Help me choose new batteries

[YurtSolar]

Greetings solar wizards!

Im a teacher who lives in an off grid yurt in northern Vermont, and need to pick new batteries for my solar system. I want something low maintenance that will be reliable. I'm leaning towards a lithium option and would like to increase my available power. What batteries do you recommend?

Current Set Up:
4 Trojan T-105 FLA batteries (6 years old)
3, 300 watt 24v panels
3 Victron 75|15 controllers
Cotek SP-1000 inverter (will possibly upgrade)
Cotek battery charger

Concerns:
1. Compatibility with current system

2. Temperature fluctuations. I heat with wood and teach during the day so there can be a drastic temperature change during the chilly months (October-May). I run a backup propane heater to try and keep things above freezing, but keeping things above freezing is always a concern. Should I consider SOK batteries with the built in heating pads?

3. Should I get 2x12v batteries or 1 24v battery?

Thank you so much for your time and support!
Evan

 

[Q-Dog]

For LiFePO4, because they use a BMS, I prefer to have batteries that match the system voltage. I also like redundancy, so 2 batteries at 24 volts would be my preference, so you don't lose all power if one battery shuts down.

Look up the specifications on your chargers to see if they have built-in lithium charge settings, or if they can be adjusted to charge lithium. I know nothing about the Cotek, but the Victron should be OK unless they are really old.

 

[YurtSolar]

Thank you @Q-Dog ! I'm looking to get batteries this week with black Friday sales and will go for 24v as you recommended.

Can anyone advise on batteries that work best for my temperature extremes (#2 above)? I've looked at the EG4 batteries but was advised that they need to be kept above 32 degrees F. That is usually the case but I never know if the temperature dips and my propane heater stops working while I'm teaching I don't want to destroy my batteries. Last year we hit -22 F and the propane heater did not keep things above freezing while I was at work. Are there other battery options I should consider? Should I go with a battery with a built in heater of some kind?

 

[Philip53]

Take a look at Trophy batteries. They have had some good reports. The owner, Dan, is very responsive and answered all my questions when I was trying to decide which lithiums to go with. I purchased two of the 48V 220ah ones back in February of this year, and they have been troublefree. Take the time to do your due diligence - lithium batteries are a huge investment, and should serve you for 10-20 years. If not abused.

Oh, they do come with heaters, standard.

www.trophybattery.com

 

[YurtSolar]

@Philip53 thank you for letting me know about trophy, I had never heard about them before. They look great and I agree with your assessment about the battery investment. It looks like Dan only has 48v batteries, which I think would mean connecting my panels to be 48v and getting new scc correct? Currently I have 3 24v panels each connected to it's own dedicated victron 75|15 scc, and they are all new so I'd rather not need to upgrade those if I don't have to.

 

[Philip53]

@YurtSolar, that 75/15 Victron is for 12 or 24 volt only. You would need a 48v MPPT. Good news is you would only need one. You could wire the 3 panels together in series (as long as the voltage of the panels did not exceed the MPPT rating). The wattage of the three panels really would not matter, but the max voltage does. A 48v system has many advantages, and is pretty much the standard in DIY home solar.

 

[Nobodybusiness]

Im a teacher who lives in an off grid yurt in northern Vermont,

You a better man than me..

 

[Rollann Cerry]

If you choose a lithium-ion battery instead of a lead-acid battery. I'm sure one 24V better than two 12V .

 

[Brucey]

Thank you @Q-Dog ! I'm looking to get batteries this week with black Friday sales and will go for 24v as you recommended.

Can anyone advise on batteries that work best for my temperature extremes (#2 above)? I've looked at the EG4 batteries but was advised that they need to be kept above 32 degrees F. That is usually the case but I never know if the temperature dips and my propane heater stops working while I'm teaching I don't want to destroy my batteries. Last year we hit -22 F and the propane heater did not keep things above freezing while I was at work. Are there other battery options I should consider? Should I go with a battery with a built in heater of some kind?

Sig solar currently has some great clearance pricing on the eg4 weatherproof heated batteries

 

[YurtSolar]

@YurtSolar, that 75/15 Victron is for 12 or 24 volt only. You would need a 48v MPPT. Good news is you would only need one. You could wire the 3 panels together in series (as long as the voltage of the panels did not exceed the MPPT rating). The wattage of the three panels really would not matter, but the max voltage does. A 48v system has many advantages, and is pretty much the standard in DIY home solar.

Aha! This is good to know. So I can wire my 3 24v panels in series (72v) to a 48v MPPT and 48V battery? I thought the voltages need to match but it sounds like that's not true? If this is the case I can upgrade my battery to 48v and a 48v MPPT and be all set?

