Is biggest best (for EV charging)?

The reality, however, is much more complicated.

As CPOs, it is our mission to give drivers what they want: a fast charge, but more importantly, is an available charger. In brief, the goal is to give the maximum useable power level to as many cars as possible at the same time.

Not all EVs are equal

Not all BEVs are created equal when it comes to charging. Some charge at much higher power than others and the charging rate is not constant over time – slowing down as the battery reaches full charge, with some batteries slowing sooner than others.

The current EV market shows that there is a large spread across both the peak charge rate that a car can achieve as well as the car’s average charging rate.

Table 1 shows the charge rates for the most popular BEVs on UK roads at the end of 2020. This shows that the peak ranges from 40kW through to 250kW with the average peak rate sitting around 100kW. This table also shows that the average charging rate whilst charging the battery from 10-80% is noticeably lower than the peak rate.

Table 1 – The table above shows the listed maximum charging power for the 15 most popular EVs in the UK at the end of Q4 2020 [Sources: Department for Transport Vehicle licensing statistics, Q4 2020, EV-Database, OEM brochures]

Some of the higher-priced, performance cars can charge at even higher rates, as shown in Table 2 below. These cars, however, only represent 2.3% of the overall UK market:

Table 2 – Charging capability of expensive performance cars [Sources: Department for Transport Vehicle licensing statistics, Q4 2020, EV-Database, OEM brochures]

The stated peak rates are only achieved under certain charging conditions (battery state of charge, temperature, etc) and typically for a very short period, usually a couple of minutes, with the charging power declining throughout the charge cycle.

For the above reasons, the peak rate is somewhat academic in the real world. The average charge power (ACP) is more relevant to everyday charging: the average power the car can take over a typical charge cycle. A recharge starting at 10% going to 80% SOC is often used for this purpose as charge rates drop sharply once the battery reaches around 80% charge.

Of the 15 most popular EV models in the UK shown above, the average ACP is around 80kW and only one model has an ACP greater than 150kW. This shows that the charging demands of most BEVs would be more than satisfied by a 150kW chargepoint.

As we see from launches of vehicles such as the Hyundai Ioniq 5 with 800v charging capability, there is a valid question whether the superior high-power charging technology seen in vehicles such as the Porsche Taycan will trickle down to mass-market vehicles in the next 5 years. However, the major OEMs have indicated that the expense and production platform changes involved mean that this technology is unlikely to be featured in mass-market EVs for some time, if ever.

Customer desires

As more and more EVs hit the road, drivers have made it clear that the most important thing is the availability of chargepoints. This is not just an increased number of locations, but also more chargepoints installed at each location, giving drivers the confidence that they will be able to get a charge when they arrive at a site. Drivers would rather wait on a charger (i.e. while charging) than wait for a charger (i.e. queuing), within reason of course. In short, more chargers is better. This leads to a key real-world issue: the availability of power to each site.

Power – not quite everywhere

Unlike petrol and diesel, electricity is all around us.

However, the grid infrastructure that serves most roads and buildings is a ‘Low Voltage’ network that can typically only allow the installation of up to two 50 – 75kW chargepoints.

To install high power chargers (HPC), or a ‘hub’ of multiple rapid chargers, requires the installation of a new substation onto the ‘High Voltage’ network, which can cost several hundred thousand Pounds.

Limitations on the power supply to a charging site is an important consideration in charger choice.

Supplying the many

A theoretical example is a site where the maximum amount of available power is 1.6MVA. Here, the different charger configuration options include:

1. 4 X 350kW chargepoints
2. 8 x 150kW chargepoints
3. 14 x 100kW chargepoints
4. 28 x 50kW chargepoints

…and so on

The first of these site configurations, with all 350kW chargers, could satisfy four Porsche Taycan drivers if the chargepoints are available. However, assuming the Porsche can utilise the charger, the car will only use the 270kW peak power for around 2 minutes, before dropping to circa 200kW. The ACP across the whole session would be 197kW, meaning that 153 kW of available power is wasted – across the 4 charging bays this spare 612kW could have seen an extra 4-10 rapid chargers installed!

As mentioned above, the average charging rate for the top 10 most common EVs in the market is around 80kW. Thus most cars will charge at their average maximum charge rate by 100-150kW chargers.

A site with eight to fourteen 100-150kW chargers will satisfy more drivers more of the time.

The benefits for the Porsche, or the few other high end-cars capable of using ultra high-power charging, are quite limited in practice with overall dwell time only decreasing by approximately 3-4 minutes.

As you can see below, popular mass-market cars on UK roads experience no additional time saving from a 350kW chargepoint compared to a 150kW chargepoint with only the Tesla Model 3 showing a very minor improvement (Table 3). And of course, the 350kW displaces two 150kW chargers or three 100kW chargers that could serve other drivers.

Table 3 – Charging times for popular UK EVs [Source: EV-Database]

In summary, the trade-off between power and availability is not as severe as it may seem:

1. Customer feedback is clear that charger availability is more important than the speed of the chargepoint;
2. 350kW chargepoints only benefit the small market segment of luxury EVs, but their main impact is a reduction in the number of chargepoints that can be installed in any location;
3. For those EVs that can utilise ultra-high-power chargepoints, charging at over 250kW is only sustained for a brief period, resulting in a minimal reduction to charging time.

Dwell time

The discussion above assumes that the driver wants the fastest possible charge so they can continue their journey as we see at ‘en-route’ sites such as motorway service areas.

However, this is not the case for all charging locations. In ‘destination’ locations such as supermarkets, shopping centres, food outlets, etc, the charge power should be selected to provide the required charge over the desired dwell time at the site. If our Porsche Taycan example visits a supermarket with a 45-minute dwell time, it only requires a 75kW charge rate to charge from 20-80% in that 45-minute period.

So, what is the answer?

As one of the UK’s largest and fastest-growing public rapid-charging networks, 2021 and beyond is seeing Osprey Charging installing sites with as many units as the grid allows, but at the right charge rate. This sees us installing units of 150kW+ at En-Route sites with a short dwell time, through to 75kW units at Destination sites with an hour dwell time.

As we see more BEVs hitting our roads in the coming months and years, Osprey and the other charging networks have the responsibility to ensure we configure sites correctly to enable as many vehicles to charge as possible, so we can truly achieve the transition to net-zero.

The Osprey network will always be open to all drivers making the transition to EVs, with 100% of units offering contactless card readers, and the added flexibility of RFID and app access for those drivers who want VAT receipts and statements on hand. But Osprey are also pioneers in roaming partnerships, being founding launch partners of the Octopus Juice Network, Zap Pay from ZapMap, and both the AllStar and Mina fleet roaming programmes. It is for these reasons that Osprey is continually voted by EV drivers as one of the most-loved networks in the UK, renowned for its reliability, ease of use, and the quality of sites.

About the author

After completing his Master’s degree in Mechanical Engineering at Loughborough University, Harry was first introduced to the EV charging sector during an internship with Investec Bank in 2018, who had recently completed an initial investment in Osprey Charging (formerly Engenie). He went on to work for an industrially focussed Strategy Consultancy whilst continuing to keep a close eye on the rapidly developing UK EV market. By the end of 2019, the market and green revolution had drawn Harry back as he joined the Osprey team full-time to help reach their ambitious objectives during their rapid expansion. Now, Harry continues to develop Osprey’s commercial proposition and builds exciting strategic partnerships with key UK and European brands to drive Osprey’s utilisation and the UK’s switch to a sustainable transport future.