Off grid cabin system replacement, suggestions and comments welcome

[LiljeQ]

Background info

Last year, just before Covid struck the entire world, my better half and I bought an off-grid summer house. It’s a property of about 15 acers, in the middle of the deep Swedish forests. We spent most of our spare time last year at the cabin – safe to say it’s our favorite spot in the world. Our long-term plan with the property is to make it a year around place.

The cabin has an existing solar power system, 12V, 300W PV-array, built in 1995. The previous owner used some ordinary sealed lead acid batteries (about 220 Ah in total) and during the autumn those stopped taking charge.

We’ve researched and looked at different options and has decided to replace the batteries with a LiFePO4 battery, new charger and PV-array. As our long-term plan is to be there a lot more, we wanted to build a bigger system but keep the initial investment low, because there are a lot of other projects that needs doing as well.

We have calculated that our consumption is at most about 1.8 kWh per day for lightning, fans (no AC of course), pumps, 4G router and WIFI, charging phones and computers. We run both stove, water heater and refrigerator on gas.

The system

The battery is a 12V 400Ah LiFeYPO4 battery set we intend to buy from GWL, with an included 123Smart BMS. The battery gives us 4.8 kWh of storage. If I’ve done the calculations right, we can go two days without any charging and still be within 80% DoD. A regular day well below 50% DoD. The SMART BMS is included and feels like a safe option for us with a smart relay that will turn of either charging or load as a last resort if the safety system of the charge controller fails. (Link: https://shop.gwl.eu/Winston-12V-set...-400Ah-cells-BMS-mobile-monitoring.html?cur=1)

The charge controller is a EPever Triron-AN 6515AN. A 60A solar controller, with a max open voltage of 150V (138V), capable of handling battery voltages from 12-48V. With battery deep discharge protection, overcharge protection, overvoltage protection and relay output to control loads. (Link: https://www.epsolarpv.com/product/44.html)

The solar array have 4 x 280W panels (Voc 38,2, Isc 9.45) in a two string of 2 panels configuration. The house and walls/roof where the current solar panels are mounted is not in the direct south but rather one wall/roof is in south-east and one to south-west. Therefore, we split the panels into two string and place one sting on either wall/roof. The two strings won't be in direct sunlight at the same time, but we maximize how much sun hits the panels over one day - and keep the array close to the house and charge controller. (Link: https://shop.gwl.eu/Solar-PV-System...y-285Wp-60-cells-ESP285-Pack-4-pcs.html?cur=1)

Surge protection (lightning arrestor), as the property is located on a hill and thunder storms are quite common we’ve also added two pair of lightning arrestors, between the charge controller and PV-array as well as the battery and rest of the system. I’ve not found as much information about this as I would have wanted but have taken some inspiration from prebuilt systems available in Sweden and found these lightning arrestors that have the same specifications. (Link: https://www.amazon.se/gp/product/B08HMXGB12/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1 and https://www.amazon.se/gp/product/B08R3F1RQX/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Extending the system in 2-3 years
In 2 or 3 years we want to extend the system to a 24V 400Ah battery by adding four more battery cells, additional cell modules for the 123Smart BMS and adding an inverter to get 230V.

Budget
We have calculated a budget for the complete system of about 4000 € as we replace an existing system we’re only going to replace some of the cabling from the panels to the charge controller as well as between the battery, charge controller and fusebox.

System diagram

 

[chrisski]

Extending the system in 2-3 years
In 2 or 3 years we want to extend the system to a 24V 400Ah battery by adding four more battery cells, additional cell modules for the 123Smart BMS and adding an inverter to get 230V.

Batteries are the one thing I have not been able to figure out how to build on. Once a battery is used in a bank, it becomes weak, and when you add a new battery, that new battery works harder. The battery may not become that much weaker, but resistance changes does not take a lot of resistance difference between the old and new batteries make the new one work harder, but there will be enough.

