Off Grid Cabin - Will this work as intended?

[willh]

Long time lurker, first time poster. I have been planning a solar system for my parents off grid cabin near Ottawa Ontario for a long time now. The cabin is boat/ATV access only and has no option to connect to the grid. The cabin is fully wired for AC and they currently use a Honda 2200w generator for power when required (lights at night, charging cellphones, basic power tools when working on the place). The cabin is currently used 3 seasons and closed for the winter but they do have a woodstove and insulation so it could feasibly be used in the winter. The cabin is usually used 3 or 4 days at a time and maybe a few week long stays throughout the spring/summer/fall.

The main objective of the solar system is to run a refrigerator full time whether they are there or not (May 1st -September 30th roughly). The next objective is to power a few lights at night, charge cellphones, run a vacuum occasionally, and a few hours of tv a day while they are there. With this system being unattended for periods of time throughout the season it needs to be as dependable and redundant as possible. Please have a look over the planned system and give any feedback you may have before we pull the trigger and start buying stuff!

Planned 48V System:

-16 Eve 230AH Cells with 200A JK BMS (~9.4KWH Storage using 80%)
-4 x 235w panels in series on pole mount 100ft away (119.2Vmp/148Voc)
-10AWG RPVU90 from pole mount to controller (100ft)
-Victron 250/60 MPPT
-Victron Multiplus 2 3kva (2400w Cont/5500w Surge Inverter Charger)
-Midnite Solar 125A Disconnect/Breaker Box (Battery to Inverter Breaker/Battery On/Off Switch)
-63a/150VDC Midnite Breaker Controller/Battery Connection
-30a/150VDC Midnite Breaker (array wire breaker/mostly a switch to shut off PV to controller)

I realize the array is quite undersized compared to the rest of the system, already have the panels and can expand this part of the system if the need arises. As the system currently sits will this power a fridge worry free for 3 seasons and still have power left for lights and cellphone charging etc when visiting. The system looks overbuilt for this on paper, will it have limitations in the realworld? Any comments, feedback, criticisms are very welcome! Only want to do this once!

Thank you!

Will

 

[MisterSandals]

The system looks overbuilt for this on paper,

Overbuilt for what daily power usage? Did you do an energy audit to see how many watt hours you use or hope to use each day?

 

[willh]

Roughly yes. The 24/7 load will be a refrigerator, ballpark 1Kwh per day with an energy star unit in the 10-15cuft range. This will be the only load that will require power constantly. I'm also interested in a freezer to fridge conversion which could potentially use far less energy but have planned for worst case scenario for the main load. While people are at the cabin (usually 4 days at a time) usage would be worst case scenario 150W per day lighting, 200W tv, 200W random small device charging.

The generator will be there still for higher/longer use one off items or a string of bad weather while people are there. My main concern is keeping the fridge running 24/7 unattended. Factoring in inverter draw of 12w and a fridge lets say 1.5KWH/day total load while unattended, do you think this will be dependable as described?

 

[Steve_S]

You'd likely spend 1/2 the amount going 24V and using an All-In-One by Growatt capable of 3000w or 4000W. More flexible, easy install (less BOS which is $$$) manageable and well known.
The little amount of Solar really won't charge the 48V.
The Solar Panels you are thinking of are likely 60Cell format... you can get 350W in 60-Cell.
Check out this site, you can even drive down to pickup. If limited to four panels, get as many watts as you can for the space & number of panels.

24V Solar Panel

24V/280AH = 7168Wh
24V/304AH = 7782Wh

See my links in my Signature, I'm in Algonquin Park area, 100% offgrid, solar, 24V/4000W system with 1190AH of LFP.
I have a Danby Energy-Star fridge which uses 240kWh for a whole year, very low power draw while running.

EDIT:
I wanted to add, that it most likely be prudent to use a 4-Panel Adjustable Ground Mount, which would allow you to readjust the panels for each season, otherwise the Average Angle for year-round production for you is 45 Degrees which can still result in snow buildup on the panels. A fairly simple Wood Based structure is not hard to do or even premade adjustable ground mounts are available at reasonable prices... Get into Pole Mounted or Automatic then things get a tad whacky.

 

[willh]

Thank you for your comments Steve, I have read a lot of posts by you and knowing you were in Ontario I hoped that you would chime in. I have looked into the All-In-One units and they do seem to check a lot of boxes. What I have a hard time wrapping my head around is the standby power consumption, using nearly twice the power as your fridge on any given day! If the idle/standby usage was even in the ballpark of the multiplus 2 I would have been on board a long time ago. Ideally whatever refrigerator that ends up in the cabin can hopefully be used on the victron search mode with a tiny 3w draw as well.

