Can The Grid Handle Charging EVs At Every Home? Let’s Use Denmark As A Model Country & Find Out

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I remember years ago when reading the late David JC Mackay’s “Sustainable energy – Without the hot air,” I would get baffled about the concept of measuring the energy use of individuals of a society, because it opened up a way for me to compare different scenarios. This made me realize just how ridiculously much energy we use on personal transportation, in the more developed parts of the world, that is.

I’m not saying I agree on all aspects of David’s claims, but the idea of being aware of how much energy you consume (transportation, heating/cooling, and household combined and converted to kWh equivalents) is very useful in my opinion. For example, if I remember correctly, an average US citizen consumes 200 kWh worth of energy every single day, a European citizen just half of that, or 100 kWh. In developed countries, most energy use is from driving (50 km per day in fossil fueled vehicles consumes 40 — 60 kWh per day given about 8 — 10 kWh of chemical energy per liter fuel), and flying (one annual long-range flight by jet uses 30 kWh per day averaged over the year), which is in stark contrast to a below middle class sub-Saharan African citizen, who never drives or flies, and thus only consumes 20 kWh worth of energy, mostly in the form of firewood or charcoal for cooking.

One could argue that once electric vehicles are the only option on the market in say 20 years, the developing countries currently establishing a basic electric grid will account for the use of EVs and will not have the problems that countries with grids already established has, because…

EVs Will Fry Our Grid! Right?

I travel around Denmark giving talks on sustainable energy, and whenever I mention electric vehicles the question of whether the national electrical grid will have enough capacity to charge potentially millions of EVs comes up more often. Presumably because more people are actually starting to consider buying an EV, which is great.

I have always answered that it should not be a problem, mainly because I believe the Danish grid is very robust thanks to the ever rising amount of fluctuating wind energy, but how could I be so sure? In fact I wasn’t. Not until I looked at some numbers. Yes, it’s just the small scale of Denmark, but the following just might do a good job as a scale model.

Is There Enough Copper In My Street?

When I started driving electric I chose to lease, because I felt there were so many things I didn’t know about living with an EV that it was nice to have a way out, and not commit financially to a certain brand or model. For this reason I just used the chargers that came with the cars. One year it was an 8 amp 230 volt charger with the Nissan Leaf. Another year was a 6 amp 230 volt charger with the BMW i3. Both cars had a relatively short range, so a full charge from the typical 20% left after a day’s driving (60 – 80 km) was done in 10 – 16 hours. It was no problem at all, and I was pretty sure I was not stressing out my local grid.

This summer I had a wall charger installed for the new EV that I chose to buy, and even though I knew the charger itself could manage 32 amps I also knew that would not be necessary. I asked my local electrician for advice on capacity and he told me that every house on my street was equipped with a 35 amp main fuse where the wire would split from the street backbone (3 phases with a maximum voltage of 400 volts between 2 phases). He told me that every house can draw 35 amps from the grid simultaneously without a problem, provided that enough electricity is being generated on the grid of course. He also told me that my solar array would counter the strain on the grid when the sun was up, provided I guided the power to my car, thus closing in on a net zero draw on the grid.

Given this information, I went for a 20 amp breaker for my EV wall charger using all 3 phases, and I set the charger itself to a maximum of 16 amps (11 kW), which in my case will charge my car at a rate equivalent to a minimum of 70 km per hour of charge (44 miles per hour). This way I was sure to have enough power for my household at any time, while at the same time not at all stressing the local part of the grid, should the amazing thing happen that all my neighbors would go and buy an electric car.

However, I read elsewhere that every residence in Denmark was only guaranteed 25 amps, so will it really hold up? According to a paper from ieee.org, we shouldn’t worry too much even in a non-managed scenario, due to a couple of more or less obvious factors: EV drivers do not arrive home at the same time, and even if they overlap and charge simultaneously at some intervals, a study from Center for Transport Analytics at the Danish Technical University shows that the average traveled distance of passenger cars is 45 km (28 miles) per day, which means charging back up to cover that distance will be done in less than 40 minutes at 11 kW on average. In other words: High charge rate = high grid load but less overlap. Low charge rate = more overlap but less grid load. The chance that everybody arrives home and charges at maximum rate in the same 1 hour window is virtually impossible. But just to be on the safe side, let’s try to scale this up, and exaggerate a bit.

Is There Enough Electricity In The Grid?

The population of Denmark is just short of 6 million souls. Let’s imagine that two-thirds of them would need to drive 50 km (31 miles) every day in an EV, alone. In my experience the average EV electricity consumption is 200 Wh per km (322 Wh per mile) in cold weather, which results in a need for 10 kWh of electricity per person per day. This means the grid must supply 4 million multiplied by 10 kWh, which equals 40 million kWh, which is the same as 40,000 MWh, which again is the same as 40 GWh of electricity every day. 40 Gigawatt-hours!? Wow. Hold that thought.

On a normal day in Denmark, which has a fair amount of wind (41% total share in 2018), a little sun, and some base capacity from biomass, waste, and coal power plants, an output to the grid of between 4 and 5 GW is normal (consumption varies between 6 GW in daytime down to 2 GW at night). On a stormy day, wind power alone can easily surpass 5 GW on its own!