If you don’t need any new hardware, your plan seems good, except perhaps buy the full battery bank now, or live with your purchase until it dies. There was a lot of hardware I did not consider that ended up costing me as much as the solar equipment when I did my RV build. The wiring, circuit breakers, and tools to strip and crimp the wires added up, along with mounts and hardware. Circuit breakers at $25 a pop and then an enclosure to put them in were more expensive than I expected.

 

[LiljeQ]

Hi Chris!
Thanks for your comment, this is how we have discussed the issues

Batteries are the one thing I have not been able to figure out how to build on. Once a battery is used in a bank, it becomes weak, and when you add a new battery, that new battery works harder. The battery may not become that much weaker, but resistance changes does not take a lot of resistance difference between the old and new batteries make the new one work harder, but there will be enough.

I've tried to search and found some information about this as well, what I've read so far our option it's perhaps not the best but it is possible. The 123Smart BMS has integrated cell balancing and monitoring and should be able to compensate and balance the older with the newer cells. Also if we stay within our estimated consumption our inital cells should be very healthy after two years of use - making the difference between the new and old cells minimal.

If you don’t need any new hardware, your plan seems good, except perhaps buy the full battery bank now, or live with your purchase until it dies. There was a lot of hardware I did not consider that ended up costing me as much as the solar equipment when I did my RV build. The wiring, circuit breakers, and tools to strip and crimp the wires added up, along with mounts and hardware. Circuit breakers at $25 a pop and then an enclosure to put them in were more expensive than I expected.

Absolutely we've planned and already acquired a lot of the additional components and tools for example circuit breakers and crimp tool. Also there is quite a lot of wiring already done in the house (for a 12V system), so that helps. In the budget we also have 500 € unallocated for these things.

 

[Steve_S]

First: Welcome LiljeQ to the forum, you will find many like-minded people doing what you are planning on already. Do have a look at the links in my signature, many things are already answered there that can & will apply to your setup.

Once a battery is used in a bank, it becomes weak, and when you add a new battery, that new battery works harder.

Not Quite, THAT is a Lead Acid hangover comment. Lithium Batteries do NOT suffer this issue, please let's not forward Lead-isms into Lithium Chemistries. The ONLY way this applies if an existing LFP bank is either very heavily used and/or heavily abused "destructively".

---

A few ESSENTIALS for LiljeQ.
Understand that 12V based systems are limited to pretty much a maximum of 2000W for an inverter, which translates into 167A draw at 12V (not derated), where at 24V Battery that draw is 1/2. 24V Based systems can support 4000W comfortably with surge handling to 10,000W. Beyond 4000W, you're looking for 48V Battery system or bigger.

IF using 24V or 48V battery bank and still wanting to run 12V devices, using a Step-Down regulated Converter is the best & cleanest solution.
For 12V system you want 20V to 12V.
For 24V system you want 30V to 12V.
For 48V system you want 60V to 12V.
This is because the Charging Voltage has to be accounted for, if not the Converter will be cooked very quickly.

Battery Bank systems:
Adding batteries in Series increases voltage but not store capacity (in Amp Hours).
Adding batteries in Parallel increases Capacity (Amp Hours) but NOT Voltage.
Batteries are the foundation to build on and to support. Wiring & planning for "now" and in the future is essential at this level. For example, 2/0 wire is 1/2 the cost of 4/0 and seems like a saving, BUT if you want to upgrade and to meet capacity you have to upgrade this "very expensive" wire the savings bite you in the back side. (And spouse will likely add a Boot Print too for good measure).

Lightning & Surge protection.
To be perfectly honest, there is some Serious CRAP being flogged for these purposes at discount prices. AVOID the Discount crap ! This is NOT the place to skimp AT ALL ! I use Midnite Solar "Protectors" as well as more of their gear, it is more costly but some of the best stuff out there. These are available on Amazon & EBay as well.

Budgeting:
Never forget to add extra for BOS (Balance of System) such as wires, fuses, breakers, connectors. All of that stuff adds up to big money FAST and it all sneaks in insidiously. We always "feel & notice" a $1000 item, but the $10 bit, $20 thing, 10 x $5 widgets and the next thing you see is dust in the wallet and nothing else in no time. Believe it or not, BOS can add 30% on top of a build with little difficulty.

