Blog: Fast charging, station capacity and economies of scale

8 June 2016

This is part 4 in a series exploring fast charging technology. In part 1 I discussedwhat fast charging is. In part 2 I discussed car batteries and the variables that influence charge speed followed by part 3 where I explained how fast the next generation of EV’s will be charged. In this blog I discuss how faster charging increases the capacity of charging stations and economies of scale.

Charging an electric car will be a mix of home charging, destination charging (at work, a supermarket, hotels, etc.), public slow charging and public fast charging.

This blog is about the relation between charging speeds, station capacity and investments, and what this means for the “total cost of infrastructure” as we move towards a larger share of pure EVs on the road. Economies of scale can dramatically lower the cost to operate a network of fast charging stations and thus lower prices for consumers. Below I will explain how (well designed) fast charging stations can expand station capacity with an order of magnitude.

Besides economies of scale, there are other distinct advantages of clustering fast chargers on a single site. Fast charging stations with multiple chargers can provide great brand visibility and thus drive growth at high-traffic locations. Stations with a roof also provide cover (and can generate electricity through solar panels) and make it easier to provide additional services in the future.

With conservative estimates, stations with two typical 50 kW fast chargers can provide a - conservative - maximum of 560 kWh per day. This enables 2.800 km electric kilometers per day. I base this on the historical data we already have on fast charging behaviour of our customers:

(1) Fast charging stations are mostly used between 07:00 and 23:00 - 16 hours of use per day.

(2) A maximum of 50% utilisation during the hours of use (half of the chargers are in use during these 16 hours).

(3) On average an EV charges at 70% of the maximum that a fast charger can provide (not all EV’s will be able to charge at full speed for the entire charge session).

In the coming years, more EVs become capable of charging at 150 kW. With more powerful chargers a single station can serve more EVs. Now let’s see what happens when we upgrade a 2x50 kW station to 4x150 kW or to 8x150 kW:

An existing station has a capacity of 204.000 kWh annually and an upgraded station more than 1.2 million kWh. A next generation station thus provides 6X more capacity on the same land area, and 12X more capacity with 8 chargers. That’s an order of magnitude improvement.

The economics of faster charging stations
The kWh capacity of a station 2.0 is six times that of a current fast charging station. However, the one-off costs (CAPEX) such as permits, grid connection, equipment, construction, installation and project management of a station equipped with four 150 kW chargers are far below that of constructing 5 additional stations. Recurring costs (OPEX) such as technical maintenance and cleaning are only slightly higher for the 2.0 station. Capacity thus rises (much) faster than costs do. Therefore the cost per kWh can decrease.

Another advantage lies in maximizing the use of a single grid connection. In many countries electricity prices are heavily taxed. Many of these taxes are regressive: the more you use per grid connection, the less you pay per kWh.

Can the grid handle this? As long as fast charging stations are connected to medium voltage rings (10kV or 20kV), station power can be scaled up in line with the expected exponential take-off of electric cars. Today supermarkets, high rise office buildings and large warehouses are routinely connected to the medium voltage grid with Megawatt connections. Fast charging stations are comparable in power draw and are well within the limits of the capacity of the medium voltage grid.

More chargers, less waiting
The other fundamental advantage of large fast charging stations is reduced waiting time. If we assume an average of 30 minutes to charge a vehicle, an occupied stall on average results in 15 minutes of waiting time for the next EV driver. With two chargers this is reduced to 7,5 minutes and with 4 chargers to less than 4 minutes. So a station equipped with multiple fast chargers greatly reduces waiting times.

More chargers also improve redundancy of the station. EV drivers must be able to depend on fast charging stations. Even when a single fast charger has an uptime of 99%, then the charger is still unavailable for 3.6 days per year. For a station equipped with two fast chargers with both 99% uptime, the time that both chargers are unavailable at the same time is reduced to less than 1 hour per year since both fast chargers operate independently of each other.

An added advantage of connecting fast charging stations to medium voltage rings is greater redundancy during power outages, because the station transformer can be fed from both sides of the ring.

Roland van der Put is the CTO of Fastned and heads the Network Operations Center. He graduated as computer science engineer at the Delft University of Technology and has a background in computers. His interest in electric cars was triggered after installing his own solar panels and driving a plug-in hybrid.

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