Where are we going to charge all our electric vehicles?
By Duane Grzyb, P.Eng.
By Duane Grzyb, P.Eng.
July 20, 2022 – Back in June 2021, Ottawa announced it will accelerate its goal of having every new light-duty vehicle sold in Canada be electric. Minister of Transport Omar Alghabra said all new cars and light-duty trucks sold in the country will be zero-emission vehicles by 2035.
That’s just 13 short years. I say short because we need a massive upgrade to the country’s electrical distribution to support this load.
Consider our electrical infrastructure
The premise is that every household will install a Level 2 charger (60A 240V) in their garage, which will ensure every electric vehicle is ready to go when needed.
A Level 2 charger installed in a home garage (existing electrical capacity permitting) will cost around $7500. This assumes you can spare more than half of your typically available 100A service to supply the typical 6-kW overnight charge.
Over the last 75 years, the typical household electric service has been increased from 60A 120/240V to 100A 120/240V for homes heated with natural gas. (If you live in British Columbia or Quebec, you may have a 200A service standard because your home is likely heated with electricity.)
With only 100 peak amps available to run your household, your EV charger may trip your main breaker. (I occasionally trip my own 100A main breaker, and I don’t even own an EV.)
What makes this even more interesting is that, historically, electric utilities have not expected all of their customers to draw anywhere near 100 continuous amps. In fact, the average available power supplied to the typical house is engineered to be about 26 amps; when customers exceed that amount, it is for short periods, and the thermal capacity of the transformers and wires can withstand the short-term overload.
A 37.5-kVA transformer can reliably serve six homes with 100A services each. However, when you do the math, you see that 100A x 240V x 6 homes equals 144 kVA—nearly 4x the transformer’s continuous rated kVA!
So, if three of those six homes attempted to use Level 2 charging at the same time (60A 240V per charger), it would add 43 kVA to a system that is rated for 37.5 kVA overall, in addition to the regular loads.
Historically, a 100A service was sized to run a stove, dryer, furnace, fridge, freezer, lights, and normal small appliances. Add to this the number of hot tubs, air-conditioners, second refrigerators, basement suites, etc., and you get a secondary distribution system that’s already stretched to the limit. I frequently spot 37.5-kVA transformers being replaced with 50-kVA units just to keep up with regular loads.
Additionally, the utility’s voltage drop calculations were done for the 37.5-kVA unit. Upsizing those transformers may cause greater than allowable voltage variation (as specified for non-utility users of the electrical code) and contributes to energy wasted through excessive conductor heating.
What is the average household?
Very few homes are single-vehicle households (mine has four). Sharing one Level 2 charger between two or more vehicles is unlikely to get the job done. Imagine heading out for work one morning only to discover a dead EV; maybe your spouse unplugged yours so they could charge theirs, or maybe it didn’t charge overnight because the air-conditioner ran most of the night, or the hot tub, and the charger’s “smart” software couldn’t charge the car due to the lack of required electricity.
(I’m not going to get into vehicle-to-grid power exchange. At 65% cycle efficiency, having your neighbour’s car put power back onto the grid to charge your car simply compounds the problem.)
In northern climates, it might be easy to think that we’ve already planned for ICE block heater plug-ins, but they can only deliver limited Level 1 charging, often on an intermittent basis. They offer little help for charging EVs. A Tesla EV draws about 300 watts at -5 C just to keep the batteries from freezing. At -30 C, a block heater plug-in may be required just to break even, never mind charging.
Furthermore, has any consideration gone toward apartment dwellers who have no garages or dedicated parking spots? What about those who have to park on the street?
Time and cost are unfavourable
My Edmonton neighborhood is served by underground distribution. To upgrade even half of the residences to support single-vehicle, Level 2 charging would require digging up all secondary power distribution along the street, upgrading the service conductors to each upgraded house, and upgrading to a 150A or 200A panel.
If the utility supply is adequate, upgrading the street-to-house conductor and household panelboard is likely to cost individual homeowners about $17,000. If three or more of the six connected homes want upgrades, the price could double or triple by the time the utility upgrades its infrastructure.
It could be argued that utility upgrades will be covered through increased electricity sales, but reality tells us that a huge amount of work is required to substantially upgrade our residential distribution infrastructure over the next 13 years. There is simply too much work to be done and not enough time in which to do it. A city’s electrical infrastructure was built over many decades—it is highly optimistic to think we can upgrade most of it in 13 years.
