German EV Study: Fast Charging not required at home

According to a Reuters report, a small pilot study of electric car charging behavior concluded that users quickly adopt to “slow charging”. The problem with this is that the participants were given Renault Zoe’s and a 22 kiloWatt wallbox for use at home. For most intents and purposes 22 kiloWatt charging borders on “fast charging”, and is certainly a lot faster than the typical 6 kiloWatt charging rate. Somehow from this installed equipment the German electric utility conducting the study concluded “consumers can be persuaded to accept slow, overnight recharging that could help avoid brownouts from surges in electricity demand or costly upgrades to power grids”.

The study was conducted in a wealthy suburb of Stuttgart by Netze BW, the local grid operator (Reuters). There were 10 households participating, and each were provided with a Renault Zoe and a 22 kiloWatt charging station. The Zoe has the capability to charge at over 40 kiloWatts directly off 3 phase AC, and it is my understanding that 3 phase AC is commonly available in Europe. Therefore Europeans have an opportunity us Americans do not have, the possibility of fast charging at home using simple equipment.

According to the Reuters report, participants at first nervously topped up their cars at every opportunity. But as the study progressed they became comfortable with the process and “soon adapted to leaving the power company to handle it as it saw fit overnight”.

The Reuters report makes it clear there was some sort of remote control in regard to charging times. Reuters says that one aspect of the program is that participants allowed Netze BW “to monitor and carry out a deferred and down-scaled charging process during a seven-and-a-half-hour period overnight”. Netze BW tried different options such as scheduling the cars to get 22 kW charging one after another, or to lower the charging rate to lengthen the charging time. The promise was that sometime during an 8 hour period overnight the car would become fully charged by the morning.

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Clearly to implement such a control mechanism – centrally managed charging of electric cars – requires some sort of networked connection. The Reuters report talks about smart grid features, but it could also be implemented over the Internet. For example several charging networks implement control protocols running over the Internet, and it is relatively easy to adjust the charging rate from the charging station.

What we can gather from this is that the participants grew to understand that the requirement is for their car to become fully charged by the time they leave home in the morning. It does not matter at exactly which minute the charging starts, nor is it important what the charging rate is, so long as they have the luxury of a fully charged car in the morning.

Gasoline car owners do not have this luxury. Electric car owners need to be smug about the luxury of having a fully charged car every morning, but not too smug.

What charging rate do electric car owners truly need?

It’s easy to think we always need to charge an electric car as quickly as possible. In part this is because of our collective experience of 100+ years of quickly refueling gasoline cars. But if we ponder carefully this question, it’s easy to come to a different answer. The best charging rate depends on the situation.

I’ve written about this at length in: What electric car charging rate do we need at home, at the office, on road trips, at airports, or elsewhere?

In another study of charging behavior, conducted in 2008 in Tokyo by a researcher at TEPCO, they found that indeed PUBLIC fast charging tended to make electric car drivers more confident and therefore drive their cars more often. In presenting those results, the researcher made it clear that fast charging is not required at home. He went over a four-quadrant analysis of which charging rate is needed in what scenario.

It comes down to the time the person is able to wait.

For example – typically at home or at the office fast charging is not required in the slightest. We are inside the home, or in the office, for at least 8 hours, and therefore the charging can take 8 hours without it impacting our life. At home the cost of charging equipment weighs on our mind, and we might prefer to have really slow charging like 3 kiloWatts or less charging speed in order to have cheaper charging equipment.

For example – when taking a road trip we need to stay on the road as much as possible, so in that case fast charging is a hard requirement.

The need for centrally managed EV charging?

The libertarian in each of us might bristle at the idea of the electric company controlling when our car charges and the charging speed. Who are they (I can hear this in my head) to make those decisions for us?

The big worry infrastructure planners have is that adopting electric cars will swamp the electricity grid, and we’ll just have brownout after brownout.

They’ll go on to say that so far there hasn’t been any problem because there aren’t enough electric cars in consumers hands to make a significant difference. But if adoption rates go to 10% or whatever, that’s when problems will kick in.

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I remember a statement at a conference 10 years or so ago that electric vehicle adoption won’t be evenly spread. Instead you’ll have the neighbor effect, where one guy in a neighborhood buys an EV then after excitedly showing the car to all the guys in the neighborhood they all buy EV’s, and then you have a cluster of electric cars all charging from the same feeder circuit. That feeder circuit will become overloaded necessitating upgrades to power lines and transformers.

Another factoid has to do with charging scheduling software. Back when the Blink project (run by ECOTality) was sending reports to the government every month, one graph had showed the typical time when charging sessions started. These clustered at 11pm or whenever it is that night-time time-of-use rates started. In other words, electric car owners set the schedule to start at the very second the electricity rate dropped to the minimum. While that’s good for the electric car owners, it meant there was a surge of electricity demand all at once at exactly the same time.

For these and other reasons the regulators believe it is important that electric car charging times and power levels vary.

In the bigger picture, the electric grid regulators see an absolute requirement for broad scale scheduling of not just electric car charging but all kinds of things. I wrote about this a couple years ago – Reporting in from California’s Distribute Energy Future.

In that telling – the rapid adoption of solar energy and wind energy resources means that the electric utility can no longer treat renewable energy as a nice little side experiment. They must begin to treat this stuff as dispatch-able energy resources. At least in California, the goal is to be able to orchestrate all kinds of energy production, energy storage, and energy distribution actions so that excess solar electricity can be time-shifted for use during the evening.

One tool to help with this is the battery packs in electric cars.

For solar power and wind power to live up to its potential it may be necessary for us to allow centralized management of not just the charging of our electric cars but all kinds of things.

About David Herron

David Herron is a writer and software engineer living in Silicon Valley. He primarily writes about electric vehicles, clean energy systems, climate change, peak oil and related issues. When not writing he indulges in software projects and is sometimes employed as a software engineer. David has written for sites like PlugInCars and TorqueNews, and worked for companies like Sun Microsystems and Yahoo.

About David Herron

David Herron is a writer and software engineer living in Silicon Valley. He primarily writes about electric vehicles, clean energy systems, climate change, peak oil and related issues. When not writing he indulges in software projects and is sometimes employed as a software engineer. David has written for sites like PlugInCars and TorqueNews, and worked for companies like Sun Microsystems and Yahoo.

One Comment

  1. In other studies, dinosaurs were found to be thin at one end, much much bigger in the middle, and thin again at the other end.

    The issues of EV interaction with the grid, for worse and for better, are interesting, including G2V, V2G, throttling, control, and incentives. Consider the implications of this soon-to-be-rolled-out equipment: https://thedriven.io/2019/07/11/nissan-sees-leaf-as-home-energy-source-says-tesla-big-battery-waste-of-resources/. I can’t wait to see the studies this will generate.

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