“Extends” or “could extend”, that is the question

This is the wrap-up of the vehicle-to-grid series. In this post, I will go back to the article bringing the news that vehicle-to-grid networks increase longevity of electric car batteries. Now that I read the paper and have shed some light on several aspects, I re-read the article to find out whether the author was correctly representing that paper.

Unfortunately, this is not the case. It already starts with the title (translated from Dutch, my emphasis):

‘Energy storage in electric car extends the lifespan of the battery’

Note the quotes. it seems to be a quotation, although I can’t find this wording in the paper and also not in the press release. The next sentence builds on this title (translated from Dutch, my emphasis):

Research at the University of Warwick in the United Kingdom shows that the charging and recharging of electricity in plug-in cars extends the life of the battery packs. A striking result with a major impact on the energy transition.

Again, note the use of the present tense, as if it is already in the bag. It is true that the paper and the press release also use the present tense when explaining the results of their simulation, but there are also a bunch of other words like “possibility”, “could”, “under certain circumstances” and so on. All these words seemed to be stripped from this article.

There was however a glimpse of one condition that has to be met to come to that increase in battery life (translated from Dutch, my emphasis):

The findings of Uddin and his research team are therefore remarkable, although the explanation is certainly plausible: The number of charging cycles (fully charged and discharged) is an important but not the only factor that determines the lifetime of batteries. The temperature of the battery, the charging current and the average level of discharge also play a major role. These factors can be precisely adjusted by loading and unloading and thus optimizing.

This complex relationship means that a smart two-way charging station extends the life of the battery.

Indeed, the researchers assumed a two way communication between the car battery and the smart grid. That is only one assumption, there were many more assumptions used in the paper, but for some reason none of these were mentioned in the article.

The reader of the article will come to the conclusion from this article that energy storage in electric car batteries extends battery life. Okay, there might be that thingy of the two-way charging stations, but many probably would have no clue about what this means anyway (I personally glossed over it completely during the first read).

A second, probably related, thing that caught my eye was how the result of the paper was explained. This is a subtitle (translated from Dutch, my emphasis):

Long-term tests indicate a 10 percent longer lifespan

This is not a one-off (translated from Dutch, my emphasis):

Uddin claims on the basis of long-term tests in the laboratory that its charging algorithm reduces the capacity loss of batteries by 9.1 percent. The power loss that the battery pack delivers is, thanks to optimum double use, even 12.1 percent smaller.

It also appears in the last paragraph (translated from Dutch, my emphasis):

The step from the optimally controlled conditions in the lab to the practice has not yet been made and is usually tough. However, if in practice even a little of the substantial laboratory gain remains, the impact of the research is enormous.

The author seems to believe that the researchers came to the result on basis of long-term tests. This however doesn’t match what is written in the paper. The long-term tests were performed to validate a battery degradation algorithm. After validation, this algorithm was integrated in a smart grid model and it was the simulation run of this model that generated the 10% figure.

It is the battery degradation algorithm that is validated, not the model that it was build into. The modeled results still need to be verified in reality.

If the author of the article really believes that the results stem from experiment, then I could certainly understand his certainty. If this 10% figure would really be measured, then the increase in battery life would be established and then it would be a matter of testing it with real life conditions to see what will remain of this gain. Then the use of the present tense would be justified.

After reading the article, the reader will come to the conclusion that an increase in battery life is possible in reality. What the reader doesn’t get is that the result comes from a model simulation and that the model is fed with rather unrealistic data. Beside the two way communication, there is also the assumption of a smart battery management system that could accurately predict the daily energy use of that driver is available (in a later paper (2018) the lead researcher acknowledged that these are “ambitious” assumptions). The reference period of the simulation is the last week of July 2016 (with a low, maybe even lowest, electricity demand), a constant number (maximum possible) cars over the entire year and a constant temperature of 18 °C throughout the entire year (close to the optimal temperature for lithium-ion batteries).

This 10% increase in longevity of the battery is therefor not even under ideal circumstances, these conditions could never ever be met in reality. In that case it is incredibly easy to get a 10% increase in battery life. It is a virtual number, not related to reality.

The article also doesn’t touch two other inconvenient findings of the paper: the algorithm didn’t allow for all cars to participate and there were moments when the car batteries were not available although they were needed. These are two findings that will have serious consequences in a real-world vehicle-to-grid situation, including the vehicle-to-grid network that was provided as an example in the article.

The article doesn’t bring the full story of what was found in the paper. The reader will be overly optimistic about the capabilities of the system and will have no knowledge about the consequences/limitations/desirability of participating in such a network in the real world.

Which, unfortunately is the sad norm in alternative energy communication.

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