Remote Cabin NH (long post)

Erik_S

New Member
Hi,
I have an off grid camp in the White Mountains of NH. I have always used a generator to power the camp when we are there. I have Honda EU2000i generator that runs everything I need. The cabin has a propane fridge, range and on demand hot water heater. The cabin is wired for 120vac with led lights, tv, radio, cell phone chargers and a 120v 1/4hp well pump (I installed a large captive are tank so the well pump runs once per day for approx 5 minutes). I just purchased 16 3.2v 200ah LiFePo4 batteries and I already have 10 400w Risen solar panels. I keep leaning towards a Victron 3000w 12v inverter because the only big draw would be the well pump once per day other than that a high load is 200 watts. I would also like to use several 12v hot water heater elements as a diversion load to run in a radiant floor heating system. I understand by increasing the inverter voltage to 24v I would reduce the wire size needed but the batteries will be within 5ft of the inverter. I think I want to go with 12v so I can look at cell chargers and tv's that can run on 12v. So after all that I am just looking for thought on the great 12v debate. I have read about some folks using a 12v heating mat inside an insulated battery box with a dedicated solar panel so when the sun is out the battery would be kept above freezing. I was wondering if anyone has tried this and how well it works? I haven't purchased the inverter, charge controllers or BMS yet until I determine the voltage. And one last thing I have the new batteries and I also have 4 12v 140AH AGM batteries can I have 2 separate battery banks with each having its own charge controller and a battery switch going into the inverter?

Thanks

Erik
 

snoobler

Solar Honey Badger
12V sounds fine for your application.

Note that going with 12V is only 10-15% more efficient, and wiring might be an issue.

4000W of solar/10kWh of batteries and your loads sounds like a crap-ton of surplus capacity. Not sure that I'd put a lot of emphasis on 12V appliances/devices unless they cost about the same.

No feedback on heater schemes.

I have mixed feelings about a switchable second bank/SCC, but it's not insane.
 

ken morgan

Solar Addict
I have basically the same components though i run on 48 volts. my cabin is on the north west flanks fo Mt. Fuji at 1200 meters elevation. It gets cold and stays cold, so here was/is my solution for keeping the batteries warm. 1/4" aluminum plate that exactly fits the footprints fo the batteries when they are in their final configuration. so if you go 12vdc then I would guess you would have a 4p4s config. on the bottom of the aluminum plate I used kapton tape to tape down 8 of the 25w 12 volt silicone heating pads (you would probably need only 4 as your bank is exactly half the size of mine.) i used two 12 volt temp controllers and I had to get a step down transformer from 48vdc to 12vdc to power the controllers with.

I tested the aluminum plate in free air with no insulation and no temp controllers. Ambient temps were 13° when i was testing. It reached 51° C (125°F) and stabilized there at the one hour mark. I then put the temp controllers on the pads and sandwiched the aluminum plate between two pieces of the insulation and set the controllers to hold the temps between 15° and 25°c so it would turn on at 15 and off at 25 and cycle as needed to keep it between those two temps. The system worked as planned so i then built the actual foam insulated box.

insulated box: I placed a 3" piece of the blue xps insulation foam under the aluminum plate the batteries on top of the aluminum plate, I then created the actual battery enclosure with pieces of the XPS foam to form sides and top that exactly enclosed the batteries. I glued the foam insulation together with spray foam (just a little does the trick) and it makes it airtight so no air leakage. the top fits tightly into the space between the four walls. with standard duct tape to seal it as I want to be able to open it from time to time without destroying the box.

The BMS sits on top of the foam with its temp sensor in the middle of the pack. the sensors from the controller are set about 1/4 of the way from the bottom. I will get some photos two weeks from now when I go back up to the cabin. and lastly I added one last temp sensor close to the middle that I will be hooking up to a third but much more expensive thermal control circuit to act as a failsafe if either of the other two unit go bad in the ON position. it will control a 48vdc relay that will kill power to the small controllers by shutting off power to them. obviously I will be watching this closely for the first couple of months, but with the BMS having the final say on charging worst case is that something dies and I cannot charge until the temps come up.

Obviously this sits in an insulated enclosure that keeps the wind and elements from it as well.

list of parts from amazon: Mods/admins if this is a no no then just let me know and i will delete.





some other small bits from digikey that I could not find on amazon.
 

