Minimize battery degradation or minimize damage from battery degradation?

In the series of posts on the battery-life saving algorithm of the University of Warwick, I made (twice) the remark that the managers of vehicle-to-grid programs would not be very keen in implementing such an algorithm. This because this algorithm, although it is hailed as a break-though, will have a negative impact on the primary purpose of these schemes, therefor tolerating (some) battery damage might be the preferred option.

That made me wonder whether I could check this. The Warwick paper was published two years ago and the Smart Solar Charging program was presented as having developed its own bidirectional charging stations, so if there is some ability to make improvements based on this supposed break-through, then this project should be the one that will show it.

I then went to the LomboXnet website (the company behind the solar charging system). If they would have implemented battery life saving algorithm (or are in the process of implementing it), then it should be really visibly advertised there. If they could claim that the system they developed is different from the others in the sense that it increases battery life (maybe even a fraction of what the paper claimed), then that would be an important selling point of their system.

I didn’t find information on the (dis)charge strategy of their charging station, but there is a link to their twitter account. Scrolling down a bit, I found a recent retweet of a newspaper article about a vehicle-to-grid system in Utrecht (the article is published on April 18, 2019):

Tweet LomboXnet 20190420

The title of the newspaper article is “Rent out the battery of your car. Do you even want that?” and the accompanying text of the tweet is “The car as short-time energy buffer”. There is a short introduction of the program, but most interestingly, about half of the article is about battery degradation (in smartphones and laptops, but also in electric cars operating in their program).

Bingo!!

In the comments, there is also a tweet with a link to the Wattisduurzaam article that pointed me to the Warwick paper. This link is provided by the author of the wattisduurzaam article and he stated that discharging to the grid could extend battery life “under ideal circumstances”. Sure, but is this system in Utrecht working under (near) ideal circumstances?

Initially, the newspaper article didn’t make much sense to me. It seems to be targeted to owners of electric cars who worry that operating in a vehicle-to-grid system might damage their battery. The puzzling thing was that the initiator of WeDriveSolar (a service offered by LomboXnet) is interviewed. WeDriveSolar is a shared car project and those who rent such a car probably wouldn’t care less whether the battery degrades faster.

Poking around at the LoboXnet website, I found that also electric car owners can request the installation of these bidirectional charging stations in their neighborhood, so it seems that the use of those charging stations is not limited to the WeDriveSolar project. Now the newspaper article makes perfect sense. Maybe they just wanted to promote the use of these stations? Or they found out that electric car owners in the city were reluctant to use these charging stations because they worry about degradation of the battery?

This is how the scheme works (translated from Dutch):

What’s the plan?
Park your car, connect the plug and the grid operators take over. They draw power from your car when the neighbors turn on their washing machine. Recharge your battery if solar panels in the neighborhood produce much at the same time. Draw power again when the neighborhood starts frying in large numbers. And so electrons flow back and forth, just as long as you hold the plug in the charging station.

If that is true, then the car battery is used quite intensively and there should at least be some battery degradation involved. Also odd, the WeDriveSolar website promotes the scheme by claiming that it is possible to drive 300 km on 1 charge (that is the range of their Renault Zoe cars), but if the grid operators are tinkering with the charge in the car, then there is no way that they can guarantee that this amount of charge will be available to the driver of the car…

Let’s look at their strategy regarding battery degradation (translated from Dutch):

But doesn’t my battery degrade then?
Possibly yes, and anyone who already had to dispose of several phones will recognize why. After charging a thousand times, it is almost done with the smartphone, a laptop or even an electric car; a consequence of degradation in the battery. Each time the battery is charged or discharged, some of the solvent in the battery disintegrates into other substances and the capacity decreases. But, the initiators say, that happens especially if you charge the battery until completely full and empty it to the last spark. If you restrict yourself to the middle, there is less degradation and therefore the managers promise not putting too much strain on your battery. Then it shouldn’t be too bad.

Is this statement correct?
‘Yes, that’s right’, says professor of battery technology Peter Notten (TU Eindhoven). Batteries do not have to degrade quickly at all, but they do because we always fully charge them. It is precisely at that last part of the charging process, from 90% to 100%, that the tension in the battery is at its greatest. Then the temperature rises, substances start to oxidize and the decay starts. And if, for example, a telephone is also plugged in a black case in the sun, this becomes even worse. Limit yourself to the central area and then the scheme in Utrecht is viable, he says. “For example, keep it between 20% and 80%, then you will have little damage.”

That is quite a collection of weasel words squeezed in just two tiny paragraphs. What does that even mean, “not putting too much strain on your battery”, “shouldn’t be too bad” and “little damage”? They promise not to put too much strain on your battery, that is very nice of them, but why don’t they just guarantee it?

That is the difference in strategy with the University of Warwick.

The Warwick paper is trying to keep the degradation of the battery as low as possible. Their algorithm calculates what will be the least damaging for the battery (discharging to the grid or staying idle) and then goes with the best option, therefor the result will always as good or better than when not operating in the scheme. They stick with that strategy, even when the consequence is that 62% of the cars can’t participate in the project (because discharging would degrade the battery more than staying idle).

The smart solar charging project doesn’t have that luxury. They offer a service (using electricity from solar panels and balancing the local grid) and it would have a negative impact on their purpose to for example exclude cars from participating because of an algorithm to save battery life. They start from the presumption that operating in a vehicle-to-grid will degrade the battery to some degree. It is true that they will certainly try to minimize this damage, but it is not very clear how small or how large that damage will be.

That vagueness is not surprising. If they want to attract electric car owners to participate in their scheme and they anticipate degradation of the battery while operating in the vehicle-to-grid, then it is best to minimize the degradation and downplay that it “shouldn’t be too bad”…

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