March marked the fifth anniversary of Japan’s catastrophic 2011 earthquake and tsunami—a disaster that tested a society’s ability to switch to different power sources. For example, battery-powered electric vehicles (EVs) were a transportation boon at a time when conventional fuel was unavailable. Technology quickly developed to tap EV batteries to power appliances.
The implications go beyond disaster needs. Even in everyday situations, “power-take-off”—also referred to as bidirectional EV energy flow—could provide a solution for managing peak versus off-peak grid energy consumption and availability, and for greater utilization of renewable energy, especially residential PV production.
After the earthquake, a number of related commercial products emerged in Japan. I spoke with David Patterson, a California-based Mitsubishi Motors R&D engineer who works on powertrain and emissions research—and is a leading proponent of EV power-take-off technology—to learn about the prospect of using EV batteries to power U.S. homes.
Home Power (HP): What was your first involvement with using power from an electric car’s battery in a building?
David Patterson (DP): It goes back to the March 2011 earthquake and tsunami in Japan. Mitsubishi Motors brought its i-MiEV electric car into the disaster areas for people to use for transportation. [Because of the difficulty of fossil fuel resupply], EVs were easier than gas cars to refuel. Our engineers pondered the idea of how to make this power available for homes, and they came up with the MiEV Power Box.
HP: What’s the MiEV Power Box?
DP: The Power Box is a simple inverter. It changes battery direct current to AC to be used in standard appliances. It’s similar to stand-alone inverters, and fairly inexpensive. It’s about the size of two shoeboxes, and it weighs about 25 pounds. You can put it in the trunk of your car to make AC energy readily available. The only twist is that there’s electronic communication in the unit that does a “CHAdeMO handshake” with the car.
We’ve taken the idea of the Power Box one step further. Nichicon, a capacitor manufacturer, builds something else for our company, a device called the EV Power Station. It’s about the size of a mini refrigerator. With the Power Station, you can supply power to the home, rather than just plugging in one appliance at a time. The Power Station hooks right up to your home’s electrical system. There’s a transfer switch to transfer home power from utility power and connect it to the Power Station. Essentially, it hooks up and functions exactly like a backup generator, with all the same protections against “backfed” power.
However, there’s only so much energy in the car battery pack, so it will only last so long. Therefore, it would not be desirable or advisable to power your entire house, but rather just critical loads.
HP: CHAdeMO is a standard for quick-charging electric cars, specifying the coupler that puts high-voltage power into EV batteries. Can you give us more details on the link between the EV and the Power Box?
DP: The Power Box uses the same CHAdeMO plug-in, fast-charging protocol, providing communication between the charger and the vehicle—which is key. The vehicle and the charger communicate and identify one another. When you plug in the MiEV Power Box, the car knows what’s being plugged in, and the car closes the main contactors. This sends DC power to the Power Box, which can be used in a single plug-in appliance. In Japan, it’s sold retail and can be used with the Mitsubishi Motors i-MiEV, Nissan Leaf, Kia Soul EV, and the Toyota Mirai fuel-cell car.
HP: Do you envision a time when the MiEV Power Box or the EV Power Station—or both—will be offered in the United States?
DP: I do, but I’m not sure when. I could see the products here in about five years, given development and regulation needs.
HP: What’s the demand for these products?
DP: The numbers aren’t big yet in Japan, but it’s starting to take off. Remember, there’s still a relatively small EV market there. But this is where it gets interesting. The technology that’s in the power station is basically the same inverter technology that PV inverters use—they change high-voltage DC electricity to usable household AC electricity—and they are found in many garages or on the sides of many American homes already. The difference is that most PV inverters are only built for one-way power transmission. Take your J1772 240-volt electric car charger and combine the two technologies—that’s the Nichicon Power Station. The Power Station can change the DC energy source (from the car’s battery) to AC electricity to power loads in a home, and it will also allow the flow of electricity from the grid to the vehicle to charge the car’s battery.
While it might seem the Power Station is basically a grid-tied battery-based inverter, it’s more analogous to an emergency generator. You would use the EV Power Station in lieu of a gas or diesel generator. The Nichicon products are not designed or marketed as a grid-tied solution. For a grid-tied solution, you would need to regulate the power and frequency, which puts you in discussion about vehicle-to-grid (V2G). What we’re talking about now is essentially vehicle-to-home (V2H).
These devices are simply and specifically to take energy from a Mitsubishi Motors i-MiEV, Nissan Leaf, Toyota Mirai fuel cell car or any other vehicle with a CHAdeMO port. The amount of energy that is released from the car is controlled by the vehicle’s software. The key is the CHAdeMO communications system. The vehicle is controlling the Power Station, which is doing the work of converting DC to AC. The car is telling the Power Station how much energy is being provided, just like it controls the power flow into the batteries with a DC quick charger.
The technology is already there. The question is whether customers want to spend, say, a few thousand dollars for this. How much would you spend to allow your car to plug into your house and use its energy during a power outage? That’s what the entire industry doesn’t know—is there a market?
When I talk to the utilities in the Northeast, they say there’s a huge number of customers who install backup generators in case of an emergency so when they have a utility outage, they have backup power for critical loads.
HP: What typical household loads could be run given the battery capacity of a typical EV?
DP: If the utility grid goes down in an emergency, you would want to use those precious kilowatt-hours for relatively minor loads with the maximum benefit during a power outage: pumps for a well; refrigeration and freezers; and powering your modem/cell phone or other communication equipment. It’s all about having an emergency backup for critical loads.
HP: If you want to charge the EV with PV when the grid is down, would the Power Station make this possible? How would that work?
DP: It’s theoretically possible with the correct wiring, but this has nothing to do with the current development of the Power Station. Yes, it can double as an EV charging station because of its bidirectional capability. But that’s not its primary function, which is to pull energy from the car and provide it to the house.
Editors’ Note: Mitsubishi Motors is not alone in its development of V2H technology. On the horizon are AC Propulsion’s tZero; ConVerdant Vehicle’s Plug-Out kit; Honda’s Power Exporter 9000; and Toyota’s V2H.