Erik_S

New Member
I have basically the same components though i run on 48 volts. my cabin is on the north west flanks fo Mt. Fuji at 1200 meters elevation. It gets cold and stays cold, so here was/is my solution for keeping the batteries warm. 1/4" aluminum plate that exactly fits the footprints fo the batteries when they are in their final configuration. so if you go 12vdc then I would guess you would have a 4p4s config. on the bottom of the aluminum plate I used kapton tape to tape down 8 of the 25w 12 volt silicone heating pads (you would probably need only 4 as your bank is exactly half the size of mine.) i used two 12 volt temp controllers and I had to get a step down transformer from 48vdc to 12vdc to power the controllers with.

I tested the aluminum plate in free air with no insulation and no temp controllers. Ambient temps were 13° when i was testing. It reached 51° C (125°F) and stabilized there at the one hour mark. I then put the temp controllers on the pads and sandwiched the aluminum plate between two pieces of the insulation and set the controllers to hold the temps between 15° and 25°c so it would turn on at 15 and off at 25 and cycle as needed to keep it between those two temps. The system worked as planned so i then built the actual foam insulated box.

insulated box: I placed a 3" piece of the blue xps insulation foam under the aluminum plate the batteries on top of the aluminum plate, I then created the actual battery enclosure with pieces of the XPS foam to form sides and top that exactly enclosed the batteries. I glued the foam insulation together with spray foam (just a little does the trick) and it makes it airtight so no air leakage. the top fits tightly into the space between the four walls. with standard duct tape to seal it as I want to be able to open it from time to time without destroying the box.

The BMS sits on top of the foam with its temp sensor in the middle of the pack. the sensors from the controller are set about 1/4 of the way from the bottom. I will get some photos two weeks from now when I go back up to the cabin. and lastly I added one last temp sensor close to the middle that I will be hooking up to a third but much more expensive thermal control circuit to act as a failsafe if either of the other two unit go bad in the ON position. it will control a 48vdc relay that will kill power to the small controllers by shutting off power to them. obviously I will be watching this closely for the first couple of months, but with the BMS having the final say on charging worst case is that something dies and I cannot charge until the temps come up.

Obviously this sits in an insulated enclosure that keeps the wind and elements from it as well.

list of parts from amazon: Mods/admins if this is a no no then just let me know and i will delete.





some other small bits from digikey that I could not find on amazon.
Awesome, I like the idea of the aluminum tray as heat transfer. Do you run the heating pads from the batteries or a separate solar panel? My thought was put a small dedicated solar panel to run the heating pads because it is only needed when charging. Now with that being said with the amount of insulation and the batteries will heat when charging I guess running off the batteries wouldn't be a bad idea. Do you have a diversion load? I heat with a wood stove and in winter it takes approx 8hrs to warm the cabin up I was hoping to use the excess power to heat water/antifreeze for radiant floor heat.

Thanks

Erik
 

Wellbuilt

Solar Addict
Ken , that is a very slick rig 👍.
I may have to try the lithium battery’s when my cheep golf cart battery’s die .
I really have no problems with the GC battery’s .
My place sees below -0 for weeks every winter .
I’ve never see the inside first floor area 1300 sf below 37o I’m supper insulated
water dosent freeze down stairs so I mite be ok with no heat .
Good read
 

ken morgan

Solar Addict
Awesome, I like the idea of the aluminum tray as heat transfer. Do you run the heating pads from the batteries or a separate solar panel? My thought was put a small dedicated solar panel to run the heating pads because it is only needed when charging. Now with that being said with the amount of insulation and the batteries will heat when charging I guess running off the batteries wouldn't be a bad idea. Do you have a diversion load? I heat with a wood stove and in winter it takes approx 8hrs to warm the cabin up I was hoping to use the excess power to heat water/antifreeze for radiant floor heat.

Thanks

Erik
Erik straight off of the battery bank. couple of other thoughts that I am toying with:

run it on a timer. set it so that it turns on at about 0300 and preheats the batteries prior to the morning charge cycle and then shuts down at 0900 or so.

possibly run all pads with just one of the temp controller, (on timer) and use the second temp controller (on a timer) set at different values to stage the heat...for instance keep it at 5°c through the night which is fine for discharge and then ramp it up to 10-15 just prior to morning charge cycle.

still playing with it in my head as too what the best configuration is. one of the electrical type guys could do a quick calculation as too how much power you use though it would vary on the actual duty cycle that you end up with. I don't think it is all that much for a 20kw lithium bank.

my biggest concern is to not heat it up too much thats why I assembled it with 8 of the pads, as my system is 48 volts, I wired four in series I can shut half of them down, or could also wire the two packs in series which by doubling the resistance from what i understand should drop output to around 25%.

