ELECTRIC TRANSPORT
THE EV STANDARDS CLASH AND THE V2G TRAFFIC JAM
Amid the EV revolution, Vehicle-to-Grid (V2G) technology offers a promising solution to the problems of renewable energy storage, grid balancing, and even enabling householders to go Net Zero. Despite the existence of this transformative technology, there lies a tussle between alternating current (AC) and direct current (DC) V2G options. In this article, Dunstan Power, managing director of UK smart charging consultancy, Versinetic, delves into the standardisation conflict and examines its effects on V2G’s widespread adoption
L
et’s first look at V2G itself. In the V2G system, cars are able to discharge from their DC
batteries into the AC grid through the use of an inverter as a reverse of normal charging. This inverter can either be in the vehicle, or in the charger. With a DC V2G system, the inverter is in the charger which passes DC to the car, whilst for AC V2G, the inverter is in the vehicle and the charger just connects the AC grid to it. Versinetic span out of ByteSnap Design,
whose engineers worked on the UK’s first fully integrated V2G charging system, the award- winning VIGIL project. The VIGIL (‘VehIcle to Grid Intelligent controL’) project built and trialled an off-vehicle communication and control platform which aimed to encourage distribution network operators, building owners and EV/EV infrastructure owners to adopt V2G (vehicle- to-grid) as part of future network solutions. Storing energy in car batteries and discharging
it into the grid seems like a no-brainer. Why, then, is V2G not more prominent?
AC AND DC SYSTEMS To better understand where the V2G holdup is, we need to recognise the difference between alternating current (AC) and direct current (DC) power systems. Domestic EV chargers are AC primarily for cost reasons, and AC long ago won the grid transmission war due to the fact that generators themselves generate AC power and it’s easier to step AC voltages up and down than DC, through the use of transformers. AC is also safer at low (hundreds of) volts due to the way the human body interacts with AC and DC shocks. Proponents of AC V2G argue for its widespread infrastructure and compatibility with existing grid systems. The advantages of AC V2G are also that the required chargers are smaller and cheaper, and the car is able to power standard AC appliances directly or even charge other vehicles. The batteries themselves are DC and for rapid
charging. Where a lot of power is being driven into the vehicle, it makes sense to have the costly and heavy AC (grid) - DC (car battery) conversion on the pavement, rather than carrying it around in the vehicle. However, for V2G, where much lower power
may be pushed from the car, the electronics (an ‘inverter’), needed to convert the car batteries’ DC to the grid low voltage AC which is not so expensive, heavy, nor requires extensive cooling. In this
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ViGIL (VehIcle to Grid Intelligent controL) Platform flow chart
scenario, the case can be argued to either have that small inverter in the car or on the pavement. Added to this, PV arrays produce DC, and the waters muddy further as there could be an argument for maintaining a DC power path from these sources to the car. And so, it is unsurprising that in creating a V2G solution, some auto manufacturers have opted for a DC output and others an AC one. There is a tussle between the two standards and
this AC and DC standards ‘war’ plays a significant role in V2G (Vehicle-to-Grid) adoption for a number of reasons. Let’s explore them below.
COMPATIBILITY AND INFRASTRUCTURE As well as the location of this crucial inverter, the standards war extends to the standards around the connectors used to pass that power. Although the Japanese CHAdeMO standard has
supported V2G for a decade over DC, this is being phased out gradually as the newer Combined Charging System (CCS) becomes the norm. CCS is an adaptation of the SAE J1772 combo which can
ENERGY & SUSTAINABILITY SOLUTIONS - Autumn 2024
handle both DC and AC transmission. However, V2G technology for this particular system will only be available from 2025. Until recently, this has meant that only a small number of car models with CHAdeMO connectors have supported V2G, most notably the Nissan Leaf. However, CCS does allow the option of either AC or DC V2G, but - as with VHS and Betamax - users will have to make the choice of which option they go for, as the chargers will be only set up for one option or the other. The AC and DC standards war could result
in different regions or companies adopting incompatible standards, leading to fragmented infrastructure development, and hindering the seamless integration of V2G technology – making it challenging for V2G systems to gain widespread adoption. Unfortunately, at this time, CCS does not yet support V2G. There are no commercially available EVs supporting AC V2G. However, Renault (with the Zoe) and BYD (with the e6) have been trialling AC
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