“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’

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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.

Two neglected findings

There are two findings in the battery-saving algorithm paper from the University of Warwick that I want to write about in this post. Both were mentioned only in passing in the paper. Although these findings are crucial information for those who want to implement such a system in the real world, these were not mentioned in the conclusion nor in the discussion nor in the list of things they want to improve upon.

These are the two findings:

Can a vehicle-to-grid extend battery-life of electric cars by ten percent?

In the previous post, I wrote about a report calculating the expected electricity price in a vehicle-to-grid system and the assumptions that went into it. One of the difficulties that was detailed in the report was the aging of the battery used in a vehicle-to-grid system. In the meanwhile, I read this 2017 article from the Dutch sustainability website wattisduurzaam.nl contradicting this. The author of the article writes that it is contra-intuitive, but that research from the University of Warwick revealed that a vehicle-to-grid system can even extend the lifetime of lithium-ion batteries…

I could somehow understand “minimize”, but a vehicle-to-grid system that extends battery life is a very strong claim.

Although the article was written in a cheering mode, it also acknowledges that battery degradation is a problem in current vehicle-to-grid systems, but that this research achieved an extended battery life. Not just a tiny extension, a whopping 10 percent extension of battery life by operating in the vehicle-to-grid system.

More averaging: impact of electric cars on the grid

The term “vehicle-to-grid” is mentioned twice in passing in the report detailing the impact of electric cars on our grid (see previous post). I wondered whether this vehicle-to-grid was the solution to their problem. After all, their calculation was done by averaging consumption, which is not really what will happen in the real world. But when they assume some top-down system of regulating demand, then I could somehow understand their reasoning.

I didn’t find any reference mentioning “vehicle-to-grid” in the report, but I wanted to know where the CREG got these assumptions from. I found that, to my surprise, the CREG earlier wrote a report on the impact of electric cars on a vehicle-to-grid system (pdf, Dutch ahead). The report is not new, it was published in 2010 with the data from 2007 and 2008. The subject of their research is the impact of the introduction of electric cars on the electricity spot market price.

The result of the 2010 report was similar to the 2016 report. They also researched the impact of 1 million electric cars and found that only 2.5% extra electricity needs to be produced on average (compared to 4% in the 2016 report) and that base load could easily absorb that extra electricity demand. The general conclusion of the 2010 report is that charging cars during off-peak hours will lower the spot prices. This because part of the capacity of the car battery could be used to trade on the energy market, buying electricity from the grid when it is cheap (during off-peak hours) and selling it at a high price when it is expensive (during peak hours).

It gets interesting when they explain their assumptions (on page 15 – 16):