when I install the new BMS next time I am at the cabin and actually start using the pack I can start running the heat for very short periods and take measurements to figure out exactly what I need for settings. good thing is I now have about 3 months before I should actually need the heater pads to work. plenty of time to experiment before it drops below 5°C
 

ken morgan

Solar Addict
Ken , that is a very slick rig 👍.
I may have to try the lithium battery’s when my cheep golf cart battery’s die .
I really have no problems with the GC battery’s .
My place sees below -0 for weeks every winter .
I’ve never see the inside first floor area 1300 sf below 37o I’m supper insulated
water dosent freeze down stairs so I mite be ok with no heat .
Good read
the original builder of my cabin actually had a mini wine cellar built into the foundations of the cabin that is well insulated and never seems to get too cold or hot. I considered putting my batteries and inverter in it but its such a long run from the panels that I was worried about line loss. I originally sized all of my wiring for 1% or less loss.... though depending upon what I see temp wise this year I might do it anyways.

in the past I had some no name AGM's from Alibaba and the batteries inside of the battery shed never got below about 3°C over the course of the winter. but that was due to heat generated by the batteries, the inverter and the solar controllers. Being that lithium's charge so much more efficiently from what I have read I can pretty much forget about any secondary heat being produced by the batteries themselves, so I did some research and built my heating pad. I think my cable runs would be over 100' from the panels by the time I buried them. I guess I could run them overhead from the shop and not bury them and possibly keep the total run under or around 60' but I would definitely have to upsize my cables coming from the solar controllers to the battery bank to avoid loss.

things to ponder.
 

ken morgan

Solar Addict
Awesome, I like the idea of the aluminum tray as heat transfer. Do you run the heating pads from the batteries or a separate solar panel? My thought was put a small dedicated solar panel to run the heating pads because it is only needed when charging. Now with that being said with the amount of insulation and the batteries will heat when charging I guess running off the batteries wouldn't be a bad idea. Do you have a diversion load? I heat with a wood stove and in winter it takes approx 8hrs to warm the cabin up I was hoping to use the excess power to heat water/antifreeze for radiant floor heat.

Thanks

Erik
funny I just noticed your comment about a diversion load. I have been mentally doodling a layout for the mother of all diversion loads... My system to date was only 4k panels. I am adding another 4k for a total of 8K . why? to bring the batteries to full charge even under less than optimal conditions, also to run a small split pack to dehumidify the cabin during the rainy months without using power from the battery.

I got 20 more panels that are the same size and rating as my originals from a solar farm that was decommissioned not to far from my cabin. it seems having a landslide take out 3/4 of your panels is a bad thing. Here they actually put solar farms on the steep slopes of small to medium sized mountains so as to not use valuable arable space...well one of them came down and I was able to purchase the extra panels. (at scrap prices)

so heres the gist of my thoughts. take a 14,000 liter stainless steel milk trucks tank weld 4 or 6 water heater bungs on both ends. take stainless pipe and run it thought the inside of the tank to act as a heat exchanger, dig a honking big hole and pour a pad at the bottom, spray about 4" of foam spray insulation on all sides of the tank except where the heating elements go in. pour concrete caps on the ends for access and then bury it. I would then set two of my tristar charge controllers to do load diversion once the batteries have hit 3.4 per cell. now I am not going to bother to do the math in regards to BTU's and all the other happy stuff, but I bet given a whole year of diversion that I can get that tank up to 90°C and then use buried insulated water lines to heat the cabin in the winter... if not at the very least I will get hot water for free. just got to make sure I add a couple of pressure transducers as well as temp sensors to tell the tristars to cut power once temp gets to 90, or if pressure exceeds xx psi. obviously a pressure pop off valve is needed as well.
 

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GeorgiaHouse

New Member
Hi,
I have an off grid camp in the White Mountains of NH. I have always used a generator to power the camp when we are there. I have Honda EU2000i generator that runs everything I need. The cabin has a propane fridge, range and on demand hot water heater. The cabin is wired for 120vac with led lights, tv, radio, cell phone chargers and a 120v 1/4hp well pump (I installed a large captive are tank so the well pump runs once per day for approx 5 minutes). I just purchased 16 3.2v 200ah LiFePo4 batteries and I already have 10 400w Risen solar panels. I keep leaning towards a Victron 3000w 12v inverter because the only big draw would be the well pump once per day other than that a high load is 200 watts. I would also like to use several 12v hot water heater elements as a diversion load to run in a radiant floor heating system. I understand by increasing the inverter voltage to 24v I would reduce the wire size needed but the batteries will be within 5ft of the inverter. I think I want to go with 12v so I can look at cell chargers and tv's that can run on 12v. So after all that I am just looking for thought on the great 12v debate. I have read about some folks using a 12v heating mat inside an insulated battery box with a dedicated solar panel so when the sun is out the battery would be kept above freezing. I was wondering if anyone has tried this and how well it works? I haven't purchased the inverter, charge controllers or BMS yet until I determine the voltage. And one last thing I have the new batteries and I also have 4 12v 140AH AGM batteries can I have 2 separate battery banks with each having its own charge controller and a battery switch going into the inverter?

