diy solar

diy solar

Off grid Cabin in NY, winter months. Feasibility, need input/advice.

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wtrey613

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Jan 15, 2021
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Google doc of Calcs and Specs

See link above with Specs and Calcs. Here is the basic info:
Daily watt demand: ~4000Wh.
Battery size: 4.3 kWH
Pannels: 4x250W panels 2S2P
Inverter: Growatt inverter 24V 3000W
Open voltage @-30 degrees : 75.6 volts
Max voltage for inverter is 145Vdc.
Generator Back up at night for overcast days.
Months of operation: Oct-Nov. Worst case sun hour for Nov, 2.85

My questions, Need feedback:
  1. Is this feasible? with temps getting down to the low teens in Fahrenheit. (Battery will be indoors but could get down to 32degrees). Also with overcast days and our load of 4kW per day. Are these able to withstand the elements? We would use a generator to recharge the battery at night as well. And we would really only use on weekends/ 4 days at a time.
  2. Leaving for long periods at a time: Could we leave this out there for a month un monitored? or should we pack in and pack out the battery? and leave the growatt and pannels?
  3. If we were to upgrade: we would likely upgrade panels from 1kw to 1.5kw. and Battery size 4.3kw to 7.3kw by adding a 3kw battery.
Thanks in advance!
 

Attachments

  • Solar work sheet for Upstate New York Cabin.pdf
    450.3 KB · Views: 11
If you're going to pack out the batteries then I wouldn't worry about adding warming pads. I suspect that lugging around a 24v battery will get old real fast and you'll want to leave it in place. In that case, a warming pad is necessary. LiFePO4 batteries should not be charged below 32° F. If the BMS and MPPT have low temperature cutoff then the battery will not get charged, but could still be discharged.
 
HRTKD said:
If you're going to pack out the batteries then I wouldn't worry about adding warming pads. I suspect that lugging around a 24v battery will get old real fast and you'll want to leave it in place. In that case, a warming pad is necessary. LiFePO4 batteries should not be charged below 32° F. If the BMS and MPPT have low temperature cutoff then the battery will not get charged, but could still be discharged.
Click to expand...
Great, we will buy some warming pads! And yes, the BMS has a low temp cut off.
Overall, feasibility of this set up, do you see any other issues? Thanks!
 
wtrey613 said:
Great, we will buy some warming pads! And yes, the BMS has a low temp cut off.
Overall, feasibility of this set up, do you see any other issues? Thanks!
Click to expand...

Insulating the battery will be important. Rigid foam panels work very well for that.

The solar charge controller will need to know the temperature of the battery, not ambient temperature.
 
How well it works all depends on the weather. If Oct and Nov have a lot of cloud cover like they usually do, you will be living off the generator. Sometimes you'll get 3 straight weeks of almost no sun. Nevermind snow.

My generator usage window spans from 3rd week of Oct to 2nd week of February. Usually the bulk of it is Oct to Dec when there isn't any significant charge from solar.
 
Seems a little undersized for the daily load.
Battery bank should be doubled in order to give you 2 days worth of power when you don't have sun.
During hunting season (at least for us here in Wisconsin during whitetail deer season) we wanted to make sure the generator was never running when we are hunting.

If it were me I would add more panels and more battery power.

Water pump looks like the biggest draw by far. Is that for a well?
 
HARG Hunter said:
Seems a little undersized for the daily load.
Battery bank should be doubled in order to give you 2 days worth of power when you don't have sun.
During hunting season (at least for us here in Wisconsin during whitetail deer season) we wanted to make sure the generator was never running when we are hunting.

If it were me I would add more panels and more battery power.

Water pump looks like the biggest draw by far. Is that for a well?
Click to expand...
Yes, Battery does seem a little undersized for the daily load, I agree.
And yes i think the battery bank should be doubled as well as a precaution.
Got it, I will probably look to upgrade the panel size and the Battery bank not this year but next.
Water pump is for a well, but we don't have the well yet (est 2022). So for this year (2021 hunting season) we may start out small, then upgrade next year.