 

[YurtSolar]

You a better man than me..

Ha! Thank you! It's a beautiful life but figuring out what to do with my solar situation is a challenge

 

[Q-Dog]

www.LiTime.com has a black friday sale on their drop-in batteries. There are a couple of 24 volts options that don't look bad, but I don't think they offer a heated battery at 24 volts. You could always build an insulated box or cabinet to keep them in ... maybe add some heating pads for the coldest times.

 

[Brucey]

Aha! This is good to know. So I can wire my 3 24v panels in series (72v) to a 48v MPPT and 48V battery? I thought the voltages need to match but it sounds like that's not true? If this is the case I can upgrade my battery to 48v and a 48v MPPT and be all set?

You'll need a new 48V inverter as well (assuming your current one is a 12V). You just can't exceed the rating of the mppt, so for example a 100/30 your panels vocs can't exceed 100V (and you want a safety margin because voltage increases as temps drop). Look on your panels and there should be a listing specifying exactly what your voc is. Depending how close to 100V it is you may want to bump up to a 150V mppt model.

 

[Hedges]

What is your power consumption? How much daytime, now much nighttime?
Lithium has characteristics that work well for many uses. It is around purchase-cost parity with lead-acid.
Lead-acid is simple and well known, has its own benefits and disadvantages.
AGM is maintenance free and has its own characteristics. Lifespan could be as little as 2 years or as long as 10 years, depending on depth of discharge and quality. I'm using AGM for grid-backup. If your application only cycle 15% DoD most nights, deeper when you get a day without sun, it could give long life.

 

[Philip53]

Aha! This is good to know. So I can wire my 3 24v panels in series (72v) to a 48v MPPT and 48V battery? I thought the voltages need to match but it sounds like that's not true? If this is the case I can upgrade my battery to 48v and a 48v MPPT and be all set?

What @Brucey said above.

 

[YurtSolar]

www.LiTime.com has a black friday sale on their drop-in batteries. There are a couple of 24 volts options that don't look bad, but I don't think they offer a heated battery at 24 volts. You could always build an insulated box or cabinet to keep them in ... maybe add some heating pads for the coldest times.

@Q-Dog Good call, I watched a video from William Prowse about adding heat pads I'll probably do that for backup insurance in winter.

You'll need a new 48V inverter as well (assuming your current one is a 12V). You just can't exceed the rating of the mppt, so for example a 100/30 your panels vocs can't exceed 100V (and you want a safety margin because voltage increases as temps drop). Look on your panels and there should be a listing specifying exactly what your voc is. Depending how close to 100V it is you may want to bump up to a 150V mppt model.

@Brucey ah yes good call, I'll need the inverter too. Current one is 24v. I believe the voc is 41 but can double check when I get home (on a plane currently).

What is your power consumption? How much daytime, now much nighttime?
Lithium has characteristics that work well for many uses. It is around purchase-cost parity with lead-acid.
Lead-acid is simple and well known, has its own benefits and disadvantages.
AGM is maintenance free and has its own characteristics. Lifespan could be as little as 2 years or as long as 10 years, depending on depth of discharge and quality. I'm using AGM for grid-backup. If your application only cycle 15% DoD most nights, deeper when you get a day without sun, it could give long life.

@Hedges very good question. To be honest I'm not totally sure. I'm going to buy a new, larger energy star fridge/freezer that estimates just under 1kwh per day (my current mini fridge uses 0.3 kwh per day). That is usually the only thing running during the day. I have 1 overhead lightbulb and 1 small reading light for night use, and I charge my laptop and phone at night. I don't have a TV or anything. I think my overall power consumption is low, and was thinking I'd plan on 3kwh per day with room to expand if needed?

 

[Hedges]

Here's one possibility, not cheap, 2x 12V 258 Ah batteries at $870 each. 6.2kWh gross.
At 25% DoD each night, technical manual indicates 2500 cycles.
If you got 4 batteries of half the capacity, could rewire for 48V if desired.
Select models may be more popular and sold cheaper somewhere.

Sun Xtender Solar Batteries - Photovoltaic Battery

The Sun Xtender Battery line consists of specialty lead-acid solar, photovoltaic batteries, and renewable energy storage batteries manufactured by Concorde Battery Corporation.

sunxtender.com

Sun Xtender PVX-2580L

The SunXtender PVX-2580L boasts industry leading life cycles providing safe, reliable and long lasting power. Recombinant gas SunXtender Deep Cycle AGM Series solar batteries are low resistance, valve regulated lead acid (VRLA) batteries. Non-Spillable maintenance free construction allows...

bdbatteries.com

You may find a deal on used but young AGM batteries. Sometimes retired from telecom.
I just picked up 24, 6V FullRiver batteries that had been used to power a tourist vehicle.

