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Musing on Vehicle-to-grid

Vehicle-to-grid (V2G) is the process of using an electric vehicles battery pack as a power source to supply power to the electric grid. This can be beneficial to grid operators who could use such vehicles to help supply power to heavily loaded portions of the grid at or near the areas most in need of additional support. It has been proposed that vehicles such as gasoline fueled hybrids could also be used in this manor although this would seem to defeat the main objective of lowering the consumption of such fuels and their conversion into carbon dioxide.

There has been much discussion recently in the electric vehicle and plug-in hybrid realm regarding the best way to design a "smart grid" and intelligent interface for such V2G capable vehicles. As such it seems appropriate to mention some of the various implementation methods that have been mentioned to this point and perhaps put forth some new ideas.

Find More links to existing V2G resources, research, and discussions!


There are a number of things to take into consideration when planning such an interface. Any system which is to be implemented should take into consideration the following. Although we should not fail, by neglecting to implement anything, simply because all of the considerations can not currently be met or because the most advanced fully interactive vehicles do not yet exist.

Some of the most basic common charge interface features should not be overlooked:

  • If you are going to provide a charge port, provide a high power port rather than only an underpowered 110vac@15a.
  • Support as many vehicles as possible, each port should consist of a variety of standard and high power outlets. Users will mostly likely carry with them cables which convert such 110/220/etc common outlets for use with their vehicle.
  • Provide the circuit breaker for each charge port at the port itself so that the users can reset it if needed.

The User

The operator of the vehicle may have minimum range needs or desires. The user may wish to have varying levels of compensation for the use of their vehicles as a grid resource.

The Vehicle

The vehicle may require a certain range always be available or have varying recharge priority. A battery electric vehicle may have a higher recharge priority than a plug-in hybrid which can revert to using gas while the pure electric can not.

The Grid

The grid operator may need varying degrees of control over dedicated vehicle charge interface infrastructure. Such a system may also be capable of communicating with the vehicles attached to it.


The problem or compensation arises with a system capable of utilizing a private vehicle as a grid resource as the vehicle is most mobile and may be difficult to track thus making it difficult to compensate the owner of that vehicle.


There are a variety of ways in which such a system could be implemented. Each with it's own advantages, disadvantages, and technical challenges.

Charge Only

The majority of plug-in electric vehicles currently available or in use are of this type. They are only capable of charging from the grid but not supplying power back to the grid.

Manual BiDirectional

A fully manual implementation very similar to net metering used with home wind and pv arrays. Such a vehicle would have the minimum hardware required to safely execute grid support, such as anti-islanding power inversion, or perhaps some sort of islanded generation mode. This type of vehicle could not be controlled by a grid operator and the owner would need to manually choose to enable the power generation mode based on time of use rates or power outage situations. Minimal protection for battery SOC limits would be required simply to ensure that the battery pack was not damaged by operating in power generation mode for extended periods.

Timed Usage

Such a vehicle would be capable of more advanced time of use and SOC profiles. This vehicle could be programmed by it's owner with an electric rate schedule in order to optimize the profit or payback from the utility. This might be achieved by charging only during off-peak and running in power generation mode when the price of power is the greatest. The vehicle could be programmed with a minimum required and desired SOC. It would then charge up to the minimum required SOC irregardless of the current electric rate. It would only run in power generation mode when more than the desired SOC were available.

Grid Request

Such a system would have grid connections for vehicle with varying levels of technology. The grid port could request various levels of support from available charge current to requested power generation. Grid operators may also have the ability to disable ports with charge only vehicles attached to reduce load.

Private Compensation

Property owners could control the way in which power were paid for and vehicle owners compensated. In the case of a home owner who's own vehicle will be connected to such a port this isn't much of an issue. Also in the case of workplace charge ports, the business may simply take on electric power costs and compensation on behalf of the vehicle owners in exchange for the ability to use those charge ports. Or the workplace may assign charge ports to specific employees to track their cost or compensation.

Public Compensation

In public locations however the vehicles operator may be required to pay for or wish to be paid compensation for power consumed or used. Some sort of monetary, paper, or electronic funds exchange meter could be used in such situations. The most tamper proof would be an electronic system, such as a "charge card". A driver of such a vehicle might be issued a type of credit card which could be used to activate a public charge port. The charge port could then debit that user for power used or credit them for power generation.

Grid Interactive

There has been much talk about wireless communication systems to track vehicles locations and their desired charge or availability for power generation and whom should be compensated for such use. This seems to be overly complex and expensive. It would also introduce the potential for involuntary tracking of an individuals.