Do you see any other feasibility issues? like leaving it out for months at a time unmonitored? is there anything we should pack-in/pack-out? Is there any issue you run into in Wisco during your hunt season that may be applicable to us?
Thanks again.
 
jtvt said:
How well it works all depends on the weather. If Oct and Nov have a lot of cloud cover like they usually do, you will be living off the generator. Sometimes you'll get 3 straight weeks of almost no sun. Nevermind snow.

My generator usage window spans from 3rd week of Oct to 2nd week of February. Usually the bulk of it is Oct to Dec when there isn't any significant charge from solar.
Click to expand...
Agreed, in that part of NY it can be very cloudy for many days at a time. We will look into upgrading the Battery Bank.
 
I'm just north of Syracuse and we are the 8th cloudiest place in the nation. NY State leads the top 25 cloudiest places in the entire US with 5 locations. Yesterday on 1 - 200 watt panel the most I could get (at peak_ was 10 watts. No sun yesterday just heavy gray clouds and rain in the am. Now compare that to Sunday when I was getting 190 watts. I'd say use a generator when your at the cabin to help. When your not there it should last.
 
wtrey613 said:
Yes, Battery does seem a little undersized for the daily load, I agree.
And yes i think the battery bank should be doubled as well as a precaution.
Got it, I will probably look to upgrade the panel size and the Battery bank not this year but next.
Water pump is for a well, but we don't have the well yet (est 2022). So for this year (2021 hunting season) we may start out small, then upgrade next year.

Do you see any other feasibility issues? like leaving it out for months at a time unmonitored? is there anything we should pack-in/pack-out? Is there any issue you run into in Wisco during your hunt season that may be applicable to us?
Thanks again.
Click to expand...
We leave ours up there year round. We went with AGM to nullify the cold. When we went up in February to cut wood, the batteries were rocking without issue, and overnight lows were in the -10 range. With our cabin being unheated, it got down to about 15-20 at night and the batteries had no problem.

You could maybe hook up a low wattage bulb in your battery box to hold heat.

Otherwise if you know for sure you won't be there for the super cold months, a 1 time yearly pack in/out wouldn't be the end of the world.
 
HARG Hunter said:
Seems a little undersized for the daily load.
Battery bank should be doubled in order to give you 2 days worth of power when you don't have sun.
During hunting season (at least for us here in Wisconsin during whitetail deer season) we wanted to make sure the generator was never running when we are hunting.

If it were me I would add more panels and more battery power.

Water pump looks like the biggest draw by far. Is that for a well?
Click to expand...

@HARG Hunter ... payin' it back ... off-grid gangsta now! :)

+1 to the well pump. Well pumps can be bastards. A large submersible pump typically has a 5X current surge and will trip the inverter (the 6000W "surge" is a joke on those units). Neighbor has a 700' deep well with a Grundfos 3hp submersible... 60A @ 230V surge... 13,800W. OUCH!

+1 to more panels.

Doc questions:

1) Upgradeability - meh. You should get 6-8 panels at the outset. Your winter sun is so bad, you'll need them. 7.4kWh too.
2) The resources you used factor average weather into the numbers. However, a generator is infinitely better than not having the option. You can configure the Growatt's behavior for AC charging, charge current and start/stop voltages. The Growatt has a weird AC charger. It starts charging at a set voltage and it ends charging at another set voltage - no absorption or float. Not a big deal, but it helps to understand that from the outset. You will set absorption and float voltages for the solar charge controller, and you will set start and stop charging voltages for the generator.

Charge time:

With 7.4kWh of capacity, that should be about 290Ah total.
You probably want to PULL 10A @ 120V from the generator, so that's 1500W - a good power for efficiency on a 2000W generator. 15 00W/28.8V = 52A.

