Will charging my EV break the grid?
Not yet. However, peak EV charging is an interesting engineering challenge. Incentives are a key way to help solve the problem.
People respond to incentives. A relevant example is the EV “feebate”. Introduced in Jul 21, the scheme resulted in an immediate increase in the percentage of new car sales that were battery electric or hybrid. Getting $8,625 off the sticker price of a new EV is a powerful incentive to encourage EV adoption. Whether the scheme was the best thing for the environment and reducing CO2 is an interesting debate, which I’ll leave for another time.
This post is part two in my series on “will my EV break the grid”. In the first post I looked at how much energy we need to supply to keep our EV fleet going, now and into the future. The key takehome here was that the additional energy required, while eventually significant, is well within the capability of the electricity supply industry to deliver. In this post, I’ll do a quick dive into the second major challenge caused by EVs, which is the peak load challenge.
Peak load is what drives investment in grid infrastructure. Most high voltage grids in the world are designed to be able to deliver the highest predicted load, given the failure of any one component, and with some margin for safety. This is called N-1 security. The interesting challenge is that electricity load during the day follows what is known as a “duck curve”. A typical example from California is shown below. So networks are designed and built with capacity that is only used for a tiny fraction of the time.
A side note is that solar PV (without storage) actually makes the duck problem worse, as you can see below - a topic of discussion for another day.
What is driving the duck curve? Load on the network tends to peak in the evening. In NZ this occurs when people get home from work, turn the heater on and start cooking dinner. There is also a bit of crossover with industrial load which only winds down gradually during the night. Increasingly people are also plugging in their EV when they get home.
How much of a problem is this? Let’s have a look at relative household load. Consider a typical household with a heatpump (2.3 kWe), electric induction stove (7.4 kW), electric oven (3.7 kW), and electric hotwater (3 kW). If all these things are going full noise when you get home, then you could be consuming upwards of 16 kW as you are cooking dinner. Interestingly, in NZ a lot of domestic installations are protected with a 63 A fuse on the street. This is 14.5 kW, so an example load here is already over the maximum that can be supplied on existing household infrastructure - that is without considering the draw from other appliances such as TVs and computers, not to mention your EV!
Is this real you say? Well as proof that this can happen here is a graph from my house from a typical August day last year. No EVs were being charged and the load spiked over 15 kW at one point.
What about charging an EV? Here is where things get interesting. I’m in the minority of EV drivers in that I have a dedicated 32 A wall charger at home, capable of charging my car at 7.4 kW. However, most people use the vehicle suppled EVSE which will charge at a maximum of 10 A, or normally only 8 A for a safety margin on old wiring. Nevertheless, even a point load of an additional 2.3 kW would be an increase on my fully electric household’s point load of around 15%, which is not insignificant.
How about if we come at this from a different angle? If all those 53,000 EVs in the country plug in at the same time, what would the grid see? This is an easy calc: 53,000 * 2.3 kW = 122 MW. This is about the full output of the Waipipi wind farm, so already we can see that the country’s EVs could have a noticeable impact on the grid’s peak load. If the fleet is 81 times bigger, then this would be a whopping 9,800 MW for simultaneous charging of the nation’s fleet. For context, the full capacity of the current NZ power system is about 10,000 MW, so we definitely could not cope if the entire future fleet plugged in and started charging at the same time.
Thankfully, most EV owners do not plug in at the same time and they also have smart EV chargers that will charge the car to take advantage of cheaper night rate power. Some power retailers are even starting to offer plans that will take control of your car and manage the charging for you. They will pay you for the privilege. A shout out here to Octopus with their intelligent Octopus plan that I’ve just joined. I get $10 credit each month and they manage my EV charging for me. This is essentially free money for me and my car continues to be ready with a full battery each morning.
As we go forward and the penetration of EVs in NZ continues to rise, smart incentives such as intelligent Octopus and control of EV charging will be key to manage the impact on the grid. This is important to ensure that we don’t overbuild our networks and we keep our energy prices competitive. Once again, I’m confident my industry is up for the challenge and can solve this problem.