Professor Willett Kempton pointing out the bi-directional inverter package installed in an EV that enables it to both receive and output power. (Image: University of Delaware)

It’s common knowledge that a major challenge for solar energy is how to store excess energy produced when conditions are right, like noon-time sun, so that it can be used later. The usual answer is batteries. But renewable energy resources are causing problems for the electricity grid in other ways as well. In a warm, sunny location like California, mid-afternoon had been a time of peak demand for the electric utility, but with solar it’s now a time of peak output.

It is very challenging for traditional power plants to cope with these sudden shifts in demand. The only means at their disposal is to ramp output up and down, which is slow and inefficient — they can’t absorb excess energy, which can lead to overproduction, wasting resources at some times, or at other times it can cause underproduction, leading to brownouts.

In 1997, University of Delaware Professor Willett Kempton co-authored a paper proposing that “Electric-drive vehicles, whether fueled by batteries or by liquid or gaseous fuels generating electricity on-board, will have value to electric utilities as power resources.”

This concept was named vehicle-to-grid (V2G) power and Kempton has guided its development ever since. Adapting to fluctuations in the grid’s electrical supply and demand could be addressed by V2G. And there is now a practical pilot project at the University of Delaware where this technology is being demonstrated with four Ford Motor Company Mach-E electric vehicles.

A solution to the problem of mismatches between supply and demand is to store energy in batteries, use an inverter to change their output from DC to AC, and connect and disconnect those sources from the grid as needed. The batteries would store energy by getting charged when supply exceeds demand and release it when demand increases.

But banks of batteries are very expensive. The answer to that problem was laid out in Professor Kempton’s 1997 paper — use the battery banks that are already in place in people’s EVs.

This was a difficult hurdle. “We realized that there needed to be new standards because we're bridging between two regulatory worlds, the automotive world and the utility world,” said Kempton.

To meet this challenge, Kempton said, “We produced a modification of the SAE J3068 EV Power Transfer System Standard to become the J3068/2 extension that covers ‘Control of Bidirectional Power for AC Conductive Charging,’ which among other things, specifies the minimum kinds of information that must be communicated to provide safe grid services. For example, how many kilowatt-hours of battery are available, or how many kilowatt-hours of empty space are there? A vital part of the related J3068/1 Standard is assigning a unique ID to each vehicle so an aggregator knows who it is talking to, no matter where the car is located — it could be plugged in at home, at work, or at a V2G-enabled charging station in a shopping mall.”

According to him, these communication codes are now also defined in the J3400 Standard for the NACS, or Tesla connector. This information is communicated by LIN-CP over the existing types of charging cables.

The hardware and software designs, as well as the regulatory structures for V2G are all in place. Now it’s up to the EV and charging station manufacturers to implement these codes in LIN-CP for their standard products.

This article was written by Ed Brown, Associate Editor, SAE Media Group. For more information, visit here  .

Topics:
Automotive Electrification Energy Standards and Standards Development

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    This article first appeared in the December, 2024 issue of Tech Briefs Magazine (Vol. 48 No. 12).

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