Lithium-Ion Batteries for Off-Grid Systems

Are They a Good Match?
Intermediate

Inside this Article

Prismatic type Li-ion battery
A typical prismatic type of Li-ion battery.
Cylindrical Li-ion battery
Cylindrical Li-ion batteries are often ganged into voltages appropriate for cordless tools.
Pouch types of Li-ion battery
You’ll find these pouch types of Li-ion batteries in radio-controlled hobbyist cars and other places where weight is a concern.
BMS cell-balancer board
This BMS cell-balancer board is mounted to a set of four LFP cells. It is typical of a BMS for EVs.
An overcharged LFP cell
An overcharged LFP cell can rupture, leaking caustic electrolyte.
Prismatic type Li-ion battery
Cylindrical Li-ion battery
Pouch types of Li-ion battery
BMS cell-balancer board
An overcharged LFP cell

For decades, lead-acid battery technology has been the mainstay of battery-based renewable energy systems, providing reliable storage and ample energy capacity. The most common battery used—flooded lead-acid (FLA)—requires regular watering to maintain electrolyte levels and venting to avoid the buildup of hydrogen and sulfuric gases. Additionally, FLAs are large and heavy, making battery replacement a challenging task for some systems.

With all of the recent action in the electric vehicle and personal electronics industries, lithium-ion (Li-ion) batteries have gained much attention. Here, we examine Li-ion battery pros and cons, and discover why most system owners won’t be swapping out their FLA batteries anytime soon.

What’s Behind Li-Ion?

“Lithium-ion” refers to a variety of lithium-based battery chemistries. Each chemistry has its strong and weak points, which means certain types of chemistries are better-suited for particular applications. There continues to be new lithium-based chemistries being developed (such as lithium-air), but it is too early to tell which will become commercially viable. See the “Lithium Battery Technologies” table for details on a few of the more common types of Li-ion chemistries.

Li-ion batteries typically come in one of three formats: pouch, cylindrical, and prismatic (rectangular-cubic). Pouch types tend to be used in small portable devices, such as smart phones and tablet PCs, or in devices where low weight is important, such as hobbyist remote control vehicles. Cylindrical forms lend themselves to powering medium-sized portable devices, such as power tools. Prismatic are generally the largest, and are typically used in electric vehicles. Prismatic types are also favored in applications that were previously powered by lead-acid batteries, such as backup or off-grid telecommunication systems. Prismatic types usually have hard corrugated sides, which creates air gaps between adjacent cells—an aid to cooling.

Suitable for Renewables?

If Li-ion has an application for residential RE storage, the best candidate is the large-format prismatic lithium iron phosphate (LiFePO4; LFP) battery. But how do they compare with lead-acid technologies?

Weight. Comparing weight versus available energy storage, an LFP is about one-third the weight of a lead-acid (LA) battery. This is a great advantage for mobile applications, such as boats/RVs, but for stationary RE applications, weight is usually a consideration only during battery change-out.

Space. At about half the volume of an LA battery with equivalent energy storage, LFPs take up far less space. This may be an advantage for mobile applications, but for stationary RE applications, size or volume is typically not a deciding factor.

Low-Temperature Capacity. The storage capacity of LAs drops by 50% at -4°F, compared to 8% with LFP. Keeping lead-acid batteries warm so that they maintain reasonable capacity in cold climates can be challenging, giving LFPs an advantage. However, LFP batteries generally should be charged at a slower rate when cold—usually no more than a C/10 at ambient temperatures below 32°F. (For example, if you have a 200 Ah battery, a C/10 charge rate will be 20 A.)

Comments (10)

John Nicholson_2's picture

Rereading and wondering if this question has any answers in the making: “Is the residential RE industry ready for LFPs?” (Being that this is published in a RE mag. I figure someone will come out with something.)

Is this the product that you made a comment on in the article: http://minibms.mybigcommerce.com/pr... ?

(As to the prior comment and reply, the link also has a contact with the photos. I don't know the the details that he keep.)

John Nicholson_2's picture

Copy.

mark roberts 2's picture

I'm using rebuilt Edison storage batteries, the cores are from the years 1907 and 1908. KOH electrolyte. They work great.. My Nephews grandchildren will be using the same batteries, decades down the road.

