a motor to be 5x its nameplate current. A 30kW surge might start a 5kW motor. 10 HP induction motor is probably rated well over that. Is that a single-phase motor? Do you need full output? How about replacing with a 5 HP that turns half the RPM?

To clarify, the answer is 8000W because it's more than 4000W.

Truly, it should be dictated by your energy needs as your solar provides your maximum sustainable energy use.

Can never have too many watts of PV panels.
You can have more watts peak than you are able use.

Aiming one array SE for 10:00 AM sun and the other SW for 4:00 PM sun will reduce peak to about 0.7 times as much and extend hours of production. Total Wh available will be somewhat reduced.

Are you going to connect panels 10s? or 5s2p? If 5s2p, you can orient one 5s string different from the other 5s. MPPT is slightly sub-optimum, but reportedly only about 2% loss (assuming the arrays don't get shadows on them.) That way the MPPT has reduced peak, more hours operation; it can handle more PV panels this way.

Of course you can also orient a string South with winter tilt to get more power then, at he expense of less production in the summer. This is where extra PV helps.

 

[GXMnow]

600Ah lead will need

how is this accomplished? Are there 12V lead acid BMS systems out there? Is there a wiring method to accommodate monitoring of the 12v “cells” would there be a better orientation for the 12V batteries to help with keeping them balanced better?
Like, set the 6P banks together on bussbars, and series them after, or vice,versa?

There are a bunch of ways to wire up a large battery bank. What is the best? Well, that depends.

I like the idea of having a redundant system, even though my initial system dos not have it. But when you start this big, you can clearly set it up as two banks. Run each set of 3 batteries in parallel, series four of those, and make two banks like that. Have them all properly fused.
And then something like this on each bank.

 

[HPaulPayne]

I expect starting surge of a motor to be 5x its nameplate current. A 30kW surge might start a 5kW motor. 10 HP induction motor is probably rated well over that. Is that a single-phase motor? Do you need full output? How about replacing with a 5 HP that turns half the RPM?



Can never have too many watts of PV panels.
You can have more watts peak than you are able use.

Aiming one array SE for 10:00 AM sun and the other SW for 4:00 PM sun will reduce peak to about 0.7 times as much and extend hours of production. Total Wh available will be somewhat reduced.

Are you going to connect panels 10s? or 5s2p? If 5s2p, you can orient one 5s string different from the other 5s. MPPT is slightly sub-optimum, but reportedly only about 2% loss (assuming the arrays don't get shadows on them.) That way the MPPT has reduced peak, more hours operation; it can handle more PV panels this way.

Of course you can also orient a string South with winter tilt to get more power then, at he expense of less production in the summer. This is where extra PV helps.

If necessary, I could change the motor on the compressor. And, I didn't even mention the welder because I plan to use that on the 10kw generator and not the solar/wind system.

Also, I must admit that I don't know all of the abbreviations used herein:
4s6p ??
10s ??
5s2p ??
5s ??
6p ??

Is the "s" for "series" and the "p" for "parallel"??

I feel pretty dumb for not knowing. But, I figured that I could ask.

Thanks for the ideas about panel orientation. I will put some serious thought and consideration into the placement of the panels.

I really like and appreciate all of the responses that I am receiving on this forum. It is already helping me learn a lot.
Paul

 

[HPaulPayne]

There are a bunch of ways to wire up a large battery bank. What is the best? Well, that depends.

I like the idea of having a redundant system, even though my initial system dos not have it. But when you start this big, you can clearly set it up as two banks. Run each set of 3 batteries in parallel, series four of those, and make two banks like that. Have them all properly fused.
And then something like this on each bank.

Two banks, instead of one??? I'm not sure why that would be beneficial. Can you explain this further?

I was planning on simply using the 24 12v batteries in the following manner: 6 strings of 4 batteries (12v, in series to produce 48v) wired in parallel.
Thanks.
Paul

 

[GXMnow]

With 2 totally separate banks, if something does fail, you can run on one bank at a bit lower power until you can fi it. I had a BMS issue with a bad balance wire connector and my whole system went down due to having just one battery system. I thought about splitting mine into 2, but instead I just bought a second bank of cells to build into another battery system, and I will also double my storage.

Doing at as 6 separate strings is not bad, but you now have 6 groups that can all get out of balance, so you should then use 6 of the balancers. Will you also separately fuse each of the 6 strings?

