zero emissions bus

Electric vehicles charging back with V2G technology

Image credit: Dominion Energy

From electric school buses to Nissan Leafs, can vehicle-to-grid technology accelerate the clean-energy revolution?

Looking for ways to support the integration of a new 2.6-gigawatt offshore wind farm, Dominion Energy, a utility in Virginia, US, has devised a plan to use batteries within electric school buses as a grid flexibility asset.  

As part of the $16m project, Dominion will provide selected local schools with 50 battery-powered buses equipped for bidirectional charging. When the vehicles are idle, the utility will store excess energy in the batteries and draw it back in peak hours.

The technology, known as vehicle-to-grid or ‘V2G’, is not new, but it is extremely nascent. Seen as a progression from electric vehicle (EV) ‘smart charging’, where vehicle batteries are recharged at the optimal time for the network, trials for V2G as an energy-management and storage asset are ongoing, but finding the right business models has proved tricky.

Dominion, however, is one of the first utilities to integrate V2G into its commercial operations, with the first 50 electric buses expected to be operational by the end of 2020.

“The unique profile of electric school buses, where they park, the hours they operate and the miles they run, means much of the electric battery capacity isn’t needed much of the time, creating a great opportunity for shared battery use,” explains Mark Webb, senior vice president and chief innovation officer at Dominion Energy.

The buses cost $325,000 each but are sold to schools for $100,000 – the same price as a diesel equivalent. At the end of the school day they will be returned to their depots and plugged into bidirectional V2G chargers. Once connected, via a digital distributed energy-management system, the utility will charge the batteries, which takes around three-and-a-half hours, at the optimal time. When the energy is needed a signal is sent to transfer power into the grid.

The bidirectional energy-management system, called APEX, is provided by Proterra, an automotive and energy-storage company based in California. It will eventually be expanded to manage all the utility’s distributed assets, including solar and wind generation.

Dan Weekley, vice president of innovation policy and development at Dominion Energy, says the buses will mitigate the need to build additional capacity to the grid and help it better integrate renewable energy, in particular wind power.

“Offshore wind will produce more electricity primarily in the evening, afternoon or night time; with this programme we can charge the batteries when those renewables produce energy and have the flexibility to use it when we need it. This helps stabilise the distribution grid for voltage levels and other factors,” says Weekley.

To integrate the technology, Dominion had to investigate specific depots where the buses may be parked and what benefit the batteries could bring to the nearby energy-distribution network, as well as what upgrades are needed to adapt local systems.

Weekley continues: “There will be, I’m sure, a learning curve as we explore and investigate different uses and ways to maximise its value as the grid evolves, because it is constantly changing due to the type of power it’s managing.”

For the project to provide real benefit to the utility’s grid management, however, it needs to be scaled up significantly, he adds. Dominion was targeting 1,500 buses by 2025, which would give it enough storage and supply capacity to serve around 15,000 homes for approximately four to five hours a day, carrying the company over peak periods, particularly in summer when schools are closed. However, this was contingent on legislation passing that would allow the utility to transfer the costs to its customers – costing each around $1.25 a month. In March the Virginia General Assembly rejected the proposal.

Nevertheless, the company says it is still committed to adding ‘at least’ 1,000 more buses over the next few years, but needs policy support to provide clarity over the financing and ownership of the buses, related electric components and infra­structure, and hopes the Assembly will reconsider as soon as next year.

Overall, however, the project has been very popular with residents, says Weekley, due to the buses’ six-times-better internal air quality compared to non-electric models, a benefit which he says goes “directly to our customers’ kids”.

School buses are a unique but somewhat limited use-case for V2G technology. For true scalability, the technology needs to work commercially for consumers and operators of EV fleets.

However, Claire Miller, director of technology and innovation at Octopus Electric Vehicles, which is part of Octopus Energy, says consumer V2G is a “fiendishly complicated product” and currently not “a massively consumer-friendly process”.  

Octopus, along with distribution network operator (DNO) UK Power Networks (UKPN), is currently running an Innovate UK co-funded consumer-focused V2G trial in south-east England, called Powerloop. The trial is one of several that are ongoing in the UK, including others by EDF Energy and Ovo Energy.

For a monthly fee, trial participants lease a brand-new Nissan Leaf, one of only two cars (the other is a Mitsubishi) that currently has bidirectional charging capabilities, and receive a free Wallbox Quasar bidirectional charger.

The charger, which the company says is the first bidirectional one available for the home, has a backend system that transmits a withdrawal schedule every half an hour, so when a customer plugs in their car, it knows when to take power.

To get a £30 reward, participants must plug in the Leaf 12 times a month for 12 hours, between 4pm and 5am, so it can be used to support peak demand at around 6pm. The battery is recharged overnight, but 30 per cent – around 40 miles – is always available ‘just in case’. Using an app, customers can override the system or set a weekly charging schedule.

Due to the complex and ageing nature of grid infrastructure, however, Miller says UKPN has to get out “paper maps and archaic documents” to assess the safety of the nearby grid infrastructure before a customer can be enrolled – which is why it’s not yet hugely consumer-friendly.

“In the past, connecting an energy-generating device to the grid was either a gas-fired power station or a large solar farm and wouldn’t happen very often,” says Miller. “Then there was rooftop solar, which at 3-4kW is low-level, whereas Powerloop is around 7kW – enough to warrant a closer look at the potential disruption to the local grid infrastructure.”

In the future, the idea is for customers to make money by selling flexibility and energy back to the grid. However, currently the value placed on this energy is not high enough, says Miller.

‘People could get free parking at shopping malls and airport car parks in exchange for allowing V2G through their vehicle.’

