Are Lithium Batteries the way to go?

ElectricLove · October 2019

A year later I'll throw this in...

Yes, Lithium is better and actually if you do the math it is cheaper!

I installed 25kWh battery bank on my home, it is an LFP bank (Lithium Iron Phosphate) from Ohmmu Energy (www.ohmmu.com/group31). I weighed it against Lead and here is the scoop:

1. Overall cost: Ohmmu has these batteries at an Intro pricing of $679 (includes shipping so that was the "all in" price) that provide 1.28kWh of capacity. This is $530 per kWh of capacity. A Fullriver DC260-12 AGM battery runs $857 and provides 3.12kWh of capacity. This is $275 per kWh of capacity.

2. Cost per "real kWh"; I needed 22.5kWh of real performance from my battery bank. With Ohmmu Lithium this means I should size at about 25kWh and run 90% Depth of Discharge cycles (Lithium performance), with Fullriver this means I would need to size at about 40kWh and run about 55% Depth of Discharge cycles (AGM performance). So total cost for Ohmmu = 25*$530 ($13,250) while Fullriver is 40*$275 ($11,000).

3. kWh of usable energy over lifetime; The Ohmmu batteries will perform as all Lithium batteries do, at 90% DOD I should expect at least 3000 cycles; this means 3000*25*.90 is the amount of energy I will get to use over the lifetime of these batteries, which is 67,500 kWh. The Fullriver batteries will perform as all AGM batteries do, at 55% DOD I should expect at least 1000 cycles; this means 1000*40*0.55 is the amount of energy I will get to use, which is 22,000 kWh.

4. REAL COST; the real cost of any functional asset is the cost divided by amount of function it provides so the $13,500 Ohmmu pack that provides 67,500 kWh of energy over its lifetime ($0.20 per kWh stored/retrieved) is FAR cheaper than the $11,000 Fullriver pack that provides just 22,000 kWh of energy over its lifetime ($0.50 per kWh stored/retrieved).

5. Efficiency; due to Peukert's losses and voltage sag a lot of energy is lost per cycle with an AGM or any Lead Acid battery, this can be as high as 50% of the total energy retrieved (meaning you use 10kWh of power to charge a pack full and then discharge it and only get 5kWh out of it), on the other hand Lithium is much better and worse case scenario is more like 90% efficiency (meaning you use 5.5kWh to charge it full and then can pull 5kWh out of it, far less gone to waste); so the cost of that wasted energy should be accounted for

6. Weight and size; who on Earth wants to lug around a 150+ lbs Lead Acid battery? My Ohmmu batteries weigh about 27lbs so I can easily build a light-weight rack to hold them and install them all on my own and at my own leisure without risk of breaking my foot if I drop one!

For points 5 and 6 I would always pick Lithium over Lead, for points 1-4 one could find some dirt-cheap Lead batteries and argue the point that they should be cheaper over lifetime but I've never seen Lead batteries that are super cheap that still provide decent performance over 1000 cycles, in the "cheapo" world you start to get down to 500 cycles or you are looking at Flooded Lead with all the nasty maintenance headaches and corrosion (and YET STILL don't give the same $/usable kWh of life)...

So, unless you absolutely cannot afford to put a good Lithium battery pack in as part of your system in terms of up-front costs alone, everyone should be installing LFP!

Photowhit · October 2019

ElectricLove said:

.... and actually if you do the math it is cheaper!

You make the same false assumptions that the sellers of Lithium batteries make. that is that you will cycle the battery very deeply every day. In most off grid situations, you want to have the capacity to go several days without charging, so you will cycle the battery pretty minimally each day.

Then you go and compare the lithium battery to a very expensive AGM battery.

Try your math on a Forklift battery which can be cycled to 20% SOC, and commonly lasts 6-10 years in daily deep cycling situations or 15-20 years in typical off grid use.

BTW, Mine lives outside, no need for any risk inside and no freeze worries. not sure why anyone is 'lugging around' any battery. Set and maintain it where is sits.

As to cost, figure $4000-4500 for a 'real' 25kWh usable capacity battery delivered. Additional cost is about a 1/2 to 1 hour month checking the battery and maybe $2-6 a year in distilled water.

softdown · October 2019

Lithium battery fire fumes are often very toxic. But I do like the light weight. My days of manhandling 170 lb lead acids appear to be quit numbered. Even ~110 pounders became a bit of a struggle after moving around a bunch.

mcgivor · October 2019

The never ending debate continues with mathematics in cost comparison, pros and cons of each, horror stories, claims of difficulty along with confusion between chemistries within the lithium ion umbrella.

To answer the question for myself I replaced my house bank FLA with Lifepo4 with like capacity, disregarding the claims of how much capacity can be used. The rational behind the decision was that eventually the LA bank would fall, needing replacement with something, but the most important reason was temperature, the LA bank is almost always above 30°C, often higher than 40°C, which as we know is detrimental. The LFP cell temperature never rises to maximum ambient even on the hottest days and well within safe operating parameters.

