Refrigerating electric car batteries?

[swbluto]

I saw someone's spreadsheet on the source of losses in a nissan leaf battery, apparently "Calendar losses" make up over 80% of the losses in his case (With less than 20% due to "cycle losses").

http://www.mynissanleaf.com/viewtopic.php?f=27&t=14275&start=180

I know that temperature is very important for the 'calendar losses' which is why I store my batteries in the coldest place in the house, and my lithium batteries are still ticking like new 4 years later (I also follow longevity-maximizing voltage guidelines, including the best charge voltage and storage voltage.). For roughly every 18 degrees increase in temperature, the rate of decay/aging doubles according to the Arrhenius equation.

I'm wondering, is it economical to refrigerate electric car batteries by using an electric outlet while the car sits?

I'm trying to imagine ballpark numbers...

$30,000 battery
$200 refrigerator/insulation unit

$100/electricity-usage per year(?)

Would it be worth refrigerating a car battery to increase longevity?

It seemed if refrigeration could increase the battery's lifespan from 5 years to 10 years, and that 10 years of refrigeration would cost $1000, it'd seem worth it.

10year timespan

non-refrigerated:
$60,000 in batteries (Buy replacement at 5 years)
Refrigerated:
$30,000 in batteries + $1000 in refrigeration = $31,000

 

[cwah]

So you'll need to heat your battery before going out? :lol:

 

[swbluto]

So you'll need to heat your battery before going out? :lol:

:lol:

20c lithium batteries can easily handle 1c use at 45-55 degrees. I really doubt it'd highly affect performance.

Presumably, if the car had a usage pattern like commuting at 7 in the morning on weekdays, it'd be programmable to stop refrigeration an hour or two before, assuming it's a "real" concern.

(And, who knows, using colder batteries might ALSO increase cycle life, not *just* calendar life. Any studies on battery temperature and cycle life?)

 

[dogman dan]

Sounds good in theory. But how do you refrigerate your battery when you get to work, and park in a lot for 9 hours where the asphalt is gooey and sticks to your shoes when you go to lunch?

One thing's for sure, around here a shaded parking under the solar panels would be the place to park an EV. Then you only park in 110F, rather than 150F.

I worried about this a lot when I got my first ping. Then I just realized that it was not something I could very easily do much about. I was allowed to charge at work, but not inside the building.

But it is one of the reasons I decided against trying to make a larger EV with a more expensive battery. I think I have a poor climate for one, unless I am in a retired person use pattern. Parking all day in that flaming parking lot has to be ageing the battery. Locally, we know our lead car battery will never last more than two years. But if you can park in a climate controlled garage, or at least under a shade tree, it would be better.

Now I am retired, and there's no way a leaf or plug in prius is in my budget. Nor cooling that garage.

 

[swbluto]

Sounds good in theory. But how do you refrigerate your battery when you get to work, and park in a lot for 9 hours where the asphalt is gooey and sticks to your shoes when you go to lunch?

One thing's for sure, around here a shaded parking under the solar panels would be the place to park an EV. Then you only park in 110F, rather than 150F.

I worried about this a lot when I got my first ping. Then I just realized that it was not something I could very easily do much about. I was allowed to charge at work, but not inside the building.

But it is one of the reasons I decided against trying to make a larger EV with a more expensive battery. I think I have a poor climate for one, unless I am in a retired person use pattern. Parking all day in that flaming parking lot has to be ageing the battery. Locally, we know our lead car battery will never last more than two years. But if you can park in a climate controlled garage, or at least under a shade tree, it would be better.

Now I am retired, and there's no way a leaf or plug in prius is in my budget. Nor cooling that garage.

It's not something I worry about a lot when it comes to eBike batteries even though I take care of them, but with the tremendous cost of e-car batteries and how much lifespan is affected by 'calendar losses', it definitely seems worth looking into. A thermally managed $30,000 lithium battery could possibly make the difference between $1500/year and $6000/year which could make the difference between financially viable and not-viable for many people. (Or, competitive or not competitive with gasoline.)

Modern electric cars are relatively new and don't really have mass market penetration yet, so 'best practices' for longevity probably haven't had much opportunity to be established among existing electric cars. (Though, active refrigeration does require an outlet wherever you'll be parking for more than 2+ hours, so it might be impractical for some people. Although, I've seen charging ports at the Google Campus and various parking lots in Austin, TX, so they're starting to sprout up where there's a demand.)

 

[swbluto]

Found out that the Chevy volt has active refrigeration, apparently designed to keep the battery temp between 76-90 degrees. I also found out that cycle life started declining below 50 degrees fahrenheit, so 50 degrees seems like the limit before cycle life starts to degrade.