Thanks

Erik
Hi!!

I’m new at this solar thing. I’m looking to run solar in my house in Georgi. I don’t live in this house full -time & I’m in the middle of no where, so running power is out of the question Any ideas on what to do? Hopefully I went about this the right way.
Thank you
David
 

snoobler

Solar Honey Badger
Hi!!

I’m new at this solar thing. I’m looking to run solar in my house in Georgi. I don’t live in this house full -time & I’m in the middle of no where, so running power is out of the question Any ideas on what to do? Hopefully I went about this the right way.
Thank you
David

You should likely start your own thread.
 

Erik_S

New Member
funny I just noticed your comment about a diversion load. I have been mentally doodling a layout for the mother of all diversion loads... My system to date was only 4k panels. I am adding another 4k for a total of 8K . why? to bring the batteries to full charge even under less than optimal conditions, also to run a small split pack to dehumidify the cabin during the rainy months without using power from the battery.

I got 20 more panels that are the same size and rating as my originals from a solar farm that was decommissioned not to far from my cabin. it seems having a landslide take out 3/4 of your panels is a bad thing. Here they actually put solar farms on the steep slopes of small to medium sized mountains so as to not use valuable arable space...well one of them came down and I was able to purchase the extra panels. (at scrap prices)

so heres the gist of my thoughts. take a 14,000 liter stainless steel milk trucks tank weld 4 or 6 water heater bungs on both ends. take stainless pipe and run it thought the inside of the tank to act as a heat exchanger, dig a honking big hole and pour a pad at the bottom, spray about 4" of foam spray insulation on all sides of the tank except where the heating elements go in. pour concrete caps on the ends for access and then bury it. I would then set two of my tristar charge controllers to do load diversion once the batteries have hit 3.4 per cell. now I am not going to bother to do the math in regards to BTU's and all the other happy stuff, but I bet given a whole year of diversion that I can get that tank up to 90°C and then use buried insulated water lines to heat the cabin in the winter... if not at the very least I will get hot water for free. just got to make sure I add a couple of pressure transducers as well as temp sensors to tell the tristars to cut power once temp gets to 90, or if pressure exceeds xx psi. obviously a pressure pop off valve is needed as well.
Ken,
I was looking at the minisplit option because it could be diversion load in winter and summer. Now I will have to look at those options. I keep thinking of using 1 or 2 hot water heaters with dc heating elements with 2 600watt elements. A 40 gallon water heater uses 5.58Kwh for a 70 degree rise. My thought is use a zone valve and a circulating pump to run in through the tubing. When I built the place I put pex tubing and aluminum plates under the subfloor. I set it up as 3 zones 1 for the second floor (bedrooms) and split the first floor in half as 2 zones. I am not looking to have the house warm for living in just keep it above freezing I am still waiting for the batteries to be delivered. I already have 10 400w Risen panels, I keep leaning towards using victron 3000w inverter I would like to add a ceel modem to keep an eye on the system and cabin remotely.

Thanks

Erik
 

ken morgan

Solar Addict
Ken,
I was looking at the minisplit option because it could be diversion load in winter and summer. Now I will have to look at those options. I keep thinking of using 1 or 2 hot water heaters with dc heating elements with 2 600watt elements. A 40 gallon water heater uses 5.58Kwh for a 70 degree rise. My thought is use a zone valve and a circulating pump to run in through the tubing. When I built the place I put pex tubing and aluminum plates under the subfloor. I set it up as 3 zones 1 for the second floor (bedrooms) and split the first floor in half as 2 zones. I am not looking to have the house warm for living in just keep it above freezing I am still waiting for the batteries to be delivered. I already have 10 400w Risen panels, I keep leaning towards using victron 3000w inverter I would like to add a ceel modem to keep an eye on the system and cabin remotely.