There is naturally a learning curve, more so when using larger prysmatic cells as opposed to drop in replacement types, but in retrospect it's not that complicated.

Price wise the cost of the 400Ah LFP, direct from the manufacturer, was about double that of the 400Ah 20h rating.GC FLA retail, though price wasn't the motivation factor.

Lead acid are very basic, rugged and reliable for the most part but can be fragile if not maintained correctly. LFP rely on electronics to prevent damage, which could be argued provide more potential failure points, which is a valid point, but as with modern car efficiency, it would not be possible without them.

Making the change was well suited to my needs being in a tropical location, perhaps not for those in extreme cold, all other benefits were not motivation factors but very welcome, I'm sold and would never consider LA again, a personal opinion naturally.

Much of the positive feedback I discovered was from other forums with users having experience dating back 15 years, mostly outside North America where there seems to be more apprehension often based on hear say than practical experience.

Everyone is free to make their choices based on the information they understand and or practical experience, but do keep an open mind because a person who fails to listen is blind.

softdown · October 2019

mcgivor said:

The never ending debate continues with mathematics in cost comparison, pros and cons of each, horror stories, claims of difficulty along with confusion between chemistries within the lithium ion umbrella.

To answer the question for myself I replaced my house bank FLA with Lifepo4 with like capacity, disregarding the claims of how much capacity can be used. The rational behind the decision was that eventually the LA bank would fall, needing replacement with something, but the most important reason was temperature, the LA bank is almost always above 30°C, often higher than 40°C, which as we know is detrimental. The LFP cell temperature never rises to maximum ambient even on the hottest days and well within safe operating parameters.

There is naturally a learning curve, more so when using larger prysmatic cells as opposed to drop in replacement types, but in retrospect it's not that complicated.

Price wise the cost of the 400Ah LFP, direct from the manufacturer, was about double that of the 400Ah 20h rating.GC FLA retail, though price wasn't the motivation factor.

Lead acid are very basic, rugged and reliable for the most part but can be fragile if not maintained correctly. LFP rely on electronics to prevent damage, which could be argued provide more potential failure points, which is a valid point, but as with modern car efficiency, it would not be possible without them.

Making the change was well suited to my needs being in a tropical location, perhaps not for those in extreme cold, all other benefits were not motivation factors but very welcome, I'm sold and would never consider LA again, a personal opinion naturally.

Much of the positive feedback I discovered was from other forums with users having experience dating back 15 years, mostly outside North America where there seems to be more apprehension often based on hear say than practical experience.

Everyone is free to make their choices based on the information they understand and or practical experience, but do keep an open mind because a person who fails to listen is blind.

So lithium is good in hot locations, bad in cold locations. I know my lithium automotive battery jump starters were junk in cold weather. Since that is the likely time to have a battery failure, I returned them.

mcgivor · October 2019

@softdown said: So lithium is good in hot locations, bad in cold locations. I know my lithium automotive battery jump starters were junk in cold weather. Since that is the likely time to have a battery failure, I returned them.

The battery cells need to be kept above freezing, if this is not possible, naturally or artificially, then they would be unsuitable. This would be one consideration in the list of pros and cons before a decision is made.

icarus · October 2019

Interesting discussion. I myself pondered changing to LI chemistry but have discounted the idea as a result of continual cold weather when my system is likely to be un-attended. That said, the idea of a dedicated PV system with a dedicated heating system simply for the battery box is an intriguing idea. For example, (with out doing any calcs) I could simply switch some portion of my PV to the heating side as needed. Since only a small portion of my PV would be needed for float charging, there might be plenty to both charge and heat.

The thermal mass is an issue. For example, my FLA battery box is ~24”x24”x30”, with 4 t-105s in it. When I come home mid winter after being a way several weeks or months, the battery box might be -20F. The house takes a fairly long time to get up to temp, and drive the cod out of the mass (a couple of days to completely get warm. The batteries maybe below freezing for several days. If, over the course of the time away, if the box was well insulated, and the heating system was stat controlled to maintain temps just above freezing, it would take very little energy to keep them at that temp, as opposed to the energy required to warm them to that temp. (Understanding the cumulative energy requirement is larger, but if you are using PV that would otherwise be “wasted” who cares?

One the building were occupied and warmed by living in it, simply switching the PV back to “normal” would restore full charge capacity to the batteries. It would be interesting to do some calcs to see how many whs it would take to maintain say 0C, with an indoor temp of say -20c for a Xlbs thermal mass, insulated with say R-50 foam. My guess is not very many.

Tony

Estragon · October 2019

FWIW, here goes...