When you run batteries in parallel, they more or less self balance between them. So if you parallel 2 or 3 batteries, before you put them in series, you are essentially making it into one bigger battery at double or triple the capacity, and can reduce the number of balancers and fuses needed. As you guessed, p is or parallel and s is for series.

Your 24 batteries can be connected as 4S6P which would be putting the 4 in series first, and paralleling only the ends. This does work, but in each series group, one battery might be at just 12.3 volts while another is at 13.2 volts. In the next string over, it could be the exact opposite. This is why each series string should have a balancer, meaning six balancers. The opposite end would be 6P4S. Here you wire 6 in parallel first, and then series the 4 groups. You only need one balancer, as the 6 batteries in each parallel group will just naturally stay balanced as the highest charged will provide the most power and even back feed the others until they balance at the same terminal voltage. Then you have 2 more options. Two strings of 3P4S with 2 balancers or Three strings of 2P4S with 3 balancers. The other advantage of having parallel groups is you can test the capacities and group them so the capacity of each group is closer. Putting the highest and lowest capacity batteries in a group will likely match two of the middle capacity batteries pretty closely. But putting the two highest in one group, and the two lowest in another group would be bad. If you have the time and patience to do a capacity test, it can be a great help. The more you do run in parallel first, the better the odds of the banks matching.

Using 12 volt AGM batteries, you do still have the 6 cells in each battery, but there is not much we can do about that. Those cells should be closely matched as they are built at the same time with the same materials. But that can't be said for the next 12 volt group of cells in the series chain, so we recommend at least keeping the 4 series connected batteries balanced. To be completely honest though, many people have used large banks of lead acid and never bothered with any electronic balancing. They would have the charger top out and run a long absorb cycle to get them all full, and then only use less than half capacity, so a little drift is not too big of a deal. But there is always that one weaker battery which is cycling more like 55% and the rest just 45% so it ends up failing early. Do you want to be able to ignore your battery bank, or will you check the cells from time to time? The balancer video I sent seems pretty cool as you can log in on your cell phone and check the battery status.

Those of us running lithium cells can't use a long absorb charge to force the cells to top balance like lead acid cells can. We have to use a BMS at the very least as an overcharged cell is far more damaging than it is with lead acid.

 

[snoobler]

600Ah lead will need

how is this accomplished?

Check current flow on individual strings w/clamp ammeter to determine if the strings are receiving the same current.

Are there 12V lead acid BMS systems out there?

"BMS"? No, but there are balancers which will transfer charge from high voltage to low voltage. I have 8 of them on my 4S2P T-1275 bank. Happened to check voltage over the weekend, during float, and they were all 13.05-13.08V - these are old batteries with varying states of health between 75% and 95%.

Is there a wiring method to accommodate monitoring of the 12v “cells” would there be a better orientation for the 12V batteries to help with keeping them balanced better?
Like, set the 6P banks together on bussbars, and series them after, or vice,versa?

6P4S would minimize the number of 12V elements you have to deal with, but for some reasons battery manufacturers never recommend this.

 

[Hedges]

If necessary, I could change the motor on the compressor. And, I didn't even mention the welder because I plan to use that on the 10kw generator and not the solar/wind system.

Also, I must admit that I don't know all of the abbreviations used herein:
4s6p ??
10s ??
5s2p ??
5s ??
6p ??

Is the "s" for "series" and the "p" for "parallel"??

Yes, series and parallel.

10 PV panels in series "10s", 10x the Voc and 10x the Vmp. No change to current.
(note that Voc increases if temperature is colder than 25 degrees C, must calculate based on record cold temperature, do not exceed charge controller spec or it will fail.

"5s2p" 5 panels in series, 5 more panels in series, then connected together. 5x voltage, 2x current.

Your 24, 12V batteries could be connected 4s6p for a 48V bank.
Or 6p4s, paralleling groups of 6 first, then connected in series. Common for lithium cells (so they share a BMS), but not for lead-acid batteries.

You can maybe run welder off the inverter, depending on peak watts and average watts. It won't has as high a surge as a motor.
if it is an inverter welder, may have funny input current waveforms that inverter may or may not like.

One guy ran a welder successfully for a while, then inverter blew up. Different inverter and it's been OK for a while. Old inverter repaired, going in a different system.

Any particular history or specifications for those AGM batteries? Some batteries are optimized for 3C discharge rate, supporting a UPS for 20 minutes. Not so many cycles. People get those used. Other batteries are optimized for off-grid or similar applications.