Hope it helps, Good Luck.
Steve

 

[chrisski]

Not Quite, THAT is a Lead Acid hangover comment. Lithium Batteries do NOT suffer this issue, please let's not forward Lead-isms into Lithium Chemistries. The ONLY way this applies if an existing LFP bank is either very heavily used and/or heavily abused "destructively"

option it's perhaps not the best but it is possible.

Did not know you could add on to a Lithium Phosphate Battery bank. Had I known that six months ago when I bought my lead acid batteries, I would have started out with the lithium’s. I had thought not adding batteries later on applied to all battery chemistries, but I’m wrong on that.

 

[LiljeQ]

Hi Steve!

Really appreciate the welcome and all the tips and pointers. I will take some time going trough it all! Just a few comments

Thanks for clearing up about the battery and difference between LiFePO4 and SLA. Am I interpreting you correctly that you don't see any problems extending a LiFePO4 with more cells later? I want to add more cells to increase to 24V, i know it still gives me 400Ah but in total an capacity increase from 4.8 kWh to 9.6 kWh.

The inverter is one of those things I would want to add later on, when I extend the battery from 12 to 24V. The system in the cabin right now is a pure 12V system so a step-down device is also something that I might add then instead of replacing devices. But mostly it's lights.

Thanks for the heads up on the additional costs! That makes me even more determined not to make the full investment going form 12v-24v and adding an inverter from the start but making those changes in later on. As the cabin is already completely wired for a 12v system my understanding is that that will work well for 24v system later on as a 12v system in general require wider cable area. I've done the calculations for new wires between the new solar panels, new charge controller, new battery and also the existing fuse box - I have those in another diagram and calc sheet.

I will look into different lightning protectors. The ones I found was exactly the same hardware that are sold by solar installers in Sweden for up to 5 times the cost. Mostly all devices sold here are DIN-mounted for standard European electrical cabinets, and not the round kind like the Midnight ones that is used in the US. But I'll have another look at options that I can find.

 

[Steve_S]

Did not know you could add on to a Lithium Phosphate Battery bank. Had I known that six months ago when I bought my lead acid batteries, I would have started out with the lithium’s. I had thought not adding batteries later on applied to all battery chemistries, but I’m wrong on that.

Unfortunately, that happens with many people who are just starting to do research and learning. Many things that apply to Lead Acid batteries do NOT apply to any Lithium Based battery systems. But to be fair, Lead Batteries have been in use for over 125 years and so much of this type of information is embedded within history and that is Hard to Change ! I have a few thousands of dollars worth of Heavy Lead which is now my secondary battery bank, it cannot be added to because of it's age and the amount of abuse it has survived.

To buy "replacement" Lead would come in just under $4000 for me (4V system) and that would give me 428AH usable.
At "today's" price, that translates into 1000AH of LFP including BMS'.
So I will put it this way.... It's a No Brainer to go LFP.

 

[Steve_S]

I interpreting you correctly that you don't see any problems extending a LiFePO4 with more cells later?

To be clear here (I know you are translating). Complete Battery Packs. Cells make up a battery: IE 4 LFP cells = 12V 4S Battery Pack. So yes, you can add extra assembled battery packs in parallel later. DO NOT PUT BATTERIES IN SERIES ! That is a can of worms.

Inverter can be installed to provide you with 220V to run any standard appliances & devices.
A Regulated Step-Down Converter can be installed to continue using existing 12V devices.

Using one 12V Battery and running 12V is OK. But when you switch to 24V, it means;
-- cracking open that battery pack and adding 4 more cells to turn it into a 24V 8S.
-- or adding an equal battery in Series to make it 24V. (not a good idea for many reasons)
-- or scrapping the 12V and replacing it with a 24V battery pack (that's just wrong on many levels)
OR just use a 24V battery NOW, with a Step-Down to run things "as is now" and you are ready with it when you do get an Inverter.