With R50 (~1') insulation making the box roughly 4x4x5' outside, 4 sides at 4x5=20x4=80sq.ft + 2 ends at 4x4=16x2=32, total area 112sq.ft. Ambient at -20, design at 40°F = 60°F delta.

112 x 60 ÷ 50 = 134btu/hr x .293 = 39w, nearly 1kwh/day.

I'm not sure if this math really works though given the large increase in surface area with insulation relative to the interior area. My guess is it would be substantially less if calculated using heat loss at various incremental depths. Also, using -20°F is low for a mean ambient. Mean delta likely more like (40-0°F=) 40°F.

Heating 250# by 60° would be 15kbtu, ~4.4kwh.

icarus · October 2019

EST,

Consider the Delta with a room temp of say -20c, and an ideal battery box temp of +1C, for a Delta of 21c. Also consider the btu load of just maintaining that +1c. I have found that the inside of my little house, when I open it mid winter is always substantially warmer than outdoor. The house nears ambient, but it also picks up considerable heat from the sun, leaving it higher than ambient in general. My recording thermometers show a over all low outdoors of ~-30, while the indoor might show a low of ~-20.

Tony

Estragon · October 2019

So ~0°F to 34°, delta 34. 112 x 34 ÷50, ~22w. Using just the interior surface area (~24sq.ft) of the box would be ~5w. Assuming really tight overall assembly, it might be somewhere in that range.

If actually doing something like this, I'd likely find a spot I could dig down several feet, and make an insulated cover extending several feet around a well sealed and insulated hatch. Ideally, it would be below the frost line, requiring little heat, likely from a water line heat trace.

My pretty well insulated cabin gets to about the recent (couple weeks) average mean daily temp. Last Jan, for example that was ~-18°C. There's virtually no sun warming (because of low sun/shade, snow covered roof, etc). Absent a cold snap, it's usually warmer outside than in when I get there (generally mid/late afternoon).

softdown · October 2019

Not fair switching back and forth between C (Canadian) and F (Freedom). j/k

softdown · October 2019

If my place wanted to be as cold as the outdoors I might be miserable all winter. I could only imagine the heating bill. As it is, with the giant passive heating sunroom, I spend $50-100/year on propane. Though I do put up with conditions that many others would find untenable. Like cooking breakfast in the 40s(F) - maybe once/year during a cold and cloudy snap.

Just takes a little propane in the early morning and evening. We are really missing the boat with passive solar heating in cold, sunny environs. Perhaps the "powers that be" don't encourage it because homes with southern exposures would be worth so much more. Creating some kind of imbalance.

mcgivor · October 2019

softdown said:

Not fair switching back and forth between C (Canadian) and F (Freedom). j/k

Not just Canada but most of the world.

softdown · October 2019

mcgivor said:

softdown said:

Not fair switching back and forth between C (Canadian) and F (Freedom). j/k

Not just Canada but most of the world.

I get that Celsius and metric are arguably better systems. You know what hell is? Using both! We screwed up a mission to Mars because both systems were used without doing the math on the difference.

My point was that Icarus used F in one post then C in the next. I was just ribbing him anyway.

mcgivor · October 2019

Would be interesting if someone would conduct an experiment ideally with LFP batteries the requirements needed to maintain a suitable temperature. Using mathematical formulas may provide some information but dynamically the results would differ significantly due to latent heat stored in the mass of the cells themselves.

My experience with high temperatures is, although the cell temperature increases as ambient increases, they remain significantly lower than ambient, for example when ambient reaches 45°C, the maximum cell temperature recorded was 36°C. Obviously it cools down overnight and the peak high is only for a limited time so it would seem logical the reverse would apply, if heated during the day the latent heat may be sufficient to maintain the battery temperature overnight, in a well insulated container.

One article I read regarding automotive LFP replacements was, if used in lower temperatures the headlights should be turned on for a while before attempting to start, this is supposed to generate some heat within the cells prior to starting /charging. My assumption would there would be limitations to this process, in -40° ambient for example. The overnight discharge therefore may provide it's own heat source, I would conduct an experiment if it were practical the coldest it gets here is ~15°C average for a few hours before sunrise, so no go on that.

icarus · October 2019

Guilty...a legacy of living on both sides of the border...a recipe for errors. T

Estragon · October 2019

I switched to °F just because it works for BTUs. There are metric equivalents for heat loss, but that's what I'm used to.

I tend to think in inches/feet mainly because available materials are mostly sized that way here (eg 4 x 8' sheet goods, 16" centers, etc.). Using baltic birch ply (6/12/18mm) and Austrian hardware for cabinets just now though, so doing the project mostly in metric.

Going back and forth is definitely a pain, and sometimes means making do with not quite the right tool (like a 1/4" mortise chisel when you really want 6mm).

The metric blue on the map isn't quite as uniform as it looks. For example, IIRC in the UK, temps are in °C, gas is sold in litres, but speed limits are MPH.

Are Lithium Batteries the way to go?

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