 

[Hillhater]

The Tesla's ( and possibly others) do have battery "cooling" systems built in, but presumably to prevent excess heat build up rather than actual active refrigeration ( more research need to confirm).
But it cannot be too much of a step to add a true refrigeration pack to those existing cooling circuits if there is a benefit to be gained.

 

[wb9k]

The Volt's battery is liquid-cooled (as are most EV battery packs), but I know of no actual refrigeration and doubt that is actually the case. Heating on very cold days, yes, but refrigeration during very hot temps seems unlikely.

If pursuing this, the optimal strategy will probably vary from one chemistry to the next. Keeping A123 cells at 50F or lower halts calendar aging completely. The cells will perform better at warmer temps (lower impedance), but age faster. Doing this is likely worthwhile in very hot climates, any cooling is better than none. Total calendar aging is driven by the average temp the cells are exposed to over their entire lives. The lower that average temp, the slower the calendar fade.

 

[Harold in CR]

Is it possible that the term "Refrigeration" is being taken too literally ? Liquid cooling would essentially be the same thing.

Now, is it even possible that a small temp controller cooling system could be built, to simply circulate liquid to keep batteries in that 60° F range? Even parking cars in a garage can elevate the battery temps in places like southern US, for instance. There, just plug it in, same as a charger. ?

Hasn't Neil Sakai just developed a cooling system for his bike battery packs ? I believe so. ?

 

[swbluto]

Is it possible that the term "Refrigeration" is being taken too literally ? Liquid cooling would essentially be the same thing.

Now, is it even possible that a small temp controller cooling system could be built, to simply circulate liquid to keep batteries in that 60° F range? Even parking cars in a garage can elevate the battery temps in places like southern US, for instance. There, just plug it in, same as a charger. ?

Hasn't Neil Sakai just developed a cooling system for his bike battery packs ? I believe so. ?

If one lived in a climate where the average temp, night and day, was something like 50-60 degrees, then refrigeration shouldn't be necessary. It could still be potentially useful for overnight parking for ordinary LiCo chemistries, and some active thermal management system could adjust the temperature of the pack through the day by controlling the flow of heating/cooling fluid to maximize the optimal temperature of the pack at a given moment. (When the car starts up, remove the cool fluid, pipe in normal temp fluid; When parked for longer periods of time, reverse. The pack would ideally be designed to allow maximum efficiency/speed in adjusting the pack's temp on demand.)

 

[dogman dan]

This is a problem for sure in my climate. Three months of the year, we get a low about 80F, but the car would likely spend the day in a parking lot with a lot surface temp between 120 and 160F. So the battery will be well over 110F by afternoon when you discharge it going home. Parked in the shade, then only ambient temp of about 110F max some days, and 102 more like the norm. Even that is pretty warm for optimal battery lifespan.

It's gotta affect calendar life. But once it's that hot, cooling anything gets very costly. More large EV's are for the rich stuff. I think eventually we are heading towards EV's but we need to get over the large thing to afford it IMO.

Gas cars no different in the size costs you equation, and by large I mean size of a Camry or Focus. Talk to people about what that thing costs you per mile to drive, and they simply go into denial. They just can't believe a 30 mile drive costs them 15-20 bucks. It's the purchase price they just refuse to think about. Then whine if gas is 20 cents higher this week. They'll drive 10 miles one way to get "cheaper" tobacco or beer, adding 10 bucks to the price without thinking about it.

Right now, with a new car with a costly payment combined with a not driving much use pattern, my Subaru is costing me $1.31 per mile, not counting maintenance. The less I drive relative to the payment the worse it gets, but if the car lasts long enough I get a payback after the loan ends. For now though, reminding myself that it costs 20 bucks to go to a nearby grocery keeps me from doing that every day. Take the cargo bike if at all possible.

 

[wb9k]

To me, "refrigeration" implies an active cooling system--usually using a chemical refrigerant and a compressor system--as opposed to a passive system in which a radiator realeases heat into the passing air. The "liquid cooling" system in an EV is really a "liquid thermal control" system with passive cooling and active heating. The heat energy usually comes from the HV battery, which drives glow plug-type heaters in the thermal control liquid. The heated liquid can be distributed to the cabin of the car for passenger heat, or to the battery itself to bring down cell impedance, or both. Many EV's can be preconditioned for driving with energy from the grid while charging, which saves on battery range and provides instant cabin heat to boot. If you can't plug it in, you probably don't want to leave a pure EV parked outside in the dead of winter for very long.