In short, the electrical infrastructure to each home was never designed to charge EVs, much like it was never designed to support A/C, hot tubs, second kitchens, etc.
Enter the humble padmount
After examining the bottleneck a bit more closely, the first place in the system where we might find additional power to charge everyone’s new EV is at the humble padmount transformer.
The first thought might be to upgrade the transformer to a bigger one, but this doesn’t address the problem with insufficient secondary conductors. Typically, the underground 120/240V wiring has been sized for 100A services and relies on significant load diversity. Still, even if it were upgraded and the main distribution circuit wiring was determined to be okay, the wiring to each individual home/breaker panel would still be inadequate without smart devices sequencing the loads.
Fortunately, the medium-voltage neighbourhood supply (typically 15,000 or 25,000 volts) is run with standardized conductors that are usually suitable for distributing a full substation feeder’s current along the entire MV ring connection. This provides the utility with flexibility for the future expansion of neighbourhoods and businesses.
When a ring does get fully loaded, the utility can modify the ring sizes relatively easily by adding substation feeders and breaking the rings into smaller service areas using street-mounted switching cubicles. The switching cubicles are larger square boxes located less frequently than the padmount transformers.
This is good news, as the supply side of the padmount transformers are robust enough to supply additional power immediately (to the capacity of the standard feeder circuit conductors supplying the overall ring load) and, ultimately, can be reconfigured relatively easily into smaller rings (via switching cubicles) to supply considerably more.
A potential solution to the shortage of EV charging infrastructure in residential areas, then, is to place public, fee-for-service charging stations at modified padmount transformer locations. They would be close enough to individual homes to be convenient, but powerful and fast enough to be shared.
A combination padmount transformer and dual Level 3 DC fast-charging station may be the solution. Here’s how it would work:
The utility isolates power to an existing padmount. The existing 37.5 or 50 kVA transformer is removed from the precast concrete base, and a new 300 kVA transformer/charger combo unit is installed. No underground work is required, and the whole process—including communications, software, commissioning—could be done in two hours.
The new combo unit continues to supply 120/240V to existing customers while having the capacity to supply two integrated Level 3 DC fast chargers. (The point-of-sale mechanics can be handled by web-based subscription or credit card, and verified by wireless communications.)
Two 120-kW chargers could recharge two EVs in 20 minutes, or top up a single EV in 10 minutes. This is equivalent to a Tesla Supercharger. By placing public chargers close to homes and apartments, residents can conveniently stop to charge on their way home. They plug in their car, pick up their mail, walk home, change clothes, etc., then go back to get their car and park it in their own driveway.
These integrated charging units would be ideal for many existing locations: parks, churches, schoolyards, boulevards, super mailboxes, apartment buildings… anywhere where there are already two parking spots (and, ideally, not right in front of someone’s house) and an existing padmount transformer.
Based on my observations in and around Edmonton, about 1 in 15 transformer locations are suitable and could be converted immediately, with no disruption to traffic or homeowners.
As installed capacity increases, utilities can modify the MV distribution infrastructure to make the rings smaller, accommodating the increased load. The increased delivery of electricity generates revenue for them and pays for the upgrades, and they only have to work on the much more configurable medium-voltage feeder ring side of the wiring.
In cases where a suitable existing padmount location cannot be found, simply add a new one. Any existing MV underground ring cable route is expandable in much the same way we add new neighbourhoods or businesses. Methods for adding precast concrete bases to existing underground ring circuits are well established.
Naturally, there will be questions of transformer/charger ownership; they are, after all, typically located on public right-of-ways. Negotiations between the utilities and municipalities and vendors to determine ownership, leasing, operations, maintenance, are required, but this is solvable via thoughtful discussion. (We see private businesses operate on municipal right-of-ways all the time e.g. internet and phone companies).
The benefits to this elegant solution are many: installation is quick and inexpensive, as it leverages existing infrastructure; there are no property ownership costs to recover in user fees, as the chargers are located on municipal right-of-ways; and the customers are already nearby.
As our governments push the agenda for electric vehicles, it is important to look for ways to provide cost-effective charging in the places where people need it at a cost they can afford. Retrofitting existing padmount transformers with combination padmount transformer/charger units may be a way to leverage existing infrastructure to expedite the adoption of EVs.
Duane Grzyb, P.Eng., is a Professional Member of the Association of Professional Engineers and Geoscientists of Alberta (APEGA), and the principal of Class 1 Zone 2 Engineering Inc., which specializes in the determination of Area Classification, as well as general electrical engineering.