I investigated the 24v route and have come to the conclusion that most of components run in the same ballpark price wise. About 1000 dollars more for this 48v system than a 24v system spec'd with the 280ah cells you listed. Really the only major difference in price between the two systems was the batteries, which makes sense given the 4.6kwh extra storage in the 48v system. It was hard to move away from the 280ah cell idea to be honest given their listed cycle capacity. After running the numbers I have come to accept that even the 230ah batteries will die of old age before cycles in the planned use scenario (Which is also kind of awesome, will be neat to see how long some Lifepo4 make it). I am also very fond of the far lower amperages involved with the 48v system.

We already have the 4 solar panels, got them used and cheap couldn't pass them up. Yes they are 60 cell units. We are actually building a pole mount ourselves and already have most of the materials gathered, again on the cheap just repurposing various used steel. The design for the pole mount allows for 4x72 cell panels but would like to use what we have. It is a pretty difficult site solar wise (beautiful large trees) and the area that gets consistent sun is 100ft from the cabin on solid bedrock. The pole mount will be bolted to the bedrock and is adjustable from nearly vertical to completely horizontal, will be in a fixed south direction. I know everyone says panels are cheap but they are far from free when you consider the price of materials to mount them on these days! If these panels wont suit the loads the first step would be to swap out the panels for larger wattage units as you have suggested, just figured why bother if this would work.. If it was as simple as slapping 6 more on the cabin roof this whole system would look different haha.

You have me a little confused when you say the little solar really wont charge the 48v. I'd definitely agree if we were talking about lead acid, but is there something I'm missing about lithium here? The way I understand it they are like a sponge and will take whatever you give them, even if it is extremely low c rate. Is there a detriment to this low of charge rate with lithium that I'm unaware of? If not then in my mind watts are watts and the panels will put the same amount into 48vs24v. Maybe more at 48 based on conversion efficiency haha? Honestly, let me know if this is an issue. Have done lots of reading, limited hands on experience.

Just out of curiousity, how big is your fridge? haha.. Wouldnt it be nice if home depot would let you slap a watt meter on a few different models over a week or two!? Would make this kind of planning far less theoretical.

 

[Steve_S]

Simply put on the panels. it takes a lot of juice to charge these batteries up within the Sun Hours available.
Standby consumption varies by make & model of gear, as well as how well the sleep, eco & powersave modes work on various makes & models also varies. My Samlex Inverter can use as little as 8W in standby eco mode but it's pulses are gnarly.

Check out these fridges. I got a Danby 11 Cu Foot model which was updated so it's not listed here now. BTW: Got it from Costco and they have sales every couple of months on them. https://www.danby.com/product-categories/apartment-size-refrigerators/ Note that not all are rated the same and not all have the EnergyStar ratings either.

 

[12VoltInstalls]

If it was as simple as slapping 6 more on the cabin roof this whole system would look different haha.

If you get any snow the advantage of ground mount is you can clean them off easily. Being your latitude- in winter- vertical “loses” some harvest but won’t accumulate snow or lose that much.
The other thing is adding a “second array” facing SSE and a SSW or SW on the first array can give you a net gain of watts over a day (made a surprisingly good impact for my system).

Once spring hits you can tilt accordingly to maximize harvest.

My situation is different but mine are always vertical- I’m so overpaneled in summer it doesn’t matter for me because I really can’t use it anyway. In your situation it sounds like you could utilize everything to a point.

 

[Horsefly]

@willh - I too have a cabin that is not used in the winter. I put in solar in 2017. We have had a propane fridge since the cabin was built in 1975, but it is aged and needing replacement, and with the new battery going in this spring (8S 230Ah LFP), we are tentatively planning on replacing the fridge with an electric.

Our system is 24V, like @Steve_S. One of the advantages of going 24V is that there are more appliances that will operate on 24VDC. In our case, our standard operating procedure is to put the inverter in standby, and with a 24VDC fridge we can completely avoid the tare loss from the Inverter and keep the fridge powered.

We're looking at this fridge: https://uniqueappliances.com/product/off-grid-13-cu-ft-solar-powered-dc-refrigerator/ It's 13cf (replacing the little 8cf propane one we have today), and they claim it will only consume 24Ah per 24 hours on 24VDC.

Edit to add: We actually completely shut down our cabin in the winter, and the cabin is unheated in the winter. So our routine is to turn off the refrigerator, prop the doors open, and take the food down to our homes in the valley. There are issues with running a fridge when its surrounding air is below freezing, so you may want to look into that.

 

[willh]

Steve, great website, looks like some very efficient options out there! I have read a lot about the pitfalls with various powersave options, seems to be not only inverter specific but also dependent on what the inverter is trying to run. For a standard fridge I would imagine ecomode would not be an option for many if not all based on what I have read (defrost timers etc). A manual defrost freezer to fridge conversion seems like a good candidate for ecomode when used with a mechanical thermostat type control. As far as charging the batteries up to full I totally agree, I would imagine with the current array setup there will be many days where the batteries are running midrange capacity. In my mind as long as the solar panels can produce roughly 2x the watts consumed by loads per day they should reach full charge somewhat frequently in 3 season use, and the total storage should allow for many days of poor solar output. Does this seem reasonable? Using round numbers, 4hrs x 940w array = 3.76kwh per day, even if the panels only output 50% of this number the result should be net positive while only running a fridge by my calculations?

