How much of NZ's electricity consumption is due to EVs?
TL;DR It's still miniscule but rising fast.
*Correction. A colleague pointed out to me an error with my original calculations. I used the “per capita” light vehicle kms as a “per vehicle” statistic which is incorrect. If I recalculate the average kms per vehicle based on a fleet size of 4.35M, the average distance travelled per vehicle becomes 10,900 km. This is about 20% higher the number I originally used. I have updated the text below.
Apologies, this post contains some maths…
I’m a huge electric vehicle fan for a whole host of reasons, both tangible and intangible. I own a Tesla Model Y, which is our sole family vehicle. Before that I had a Model 3, and prior to that a 2013 Nissan LEAF. The LEAF got me “hooked” on EVs and I’ve never looked back. When discussing the topic of EVs with friends and colleagues, I often get a question along the following lines: How will the grid cope when we have millions of EVs on the roads? Or more directly, a statement like, we can’t convert everyone to EVs because the grid will never cope. I’m here in this post today to debunk these uninformed statements.
It’s actually pretty straightforward to calculate the impact on the grid of EVs. But before we get to that it’s worth clarifying that there are actually two issues that we electrical engineers are concerned with:
The total additional energy we need to supply to charge the EVs.
The extra peak load that coincident charging of EVs adds to the grid.
I’m going to mainly discuss issue #1 in this post and leave issue #2 for another time. This one is also overblown, but has some interesting nuances worth discussing.
So how to estimate the total energy required to charge NZ’s EV fleet? To do this we need four numbers:
How many EVs there are in NZ
The average kms driven per day by each EV
The average energy consumption per km driven
The efficiency - plug to wheels.
How many EVs are there in NZ? This is easy to answer and this website is a great resource: https://evdb.nz/growth-evs-nz. Here we can see, that as at the end of April 2023 there are 53,745 EVs, about 1.23% of the total fleet. For the purpose of this discussion I’m ignoring PHEVS.
What is the average kms driven per day by EV drivers? This one is slightly harder to answer, but luckily the Ministry of Transport keeps statistics. On this page we can see that the average light vehicle in NZ travels an annual average of about 10,900 km. This has dropped slightly since the pandemic, but for our purposes lets leave it at 10,900 km or approximately 30 km per day. We are also assuming that the average EV driver drives about the same as an ICE driver. This may or may not be true, but this is about the best information we have currently.
What is the average energy consumption per km for EVs? This is also a slightly tricky question as it varies considerably by EV. My Model Y currently has a lifetime average of 160 Wh/km, but this excludes stationary energy consumption. Tesla’s are also the most efficient EVs. On this basis, I think it’s reasonable to use a number of 200 Wh/km as a baseline average efficiency for the fleet.
The final piece to the puzzle is the plug to wheels efficiency. Again this varies by EV and whether the car is being fast charged or slow AC charged. A typical AC charging efficiency is around 90%, but for a conservative estimate, lets use 80% as a fleet average.
So what is the daily average energy consumption of the NZ EV fleet? Let’s do the maths:
53,745 EVs * 30 km / day * 200 Wh / km / 0.8 = 403 MWh / day.
403 MWh / day sounds like a big number. Let’s put it in perspective though. The Waipipi wind farm, just one of NZ’s wind farms, produces an average of 1,250 MWh per day. Therefore, Waipipi alone could provide all the energy needed for an EV fleet about three times the size of NZs.
Yet another perspective, yesterday the 10th of May, NZ consumed 113 GWh. EV charging represented just 0.36% of this. So supplying our current fleet of EVs is currently just a rounding error on our electricity consumption.
But wait you say. What if the whole fleet is converted to EVs? Well firstly, this is not going to happen overnight, but even if it did, what would be the energy consumption? Currently EVs are approximately 1 in 81 vehicles, so if the whole fleet were EVs, the consumption would be 81 times higher. 0.36% * 81 = 28.9%. Now this is certainly no longer a rounding error, but it’s definitely within the industry’s existing capability to supply this much additional energy, especially given a few more years to build out some new power stations. Many are currently in the pipeline.
So in summary, EVs are awesome. They are also super-efficient and we should be replacing our fossil fleet as quickly as we can. We don’t have to worry about the additional load on the grid. The industry has this under control.
Next time, we’ll dive into the peak load issue a little more.