Mark Roberts

Randy Richmond's picture

Nickel-Iron batteries (which use potassium hydroxide electrolyte) like the Edison type have their place, and are very hard to beat for longevity. But their specific energy (energy/weight) and specific power (power/weight) is about 1/3, their energy density (energy/volume) is about 1/7, and their price (new) per Whr is about 3 times that of LiFePO4 (LFP). Their charge & discharge rate are much lower than LFP or LA (lead acid) and their charge profile (V-A vs time) can be tricky if you want to avoid thermal runaway. If weight, space, and instantaneous power are not a concern, and if one can afford the 3x up-front cost (new), their lifetime cost/Whr could be less than LFP. If used batteries with less than 30 years on them can be found (or if lucky, in the 100 year range like yours), the price could be very attractive. I understand that Exide took over the Edison Nickel-Iron batteries in 1972 and stopped making them in 1975.

mark roberts 2's picture

I've never had a problem with run away thermal and they get overcharged on a regular basis. My inverter and charge controller will only charge at about what is considered mid-range charging voltage for the batteries, 32 or 33 volts ( magnum inverter and midnite 250 controller. I force float at 31.5 volts. Its a 24 volt 500amp battery bank. Run them down to 19.5 volts. I dont really worry about over charging or undercharging too much.

My guess is as more and more farms and rural homes found utility power available after WW2, the market for Edison storage batteries slowly dried up. Excide bought them out and buried the technology. Its kinda amazing how much information is out there now compared to 10 yr.s ago when I 1st started researching nickle iron batteries.

10yr.s ago one would've thought the battery industry didn't really get started until the 1940's for the lack of information available..

Randy Richmond's picture

Hi John, I looked at the link and saw what appears to be LA paralleled with LFP batteries (I don't know how the capacitors are wired in). In general, mixing battery chemistries is not recommended because the voltage for the various charge stages are hard to match-up between LA and and other chemistries. Fortunately, 6 cells of LA (at 2.2V each) is about the same as 4 cells of LFP (at 3.3V each), so paralleling them may be OK for discharging, but I would still be concerned that during charge, the differing charge characteristics might prevent one or the other of the chemistries from being properly charged. Also, one can expect the LA batteries to reach end of life much sooner than the LFPs, and when they do, the LA batteries will be a drag on the LFPs, reducing the efficiency of the whole setup. If the guy who did this conversion is doing data logging or recoding his experience (e.g. the actual usable watt-hour capacity, how many cycles, etc.), it would be interesting to have the hard data to see how this actually plays out for him. Regards, Randy (author)

John Nicholson_2's picture

A friend of mine in the North Texas Electric Auto Association www.nteaa.org/ made a car which used both LA and LFP. The idea is to use LA as a buffer for the LFP as to balance and charge them. I have moved and so it has been a while since I check on the setup, but it might be something to think and write about. Here are some photos of it: http://www.flickr.com/photos/mbarkl...

Randy Richmond's picture

Richard, thanks for the question. In the next issue of HP, there will be a companion article about LiIon batteries in EVs. The article will have a table with the specs for the large format LFP batteries. You will see that the rated discharge low temp is -4F, and the rated charge low temp is about 30F. Unless you can keep LFPs above -4F they would not be a good solution for you. In the contiguous 48, even in Minnesota, many EVers find that insulating their battery box, and putting a heater mat under them (powered while plugged in), can keep their batteries warm enough, but at -75F even those measures may not work. Unfortunately, I've not explored battery options for such extreem low temps. You might browse through www.batteryuniversity.com and see about other battery chemistries that might work at those temps. But its likely that you will be trading low temp performance for some other aspect (such as lower power or energy density). Best regards, Randy, Author.

Scott Russell's picture

Thanks for weighing in, Randy. Your new article on Li-Ion batteries is now available on the site at https://homepower.com/articles/lith...

Richard Kemper_2's picture

Just how cold are LiFePo batteries able to withstand? Here in Tok, AK, we have a problem with even fully charged flooded lead-acid batteries slushing up at -75F or so, and we get that low in most years. Will this kind of cold damage these very expensive items, and what kind of performance (if any) could I expect? FLA are pretty much useless for EV power in winter, but would LFP be viable?

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