290Ah/52A = 5.6 hours from dead empty to 100%.

Reality is slightly different. If you set the Growatt to turn on charging at about 24V, that's around 20% SoC. It will not fully charge it due to the odd way it works, so you'll probably get to about 90% SoC at end of generator charge.

Thus you only need to replenish 70% of the 290Ah or 203Ah. That would take 203Ah/52A = 3.9 hours (recharging from 20% SoC to 90% SoC)

Obviously, you would need to manually start the generator once the Growatt hits the 24V lower limit.

3 &4) Battery temps are the only concern. You have low temp charging protection, but if it's consistently below freezing, it could conceivably never charge.

In addition to insulating, consider:

diysolarforum.com

LiFePO4 Battery Warmer Install

This is my install of a custom set of battery warmers from Ultra Heat. I had contacted them through email asking about a warming profile for LiFePO4 batteries. They responded with a design to my specifications, including warming pads that fit my batteries exactly. While I initiated the...
diysolarforum.com diysolarforum.com

or

diysolarforum.com

Simple, Indipendent Battery Box Heater

To get the document, click on the orange button at the top of the page. This is a simple 20W battery Box heater that operates independently of the rest of your system. I use this for storing unused cells in a very cold climate, but it can be...
diysolarforum.com diysolarforum.com
 
HARG Hunter said:
We leave ours up there year round. We went with AGM to nullify the cold. When we went up in February to cut wood, the batteries were rocking without issue, and overnight lows were in the -10 range. With our cabin being unheated, it got down to about 15-20 at night and the batteries had no problem.

You could maybe hook up a low wattage bulb in your battery box to hold heat.

Otherwise if you know for sure you won't be there for the super cold months, a 1 time yearly pack in/out wouldn't be the end of the world.
Click to expand...
Okay so AGM Batteries for the cold weather. I might just jerry rig a heating pad around the battery box, but i reached out to the BigBattery guys to ask about heating solutions during the cold weather. We also get similar temperatures as you do. Not as cold as -10. but low teens and single digits.
 
efmrrt said:
I'm just north of Syracuse and we are the 8th cloudiest place in the nation. NY State leads the top 25 cloudiest places in the entire US with 5 locations. Yesterday on 1 - 200 watt panel the most I could get (at peak_ was 10 watts. No sun yesterday just heavy gray clouds and rain in the am. Now compare that to Sunday when I was getting 190 watts. I'd say use a generator when your at the cabin to help. When your not there it should last.
Click to expand...
Thanks! would love to know more about your set up and your cloudy days as well! So you only get 10Kw during the day?? or for that hour?
I will DM you. And we are planning on 1kw-1.5kw solar cell system (6x250W). and have a 2200 honda generator as a back up for cloudy days (Not sure if that will be enough).
 
snoobler said:
@HARG Hunter ... payin' it back ... off-grid gangsta now! :)

+1 to the well pump. Well pumps can be bastards. A large submersible pump typically has a 5X current surge and will trip the inverter (the 6000W "surge" is a joke on those units). Neighbor has a 700' deep well with a Grundfos 3hp submersible... 60A @ 230V surge... 13,800W. OUCH!

+1 to more panels.

Doc questions:

1) Upgradeability - meh. You should get 6-8 panels at the outset. Your winter sun is so bad, you'll need them. 7.4kWh too.
2) The resources you used factor average weather into the numbers. However, a generator is infinitely better than not having the option. You can configure the Growatt's behavior for AC charging, charge current and start/stop voltages. The Growatt has a weird AC charger. It starts charging at a set voltage and it ends charging at another set voltage - no absorption or float. Not a big deal, but it helps to understand that from the outset. You will set absorption and float voltages for the solar charge controller, and you will set start and stop charging voltages for the generator.