Your battery is about 75% larger than mine (which I use for backup during rare grid failure).
If you avoid running loads at night, for instance turn off refrigerator/freezer and let it coast on the cold it has, you can reduce cycling of the battery. You may be able to get 10 years or so cycle life limiting DoD to 15%, give or take depending on what vendor specs say.
Try to enable discretionary loads only when there is spare PV production beyond what's needed to charge battery.

 

[HPaulPayne]

With 2 totally separate banks, if something does fail, you can run on one bank at a bit lower power until you can fi it. I had a BMS issue with a bad balance wire connector and my whole system went down due to having just one battery system. I thought about splitting mine into 2, but instead I just bought a second bank of cells to build into another battery system, and I will also double my storage.

Doing at as 6 separate strings is not bad, but you now have 6 groups that can all get out of balance, so you should then use 6 of the balancers. Will you also separately fuse each of the 6 strings?

When you run batteries in parallel, they more or less self balance between them. So if you parallel 2 or 3 batteries, before you put them in series, you are essentially making it into one bigger battery at double or triple the capacity, and can reduce the number of balancers and fuses needed. As you guessed, p is or parallel and s is for series.

Your 24 batteries can be connected as 4S6P which would be putting the 4 in series first, and paralleling only the ends. This does work, but in each series group, one battery might be at just 12.3 volts while another is at 13.2 volts. In the next string over, it could be the exact opposite. This is why each series string should have a balancer, meaning six balancers. The opposite end would be 6P4S. Here you wire 6 in parallel first, and then series the 4 groups. You only need one balancer, as the 6 batteries in each parallel group will just naturally stay balanced as the highest charged will provide the most power and even back feed the others until they balance at the same terminal voltage. Then you have 2 more options. Two strings of 3P4S with 2 balancers or Three strings of 2P4S with 3 balancers. The other advantage of having parallel groups is you can test the capacities and group them so the capacity of each group is closer. Putting the highest and lowest capacity batteries in a group will likely match two of the middle capacity batteries pretty closely. But putting the two highest in one group, and the two lowest in another group would be bad. If you have the time and patience to do a capacity test, it can be a great help. The more you do run in parallel first, the better the odds of the banks matching.

Using 12 volt AGM batteries, you do still have the 6 cells in each battery, but there is not much we can do about that. Those cells should be closely matched as they are built at the same time with the same materials. But that can't be said for the next 12 volt group of cells in the series chain, so we recommend at least keeping the 4 series connected batteries balanced. To be completely honest though, many people have used large banks of lead acid and never bothered with any electronic balancing. They would have the charger top out and run a long absorb cycle to get them all full, and then only use less than half capacity, so a little drift is not too big of a deal. But there is always that one weaker battery which is cycling more like 55% and the rest just 45% so it ends up failing early. Do you want to be able to ignore your battery bank, or will you check the cells from time to time? The balancer video I sent seems pretty cool as you can log in on your cell phone and check the battery status.

Those of us running lithium cells can't use a long absorb charge to force the cells to top balance like lead acid cells can. We have to use a BMS at the very least as an overcharged cell is far more damaging than it is with lead acid.

WOW!
That is a lot to absorb and learn. I've really come to the right place with my questions.

Thank you.
Paul

 

[HPaulPayne]

Yes, series and parallel.

10 PV panels in series "10s", 10x the Voc and 10x the Vmp. No change to current.
(note that Voc increases if temperature is colder than 25 degrees C, must calculate based on record cold temperature, do not exceed charge controller spec or it will fail.

"5s2p" 5 panels in series, 5 more panels in series, then connected together. 5x voltage, 2x current.

Your 24, 12V batteries could be connected 4s6p for a 48V bank.
Or 6p4s, paralleling groups of 6 first, then connected in series. Common for lithium cells (so they share a BMS), but not for lead-acid batteries.

You can maybe run welder off the inverter, depending on peak watts and average watts. It won't has as high a surge as a motor.
if it is an inverter welder, may have funny input current waveforms that inverter may or may not like.

One guy ran a welder successfully for a while, then inverter blew up. Different inverter and it's been OK for a while. Old inverter repaired, going in a different system.

Any particular history or specifications for those AGM batteries? Some batteries are optimized for 3C discharge rate, supporting a UPS for 20 minutes. Not so many cycles. People get those used. Other batteries are optimized for off-grid or similar applications.

