Image: Daniel Bönnighausen

DC only! Why direct current infrastructure is gaining ground

Fast charging with direct current is the only economically viable and practical solution for public spaces in the foreseeable future, finds our author Christoph M. Schwarzer. He also dares to look into the more distant future and believes that DC will not only prevail in public spaces.

AC or DC? Alternating current (AC) and direct current (DC) were once the cause of minor opinion wars. Some were certain that installing a large number of AC charge points was sufficient, but others were convinced that high-power DC points were the only way to go.

However, the early days of electromobility are over. Given the mass ramp-up, fast DC charging will become dominant and increasingly prevail. The more electric vehicles there are, from passenger cars to heavy goods vehicles, the more compelling this phenomenon becomes: no scaling without DC! However, this does not mean the end of the AC wall box, which will remain the optimal application at home for the foreseeable future.

Today, there are four core areas of charging infrastructure:

Long-distance charging on motorways
Opportunity charging at publicly accessible car parks
The workplace
Your own home

Fast charging with direct current is a given on long-distance motorways. If you are travelling, you want to have to take a short break only. In many cases, people think exclusively from the user’s perspective, i.e. focussing on the charging capacity of the electric car. The 800-volt systems of the e-GMP platform from the Hyundai Group currently set the benchmark in the mass market. The factory specification of 18 minutes to charge from 10 to 80 per cent is often achievable.

10 minutes to 80 per cent SoC is within reach

This value corresponds to a C-rate of around 2.3. 4C or 5C and will be a matter of course in the second half of the decade. Instead of 18, only a good ten or even fewer minutes will be needed.

What is pleasant for the driver is a simple necessity from the point of view of the infrastructure industry. According to the German Association of Energy and Water Industries (BDEW), 1.3 million electric cars were on the road in Germany on 1 October. That corresponds to about 2.7 per cent of the market. Things will get tight if there are 30, 50 or 100 per cent EVs plus thousands of trucks. Space for installing charging points along the motorways is limited, and the areas also cost money to rent or buy.

Queuing is already a reality on Friday or Sunday afternoons in Germany. The consequence: as more and more electric cars are on the road, as much electrical energy as possible must be charged as quickly as possible. Otherwise, the system won’t work.

Lars Walch, Vice President of Sales E-Mobility at EnBW (Energie Baden-Württemberg AG), sees fast DC charging as “the best customer experience”. EnBW has a unique role because it operates in the tradition of a utility. It produces and distributes electricity and is used to thinking long-term for its infrastructure.

All are betting on DC

In the long run, only charging with direct current offers operators the prospect of profit from their investments in charging parks, transformer stations, foundations and roofs. Walch knows that there is money to be made from charging infrastructure, but that is yet to happen. In the meantime, EnBW has commissioned at least one site (on average) per workday in 2023 – all of them DC.

When we look at the market, we see that EnBW’s main competitors are either from the car industry (Ionity and Tesla) or from the oil industry (BP’s Aral Pulse and Shell Recharge). Oil companies are clearly preparing for the day when they are sued in some international court for decades of CO2 emissions and need a defence strategy.

In this context, we should not overlook the many municipal utilities in Germany. Here, too, the realisation is gaining ground that public charging cannot be achieved with unprofitable AC columns but only with DC parks. AC is a waste of parking space and time.

HPC columns at supermarkets have great potential

In any case, capacity utilisation is at a constant 12 per cent, says the BDEW. In other words, if the number of electric cars and charging points is growing, but capacity utilisation is unchanged, it suggests a reasonable expansion rate and not an excess of one or the other. Even though some may have us believe that Germany is headed straight for a blackout, that is not the case. On the contrary. The country is on the right track.

The most crucial element for urban and densely populated areas is opportunity charging at privately owned, publicly accessible DC charging parks. In other words: in the supermarket car park. There is enormous potential here that owners are increasingly tapping into. It is no longer a vision of the future that EV owners will prefer to drive to a shopping centre where they can fill up their traction battery as they shop.

That may even be the case in rural areas, where the best solution is to have your own parking space with an AC wall box. But not everyone has one. Even in the city, public transport does not replace car ownership. That only applies to certain mobility groups in the epicentre of larger cities.

In metropolitan regions, there will be opportunity charging at public charging parks at shopping centres and charging parks operated by the oil industry. Land has never been so valuable: anyone can see how a row of petrol pumps at Aral and Shell is being replaced by charging points. And then comes the next one.

