Published Wednesday December 17, 2017:
Will Electric Vehicles Sink the Electric Grid?
What happens when every vehicle on the road is replaced with an electric one? How will the power grid handle all this uptick in load?
It gets worse when an EV charges up rapidly because they draw a lot more power from the grid. My Chevy Bolt draws about 46kW when plugged in at a ChargePoint charging station. In theory the car can draw up to 80kW if the charging station can supply it.
A Tesla Model S or X draws up to 145kW of power when charging off of a Tesla supercharger.
In the future we may see cars able to charge their batteries in only 5 minutes. The power draw required to do this is on the order of 1 million watts. If many vehicles were all charging up this quickly and simultaneously, it doesn't take an engineer to realize that this would overwhelm the electric grid.
As an electrical engineer, I am not concerned because most of the time, electric vehicles use destination chargers that charge up more slowly and at night.
Currently at night, the electric demand on the power grid goes way down and the power plants have to throttle back 60-75% of their generating capacity just to keep the grid from having too much voltage on the lines.
When a fossil fueled generator like a coal plant or gas turbine throttles back, they become less energy efficient and actually pollute more, (per kWh of energy). They also generate less revenue and become less profitable because they are selling less energy but still incur wear and tear. Having lots of electric vehicles drawing a constant, predictable, steady state power draw from the grid for hours at a time over night would be a welcome boon to all the existing, idling power plants.
Charging slowly at home takes less time than pumping gas:
Charging at home also costs less and is super convenient. I drive about 70 miles a day. I plug in my Chevy Bolt about 2 times a week. It takes 7 seconds to plug it in and about 7 seconds to unplug it. So about 7 x 4 = 28 seconds a week (let’s just call it 30 seconds) is spent actively doing something related to charging up my vehicle. The rest of the time the car is charging is not my concern as I am engaged in doing other stuff. Compare this to a gas car where you are pretty much captive, standing by a dirty gas pump, watching the numbers spin up and breathing in fumes for 3 minutes a week, (not counting travel time to and from the gas station).
After a year, charging an EV at home takes 30 seconds x 52 weeks = 1560 seconds or 26 minutes of my time.
Pumping gas each week for a year takes 3 minutes x 52 weeks = 156 minutes.
The time saved not pumping gas and instead charging at home is over 2 hours a year.
A typical power draw while charging at a destination charger is 960-1440 watts from a 120V outlet or 3,600 to 7200 watts on a 240VAC outlet or L2 charging station. Tesla home charging stations can draw upwards of 9600 watts.
The grid will benefit from this extra demand during the nigh time hours.
Here's a graph of the power draw when charging a Chevy Bolt overnight. The 2 sets of spikes on top-middle are not real but are an artifact of the monitoring software. This is steady state, continuous power. The on-board charger corrects the power factor to nearly 1 making it essentially all resistive power.
While there is some risk of overloading a small distribution transformer (10kVA or less), in modern residential neighborhoods 4-5 homes typically share a 50kVA transformer. Six cars could charge up simultaneously without any issues, (6.6kW x 6 = 39.6kW or 7.2kW x 6 = 43.2kW) and there would still be sufficient margin to run all the homes overnight too.
With shared scheduling, (where smart chargers take turns charging), you could in theory have 30 electric vehicles all getting power from the same distribution transformer. That's 6 electric cars per household. What family has 6 electric cars and drives them all daily? If you do, just schedule their charge times and it won't cause problems.
But what about rapid chargers?
For CHADEMO, CCS and Tesla super chargers, they still do draw an enormous amount of energy from the grid and the companies who operate this equipment pay a premium for the availability of that power.
They pay what is called a demand charge where the maximum power draw for the month (even if it is only used for 15 minutes a month) is billed about $9-12 per kW of power draw.
So for a 145kW Tesla super-charger, Tesla is charged $9 x 145 = $1305 per month per charging station, just for the demand charge.
If a 50 stall charging station had all 50 stalls occupied (every 2 stalls share 145kW of capacity), Tesla would be charged $9 x 145 x 25 = $32,625 per month. Ouch!! That doesn't even include the energy costs for the electricity which ranges from 5 to 7 cents per kWh for wholesale electricity.
In the future, to reduce demand on the grid, all rapid chargers will migrate over to utilizing stationary battery storage. Instead of hundreds of kilowatts or even megawatts of power for minutes at a time, these next generation rapid chargers will draw steady state continuously and let the stationary battery handle the brief but high-power surges. By incorporating stationary batteries, a 50 stall station would only have to draw perhaps 5% of its capacity continuously for charging the stationary batteries. Instead of a $32,625/month demand charge they will only pay a $1631/month demand.
If solar panels are installed at each charging location and they are appropriately sized to provide 70% of the needed energy, the demand charge would only be $489/month and the total cost of energy would also drop by 70%.
In short, EVs will dominate the roads and the electric grid will love it.