I’ve been working on EV charging since 2014, and in that time have heard some deeply weird opinions on EV charging and the various ways it will destroy the grid.
There are three main classes of EV Charging weirdness; energy problems, capacity problems and technical problems. I’ll start with the technical because there’s only one major example:
Technical Problems
In the early days, distribution network service providers (DNSPs, like Essential Energy in NSW) would look at our connection applications and mostly wave them through as just another big load. But every now and then the application would land on the desk of someone a bit more curious, who would wonder why 500kVA was being connected to an abandoned parking lot and go looking for more details.
Big DC chargers have big rectifiers, and any electrical engineer worth their salt knows that (old) rectifiers produce harmonic distortion. This changes the shape of the AC voltage curve, often by sort of reflecting smaller waves back through the network, hence the harmonic part of the term. Instead of a beautiful, perfect sine curve, something might reflect a sine curve at 100Hz, rather than 50Hz, so the waves add up some times and subtract at others. The grid gets impacted by the way the device uses the power supply.
The most classic example of something that introduces harmonic distortion is a cheap hair dryer. At full power the hair dryer draws as much current as it can and turns it into heat, the motor and heater in perfect sync with the grid. But that gets a bit hot, so there’s a half power on the hair dryer as well. To achieve half power, this switch drops a diode into the power circuit which means the dryer only uses half the sine wave now. Instead of using the whole curve, above and below zero, it only uses the bit above zero, like a series of speed bumps. If the dryer is only using the positive, where does the negative go?
Back out to the grid, as harmonic distortion.
50 years ago the only big rectifiers were making power for train and tram lines, and engineers knew they needed to take precautions to manage them. Typically they would try and isolate the harmonics by using a transformer, which dampens those weirder edges transforming the curve between coils. The train supplies are manageable because they’re big, dedicated sites with all the engineering bells and whistles. What is going to happen when they start plonking big rectifiers everywhere, will it poison the sine curve for everyone else?
Fortunately, charger manufacturers are across this problem and have implemented fixes and tests to show their harmonic distortion performance. It’s usually a self solving problem; if the big rectifier is separated from the rest of the grid by a transformer, say a dedicated 500kVA distribution transformer, the distortion will largely be limited to that little bit of the grid and no problem for any other users. Some manufacturers include an isolation transformer in the design of their charger, separate to any potential distribution transformer. And all of them now perform “Total Harmonic Distortion” tests as standard and can issue reports saying that “THD<5%” should anyone start asking questions. But, I think the industry has caught up with this in parallel, because I haven’t been asked THD questions for a few years now.
Energy Problems
“Where is all this electricity going to come from! We will need to quadruple generation! And it’s all coal anyway!”
Starting with coal, yes it is a problem that we still make a lot of electricity from coal, but we can solve it in parallel with rolling out EVs by transitioning to clean energy for our electricity. Even with current power technology EVs are a better result for the climate, and will keep getting better over time. For me the gold standard study into this is from Auke Hoekstra, helpfully summarised and linked in this RenewEconomy article.
How much electricity does an EV need? In Australia the average daily drive is about 40km, roughly 15,000km per year, spread out over 365 days. Assuming 20kWh/100km for an EV seems about right, it’s been my rule of thumb for 5 years now, so to drive 40km your EV will need about 8kWh per day.
The average Australian house uses about 20kWh/day. So adding 8kWh to a house load increases it by about 40%. Not multiples of normal house use, a 40% increase.
Where will this energy come from? The grid, but we need to make sure it’s clean power. EV drivers can ensure their power is clean by adding solar and plugging in at the right times. To deliver 8kWh/day in Australia requires only 2kW of solar, plus another 5 to cover the house load. This nice graph from APVI shows the average household system in Australia is now over 8kW, so I’m taking that as evidence that adding enough solar to cover your house and car load is feasible, and fairly practical. It’s what we’ve done.
Solar, and home charging, will be difficult for some people, particularly those renting, living in apartments or in one of those nightmare streets in Sydney where you park wherever you find a spot and that could be 6km from home. These folks will rely on public charging, and how clean their electricity is depends on the procurement practices of those running the network. I work at Chargefox, Australia’s largest public charging network, and we work hard to make sure all the power we buy is clean power. When I worked at Tesla AU they did the same thing, and I’m hearing that other networks building in Australia are doing the same thing.
So on energy, yes we can supply the additional electricity and yes it can be clean power. There’s work to do, but definite pathways to get there.
Capacity Problems
These are probably the trickiest for lay people to get their heads around, because capacity problems are time dependent and can occur anywhere. I banged on at length about capacity problems in the Battery Post, but I’ll summarise here.
Capacity problems occur anywhere in the electricity network where too much power tries to flow. They can occur in your home switchboard when you try and run the dryer, oven and iron at the same time. They can occur in suburb-scale substations when every house in the suburb is trying to pump solar back into the grid, exceeding the capacity in reverse.
