Off late, our obsession with catchy headlines has left little room for nuance when discussing rapid charging. The current discourse focuses on battery packs or chargers, not battery packs and chargers.
The reason for this is simple - we’ve never had to think about energy as a two-sided problem 🤷
For over 100 years, energy companies and conventional OEMs have worked in isolation. While energy companies focused on discovery, extraction, refinement & distribution of fuel, OEMs focused on vehicle-side of design, assembly, performance and distribution.
The only time they’ve had to interact is when a vehicle rolled into a fuel station and the attendant stuck a nozzle into the vehicle’s fuel tank. The end.
The very act of transferring energy into the vehicle isn’t dependent on the vehicle. Vice versa, filling petrol/diesel from different fuel stations doesn’t impact your vehicle’s health & performance.
It’s the exact opposite in the world of EVs as:
Your energy partner impacts everything from recharge time to battery health.
Today, transferring energy from the grid to an EV is simple if you’re passing a nominal amount of electricity over 4-8 hours as the stress placed on both the charging station and the battery is fairly low.
That changes when you’re rapid charging an EV in 15 minutes because a large amount of energy is delivered in a short period of time - the level of stress it places on the charging station, the battery pack & everything in between is immense.
Previous attempts to achieve 15-minute rapid charging involved:
Innovating with new cell technology - granted, some have achieved it at a cell level in the lab but it falls short at a vehicle level as the systems around it - the charger, cables, BMS, battery pack architecture and software can’t handle the stress placed on it.
Marketing gimmicks by large companies that defy the basic laws of physics by assuming a larger charger = faster charging.re can’t handle the stress placed on it.
The reality is
A larger charger does
not mean faster charging.
Regardless of how big & powerful a charger is, an EVs battery pack simply cannot accept energy beyond a point.
Why? Let’s break it down.
Every EV comes with something known as a C rating - an indicator of how much average power an EV can accept when charging from 0 to 100%.
How do you calculate it? - Look up how long it takes an EV to charge from 0 to 100% and divide 60 mins by that number.
So if an EV claims to fully charge in:
15 mins
60 Mins
240 Mins
You get the drift.
🚗 Example
Now, let's assume your EV has a 10 kWh battery pack that has a C rating of 0.25.
The power this EV can accept when charging is 0.25*10 (battery capacity) =
2.5kW.
No matter how powerful the charging station is, your EV can only take in an average power of 2.5kW to fully charge in 4 hours. It's impossible to fully charge it in less than 4 hours & pump in more than 2.5kW of power.
Even if someone wanted to charge the above mentioned EV using a 50kW DC
fast charger, its *actual* utilisation would only be: (2.5kW/50kW) *100 = 5%.
Now, if only 5% of your charging station is being utilised for a period of 4 hours -
Energy throughput is dismal leading to high user tariff and low charging station profitability.
Alternatively, in the above scenario, setting up 2.5kW charging stations would solve for 100% utilisation but due to a 4 hour recharge time, you would have to set up several chargers to avoid congestion at the station. While this works for one-off emergency situations, it’s impractical on a daily basis as you’d have to tackle problems like real estate utilisation, organised parking availability and finally - do you really want to sit around and wait for your EV to charge in 4 hours?
We’ve previously spoken about why Exponent-powered 15-min full charge achieves maximum energy throughput and is the foundation for a profitable EV charging infrastructure.
For more such deep dives, keep your eyes peeled for the next edition of the Blueprint!