12voltinstalls, the pole mount planned would have the top of the panels at a maximum height of 10ft while oriented nearly vertical. While winter use isn't all that likely it is still a nice option to plan for, at this height the panels could be easily reached with a soft brush to pull any risidual snow off if required. If used in the winter power requirements would be extremely low as there would be no need for the refrigerator, just lights/tv/device charging so solar wouldn't be a huge concern given storage capacity of this system and available generator charging. In the event that more solar is required I think our first most efficient step would be trading panels in for higher output units, could nearly double output by this method alone. In the event a second array is added in the future that is very useful information. Would both arrays be wired into the same controller still in this situation? As in a 4s2p type connection?

Horsefly, thanks for the input. I have looked extensively at the DC refrigeration options out there and have some hands on experience with them actually. In the past I worked for a few different remote fly in fishing/hunting operations that had a variety of different brands of dc refrigeration units. They all performed very well and never seemed to be an issue in their relatively small solar systems. In my experience they are far superior to propane fridges in keeping things at a consistent temperature. With that said the cost of the DC units are pretty high, I came to the conclusion the money would be better spent on a better inverter (need an inverter anyways) and battery capacity. Also decided for me it would keep the system simpler as a whole, with the inverter being the only load in my planned system I figure I can use it's adjustable low voltage cutoff as extra protection before BMS intervention (redundancy). Could use a battery protect type item with a DC fridge but again, just more components and want to keep it simple. With that said, the unique dc appliances in my experience are dependable and efficient so I'm sure you will be happy with that selection if you move forward.

 

[willh]

Horsefly (re:edit) - Yes I can imagine there can be issues with running some refrigerators in cold ambient temperatures. This cabin is normally closed up as you describe in the winter. It is insulated and has an airtight wood stove so winter use is a possibility, if on the rare occasion the cabin gets used in the winter there would be no need for refrigeration.

Have you considered what you will do with the batteries during the winter time? From what I have read these lifepo4 batteries should be fine to leave on site disconnected near the 50% SOC range? My current plan would be to do just that unless I find out otherwise. The batteries will be stored inside the cabin out of the elements but could be as cold as -30 for a day or two at a time (worst case).

In the event that winter use of the cabin happens the plan of action would be to arrive in the morning and get the cabin/batteries well above zero with the woodstove throughout the day before putting the system online. Anyone see anything wrong with this approach?

 

[12VoltInstalls]

4hrs x 940w array = 3.76kwh per day, even if the panels only output 50% of this number the result should be net positive while only running a fridge by my calculations?

Sounds about right for a wildhat guess imho

Would both arrays be wired into the same controller still in this situation? As in a 4s2p type connection?

I have total 800W doing that right now, with another unrelated 200W pushing into my neighbor’s “grid.”

With that said the cost of the DC units are pretty high, I came to the conclusion the money would be better spent on a better inverter

You can get a not-frost-free 10.5ish cubic foot fridge/freezer that uses 60-80W running at homeo depot for ~350.
I’m running 4.8cf ??? ish at the same watts since May with the 1200W inverter on 24x7 with no issues (until winter where we might not see sun for a week here). Summer I had plenty of capacity. So for under $600 you can do what you need. FYI the 4.8cf cost me $159 or something like that and I used the same inverter I’ve been running for four years.

 

[12VoltInstalls]

plan of action would be to arrive in the morning and get the cabin/batteries well above zero with the woodstove throughout the day before putting the system online

With lead acid just turn it on. Mine has run to -15*F with my batteries outside, and it’s going to be -20 tomorrow night…

 

[willh]

Sounds about right for a wildhat guess imho

I have total 800W doing that right now, with another unrelated 200W pushing into my neighbor’s “grid.”

You can get a not-frost-free 10.5ish cubic foot fridge/freezer that uses 60-80W running at homeo depot for ~350.
I’m running 4.8cf ??? ish at the same watts since May with the 1200W inverter on 24x7 with no issues (until winter where we might not see sun for a week here). Summer I had plenty of capacity. So for under $600 you can do what you need. FYI the 4.8cf cost me $159 or something like that and I used the same inverter I’ve been running for four years.

What inverter are you using for this? Great to hear some real life numbers/examples. Also will have to do some investigating, didn't think you could even get a not-frost-free unit these days, will look into it.