Charge time:

With 7.4kWh of capacity, that should be about 290Ah total.
You probably want to PULL 10A @ 120V from the generator, so that's 1500W - a good power for efficiency on a 2000W generator. 15 00W/28.8V = 52A.

290Ah/52A = 5.6 hours from dead empty to 100%.

Reality is slightly different. If you set the Growatt to turn on charging at about 24V, that's around 20% SoC. It will not fully charge it due to the odd way it works, so you'll probably get to about 90% SoC at end of generator charge.

Thus you only need to replenish 70% of the 290Ah or 203Ah. That would take 203Ah/52A = 3.9 hours (recharging from 20% SoC to 90% SoC)

Obviously, you would need to manually start the generator once the Growatt hits the 24V lower limit.

3 &4) Battery temps are the only concern. You have low temp charging protection, but if it's consistently below freezing, it could conceivably never charge.

In addition to insulating, consider:

diysolarforum.com

LiFePO4 Battery Warmer Install

This is my install of a custom set of battery warmers from Ultra Heat. I had contacted them through email asking about a warming profile for LiFePO4 batteries. They responded with a design to my specifications, including warming pads that fit my batteries exactly. While I initiated the...
diysolarforum.com diysolarforum.com

or

diysolarforum.com

Simple, Indipendent Battery Box Heater

To get the document, click on the orange button at the top of the page. This is a simple 20W battery Box heater that operates independently of the rest of your system. I use this for storing unused cells in a very cold climate, but it can be...
diysolarforum.com diysolarforum.com
Click to expand...

We plan on getting this water pump actually :
groundfos 1HP SO with my math that's 240V at 11.2 amps so 2,688watts per hour of use? So if we only use it for 15mins, that's around a day that is 672Watts. They say it has a soft start, are you saying these still surge at insanely high wattage?

And we will most likely do a 1.5kw-2.0kw panels (8x250watt) to start given the sun is so bad during these months.

We have a honda Eu2200i generator so i think your math checks out on that. Its rated AC output is 120V 2200W max. (18.3A), 1800W rated (15A). and has a 20A 125V Duplex receptacle. I still have to figure out how to calculate that. So give or take 4 hours to recharge?

And for keeping the BigBattery insulated, we will likely use heating pads and Jerry rig it around the big battery.
 
I'm somewhat North of you by a few hundred miles but suffer similar weather in general.
Have a peek at the "About my System" link in my signature which might prompt a few thoughts & ideas for ya.
Having enough panel to charge the battery bank reasonably on Low Sun Days is a PITA. If the panels can have the angle changed for 4 seasons that can make a huge improvement.

On the Water Pumping part... NO BS, the only practical pumps to use with Solar Systems & Inverters are SOFT START pumps anything else is idiocy, plain and simple. Soft Start systems for water pumps, AC & Refrigerators do not have a massive surge pull, is easy on inverters & batteries alike and they outlast others because the motors are not stressed.

I use a GrundFos SQ-5 120V Softstart Deep well pump, which is 260' deep, pushes to a 50 Gal Pressure tank and then 75' to house. You never notice any pressure change (bonus when in shower ). The pump starts at 550W and increments up to 1100W by the time it cuts off at 52PSI. 240VAC is NOT NEEDED - that wives tale pile is something else. IF the only thing you need 240V for is your pump, seriously think on it. If you want 240VAC as a standard install with 120VAC legs because you have extra appliances / devices that need it then that is another thing.

LINKS:
GrundFos SQ Family General: SQ | Grundfos
GrundFos SQ Flex Series (AC & DC variants) SQFlex | Grundfos

The Honda 2200 is 2200W MAX or 1800W running. This is quite limited with regards to running a charger. To charge at 24V/40A the AC Input from the genset will push the 15A plug to the edge of it's limit. I use my Inverter/Charger when needed in winter and it is set to 80A Charge Rate (910AH of battery) which uses 120V/22-25A on the L5:30 plug pending on passthrough voltage to house.
 
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