The future of EV charging
Are vehicle-to-grid and vehicle-to-home coming soon? And could DC chargers find their way into homes? Bryce Gaton looks at changes that may be just around the corner for electric vehicle charging.
A reading of my recent series of articles on EV charging in Renew would suggest that DC is the charging system of choice for both long-distance travel and fast recharging for those without easy access to AC charging at home, while AC charging is king for everything else as it is simpler, cheaper and more convenient.
However, that neat arrangement is about to have a shake-up. Just over the horizon are a crop of vehicle-to-grid (V2G) and vehicle-to-home (V2H) bidirectional charging systems, all based on DC charging. In addition, a batch of smaller DC chargers are coming to market—and there’s a suggestion from at least one manufacturer to make DC the preferred charging mode for all EV charging.
Vehicle-to-home and vehicle-to-grid
So what are vehicle-to-home (V2H) and vehicle-to-grid (V2G), apart from yet more EV charging acronyms? Both are bidirectional charging systems, that enable both charging an EV battery and drawing energy from it for uses other than driving the car.
With V2H, as its name suggests, you can draw energy from the vehicle’s battery to power your home. V2H is touted as the way to combine vehicle and home energy storage into one battery, thus eliminating the financial and material costs of a second battery. That EV battery can then provide backup power during a blackout or be used to avoid importing from the grid at times of high tariffs.
V2H systems are a ‘behind the meter’ solution: the energy drawn from the vehicle battery and used by the home isn’t seen by the grid (or your energy provider) at all. V2G is the next layer above this, where the vehicle can provide power back to the grid as well as charge from it, and is smart-grid enabled to provide energy on demand.
V2G will enable EV owners to take advantage of proposed future energy tariffs that would provide favourable rates if a certain percentage of the battery is able to be used as a grid support system. When the national EV fleet becomes larger, V2G systems will become an excellent way to smooth grid demand fluctuations without suppliers having to build and maintain additional peak-power generation.
However, V2H and V2G systems, while long awaited, have yet to be delivered. The first stage is likely to be V2H systems. They offer the obvious advantage of needing only one battery to provide both home storage and mobility instead of two—and they have a much larger storage capacity than typical home battery systems. They also provide the ability to recharge away from home at low or free rates, and then feed that energy back to the home at times of higher tariffs.
V2H systems are yet to be certified for use in Australia and the systems currently available are only for vehicles that use the CHAdeMO DC charging plug (Nissan and Mitsubishi vehicles only). Bidirectional charging for vehicles with CCS charging plugs (the emerging standard used in all other vehicles) is in development though, and planned to be available by 2025. 2025 also appears to be the likely date for V2H systems to become readily available in Australia.
V2H and home V2G systems do have some disadvantages compared to a fixed home battery. One obvious issue is that they don’t provide 24/7 backup capacity, as the system is dependent on the car being at home and plugged in. They’re also currently more expensive to buy and install than a standard home battery storage system, and that’s just for the system, without battery.
And while DC charging can be faster than AC charging, for most homes it does not significantly increase charging speed. The home connection to the grid is the limiting factor; for single-phase homes, around 7.2 kW would still be the maximum charging rate. Three-phase homes are a different matter though, as discussed in the next section.
Smaller DC chargers
Currently, DC chargers are all larger systems, bolted to the kerbside. They range between 50 kW and 350 kW depending on the available power supply and the pocket depth of the installer. They are also unidirectional—they charge the EV but cannot draw off power to feed the grid.
However, a range of smaller capacity 11 kW and 22 kW DC chargers are about to come onto the market. Designed for three-phase homes and factory sites, they can provide significantly faster charge times (60% faster than 7.2 kW at 11 kW in a home and up to three times faster for a commercial 22 kW unit). These units are also intended to later add smart-grid and bidirectional/V2G capabilities, enabling businesses and homes to take advantage of future flexible demand and V2G tariff structures.
Although flexible demand tariffs are in their infancy (and there are no V2G tariff structures at all), they could potentially lead to thousands of dollars in electricity cost savings if the business allowed the grid to selectively recharge their car fleet at low demand periods and turn their charging down or off at unexpected peaks. An additional layer would be the use of V2G technology, where the EVs could even provide power to the grid during high demand times. Both of these ideas rely on ‘smart’ chargers (where the grid can communicate with the charger and control EV charging/discharging). Currently one of the biggest hurdles to smart charger adoption is a regulatory one, with a significant debate happening in Australia on which grid communications standard to use.
Portable DC chargers
An alternative to a fixed wall or pillar charger is to make the DC charger portable, and there is a small but growing range of these. Although not lightweight like a portable AC charging unit, they do make a great addition to the intrepid EV traveller’s toolkit for remote trips. Capable of plugging into most three-phase AC outlets, up to 22 kW DC charging can be achieved through one of these. The Designwerk MC22 (pictured, www.designwerk.com/en) weighs in at 22 kg—not light, but it’s certainly lighter than earlier design SETEC 22 kW units (www.setec-power.com) at 40 kg!
Along with the development of smaller DC chargers is a suggestion by at least one manufacturer to drop the AC to DC rectifier currently built into EVs. Their preferred option is for all charging systems to be both DC and bidirectional, enabling cost savings for EV manufacturers (by leaving out the AC to DC rectifier), reduced energy costs for charging system owners (by taking up bidirectional tariffs) and infrastructure cost savings (as less peak-power generation is needed). What it does for future owners of EVs with no AC charge port, a low battery, lots of power points around and no DC charger in sight is another question.
