Interesting Battery Comparison on YouTube

[Laurie Forbes]

This EE claims, on a life cycle $/KWH basis, that in spite of the higher purchase cost of Li vs LA, the cost of Li batteries is much lower than LA AGMs and even lower than FLA batteries.

Eg. $0.09/KWh for Li, vs an average of about $0.55 for three types of AGMs and $0.19 for FLAs.

This surprises me to say the least and was wondering if any folks here might be able to comment.

[Rob Beckers]

It's a tough comparison, and in a sense it falls in that saying of "there are lies, damned lies, and statistics"...

Take an average cost battery like a Battle Born 12V 100Ah for $1,175: That's 1.2 kWh in usable storage, and if average use cycles them 80% you'd expect about 4500 cycles. That would makes 4500 x 0.8 x 1.2 = 4,320 kWh for $1,175, or 27 ct/kWh.

Now take a decent deep-cycle FLA such as a Rolls S-550 for $486. They are 6V 445Ah or 2.6 kWh, of which in reality 50% is actually usable on a regular basis, so 1.3 kWh. Those batteries will do 1900 cycles at 50% DOD. That makes 1900 x 1.3 = 2,470 kWh, or 20 ct/kWh

A good AGM such as a Fullriver DC400-6 is $720. Those are 6V 415Ah or 2.5 kWh, with again 50% usable on a regular basis, or 1.3 kWh (if we're generous). They are good for 1300 cycles at that DOD, or 1300 x 1.3 = 1,690 kWh. Per kWh that works out to about 43 ct/kWh.

With those numbers Lithium-ion compares favourable to sealed lead-acid, and FLA is only slightly cheaper. However, there are other factors and some unknowns: In reality very few people actually get the full cycle-life out of lead-acid batteries (in particular AGM batteries). Most will pooch them well before their due-date, which makes lead-acid more expensive, sometimes much more expensive (I've seen battery banks killed within 2 years instead of the 10-12 years they should have lived).

Most regular off-grid users will not cycle lead-acid batteries to 50% DOD on a regular basis. Those are design numbers that only really happen during the dark days of winter. Much of the year they will be cycled much more shallowly. While that gets you more cycles, there is still the calendar-life limit for batteries, and it makes lead-acid quite a bit more expensive.

Lithium-ion too has its issues: While in theory they have long cycle-lives, they also have a calendar-life of about 20 years for the chemistry and many will not reach that cycle-life before their batteries give out. Many will no really cycle as deep as 80% on a regular basis either. Both factors will drive up the cost per kWh.

The jury is also still out on longevity of lithium-on (or more specifically LiFePO4 as a chemistry): The cells may have the claimed longevity, we see that in 99% of broken batteries the Battery Management System (BMS) fails. Since most li-ion batteries cannot be opened or repaired that is the end of the battery. I strongly question if the average battery will make 20 years, or if their BMS will fail sooner.

My 2 cts...

-RoB-

[Laurie Forbes]

Thanks Rob for your analysis. I'm still not sure however why your cost figures for Li are approx. three times higher than the UTube vid.

In any case, I note your packaged solar systems utilize the FLA batteries whereas it seems to me that, even using your cost numbers, the Li would be the better buy, even if one had to finance the purchase price due to the higher upfront cost (this being mainly due to the no maintenance requirement for Li).

I'd be curious to know what fraction of your clients go with Li over FLA.

[Ralph Day]

Well Laurie, Rob sells them all. I picked up my Surrette S550's a little over 2 years ago and noticed Li 12 volt batteries in his warehouse...2 pallet loads. That's probably $20K in product before MSRP markup.

Ralph

[Laurie Forbes]

Hey Ralph, I have perused Rob's web store and have indeed noted both types of batteries are offered. I am still a bit unclear though why FLAs still seem to be considered the preferred option (for stationary applications) vs the LiFePo batteries.

[Rob Beckers]

Hey Ralph, I have perused Rob's web store and have indeed noted both types of batteries are offered. I am still a bit unclear though why FLAs still seem to be considered the preferred option (for stationary applications) vs the LiFePo batteries.

It's cost Laurie.
Anything but a really small battery bank is just unaffordable. While in the long run lithium-ion may be comparable, the initial investment is very different.

-RoB-

[Laurie Forbes]

It's cost Laurie.
Anything but a really small battery bank is just unaffordable. While in the long run lithium-ion may be comparable, the initial investment is very different.

-RoB-

For sure - that's why I mentioned financing as a possibly viable route for some.

It would be interesting to do a PV (present value) analysis on the purchase to see what the actual $ numbers are.