Ever since the modern electric vehicle era kicked off in the mid-2000s, one of the holy grails that automakers and utilities have been aiming for is bi-directional charging or the ability to pull electricity out of an EV battery when needed. So far, applications have been very limited in part because of a lack of standards which are still evolving, but progress is being made. The latest example is a new pilot project between General Motors
GM
and California utility PG&E.
It makes sense that PG&E would be anxious to deploy bidirectional charging since its service area across much of northern California includes the highest concentration of electric vehicles in the U.S. PG&E has also become somewhat notorious in recent years for having frequent rolling blackouts during some of the hottest summers on record.
This GM/PG&E pilot won’t be the first such program, but it may turn out to be one of the largest programs to date. The Japanese CHAdeMO DC charging standard has incorporated bidirectional capability for many years and home inverter systems have been available for the Nissan Leaf in its home market since the first generation model. Ford is also including an intelligent power backup capability on the F-150 Lightning pickup that goes into production in a few weeks.
The Ford system will work with a smart inverter that needs to be installed in the garage. The inverter includes an automatic transfer switch that disconnects the home circuit from the grid when power goes out and allows power to flow from the truck’s battery into the home.
The system being developed and tested by GM and PG&E will follow a similar path so that energy from the EV batteries won’t be flowing back into the grid. The first stage of the pilot beginning in summer 2022 will take place at PG&E labs in California. GM’s new EVs have the capability to flow energy in or out and new software-based communications protocols are being developed to manage that flow.
The companies will be testing both AC and DC energy flow. For AC, the on-board power electronics of the EVs will convert the DC from the battery so it can power a house. For DC, an off-board inverter similar to what Ford is using will be installed. The goal is to begin customer trials by the end of the year. One of the key differentiators from Ford’s system is that this will be set up as a demand response system. During periods of peak electric demand, PG&E will be able to trigger the transfer switch in users homes, taking it off the grid and switching over to powering from the EV. The Ford system is not remotely controlled at this time.
Once everything is defined, all of GM’s new EVs will be able to support this bidirectional charging. As with the F-150, owners will be able to specify a minimum charge level so that an extended power outage won’t completely drain the vehicle battery. In most cases, starting with a mostly full battery should still provide at least 2-3 days of power for an average home.