Thanks

Erik
Erik, how did you get the figure of 5.58Kwh for a 70° rise? Is that Farenheight or Celcius. if you know the formula to figure for temperature rise v/s input power v/s time I would love to have that for my own calcs. Thanks

Ken
 

ken morgan

Solar Addict
Ken,
I was looking at the minisplit option because it could be diversion load in winter and summer. Now I will have to look at those options. I keep thinking of using 1 or 2 hot water heaters with dc heating elements with 2 600watt elements. A 40 gallon water heater uses 5.58Kwh for a 70 degree rise. My thought is use a zone valve and a circulating pump to run in through the tubing. When I built the place I put pex tubing and aluminum plates under the subfloor. I set it up as 3 zones 1 for the second floor (bedrooms) and split the first floor in half as 2 zones. I am not looking to have the house warm for living in just keep it above freezing I am still waiting for the batteries to be delivered. I already have 10 400w Risen panels, I keep leaning towards using victron 3000w inverter I would like to add a ceel modem to keep an eye on the system and cabin remotely.

Thanks

Erik
so I found a way to calculate out temp rise vs power used. how accurate it is is beyond me. I might have to size my tanka bit smaller (like half) to get any useful work out of it. still doodling with numbers at the moment.

Good luck.

Ken
 

Erik_S

New Member
Ken,

This is what I found:

BTU formula > 1 BTU = 2.931 x 10–4 Kwh (kilowatt hours).
BTU = 2.931 x .0001 = .0002931 Kwh
Therefore it takes .000239 Kwh to raise 1 pound of water 1° F

30 Gallons of water x 8.34 = 250.2 lbs
40 Gallons of water x 8.34 = 333.6 lbs

Calculation using 40 Gallon water heater:
> Ordinary 40 gallon water heater in attic. Temperature in attic = 50° F. Temperature of water in tank = 50° F.
> Water in tank weighs 333.6 lbs.
> How much electricity is needed to raise temperature of full tank to 120° F.
> 120° minus 50° = 70° > so the temperature needs to go up 70°
> Multiply 333.6 x 70 x .0002391 = 5.58 Kwh


Erik
 

ken morgan

Solar Addict
Ken,

This is what I found:

BTU formula > 1 BTU = 2.931 x 10–4 Kwh (kilowatt hours).
BTU = 2.931 x .0001 = .0002931 Kwh
Therefore it takes .000239 Kwh to raise 1 pound of water 1° F

30 Gallons of water x 8.34 = 250.2 lbs
40 Gallons of water x 8.34 = 333.6 lbs

Calculation using 40 Gallon water heater:
> Ordinary 40 gallon water heater in attic. Temperature in attic = 50° F. Temperature of water in tank = 50° F.
> Water in tank weighs 333.6 lbs.
> How much electricity is needed to raise temperature of full tank to 120° F.
> 120° minus 50° = 70° > so the temperature needs to go up 70°
> Multiply 333.6 x 70 x .0002391 = 5.58 Kwh


Erik
crunched some numbers and that made a lot more sense. came up to roughly 110 days to raise from 50°f ground water to 170°f in tank at 2000 watts time 4 hours.

Assuming that half the days are a waste due to cloud cover or rain or snow, so it should take about 220 days to heat a 12kl tank up to 170°.

Figuring for the losses due to heat sink effects even with the earlier mentioned 4" of foam insulation after one year that 12Kl tank (3.2K gallons) should be able to produce house level heat + hot water after about one year of soaking up diversion. mind you I am assuming that the extra 4Kw of panels are all the diversion will get, and that they only produce half of their rated output for only 4 hours a day. In reality they should get more due to the other 4k of panels going into diversion after 2 or 3 hours and expanded solar collection in the summer months. time to browse the truck auctions for a milk truck with a blown motor.... :)
 

ken morgan

Solar Addict
so the next question is should I use some cheap high frequency inverters and just run a normal 240 volt hot water control system, or would the losses of some cheap aims inverters prevent me from reaching my goals... so many ways to waste my paychecks and so little time!
 

SolarPrep

Solar Enthusiast
Ken,
I was looking at the minisplit option because it could be diversion load in winter and summer. Now I will have to look at those options. I keep thinking of using 1 or 2 hot water heaters with dc heating elements with 2 600watt elements. A 40 gallon water heater uses 5.58Kwh for a 70 degree rise. My thought is use a zone valve and a circulating pump to run in through the tubing. When I built the place I put pex tubing and aluminum plates under the subfloor. I set it up as 3 zones 1 for the second floor (bedrooms) and split the first floor in half as 2 zones. I am not looking to have the house warm for living in just keep it above freezing I am still waiting for the batteries to be delivered. I already have 10 400w Risen panels, I keep leaning towards using victron 3000w inverter I would like to add a ceel modem to keep an eye on the system and cabin remotely.

Thanks

Erik
Erik: I'd just get a bigger tank to add to your current setup, which is a great way to go. In cases where I am not using any ferrous metals in the main system, I tend to go with a big air pressure tank, and plumb it to an inexpensive heat exchanger so it forms its own loop.
 
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