DC charging effect on battery life
The elephant in the room (or the mouse?) has always been the reports of battery degradation related to the number of charge cycles. Early Nissan Leafs (2011 to 2014-ish) were known for this, due to a combination of no thermal management system within the battery pack and a cell chemistry that was prone to degrading when subject to excessive heat. DC charging only exacerbated the problem, as higher current charging means higher battery temperatures during charging.
In addition, V2G could potentially considerably increase the number of charge cycles from the once or twice a week that is the norm for long-range EVs. But Nissan for one don’t seem deterred by this: they are prepared to guarantee their current EV batteries even when used with a V2H/V2G system. It will be interesting to see what the other manufacturers do when CCS bidirectional charging becomes available.
These days, most EV manufacturers use liquid-cooled battery packs and the cell chemistries have evolved significantly (and are continuing to do so), so degradation through temperature, chemical or number of charge cycles is lessening. But cell degradation in lithium cells is still primarily related to heat and charging rate, so it is good to be wary of anything that significantly heats the cells, rapidly changes their state of charge or adds to their charge cycles.
EV manufacturers are well aware of this, given they don’t want a flood of warranty claims. Hence, actual EV charging rates are increasing at a slower pace than DC charger rates. Although 350 kW DC chargers are rolling out now, EV manufacturers have been holding back their maximum DC charging rates to what they are prepared to provide eight to ten year guarantees for. For instance, the Kona electric has a maximum DC charge rate of 70 kW, and for the Jaguar I-Pace it’s 100 kW.
However, improvements in battery construction, chemistry and thermal management are underway, to the point that Porsche is confident enough in their batteries to announce the Taycan will be charging at 350 kW before the end of 2020.
Setting aside the issues with the early Nissan Leaf batteries, the usage data coming in seems to show EV cell degradation to be in the 1% to 2% a year range, and little to no increase in this if DC fast charge is used more often than ‘usual’. This would leave around 80% battery capacity after 10 years.
Even if you deem this too low for your driving needs, the cells still have a value to be recycled into grid and home storage systems. Experiments in this area by several EV and battery manufacturers have already begun. And, given new cell prices are on a continuing downward trend, the cost of replacing a battery in the future should not be as prohibitive as it has been in the past.
Looking into the crystal ball
By 2025, V2G should have begun to make significant inroads into the electricity market, and smaller bidirectional DC chargers for business and three-phase home use will be available. But what will this mean for adoption of V2G and V2H? I preface this part by saying that all predictions about the future of a technology are fraught. My set of personal predictions about domestic systems are based on the following observations.
V2G tariff choice for home users will be problematic as the car may not always be plugged in at home, especially as autonomous vehicles start appearing: your EV may then be anywhere and charging anywhere. What electricity retailer is going to offer a domestic V2G tariff if the battery storage cannot be guaranteed to be present?
Similarly, using V2H for storing excess solar production and providing blackout protection has its limitations as the system relies on the EV being present and plugged in. The ‘lived experience’ of a V2H system could become quite annoying. As an owner of a longer range EV myself, I plug in to charge once a week or less. Remembering to plug in or unplug every time I arrive or leave would rapidly become a chore.
Therefore my crystal ball suggests that home battery systems will still be preferred over V2H as they provide permanent coverage to soak up excess solar generation and backup in the event of blackouts. And the favourable tariffs for V2G-like support of the grid could use those same home battery systems (once a grid communications protocol is settled).
And the cost of a fixed home battery is likely to come down. One option is that, as older EV batteries are replaced, fixed home battery systems will be made from recycled EV battery cells, ‘closing the loop’ for lithium cell manufacture/recycling and significantly reducing the cost.
Considering all these factors there may ultimately be no real appetite for home V2H/V2G systems.
As an aside, an additional possibility for recycling older EV cells will be their use as ‘big battery’ grid backup systems. This would result in a life cycle of 20 to 25 years, thereby further reducing a cell’s already reasonable lifetime carbon footprint. These big batteries will also have the benefit of providing for more stable, reliable, cheaper and greener electricity supplies, eliminating the need for peak-power generators and further enhancing the choice of renewable energy sources such as wind and solar over coal, gas and nuclear.
V2G options for business and DC charging networks will also be a boon for reducing energy costs and providing extra grid capacity as an additional form of ‘big battery’. These users will be the likely winners in a V2G system rollout. Thus, lower-rate DC chargers (11 kW and 22 kW) could become the charger of choice for business and even community level charging, as the V2G tariffs could offer significant electricity cost savings over unidirectional AC charging tariffs.
Looking further into the increasingly murky depth of my crystal ball, I would suggest that for the home user, AC charging will dominate well into the future as most homes are single-phase and charging/discharging via a V2H system that you need to always plug into is not as convenient as just plugging in once or twice a week (or less). AC charging systems will also become ‘smart’, meaning they will incorporate grid communication systems to enable them to take advantage of off-peak and demand-based EV electricity tariffs.
However, the applications of DC charging are very likely to expand well into the grid itself as V2G and big-battery systems develop and grow as a natural result of the expansion in the worldwide EV fleet in combination with the opportunity for providing a second-life use for older EV battery cells.