With lead acid just turn it on. Mine has run to -15*F with my batteries outside, and it’s going to be -20 tomorrow night…

Planned batteries are lifepo4, with lead acid I'd leave them connected all winter whether I was there or not.

 

[12VoltInstalls]

What inverter are you using for this?

Giandel pure sine 1200W

didn't think you could even get a not-frost-free unit these days, will look into it.

cheap / small units

Planned batteries are lifepo4

no doubt lifepo has some advantages but you can’t charge them when cold. If that’s not an issue…

If you want some winter use lead is an option. Less moula up front; possibly less money long term with care but LiFePo is a fairly reasonable longterm spend and most say they’re gonna cost a lot less over time.

 

[willh]

Giandel pure sine 1200W

cheap / small units

no doubt lifepo has some advantages but you can’t charge them when cold. If that’s not an issue…

If you want some winter use lead is an option. Less moula up front; possibly less money long term with care but LiFePo is a fairly reasonable longterm spend and most say they’re gonna cost a lot less over time.

If Lifepo4 ends up delivering the cycles they are supposed to be capable of it should be a far cheaper/efficient option long term by my calculations. Time will tell. Winter use of the cabin will involve starting a fire either way so waiting half a day for the batteries to warm up before connecting the system is a small inconvenience compared to the positive attributes of lifepo4 throughout the rest of the year. And again, currently the cabin doesn't get used in the winter, but system should still be usable if that were to change.

 

[Horsefly]

Have you considered what you will do with the batteries during the winter time? From what I have read these lifepo4 batteries should be fine to leave on site disconnected near the 50% SOC range? My current plan would be to do just that unless I find out otherwise. The batteries will be stored inside the cabin out of the elements but could be as cold as -30 for a day or two at a time (worst case).

I thought about just disabling everything, but I'm the furthest away from the cabin, and my siblings will not probably like the idea of having to do something and wait to get them warm.

My goal is to make it so people can walk into the cabin, take the inverter out of standby, and have everything work. They are used to that with our AGM batteries, so I wanted to have it work the same with my LFP upgrade. I documented the insulated, heated battery box I built here. Near the end of the thread you'll see that my repeated testing seems to indicate that keeping the batteries between 50°F and 60°F will take between 3Ah and 7Ah per day (probably closer to 3). We will have the solar charge controller on all winter, and the last 3 winters we've never had the panels covered to the point of no generation for more than 3 days at a time - Less than 10 days total for the winter. So I'm pretty confident it will all be fine all winter.

 

[willh]

I thought about just disabling everything, but I'm the furthest away from the cabin, and my siblings will not probably like the idea of having to do something and wait to get them warm.

My goal is to make it so people can walk into the cabin, take the inverter out of standby, and have everything work. They are used to that with our AGM batteries, so I wanted to have it work the same with my LFP upgrade. I documented the insulated, heated battery box I built here. Near the end of the thread you'll see that my repeated testing seems to indicate that keeping the batteries between 50°F and 60°F will take between 3Ah and 7Ah per day (probably closer to 3). We will have the solar charge controller on all winter, and the last 3 winters we've never had the panels covered to the point of no generation for more than 3 days at a time - Less than 10 days total for the winter. So I'm pretty confident it will all be fine all winter.

I have seen that post before, didn't associate it with you off the top of my head though. The whole system you have put together is very neat and tidy, looks professional. The battery box is an excellent idea and in the future if our cabin starts to see winter time usage I will likely be asking for updates on its performance. I know what you are saying about other people using it and keeping it simple and I totally agree.

 

[Horsefly]

You need 5 times the amount of panels you currently have if you're planning on running a fridge full time.

Without the math, that seems like a bold statement. It seems like it would depend on what fridge, right?

Earlier in this thread I pointed to one whose spec says it consumes 24Ah / day on a 24V system. I only have ~1700W of panels (NOT 5 times what the OP is talking about) and I'm pretty certain we can handle that fridge.

 

[Horsefly]

Where are you located?

Op also said he wanted to run a normal 120v fridge.

Takes a lot of juice to do that when you're getting 5% of rated panel output while it's raining and gloomy up north.

Oh I agree he's got a difficult set of requirements. But 5x? I'm just asking what the math is. For that matter, is there something to the 5% figure?

 

[willh]

Thanks for the input, location is near Ottawa Ontario. I'm not against a DC fridge but it seems that there are a lot of viable 120v options to be had. Steve posted above that his danby fridge uses 240kwh/yr for example. So 657w fridge plus inverter standby of (13wx24hrs) 312w, say 1100w per day to run the fridge including inverter inefficiancy. Battery should run this for 8 days without solar. I figure that accounts for the bad weather and on a decent day the panels should produce atleast twice as much as the system consumes to catch up. Honestly asking if this is out to lunch? What would you expect to see out of 4x230w panels on a normal summer day? Like in your actual experience, not just sun hrs x the watts.