On Lightning/Surge protectors. I know standards are a bit different across the EU. We in Canada have differences from the American's as well but much more subtle obviously because of the whole 120VAC & 240V Split Phase. IF you are choosing protection devices which are used by local Pro Installers and accepted by your electrical authority as good devices, then use those. I really like DIN mounted gear myself.

 

[LiljeQ]

Ssing one 12V Battery and running 12V is OK. But when you switch to 24V, it means;
-- cracking open that battery pack and adding 4 more cells to turn it into a 24V 8S.

Steve, thanks again for your comment, but I don't think you didnt understand my first post. I'm talking about adding CELLS in series, not complete batteries. The package I'm buying from GWL is a set of four cells with a BMS. Then in 2-3 years I'm adding 4 more CELLS to it, and extending the 123Smart BMS as well.

 

[Steve_S]

You are assuming that the same cells will be available later, I would NOT bet on that.
The 123 BMS today is not what it was 3 years ago and won't be what it is today in three years from now.
This is a fast-evolving world when it comes to batteries, BMS and equipment in general.
Adding "Fresh Cells" into a Pack after a couple of years of service is begging for trouble and an open Invitation to have Murpy's Laws applied to you.

Murphy's law is an adage or epigram that is typically stated as: "Anything that can go wrong will go wrong".

The more critical, the more likely Murphy will intervene.

From the Lyuan Doc LINK in my Signature

 

[LiljeQ]

Adding "Fresh Cells" into a Pack after a couple of years of service is begging for trouble

So, to get into the solving problem a bit: Do you think it would be a better option for me to go for 8 cell, 24 v, 200ah battery pack right away and then in 2-3 years add another 24v, 200 ah battery pack (or more depending on the options available then). That option would still be within my budget.

 

[Steve_S]

So, to get into the solving problem a bit: Do you think it would be a better option for me to go for 8 cell, 24 v, 200ah battery pack right away and then in 2-3 years add another 24v, 200 ah battery pack (or more depending on the options available then). That option would still be within my budget.

Yes, I believe if your "Target" is to go up to 24V, then consider the Battery Pack like the foundation of a house. A Solid Foundation makes a base to build upon. Again a GOOD 30V to 12V step-down converter (NOT a Buck Converter they are pure crap and cannot be depended upon) will keep all your 12V stuff running as-is/where-is.

Go be aware, that GWL is a Good Vendor with good reputation BUT they are also quite pricey as in "premium priced", there are better deals to be had within the EU. One of our Norwegian ? (I think) members could likely aim you at some better deals, so I am tagging @upnorthandpersonal so he may be able to chime in with further info.
.

 

[efficientPV]

I feel like an alien here. My camp has refrigeration, hot water for showers, dishwasher with heated dry and a LG cloths washer. Its has its own hot water tank and I feed hot water into the cold fill so all cycles use hot water. Nice to pull out steaming clothes at the end of the cycle. All this operates on PV with just one car battery. Oh, and that battery has to have a full charge in the evening because it has to run something to keep me alive.

 

[FilterGuy]

Lightning & Surge protection.
To be perfectly honest, there is some Serious CRAP being flogged for these purposes at discount prices. AVOID the Discount crap ! This is NOT the place to skimp AT ALL ! I use Midnite Solar "Protectors" as well as more of their gear, it is more costly but some of the best stuff out there. These are available on Amazon & EBay as well.

I second what @Steve_S said and add this:
What is being discussed here are surge protectors.... but they do not and can not protect against a direct lightning strike. You can install lightning protection systems with air terminals (lightning rods) and separate grounding, but even that might not help in a direct strike.

Also, when you design your system, proper grounding is critical. For avoiding problems from nearby strikes, the two things to avoid are
1) Multiple connections between earth ground and your grounding system
2) Ground loops.

I am working on a series of 4 articles about grounding for the resource section. I published the first one at the link below and it covers some of this.