So let’s stick with the 5 GW figure which the Danish grid is more than capable of handling. That gives us 24 hours multiplied by 5 GW which equals 120 GWh of electricity. Boom! That’s 3 times the requirement for the EVs planned above, and in fact, the core grid is built to handle twice that load, about 10 GW. But wait a minute. We generate around 100 GWh of energy every day in Denmark now, and there are only a few thousand EVs on the road. So who’s using all that power?

The Big Power Consumers

I reached out to Thea Gehrchen at GreenMatch.dk to find out more, since she had recently provided me with some interesting insights on the most energy intensive industries in Denmark, and sure enough she had a new article ready with the 2018 numbers of electricity consumption grouped by municipalities. This would help me assess whether EVs will fry the grid!

It turns out that if you take all electricity consumption into account, with industry being the largest consumer, and relate it to total population, you get 524 kWh per capita for December 2018, or 16.9 kWh per capita per day. If used only for EVs that would translate into 85 km (52 miles) of transport for every single individual, in theory.

Looking at the municipalities with sparse population and heavy industry, you get 35.8 kWh per capita per day. And in contrast, densely populated municipalities without much industry consume 8.19 kWh per capita per day, which is still enough to drive 41 km (25 miles) — again, in theory.

Since we are at most considering two-thirds of Danes needing to travel at most 50 km per day on average, but considering that they would actually not be doing so in one car each but often travel more than one in each car and actually using electrified trains and buses too, we would be looking at a surplus consumption of much less than 10 kWh per capita per day added to the almost 17 kWh on average consumption stated above. This is mostly speculation, but it is interesting to think that a scenario where the load on the grid is rising maybe only 50% would completely displace all fossil fueled surface passenger transportation.

Given that the grid in general is built to withstand a peak load of double the average does give you a hint that the electricity backbone is quite capable of serving millions of EVs. Really? Is it that simple? Nah, not quite…

My mind drifts as I look out my window and see the two 900 kW wind turbines spinning a couple of miles away, imagining that an EV charging station right there on that hill connected to those turbines could fully charge 40 new Renault Zoe EVs every hour at peak wind without breaking sweat!

Managed Charging

The question still remains whether the step-down transformers (10 kV to 400 V) supplying electricity to streets will overload and/or if the final stretches of copper wires to households will be able to carry enough electrons if everybody got EVs. There will be streets that need to be upgraded, but in fact a new report from Danskenergi.dk suggests that this would only cost DKK 3 billion ($442 million) nationwide, although the aging grid as such, regardless of EVs, needs upgrading at an estimated total cost of DKK 29 billion ($4.3 billion) by 2030. The overall solution that will prevent radical measures like load shedding is without a doubt managed charging. This can be done manually or automatically at many levels.

I do micro management of my own charging to some degree, meaning that I always consider when to charge and at what amperage. I have solar panels and it is of course only natural for me to prioritize charging when the sun shines. It’s the cheapest option and it puts the least load on my local part of the grid. But that’s not all. The software in my car allows me to select amperage and also schedule my charging, and even turn charging on and off from my smartphone.

If I am in no rush, and the sun isn’t shining, I set my amperage low and let the car charge slowly. If I need to travel far early one morning I schedule the car to charge at high amperage to reach 100% state of charge just before departure, thus drawing heavily on the grid at a shorter period of time where capacity is high at night and getting the benefit of a warmed up battery and cabin resulting in more comfort and better mileage. Note that we have almost flat rate electricity pricing in Denmark due to an outdated taxation system.

The step from this manual approach to a more automated intelligent approach is straightforward. The cars, the chargers, and the electricity metering equipment are getting smarter and mostly ready to take over. This report from Maisy.com on Nissan’s experiment on V2G (Vehicle to Grid) power management is very clear on this: “Residential peak period loads can be completely offset with an EV market share of only 10%!” But even just managing charging without having the cars work as a virtual power plant should be enough to prevent any problems on existing grids.

It goes without saying that strong price management will support all these strategies. So am I worried that the grid will melt when people realize EVs are cool, fun, and cheaper to run? Not at all. First off, there is a demand and supply issue meaning that I would be very surprised to see more than half a million EVs on the streets in Denmark by 2030 (1 in less than 10 people). Secondly, the charge management systems are developing very rapidly, and thirdly, it will be even more convenient charging when you’re away from home as you see chargers pop up at supermarkets, hotels, leisure parks, and everywhere along high power non-residential backbones! Which is of course essential for people living in apartments who do not have the luxury of a wall charger at a fixed parking spot. And we have not even talked about stationary batteries, small residential or big grid systems. They might not even be necessary, but they can come in very handy at sites with fluctuation problems, and thus removing that last bit of “supply-anxiety.”

In any case, when talking strictly EVs, all this would be completely irrelevant once every gas station along main traffic routes has been converted with a handful of +100 kW charging stalls. As soon as small and cheap EVs start coming to market, there is no reason not to get electrified, because the grid will get ready along the way.

All photos by the author