Up to this point, everything is clear: due to the scarcity of space and the upscaling of electromobility, there is no way around the fastest possible DC charging. It has been happening for a long time and will become even more so against the backdrop of the megawatt charging system (MCS) for electric trucks. And if peak loads in the high-voltage grid become too expensive, stationary buffer storage systems must be built.

DC charging in the company car park?

But that doesn’t matter in the company car park. Here, you can comfortably plug into wall boxes with alternating current. Right?

That’s not certain, either. Projects such as Go EV argue that, above a certain size, it is no longer more expensive to rely on DC instead of AC. The principle is called Dockchain: a kind of main charger supplies many individual DC points with electricity depending on demand. The system can be flexibly expanded, and it offers the option of fast charging when required.

So it is by no means set in stone that large company car parks have to be equipped with a large number of AC points. It is probably only an interim solution.

What remains is the home application. That is where most people charge. Nowhere will the AC wall box be in operation for as long as in your own garage. Although comparatively small amounts of electricity are converted here – that is not the point. Private owners can charge as slowly as they like. Incidentally, it also protects the traction battery and thus promotes durability.

More and more DC wall boxes will soon show that the last word has not been spoken here either: they are best suited for bidirectional charging.

The German company 1komma5 Grad gives an example of what an advanced home system could look like in the medium term. The whole thing becomes interesting when an electric car with bidirectional charging capability is combined with a DC wall box, a photovoltaic system and a stationary buffer storage unit.

DC wall boxes are still the exception, and they are also expensive. The argument in favour of DC: both the photovoltaic system and the traction battery work with direct current anyway. Conversion losses from DC to AC and back are thus avoided. This factor is definitely relevant. The economic question now is how well the producers of the DC wall boxes succeed in reducing costs.

If this is the case, AC wall boxes will also lose ground in the private sector. But probably after 2030.

The car industry would be delighted if it could eventually dispense with the internal AC charger. It doesn’t matter which continent the manufacturer comes from: if it is possible to do away with a component that costs money, takes up installation space and weighs a lot, the car industry will be thrilled to do so. A typical 11 kW charger now costs less than 200 euros. It adds up if it can be saved millions of times over.

As a result, it is plausible to assume DC only in a scenario with 100 per cent electric vehicles. That could take a very long time, perhaps until 2050. But it is not out of the question.