Grounding Made simpler - Part 1: AC/houshold grounding

To get the paper, click on the orange button at the top of the screen. The subject of grounding is a complex, multifaceted subject, that is often treated as an after-thought but needs to be considered from the beginning of the design and build...

diysolarforum.com

The article is US centric, but the concepts are the same.

I hope to upload the rest of the articles soon. (They are written but I have some folks reviewing them).

 

[LiljeQ]

Also, when you design your system, proper grounding is critical.

Thanks FilterGuy, I'll follow your guide closely.

 

[FilterGuy]

Not that you should do anything less on your off grid system, but a properly grounded off-grid system is probably less susceptible to lightning than an equivalent grid tied system simply because they don't have the grid funneling in surges from more distant strikes.

 

[MattiFin]

Background info
in the middle of the deep Swedish forests. --Our long-term plan with the property is to make it a year around place.
---
We have calculated that our consumption is at most about 1.8 kWh per day for lightning, fans (no AC of course), pumps, 4G router and WIFI, charging phones and computers. We run both stove, water heater and refrigerator on gas.

Next door neighbor here(Finland)

Biggest trouble with your current plan is the winter. I don't know where you are located exactly but you can probably count on to have about 0% solar available for mid-winter. Many of our North American cousins probably won't recognize how far up north Scandinavia is (and how damn cloudy the winter usually is)
I'm living in most southern part of Finland in capital city(Helsinki) and we are at same latitude as Anchorage in Alaska.

On the other hand your 1.8kWh per day sounds really pessimistic or inefficient and you should be able to improve a lot on that.

4G router: 72Wh/24h (my own, old huawei B593)
small cabin lightning: 180Wh (highly variable depending on your habits)
Charging 2 phones once per day: 20 to 60Wh
2x Efficient laptop: 2x20W average, 320Wh if you use total 16 hours

 

[LiljeQ]

Hey Matti!

Nice to hear from a neighbor! And yes, we're probably around the same latitude

For now we're almost never at the cabin mid winter. We use it mostly in the summers. We want to change that in time but for now it's just not possible for many reasons. So, from October - November to February-Mars I have planned to turn the entire system off.

About the consumption, I think I'll must clarify: it's a very pessimistic and inefficient estimate - it's a worst case senario so to say. I should have been more clear on that - just wrote "at most". The average is considerably lower.

Whats your solution to winter and the dark and cloudy times (I completely agree on that btw)?

 

[MattiFin]

Hey Matti!

Nice to hear from a neighbor! And yes, we're probably around the same latitude

For now we're almost never at the cabin mid winter. We use it mostly in the summers. We want to change that in time but for now it's just not possible for many reasons. So, from October - November to February-Mars I have planned to turn the entire system off.

About the consumption, I think I'll must clarify: it's a very pessimistic and inefficient estimate - it's a worst case senario so to say. I should have been more clear on that - just wrote "at most". The average is considerably lower.

Whats your solution to winter and the dark and cloudy times (I completely agree on that btw)?

Just a plan at the moment but: Move the RV and panels 3000 km south to Spain or France

Biomass to heat&electricity CHP (aka burning wood) would be only feasible option for winter unless you want to run generator on old dinosaurs. Biomass would be also indirectly solar power and solves the storage problem for winter.. Unfortunately the co-generation power plants won't scale down easily and operating them is quite involving.

IIRC even up here in Scandinavia 1 ha (100x100m) plot in favorable location produces approx 10 tons of dry biomass per year.

Propane generator with heat recovery would be high efficiency and not worse than your current solution ecologically(if such a thing counts)

 

[MattiFin]

EU PVGIS tool is super handy for "what-if" scenarios:
https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html (select the off-grid option)

Playing around with numbers:
Cut the consumption to 1 kWh per day.
Swap the batteries to 560Ah 12v EVE pack from alibaba (saves 1400 euros)
Use the saved money from batteries to seriously oversize the panels and tilt for winter production (20pcs 285W panels)
Based on above calculator you would have enough power for year around except december-january.