Plug-In Vehicles and the Power Grid
By Kevin Miller
As evidenced by the slew of electric and plug-in-hybrid vehicles seen at NAIAS this week as well as in LA last month, zero-emission plug-in electric vehicles (PEVs) will soon be silently whirring into driveways and garages near you. While the fallacy of calling these vehicles “zero emission” won’t be addressed here (other than a note that you’re fooling yourself if you think the coal-fired power plant generating your electricity is “zero emission”), the impact on the electric distribution network that recharges those PEVs will.
At last month’s LA Auto Show, California’s regional electric utility Southern California Edison (SCE) had a booth and representatives for the purpose of informing consumers about their options for variable rate plans for recharging their PEVs, and also asking customers to let their utility know when they’re planning to install a PEV charger at their residence.
While it is admirable that utilities such as SCE are preparing for the additional loads of PEVs, some critics believe the utility is putting its proverbial cart ahead of its horse. As Autosavant reported almost three years ago, a 2006 study by the US Department of Energy study determined that the nation’s existing electrical grid has enough capacity to accept the addition of 180 million plug-in vehicles. That is a really big number; consider that about 10.4 million new vehicles were sold in the US in 2009, so it would take at least 15 years for our country to reach 180 million vehicles, and that is assuming that every car sold has plug-in capability, which it won’t. So you might ask why utilities are so worried about the additional electrical load coming from PEVs? There are a few reasons.
Today, when you go out and buy a new car, you can take it off the dealer’s lot and drive it around for hours, showing it off to all of your friends and carving your favorite canyons in an ecstatic state. You know that when you get low on fuel you can drive it to the nearest filling station and buy more. With an electric vehicle, it isn’t quite that easy. If you haven’t installed the charger at your house before you bring the EV home, you aren’t going to have very much fun with it, as it’ll be out of juice and you’ll have no way to recharge it. Even if the car can plug in directly to an electrical outlet without needing a separate charger, many garages will need to have the appropriate electrical receptacle installed in order to be able to plug the vehicle in.
So the first tenet of SCE’s PEV awareness campaign is to make customers aware that they need to make their garages ready for their EV purchase by having a charger or receptacle installed. The type of existing electrical service in the home will determine whether upgrades to the home’s service are required, and will also dictate the supply voltage to the charger, which will have an effect on charging time if the home doesn’t have the desired voltage or current available. It may take a week or more to arrange to have the charger and any associated circuits installed by an electrical contractor and have the necessary inspections take place, so it’s a good idea to do that before you bring the car home.
The second tenet of SCE’s campaign is to inform customers of different rate plans available based on power usage and the time of day people choose to charge their PEVs.One of the challenges that any electric utility faces right now is that they have no way of knowing just how high the demand will be for PEVs. If relatively few consumers buy the cars, their effect on energy consumption in a distribution grid will be negligible. However, if a lot of people buy PEVs, and all charge them at the same time, the electric distribution grid may become overloaded, causing brown-out or power loss in certain areas. To understand why this might happen, let’s take a quick look at the typical electrical supply grid for a neighborhood.
Electricity is transmitted from power plants (whether those are coal-burning, hydroelectric, wind, solar, or other) to substations at a high voltage. At the substations, the electricity is stepped down to “medium voltage”, where it is distributed to neighborhoods. Neighborhoods have transformers which step the voltage down further; a typical neighborhood has perhaps six to ten homes supplied by a such a transformer. You’ll see the transformer either as a cylindrical metal thing up on a power pole, or in a squarish metal box sitting on the ground with HIGH VOLTAGE warning stickers all over it.
Neighborhood transformers are sized to supply an average neighborhood with typical power usage. In Southern California, those transformers are able to accommodate homes with air conditioning or heating, electric cooking appliances, and electric clothes dryers. Assuming that the PEV charger has the same approximate current draw as an average air conditioner (somewhere around 220-240 VAC, 3 kW), adding one or two PEVs to a neighborhood won’t likely be a problem for the distribution system. However, if every house on the block ends up with a PEV and they all charge at the same time of day (especially if other large electrical loads are operating at the same time), the possibility exists that supply circuits could become overloaded, leading to a brown-out or power failure condition. By contacting the utility ahead of time, SCE’s goal is to be able to upgrade their distribution network at the neighborhood level where needed, so that power delivery is seamless and uninterrupted.
Of course, the rate of power usage in in our society not static, but instead is dynamic. Most power is used during the day, when people are working; their computers or tools are running, as are air conditioners or heaters in offices, stores and homes. After work, the load switches to HVAC, cooking, laundry, and entertainment. Finally, when people go to sleep and turn off the lights, energy usage falls to its lowest level of the day. That being the case, SCE would like to encourage PEV owners to recharge their cars overnight instead of mid-day. to that end, they have implemented different electric rate structures which make it less expensive to recharge vehicles during off-peak hours.
While the overall power grid is capable of supporting the addition of plug-in vehicles, neighborhoods and homes may require upgrades to facilitate charging those vehicles. A PR campaign on the part of electric utility providers serves the purposes of letting the customers know what steps they should take to prepare for a plug-in vehicle purchase, and also encourages the customer to let the utility know when they are going to purchase a PEV, so the utility can proactively upgrade their neighborhood distribution system if required.
COPYRIGHT Autosavant – All Rights Reserved