You could arrange for fridge to shut off at night and coast (ice battery, less cycling of AGM battery.)

 

[gotbeans]

Thank you @Q-Dog ! I'm looking to get batteries this week with black Friday sales and will go for 24v as you recommended.

Can anyone advise on batteries that work best for my temperature extremes (#2 above)? I've looked at the EG4 batteries but was advised that they need to be kept above 32 degrees F. That is usually the case but I never know if the temperature dips and my propane heater stops working while I'm teaching I don't want to destroy my batteries. Last year we hit -22 F and the propane heater did not keep things above freezing while I was at work. Are there other battery options I should consider? Should I go with a battery with a built in heater of some kind?

Definitely insulating the battery pack with any insulation really (I always recommend rockwool/mineral wool at home depot/lowes because it can't catch fire)
We're having a discussion on it here: https://diysolarforum.com/threads/reptile-heating-pad-to-keep-lfp-batteries-warm.72603/
as I said in that post It's about to hit 23 tomorrow which is far from -22 but I'm only using a cheap reptile pad to keep them heated and I'm heating it to 80F lol.. just for fun. But it really takes almost no energy. Insulation is the key.
So in comparison to a propane heater that's a massive difference. I think with heated batteries + some insulation you'd have literally no issue even at colder like -40F. Could also do unheated batteries and just get a better thermal pad.
Maybe get a heating pad even with heated batteries though, just in case they need some extra heat.
but definitely do some insulation 4-12 inches around them and it's going to keep heated very easy.
You can stick one of these in it to see the temp / control some extra heater if you want something extremely easy / plug & play

https://www.amazon.com/gp/product/B0957NYW37/

Optionally you can dig a hole and frame it out and bury your batteries with self heating, that'd keep them warm as well. And even insulate the buried box further... Also give you more space

Aha! This is good to know. So I can wire my 3 24v panels in series (72v) to a 48v MPPT and 48V battery? I thought the voltages need to match but it sounds like that's not true? If this is the case I can upgrade my battery to 48v and a 48v MPPT and be all set?

It seems half way down the thread you're looking at redoing/buying everything you have instead of just the battery?

If so, this seems to be the only thing you need since you only run a refrigerator and some lights. Obviously it'll handle more

Your system is pretty much like this one, plus some solar panels

Mobile 3,000W System

Dead Simple Solar Power System! 3,000W AC Output 1,800W AC Input 5,000W PV Input PV Voltage Range: 120-500V Scalable Easy to Build! This took me 25 minutes Can be mobile or stationary Turn off the...

www.mobile-solarpower.com

Personally I'd just get the 24v batteries like you were originally. But I guess with that inverter/controller you can add a lot more panels.
Downside to single input is the solar panel array will not do as well if there's shade around and you look like you have a lot of trees all over.
Having separate panels with separate charge controllers helps get the full potential from each panel individually

 

[YurtSolar]

Here's one possibility, not cheap, 2x 12V 258 Ah batteries at $870 each. 6.2kWh gross.
At 25% DoD each night, technical manual indicates 2500 cycles.
If you got 4 batteries of half the capacity, could rewire for 48V if desired.
Select models may be more popular and sold cheaper somewhere.

Sun Xtender Solar Batteries - Photovoltaic Battery

The Sun Xtender Battery line consists of specialty lead-acid solar, photovoltaic batteries, and renewable energy storage batteries manufactured by Concorde Battery Corporation.

sunxtender.com

Sun Xtender PVX-2580L

The SunXtender PVX-2580L boasts industry leading life cycles providing safe, reliable and long lasting power. Recombinant gas SunXtender Deep Cycle AGM Series solar batteries are low resistance, valve regulated lead acid (VRLA) batteries. Non-Spillable maintenance free construction allows...

bdbatteries.com

You may find a deal on used but young AGM batteries. Sometimes retired from telecom.
I just picked up 24, 6V FullRiver batteries that had been used to power a tourist vehicle.

You could arrange for fridge to shut off at night and coast (ice battery, less cycling of AGM battery.)

Hi @Hedges ! Is there an advantage to getting 12v batteries instead of 24v? I was planning to get 24v batteries if I stick to the 24v system, or 48v if I upgrade to a 48v system, instead of linking 12v batteries together. I like your idea of cycling the fridge - I bet I could get a smart outlet to do that timing wise?

