New Bidirectional Tech Lets EVs Power Homes

This Week in Engineering explores the latest in engineering from academia, government and industry.


Episode Summary:

Electric vehicles have been around for over a century, and in that time the flow of electrons operated in a single direction: into the vehicle’s battery. However, that may not always be the case in the future. General Motors and Pacific Gas & Electric, a California utility, have announced a joint venture to develop a computer-controlled bidirectional charging system which will allow electric vehicles to send current into the home. The system is designed to address grid power interruptions and is based on GM’s Ultium electric vehicle platform. The system is expected to be developed quickly, with customer trials by the end of 2022. 

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Transcript of this week’s show:

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Electric vehicles have been around a long time. The first practical examples were produced in the late 1880s, and in the early decades of the automobile it was unclear whether battery, electric or internal combustion engines would dominate the industry. Heavy lead acid batteries and inefficient, poorly controlled motors allowed gasoline powered vehicles to rapidly overtake EVs in performance, and by 1910, EVs rapidly fell from favor.  

Interest in electric vehicle development, however, has been continuous. Now, propelled by Tesla, all major automakers are launching large numbers of new electric vehicles. Fueling those vehicles, of course, means public and home charging, which requires connection to an electric utility’s power grid.  

Like gasoline, the energy flow is one way: into the vehicle. But does it have to be this way?  

General Motors and a California electric utility, Pacific Gas & Electric, don’t think so. They have announced a collaboration to use GM electric vehicles as backup battery systems for home use during grid power interruptions.  

PG&E is a California utility, and California has experienced multiple grid outages due to wildfire damage to distribution infrastructure and the need to black-out service in high-risk areas preventatively, as high winds and powerlines are themselves a fire risk.  

So-called bi-directional charging, however, adds system complexity. Household service in America is 60 Hz AC at a nominal 240 V single phase, and the current must be rectified for electric vehicle battery charging. Running the process in reverse requires that DC current be fed through an inverter to generate alternating current, and the AC must have sufficient voltage and waveform regulation to closely match the power quality of grid electricity. A further complication is the need to automatically handle the switchover from grid to EV-sourced household power, then back again as grid power is restored. 

Bi-directional charging is not a new idea, but American utilities face a particular challenge: in the absence of a national standard, will backup power be controlled in isolation from the grid, or centrally controlled to allow the potential for battery feed into the grid with the possibility of net metering and load leveling for neighborhood or even citywide systems.  

Software will be the key, and the GM/PG&E pilot will test software-defined communications protocols. The joint team plans to work very quickly, with pilot testing with consumer trials by the end of the year.  

Why so fast?  

The electric car industry is experiencing a sort of “gold rush” culture, with automakers jockeying for volumes to establish de facto standards in areas like control software and battery chemistry. Electric utilities that can develop workable control methodologies can establish standards that will allow all automakers to build compatible EVs.  

As electric vehicles increase in popularity, the benefit for power companies is considerable. Net metering already exists in some jurisdictions for customers equipped with solar panels, but some experts warn that increased use of electric cars will create difficulties for utilities, requiring either increased baseload capacity or more robust load leveling technology, or both. Grid-scale battery storage is already in use for this purpose, but hundreds of thousands of EV batteries, all grid connected and operating through software-controllable inverters could provide a sort of remote, pay-as-you-go load management solution for electric utilities.  

Ford has developed an independent bi-directional system for the upcoming F-150 Lightning electric pickup, and PG&E is also working with that company on bi-directional charging. The amount of charge stored in California’s garages and driveways must be a tempting resource. How tempting? One in five electric vehicles sold in the United States are based in PG&E’s service area, representing 6,600 MW of available capacity.

Written by

James Anderton

Jim Anderton is the Director of Content for ENGINEERING.com. Mr. Anderton was formerly editor of Canadian Metalworking Magazine and has contributed to a wide range of print and on-line publications, including Design Engineering, Canadian Plastics, Service Station and Garage Management, Autovision, and the National Post. He also brings prior industry experience in quality and part design for a Tier One automotive supplier.