5 Comments

about „DC only! Why direct current infrastructure is gaining ground“

28.12.2023 um 01:00

Sorry, I have to disagree with this analysis on a number of points.First of all: DC units are far more expensive than AC ones. Based on a web search, 25kW DC units cost between €9000 (ABB Terra) and €5000 (Hydra Dion). By contract, some AC units come in below €500. This is a factor of 10 and, if we're comparing the installation of these units like-for-like, you'd be mad to choose the DC units. It could be argued that the cost of DC technology might come down, as might the cost of AC, and that you might fit a different kind of unit than the ones currently on the market, but this is the current state of the art.Additionally, higher-power on-board chargers are becoming more common. Renault has fitted at least 22kW AC charging to every one of its BEVs ever made, the Volvo EX30 has 22kW as standard, as do the new Smart EVs. On-board chargers are an application space where the new semiconductor technology gallium nitride is targeting adoption, increasing semiconductor device cost but decreasing the size and cost of the required transformer core, as well as improving system efficiency.There is major scope for change in public charging hubs (particularly DC, but also AC). At the moment, DC rapid charging hubs rely on a dedicated transformer to step down from the medium voltage distribution grid (~11kV) to low voltage (415V line-to-line, 240V line-to-neutral), with the AC-to-DC conversion stage still requiring a 415V input feed. This adds cost, both in high current hardware and the dedicated transformer. Moreover, most charger systems available today are designed for a closed system of AC-to-DC and DC-to-DC dispensers, with a maximum number of DC-DC units, limited scope to integrate battery storage to the DC microgrid and no opportunity to expand the DC microgrid with more AC-to-DC units. Charger manufacturers need to deliver technological advancements: AC-to-DC units that can connect directly to 11kV, DC microgrid sharing systems that can expand to an arbitrary (or at least much larger) number of AC-DC and DC-DC units, and easier integration with energy storage units. I expect charger manufacturers (ABB, Tritium, Alpitronic etc.) are currently investigating this.This kind of system seems to be similar to what Go Eve is proposing, but I struggle to see how it can compete with AC on cost. An AC charging point is extremely simple, consisting of little more than a relay and a square wave generator. To supply enough AC energy for a charging hub (e.g. a supermarket charging hub or workplace car park) would also require a dedicated transformer, similar to existing DC systems, but the cost for an AC dispenser is then extremely low. While the cost of a DC dispenser can be brought down by sharing the AC-DC unit and connecting to a DC microgrid, I struggle to see how the cost can be brought to parity with an AC dispenser. The DC dispenser will always include a transformer, semiconductor devices and a microcontroller, with the cost of the transformer and semiconductors scaling with power. The site's revenue opportunities improve if the DC dispensers can deliver >22kW, but this will drive the price of the units up, too.I should note that AC systems seem to be lagging behind DC in power sharing. With DC charging consisting of little technological walled gardens, they've been able to deploy rudimentary, proprietary power sharing arrangements. Technologically speaking, AC dispensers should be capable of exactly the same kind of power sharing, with protocols like OCPP enabling this, but the technology hasn't really been deployed this way yet.Finally, integrating a DC wallbox charger into a home energy system is a compelling prospect, but this relies on the home already being fitted with an inverter (and one which supports an extra DC power feed). This will vary by market: I'm based in the UK, where few houses are fitted with solar, though I gather rooftop solar is more common in places like Germany. It's important to understand the underpinning technology here, too: CHAdeMO has supported bidirectional power transfer since it was introduced, but CCS has only supported it for a year and a half, since the charger-to-vehicle communications protocol ISO 15118 was updated. The update to ISO 15118 also included commands for AC bidirectional power transfer, including requests for active and reactive power, requests for frequency and a grid-forming mode. Where a house is not already fitted with an inverter, upgrading an AC wallbox to one which supports ISO 15118-20 digital comms will be much cheaper than fitting an inverter to the building. The EV's on-board charger will have to be upgraded to bidirectional, but this adaptation is not very expensive, and where it's been offered as V2L, customers have been interested in the upgrade. Hyundai Group is leading the way, having conducted AC V2G studies in Utrecht.For all these reasons, I predict that DC charging infrastructure will remain limited to high power (50kW and above) highway charging. Meanwhile, on-board chargers capable of 22kW and/or bidirectional power transfer will become more common, with charging infrastructure being deployed as 22kW AC dispenser units. For bidirectional home charging, I predict AC-coupled systems will dominate, utilising ISO 15118-20 capable wallboxes and on-board V2L chargers.

Páv

04.01.2024 um 09:22

DC microgrid with multiple AC-to-DC cabinets feeding same microgrid is exactly what a larger Tritium Veefil-PK installation is. Or Tesla V3 Supercharger. This has been done, and it does not look economically superior to a load balanced all-in-one units, see all those large alpitronic sites in continental Europe.Load balancing AC points over OCPP is common, in fact any non-trivial AC deployment already have it. No one will reserve 100 times 22 kW for AC in a company parking lot.And you missed the large picture. Commercially, charging as a core business, AC is not profitable and never will be, no matter that units are cheaper, because the amount of energy you can sell is just so much lower than on DC. So yes we will still see AC as a money losing amenity at destinations. But I think street-side AC will die off the minute municipalities shop subsidising it.

Alex

28.12.2023 um 12:54

I see the opposite problem. There are plenty of nice new charging stations near me (in Germany) but they are always empty. 10% to 12% utilisation is not a way to run a business. Even worse, they are charging the standard (expensive) rate all the time, even when wholesale prices are negative (and the grid is desperate to dump surplus electricity). DC charge stations need to offer dynamic pricing, and tempt people to bring their cars on Sunday evenings and save the grid.

Rick Collins

30.12.2023 um 22:35

I could not find much of value to read in the first quarter of the article, so I bailed. Here is the simple fact, electricity is distributed to our homes, commercial centers and pretty much any other place we might want to charge, as AC. The only reason they use DC to charge at the faster rates, is because an AC to DC converter is required. The equipment to do that at the higher wattage rates (75 kW and above) is bulky, heavy and expensive. So instead, they put this equipment in the charging site, saving money and providing more room and weight capacity in the EV.You don't need to dig into the details of profitability of charging companies. There will always be to modes of away from home charging. Level 2 will be used in standard parking lots where the cost of the charger is no more than the cost of the parking space. Higher level charging will be used mostly near highways where people need to charge up quickly, just like gas cars do on road trips.

Terry

30.12.2023 um 23:15

Also, this very fast DC charging push is fine for some, but I would often prefer a 45min to an hour charge so I can stop for food or shopping without having to move the car. Around 22kw would be fine for this and a low cost charger would allow more car parking spaces to be available.