Definitely insulating the battery pack with any insulation really (I always recommend rockwool/mineral wool at home depot/lowes because it can't catch fire)
We're having a discussion on it here: https://diysolarforum.com/threads/reptile-heating-pad-to-keep-lfp-batteries-warm.72603/
as I said in that post It's about to hit 23 tomorrow which is far from -22 but I'm only using a cheap reptile pad to keep them heated and I'm heating it to 80F lol.. just for fun. But it really takes almost no energy. Insulation is the key.
So in comparison to a propane heater that's a massive difference. I think with heated batteries + some insulation you'd have literally no issue even at colder like -40F. Could also do unheated batteries and just get a better thermal pad.
Maybe get a heating pad even with heated batteries though, just in case they need some extra heat.
but definitely do some insulation 4-12 inches around them and it's going to keep heated very easy.
You can stick one of these in it to see the temp / control some extra heater if you want something extremely easy / plug & play

https://www.amazon.com/gp/product/B0957NYW37/

Optionally you can dig a hole and frame it out and bury your batteries with self heating, that'd keep them warm as well. And even insulate the buried box further... Also give you more space


It seems half way down the thread you're looking at redoing/buying everything you have instead of just the battery?

If so, this seems to be the only thing you need since you only run a refrigerator and some lights. Obviously it'll handle more

Your system is pretty much like this one, plus some solar panels

Mobile 3,000W System

Dead Simple Solar Power System! 3,000W AC Output 1,800W AC Input 5,000W PV Input PV Voltage Range: 120-500V Scalable Easy to Build! This took me 25 minutes Can be mobile or stationary Turn off the...

www.mobile-solarpower.com

Personally I'd just get the 24v batteries like you were originally. But I guess with that inverter/controller you can add a lot more panels.
Downside to single input is the solar panel array will not do as well if there's shade around and you look like you have a lot of trees all over.
Having separate panels with separate charge controllers helps get the full potential from each panel individually

@gotbeans That was an excellent video, thank you for sharing. I am impressed by William's videos and tutorials. I am very intrigued by the insulated box idea and using a heating pad, I think I will use that strategy. Is there a heating pad you recommend? I saw William made a video of some that he recommends, I might just go with those but you are more in the know than I am in this conversation.

Oh, snap! I never heard or thought of burying batteries. Thats INTENSE!

I am thinking about 3 options: (1) replace the batteries, (2) replace the batteries and the inverter, or (3) replace everything with a 48v system. I like that mobile system he created. I think 48v scares me a little bit, and I would need more solar panels to compensate for the idle draw of that large all in one unit. You are right that I am very much in the woods with lots of trees around, and I did just as you recommend to help with the shading issue I currently have my 3 panels each hooked to its own Victron scc. I guess because of those downsides I agree with you about just replacing the 24v batteries and maybe the inverter, so either options 1 or 2 above.

What do you think about my current idea? Buy 1 or 2 24v 200 ah batteries, add a heating pad, and stick with the 24v system. I saw this 3000w 24v Giandel inverter recommended by William Prowse, and it is on sale. I feel like this would be a huge upgrade in my system, but the Amazon page says that inverter has a "Battery Capacity: 300 amp hour." Does this mean I can not connect it to 2 24v 200 ah batteries, because that would have 400 ah total? From what Ive been reading this system with separate inverter, charger, sccs, etc would have a much lower draw than the all-in-one units available.

I am very much appreciating of everyone on this forum helping me think through this project!

 

[Hedges]

It is generally better to have single string of cells/batteries on a system rather than multiple in parallel.
If you are building 24V today and plan to move to 48V later, then (at least with lead-acid) you might make two parallel strings for 24V, so you could rewire for 48V.

Lead-acid batteries are heavy, and I find the easiest to move with a dolly if no more than 100 to 150 lbs. My battery has eight, 6V 405Ah batteries of that weight. For a larger bank, could be 24, 2V 1200 Ah batteries.

A single 24V lead-acid battery, if available, might be convenient for you.

Individual 2V cells (or accessible busbars) makes it possible to charge them individually. Otherwise, "equalization" is over-charging the entire battery, bubbling the fully charged cells, in order to to bring up the low ones.

For lithium, definitely best to get a single 24V or 48V battery, because then a single BMS can balance all cells.
You can connect multiple lithium batteries in series, but only if documentation says they support that configuration - when BMS disconnects, it is exposed to entire pack voltage.

If you're going with lithium, make the switch to 48V up front. You can get 100 Ah 48V server rack batteries from about $1200 and up, but you may want something with heating. There are 12V heated "drop-in" batteries.

Here is a very interesting product - larger 280 Ah, 48V, weatherproof. Priced around $4000.

WallMount All Weather - EG4 Electronics

EG4 Electronics

eg4electronics.com