In the American southwest, heat is an ever-present enemy, and today's systems are probably a little less able to deal with this as effectively as they do the cold. This is because of the lack of active refrigeration in every system out there as far as I know. Hopefully this makes clear why I think the distinction matters. We can get by driving around without true refrigeration of cells, but being parked for long periods of time in oven-like conditions kills calendar life. I think we'll be seeing improvements in battery chemistry to make cells more robust against heat and cold as the primary fix for this issue, but if that can't be taken far enough, perhaps you'll see systems with active refrigeration of cells while the car is plugged in.

Today's ebikers would do well to take their packs indoors whenever possible if it's over 80F outside. If your cells are getting hot enough to damage themselves in the course of regular riding, then your battery is too small for the job you are asking it to do in your environment. I would think using a bigger pack would be about as economical as adding an elaborate cooling system to an existing battery. The bigger pack would also yield a capacity gain, as opposed to a capacity expense.

 

[Kingfish]

This is a very interesting thread.

I use the term “cold” with deference because cold can kill a battery. So to say “cooling” would imply taking something down below STP which would impact performance – though perhaps the one caveat towards longevity. Cooler temps surely reduce the active decomposition batteries face from the moment they are constructed; I have known since I was a child that common batteries last longer if they’re stored in a fridge rather than left out in the uncharted environment of a garage.

The guys in warmer climes have a point though. I would think that if the battery compartment was well-insulated then an active cooling system could be employed – although I imagine the refrigeration cost might be expensive depending on the medium. Are we talking about R12 or glycol or maybe something else? What level is required to drop the battery down enough to be satisfactory?

Upon reflection I like a warm battery because – well, I live in a normally cool clime, so a hot day gives me 10% more production. It’s a fluke most of the time, and breaking 100°F/40C is rare as a blue moon.

But I’m keen on thermal drains and I’m trying to imagine a low-cost method to achieve that effect through material engineering. Plumbing systems are IMO expensive and cause for drag. If we can quantify the amount of energy to bleed out, perhaps we can come to terms with reasonably low-cost solutions – easy simple stuff, even DIY level. It doesn’t need to be a mystery. 8)

Tending to the needs of the many, KF

 

[dogman dan]

I think thermal mass and some insulation to keep the battery at an optimum temp during discharge is good, if not mandatory. Don't want a hot center of the pack in a large car battery.

And in very cold climes, you'd want to plug in the car, so you don't have a pack actually freeze. Or have a battery powered pre heat, say one hour before you normally drive it starts bringing the pack above 50F.

But the flip side, cooling in the summer is just technically harder and more expensive than a small electric heater. You load an additional AC powered air conditioner to chill the liquid thermal material and circulate it? Ideally of course, you park all day in a shaded space with a plug. It could be fairly affordable to run, if the box is insulated so the 140F parking lot matters less. But shade would cut that cost quite a bit.

I sort of see the doctors office having one space with such amenities, but you won't get it where you work, unless you are the business owner. The rest of us will just wear out the battery faster.

 

[wb9k]

Kingfish,

You might want to check out some of the phase changing materials that are out there now and being targeted at precisely what you're talking about. Charged magazine has had articles in the last few issues on a couple of them.

http://chargedevs.com

 

[tomjasz]

Refrigerate, worth the watch. Check out last 15 minutes.

https://m.youtube.com/watch?v=pxP0Cu00sZs

 

[battman]

I think thermal mass and some insulation to keep the battery at an optimum temp during discharge is good, if not mandatory.

+1 on the insulation if you can take your pack indoors on a hot day after riding. I live in Phoenix and have a 36Vx15AH pack inside an aluminum box that I insulated to protect the cells against vibration and shock. Turns out that this insulation has a significant added benefit for limiting temperature rise on the ride home in summer too. For example, on a 110F day I left work with the temperature inside the box at 78F. At the end of the 45 minute trip the temperature was 96F, pretty warm but still well below ambient. The temperature rise was linear throughout the ride.

Phase change materials may be worth looking into, but something as simple, cheap and light as Styrofoam would likely perform just as well for many uses cases.

 

[Punx0r]

Interesting paper here:

http://physlab.lums.edu.pk/images/a/a5/Cooling_paint.pdf

Basically, it's not that it's black paint, it's that it's paint (any colour) Vs. bare metal. The author asserts that the classic physics class explanation of black body emissivity and cooling of an object is misleading - a white painted object would cool at the same rate as a white one. The explanation is that the body's reflecting properties at visible wavelengths are usually not the same at infra-red wavelengths. Sounds plausible.

However, if the know the emissivity data for your paint (like the ones recommended above) and it's black and it works, crack on!

Bottom line: bare shiny metal is a poor emitter of thermal energy compared to a painted surface.