Your battery is about 75% larger than mine (which I use for backup during rare grid failure).
If you avoid running loads at night, for instance turn off refrigerator/freezer and let it coast on the cold it has, you can reduce cycling of the battery. You may be able to get 10 years or so cycle life limiting DoD to 15%, give or take depending on what vendor specs say.
Try to enable discretionary loads only when there is spare PV production beyond what's needed to charge battery.

This is some great info and advice. Thank you very much.

I have a timer setup on certain items so that they are on only when necessary. Examples are: Refrigerator, freezer, battery charger for 18v tools, etc. Other things, such as the cellular phone signal booster is on 24hrs but doesn't draw very much.

I often overdo it when it comes to infrastructure items like water supply, battery banks, and solar panels. But I'm off-grid in the mountains of Montana and the weather can be unpredictable sometimes.

All of this advice is very welcome and I am learning more than I expected.

Thank you.
Paul

 

[Hedges]

Priority switching, like temporarily turning off A/C when a well pump is needed, is another possibility. A large above-ground tank effectively stores energy; only a small booster is needed.

I haven't automated much except using a Harbor Freight digital timer to enable an electric water heater (240V but I'm using 120V) during off-peak grid rates. And automatic setback thermostat for heating & A/C. I manually run laundry and pool pump off-peak. My air compressor has a mechanical timer because otherwise I forget to turn it off.

What I want to do is take "on-grid" and "battery charged" or "surplus PV" signals to enable refrigerators, select between gas vs. electric heat, etc. so on-grid I use power off-peak, but off-grid I avoid nighttime loads and run discretionary loads once batteries are recharged and PV can power them. Presently, I'm not necessarily going to notice when the grid goes down so could run the battery down (especially since I use electric heat while on-grid.)

 

[HPaulPayne]

Priority switching, like temporarily turning off A/C when a well pump is needed, is another possibility. A large above-ground tank effectively stores energy; only a small booster is needed.

I haven't automated much except using a Harbor Freight digital timer to enable an electric water heater (240V but I'm using 120V) during off-peak grid rates. And automatic setback thermostat for heating & A/C. I manually run laundry and pool pump off-peak. My air compressor has a mechanical timer because otherwise I forget to turn it off.

What I want to do is take "on-grid" and "battery charged" or "surplus PV" signals to enable refrigerators, select between gas vs. electric heat, etc. so on-grid I use power off-peak, but off-grid I avoid nighttime loads and run discretionary loads once batteries are recharged and PV can power them. Presently, I'm not necessarily going to notice when the grid goes down so could run the battery down (especially since I use electric heat while on-grid.)

Good advice. But I think that I might be something of an anomaly.

I have a separate off-grid power system for my well water supply. It is my first try at solar/wind power and it is a 12v system.

My well is a very reliable, but low-flow, supply. It only produces a little more than 1gpm. I have a 220v Grundfos pump in the well and it sends water to two interconnected underground cisterns that hold 2,200 gallons each. When a float valve signals the pump that the cisterns are full, it shuts off the water supply. Inside one of the cisterns is a 220v Grundfos "on-demand" variable speed/pressure/flow pump that is controlled by a computer - based upon demand.

This power is supplied via an AIMS PICOGLF40W12V240VS 4000w (12,000W peak) pure sine wave Inverter-Charger 12VDC 240VAC Input to 120/240 VAC. The electricity is generated by two banks of 3 Longi 360w bi-facial panels. Each bank has an Outback Flexmax 80 charge controller that feeds into the battery bank. Also feeding the batteries is a Missouri Wind and Solar 1600w wind turbine kit w/digital solar/wind charge controller. I will soon be adding 6 100w solar panels that will be connected through the solar/wind charge controller. The battery bank is 16 of the 6v Trojan SPRE 06 255 wired in series/parallel that provides me with more than 10.8kwh (at 50% DOD).

Not only does this supply power to my water system, but it also completely supplies my "RV hookup" (camper trailer) that is located outside of my workshop and my apartment that is connected to the workshop.

As you can see, I do believe in redundancy and a bit of overkill. ;-)

After I finish my workshop power system, I will begin the system that will power the house that I will soon be building. All of it will be off-grid using solar and wind with generators backing-up each system.

The picture is the timers that I use to control outlets that power the fridge, freezer, and other things that don't need to run constantly.

Paul