The key thing to remember here, and it brings us back to our friend at the start, is that EV chargers are just another electrical load. They are not special. It’s just like installing a new air conditioner or water heater. It’s a thing that uses electricity, being added to a system that is designed from the ground up to add new things without breaking it.
There is quite a bit to unpack with capacity problems and how they’re managed, so we’ll start at the house level.
Say you buy a beautiful second hand 2014 Leaf and want to install a charger at home. You will call an electrician and ask them to install the charger. The electrician’s full time job is connecting new electricity things and making sure they don’t break anything when they do it. So when they install the charger at your house they will make sure the sum of the potential loads in your switchboard does not exceed the capacity of the switchboard. And if something goes wrong, someone adds 3 heaters to a single power point, then the circuit that is drawing too much current will trip, disconnecting the demand and protecting the switchboard.
But what if everyone on a street installs a charger, every single house with enough capacity to fully use their connection? This can become a problem at the local distribution transformer, which is kind of what the tweet in question is talking about. The difference is though, that in the absence of any protections, yes installing too many chargers can wreck a transformer, but for the same reason turning on too many heaters doesn’t wreck your house switchboard this won’t happen.
The transformer has fuses and circuit breakers too. If everything goes wrong and too much is demanded from the transformer, with or without EV chargers, the circuit breaker will trip or the fuse will blow. This happens only very rarely, because the electricians are all working within limits, and those limits sum to the transformer. But if someone makes a mistake only the fuses in the transformer will blow, there’s no way that the lifetime will be decreased by orders of magnitude.
Play this forward and you can see it being a problem if everyone installs a charger and all try to charge at the same time. Transformers rely on two things to stay safe; “diversity” of loads, and thermal protection of something big and heavy. Transformers are actually quite resilient and can run at much greater than their rated load for short periods of time. A 500kVA transformer can flow 500kVA constant, and peak to 650kVA for an hour or more, some could even get to 1000kVA for a short period. It’s a heat problem. When it’s overused it gets hot. Heat builds until something fails. But they’re big, heavy objects, usually with oil cooling, so a sudden burst in heat can be absorbed and dissipated. Even more so when the transformer is up a pole and it’s a cold day.
Diversity in loads is the degree to which they don’t coincide. Say you have 100A of potential loads at your house, but you never operate them all at the same time, maybe the highest you’ve ever demanded is 50A. You could say you have diversity of 50%. Local distribution networks work on the same theory, that it’s very unlikely that everyone will use enough load at the same time to test the transformer. And if they accidentally do, the fuses fail, not the transformer.
This is an unsatisfactory management strategy, relying on fuses to save transformers, so new technology is coming to manage this. There is a risk every house in the street could plug in at the same time and cook the transformer. How can we manage that better?
With Smart Charging, and this can solve almost all capacity problems in EV charging I’ve seen. The problem of too many chargers on a circuit is already happening in some commercial buildings and is analogous to too many houses on a street turning on at the same time, but it’s the building switchboard under threat, rather than the local transformer. Smart charging relies on the fact that capacity problems are typically very short lived, so if you can defer a load for a little while, chances are you can avoid the congestion. On a suburb scale, that means deferring EV charging until after the 7pm peak, which is easy. Cars are usually stationary for 12 hours and only need a few hours to fully charge.
Using EV chargers with internet connections, it’s possible to orchestrate all of the chargers together and make sure they don’t all draw at the same time. Chargers have a language protocol that allows their power to be turned up and down with standardised commands. So a smart charging system will measure the demand at the switchboard, and then turn chargers up or down to make sure the total doesn’t exceed the design limit. Then another layer of smarts can be applied over this to make sure the cars charge the way you want. Maybe car 3 needs to be full by midday, but car 4 can wait until 4pm. The system can handle all of this. These systems are already in use now, using connected residential chargers and railway commuter car parks.
That covers all the small chargers, what about the big ones? The massive inter-city charge sites that can charge a car in minutes rather than hours?
All of these same protections continue to apply at larger scale, it’s just different people giving approval. Rather than your local electrician giving permission to connect, it’s the network operator making sure we don’t add too much load to the circuit. Rather than your local distribution transformer getting overloaded, the 11,000V network could get overloaded. But it doesn’t get overloaded, for the same reasons; there is a strong process controlling new connections; there is diversity in the loads allowing more to be connected than can run at the same time; if by chance they do demand too much at once, fuses and circuit breakers protect the equipment; and if we find we’re hitting those safeguards regularly we can apply smart charging and control point metering.
This is a long way of saying that yes, there are some technical challenges with adding EVs to the grid, but they are surmountable problems, that can be solved with existing technology and systems. EV chargers are just another load, being added to a system designed from scratch to add new loads. EVs are coming and the grid is cleaning up in parallel. I feel like I’ve said this a bit recently but:
It’s working. Keep going.
Evcricket's Energy 