Understanding EV Charging

Jargon Busting: the basics of EV charging

Electric vehicles can feel like a step into the unknown – but the most important terminology is simpler than it seems.

What is a kilowatt-hour?

A kilowatt-hour (kWh) is a unit of energy. It’s how electricity is measured when it’s sold or consumed, similar to litres (or gallons) of fuel for a petrol or diesel vehicle.

Think of an EV’s battery as its fuel tank. A larger capacity pack stores more kWh of electricity and can extend the range, but it’ll also take longer and cost more to fully charge. The cost of charging and the vehicle’s efficiency are both measured on a per-kWh basis – instead of per-litre or gallon.

What is a kilowatt?

Kilowatts (kW) are a unit of power – or how quickly energy can be transferred from point to point. For EVs, it’s most commonly used to compare charging speeds. The higher the kW rating, the faster the vehicle is charging.

Charging speeds have increased dramatically over the last decade. Whereas early public chargers were often rated at 3.7W or 7.4kW (adding 25-50km per hour plugged in), the fastest units can now output up to 350kW (more than 150km in ten minutes). You’ll usually find the latter close to busy cross-country routes, where drivers are looking to recover lots of range during a short rest stop.

However, the vehicle’s on-board charger is usually the bottleneck. Plug-in hybrids tend not to be able to draw more than 7kW, as they can use a combustion engine for long-distance driving, while most EVs reach their limit between 100 and 150kW and slow down significantly once they reach an 80% charge. That’s usually enough to cover the next leg of a journey without waiting to get to 100%.

What’s the difference between AC and DC charging?

Electricity can be transmitted and stored in different forms, and electric vehicles use two of them.

The electrical grid (and most household appliances) use what’s called alternating current (AC), where the flow of electrons constantly changes direction and magnetic polarity. AC makes it easy to raise the voltage and transmit energy across the country, then step it back down again once it reaches its destination. In a battery, electrons can only flow in a single direction between two terminals – this is called direct current (DC).

Most home, workplace and destination chargers supply AC electricity from the grid to the vehicle, which uses an inverter to convert it to DC for the battery then back to AC for the motors while driving. The size of that inverter is restricted by the space on board, which in turn limits the charging speed. Even the fastest AC units can only output up to 43kW.

DC chargers convert AC electricity to DC before supplying it to the vehicle, where it goes straight into the battery. These have a large inverter which can handle significantly more power and provide a much faster charge – up to 350kW. However, they are larger and more expensive than AC chargers and require a dedicated electricity supply.

Is there a European standard for EV charging?

Yes. European vehicle manufacturers standardised the Type 2 (Mennekes) AC connector in 2014, alongside the Combined Charging System (CCS) which adds two additional plugs for faster DC charging [1, 2].

Some early plug-in vehicles (such as the Nissan LEAF, Mitsubishi Outlander PHEV and Kia Soul EV) use the Japanese CHAdeMO DC standard with a separate Type 1 AC connector. However, all new plug-in hybrid and electric vehicles sold in Europe have Type 2 sockets, while those that can rapid charge have the CCS pins too.

Compatibility is rarely an issue. Most public AC chargers have a Type 2 socket, which means drivers can bring their own cable and plug into whatever is on the vehicle. DC chargers have tethered cables, and many sites still offer CHAdeMO alongside the more common CCS connector.

What is smart charging?

One of the common concerns about electric vehicles is charging will overload the electrical grid. Demand fluctuates throughout the day, with peaks in the morning and evening – the latter could be exacerbated if drivers plug in after work. On a smaller scale, depots charging several fleet vehicles at once could exceed their available power supply.

Smart charging is designed to flatten those demand spikes, either by deferring the charge session until a pre-set time or enabling chargers to respond intelligently to the load on the grid. The UK already requires all home and workplace chargers to be capable of doing so [3] while some units – including Konect’s – can be integrated into a wider energy management solution to reduce the need for expensive grid connection upgrades.

What is Vehicle to Grid, and Vehicle to Load?

Vehicle-to-Grid (V2G) is the next stage in a smarter energy ecosystem. It enables electric vehicles to sell energy from their batteries back to grid, effectively adding capacity during periods of peak demand. Industry association CharIN claims vehicles could earn up to €650 per year by integrating V2G [4].