Clara Serrano, Aston University

Drawing parallels with rooftop solar, where feed-in-tariffs were initially propped up by the government, a similar approach may be needed for V2G or for utilities to “inflate the price” to cover the cost of the service being provided, she says. Octopus Electric Vehicles is working with the retail arm of the company and regulators to address this issue, but the segregated structure of the UK energy system can make it challenging.  

“What we’re providing through V2G helps the whole grid, because it mitigates the need for having gas power to increase energy supply at peak demand. It is also a very local solution to this challenge. Therefore, the emphasis is on energy retailers and grid operators coming together to make it work financially,” says Miller.

Unpredictability is also an issue; it’s impossible to guarantee when customers will actually plug in their cars. Octopus is monitoring customer behaviour, which at the end of the trial it will extrapolate over larger numbers to calculate how much energy might be available at any given time.  

Dr Giulia Privitera, delivery manager for low-carbon technologies at UKPN, says the company has also demonstrated that V2G can work and sees it as an opportunity to support the network and reduce the need for upgrades when more EVs start using the grid. UKPN estimates that between 1.9 and 4.1 million EVs will be on its three networks by 2030. BloombergNEF estimates that by terawatt-hours electric vehicles could account for as much as 16 per cent of the UK’s overall energy demand in 2040.

“As a DNO we can incentivise customers to discharge by adding an export fee as a reward. We would do that at times where it would benefit the network and take pressure off it,” says Privitera.

“Additionally, for commercial fleets that might have vehicles at base and not used at certain times, we could contract with them to use their batteries to relieve pressure on the network,” she adds.

Enel X, which develops products and services for the energy sector, has also run several trials of V2G technology since 2012. But Giovanni Bertolino, head of e-mobility for US and Canada at the company, does not think the market is ready yet because there is no clear regulation and the infrastructure is expensive.

Bidirectional inverters can convert DC to AC and AC to DC, while unidirectional inverters just convert AC to DC. Today, EV-charging infrastructure can use both inverters, but it’s most common to convert the AC energy coming from the grid to DC to fast-charge a vehicle.  

“Currently there is less demand for the bidirectional inverter technology than one-​directional, which makes it more expensive; I think the economics are now much more in favour of centralised storage, but that could change,” says Bertolino.

Ryan Fischer, associate for electric vehicles at BloombergNEF, says an interesting point of discussion around the cost of technology is whether AC V2G charging, instead of DC, will be possible.

“AC V2G charging has some technical constraints with the grid interconnection and would require car manufacturers to incorporate more of the functionality currently onboard the chargers within the vehicles, which could significantly reduce the cost compared to a DC version. This could make the customer proposition more attractive,” he says.

Having more manufacturers of the technology could also bring the price down and provide more technical and maintenance support, says Clara Serrano, a senior engineer and EBRI plant manager, at Aston University.  She oversaw a V2G trial with partners Nortech Management, Grid Edge and ByteSnap Design, which concluded in February.

Furthermore, Serrano says protocol and interoperability are important. The trial at Aston, which was funded by the UK’s Office for Low Emission Vehicles and the Department for Business, Energy and Industrial Strategy, in partnership with Innovate UK, demonstrated the VIGIL V2G (VehIcle-to-Grid Intelligent controL) platform using four chargers.  

According to Serrano, it is the UK’s first comprehensive communication and control platform for managing V2G systems and electrical networks. It can also support multiple chargers, including AC and DC.

During the trial, Serrano and her colleagues monitored the impact of the two-way energy flows on battery degradation, an issue that could affect car warranty.

“We found it’s important to consider ‘calendar’ degradation, which means even if the car is parked and the battery is idle it is still degrading,” she explains. “This occurs more when a battery is at higher state of charge. Therefore, contrary to perception, V2G could actually help extend the life of the battery, but more research is needed.”

Overall, she says, there are challenges that need to be addressed, including establishing control and trust between all the different stakeholders, but there are opportunities, too. “People could get free parking at shopping malls and airport car parks in exchange for allowing V2G through their vehicle,” she says.

David Slutzky, founder and CEO of US-based Fermata Energy, disagrees with the characterisation that V2G for EVs is not already a commercially viable proposition.

The company has developed an ‘off-the-shelf’ bidirectional 15kW EV charger and proprietary software system. In March, it was the first in the world to be certified to a new North American safety standard, UL 9741. The company, which has secured investment from Japanese power company Tepco, has done several trials of its technology ‘in private’ and intends to scale in 2021, selling aggregate car-battery storage and energy supply back to the grid, initially from fleets of cars.

Slutzky, who was a senior policy advisor at the White House and Environmental Protection Agency during the Clinton Administration, says he created Fermata to accelerate the adoption of electric vehicles and to help the transition of renewable energy on the grid.

“V2G sits at the intersection of those two objectives. The biggest obstacle to the technology is penetration of EV ownership, which, in my opinion, is prohibited by them being pricey; but if people can earn money while they’re parked, which is 90 per cent of the time, that will disrupt the total cost of ownership value proposition compared to an internal combustion engine vehicle,” he says. “If a quarter of the cars in the US were Nissan Leafs, which has a 6.6kW battery, there would probably be enough energy storage equivalent to the entire grid.”

Beyond selling services back to the grid, Slutzky says V2G can also provide energy security for residential EV owners who experience regular power outages – a problem, he says, that will become more common because of climate change.

In May 2020 it was reported that Tesla, one of the most popular EV brands on the market, has started integrating bidirectional batteries into its Model 3. This is news that could be a game-changer for the concept and speed up its market penetration.

“I think the scalability of V2G is so huge it will truly disrupt both the auto industry and the electric power industry globally,” Slutzky reaffirms.

“And what’s nice about it is the carbon impact of that transition, from both adoption of EVs and increased integration of renewables, will be huge.”


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