However, V2G requires specific charging equipment and it’s only supported by a handful of vehicles at the moment. The CHAdeMO connector was designed for V2G [5], which means the Nissan LEAF and e-NV200, Mitsubishi Outlander PHEV and i-MiEV are all capable of bi-directional charging.

Early versions of the CCS standard don’t support V2G. It’s enabled by more advanced functionality, particularly the ‘Plug and Charge’ communication protocol, which allows the vehicle and charger to share more information – primarily for automated billing [6]. CharIN expects CCS-based V2G to be commercialised in 2025 [7].

What is 800-volt charging?

There are two ways to increase the power output of an EV charger; more current (amps), or more voltage. Today, most electric vehicles use a 400-volt charging system – but Audi, Porsche, Hyundai and Kia have upgraded to 800-volt [8, 9], and large powertrain suppliers such as GKN Automotive are also doing so [10]. This offers significantly faster charging speeds, but without the heat and efficiency challenges resulting from a higher current.

Switching to 800-volt technology could also transform long-haul trucking by enabling megawatt (1,000kW) charging for heavy-duty vehicles. These have much larger batteries, so require significantly faster charging to top up while loading or during mandatory rest period.

Megawatt charging hasn’t been commercialised yet, but CharIN established a “task force” of members to work on a standard in 2018, and Siemens has recently demonstrated the technology using an adapted prototype truck [11, 12].

REFERENCES:

[1] Mennekes. (n.d.). Mennekes History. [online] Available at: https://www.mennekes.co.uk/company/about-us/we-are-mennekes/mennekes-history/ [Accessed 23 Aug. 2024].
[2] European Union. (2014). Directive 2014/94/EU of the European Parliament and of the Council of 22 October 2014 on the deployment of alternative fuels infrastructure. [online] Available at: https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32014L0094 [Accessed 23 Aug. 2024].
[3] UK Government. (2024). Regulations: Electric Vehicle Smart Charge Points. [online] Available at: https://www.gov.uk/guidance/regulations-electric-vehicle-smart-charge-points [Accessed 23 Aug. 2024].
[4] CharIN. (n.d.). Vehicle-to-Grid (V2G). [online] Available at: https://www.charin.global/technology/v2g/ [Accessed 23 Aug. 2024].
[5] CHAdeMO. (n.d.). CHAdeMO Technology: Vehicle-to-Grid (V2G). [online] Available at: https://www.chademo.com/technology/v2g [Accessed 23 Aug. 2024].
[6] CharIN. (n.d.). Plug & Charge. [online] Available at: https://www.charin.global/technology/plug-charge/ [Accessed 23 Aug. 2024].
[7] InsideEVs. (2019). CharIN CCS Combo Standard to Offer V2G by 2025. [online] Available at: https://insideevs.com/news/342354/charin-ccs-combo-standard-to-offer-v2g-by-2025/ [Accessed 23 Aug. 2024].
[8] Porsche Media Center. (n.d.). The Porsche Taycan: The Battery. [online] Available at: https://media.porsche.com/mediakit/taycan/en/porsche-taycan/die-batterie [Accessed 23 Aug. 2024].
[9] Hyundai. (n.d.). E-GMP: The IONIQ Revolution. [online] Available at: https://www.hyundai.com/worldwide/en/brand-journal/ioniq/e-gmp-revolution [Accessed 23 Aug. 2024].
[10] GKN Automotive. (2021). GKN Automotive Accelerating Advanced Development of Next-Generation 800V eDrive Technologies as EV Demand Increases. [online] Available at: https://www.gknautomotive.com/en/media-centre/news-releases/2021/gkn-automotive-accelerating-advanced-development-of-next-generation-800v-edrive-technologies-as-ev-demand-increases/ [Accessed 23 Aug. 2024].
[11] CharIN. (n.d.). Megawatt Charging System (MCS). [online] Available at: https://www.charin.global/technology/mcs/ [Accessed 23 Aug. 2024].
[12] Siemens. (2024). Megawatt Charging System: Siemens Delivers 1 MW Charge for First Time During Testing. [online] Available at: https://press.siemens.com/global/en/pressrelease/megawatt-charging-system-siemens-delivers-1-mw-charge-first-time-during-testing [Accessed 23 Aug. 2024].