My Electric Avenue was a ground-breaking project that set-out to evaluate the likely effect on local electricity distribution networks of a future in which a high proportion of drivers opt for plug-in vehicles. Anthony Smith reports.

There can be little doubt that the market for electric vehicles is beginning to gain significant momentum: early adopters are turning into repeat customers, and the concept of relying upon personal transportation powered largely or entirely by electricity rather than gasoline or diesel is becoming increasingly mainstream.

In the UK, for example, approximately 48,000 plug-in vehicles were registered in 2015 compared with just 3500 two years earlier. Plug-in vehicles currently represent 1.7 percent of UK new car registrations, with customers able to select from 38 different plug-in hybrid and pure battery electric models.

While this growth in the market for plug-in vehicles is almost universally viewed positively in terms of promoting local air quality, there is a growing recognition that the recharging requirements of this expanding electrified fleet are going to place a significant new burden on the electricity network.This is less of a concern at the grid level, where additional loads can be managed and accommodated using well proven methods; rather, it is in the area of the local low voltage (typically 240/415 V) distribution networks that the headroom for additional loads may be more restricted before thermal or voltage issues are likely to occur.

In order to assess the impact of this future load pattern, a multi-partner research project known as ‘My Electric Avenue’ was initiated. Scottish and Southern Energy Power Distribution (SSEPD) was the “host” distribution network operator (DNO), while EA Technology was appointed by SSEPD as the project coordinator.Other partners included Nissan, leasing company Fleetdrive Electric, DNO Northern Powergrid and low carbon transport consultancy Zero Carbon Futures.Project subcontractors included The University of Manchester and De Montfort University, along with Automotive Comms, Creative Concern, and Ricardo, which was contracted to provide independent overall technical oversight via a periodic review process.

Testing future network resilience to EVs

My Electric Avenue set out to create a series of ten test clusters of EV users, whose homes share the same low voltage feed from a local substation.Each cluster comprised around ten vehicles, giving a total of approximately one hundred in the technical trial. This technical trial would thus provide hard data on the likely performance of ten different distribution network low voltage feeders when subjected to a comparatively high level of EV use. It would also provide a test bed for the evaluation of EA Technology’s proprietary ‘Esprit’ demand management technology (see box). Separately to the technical trial, a further ‘social’ trial focused on a slightly larger sample size of 120 EV users – this time unconstrained geographically by network connections – and sought to evaluate the behavioural aspects of vehicle recharging such that future network demand could be predicted in terms of the long term usage patterns of different customers.

In creating what has been one of the largest evaluations of EV charging patterns in Europe – and perhaps the world – the My Electric Avenue team made significant use of social media, and the recruitment of so-called cluster champions who, armed with a distribution network map, would set out to recruit other participants who shared the same sub-station feeder.

Low voltage networks - the weakest link

“Our focus in this project was on the DNO-managed low voltage distribution networks, which represent the weakest link in the chain of the electricity supply system,” explains Tim Butler of EA Technology.“A future EV fleet potentially represents a significant new load which will be linked to the socio-economics of each neighbourhood.People generally have predictable working and commuting patterns, and these will affect demand significantly.”

To illustrate the nature of the scale of the potential problem facing DNOs, Butler outlines how each domestic property in the UK is fitted with a main cut-out fuse, typically rated at 100 A. It is currently a legal requirement on the DNO to provide this capacity load (a nominal 24 kW) at any instant should the customer so demand it.This is massively higher than the ‘after diversity maximum demand’ (ADMD) level used for planning purposes – in effect it represents the power demand expected of a typical property, with average demand during the evening peak of around 1 kW.At present most customers would never come close to drawing at the nominal capacity of their connection, but with the latest generation of EVs boasting increasing battery capacity and higher capacity charging – for example, the latest-generation Nissan Leaf is now offered with a 30 kWh battery and 7 kW charging – the scale of the potential problem is clear.

Unexpected morning peaks

The My Electric Avenue team found that demand due to EV charging followed some of the expected patterns, but there were some surprises too.The evening peak coinciding with the return home from the daily commute was as expected, but there is also a similar peak in the morning. This was found to be associated with the preconditioning of vehicles in cold weather, as well as those either returning from early out and back driving such as school runs, or from night shift working.This morning peak can be problematic as preconditioning cannot be time-shifted through demand management – it must by definition occur shortly before the morning commute – and this comes on top of significant resistive loads such as cookers, kettles and electric showers.

It was interesting too that non-managed demand for EV charging tended to peak again around midnight, as users set timers to make use of cheaper night-time electricity tariffs. While this is an attractive outcome in terms of grid-based load management, it represents another peak that needs to be controlled locally on the low voltage feeder in order to prevent thermal or voltage problems.

When should DNOs start worrying?

Even when managed using Esprit, the My Electric Avenue project showed that the addition of EV charging at just a maximum 3.5 kW level effectively doubles ADMD to close to 2kW – there is no longer a morning peak as demand just rises and flat lines at that level through the day, before peaking at double existing levels in the evening.

Analysis of the impact of EV charging on a number of feeders included in the study showed that an EV market penetration of around 40 percent would lead to overloading of many networks. This level effectively means just four in ten houses having one vehicle with a recharging capacity of 3.5 kW.

“The project has shown the sensitivity of distribution networks to EV penetration in the vehicle market,” continues Butler. “It’s something of a perfect storm for DNOs: EV uptake is happening more quickly than DNOs had expected, and some of the most heavily loaded networks may well be those in which EVs are considered attractive by customers.”

Urgency for power and automotive industry collaboration

The project feels that much higher level collaboration between the automotive industry and DNOs will be key to the successful widespread roll-out of plug-in vehicles, but that there is a cultural challenge to be overcome. “The automotive and electrical distribution industries are two very different cultures,” explains Butler. “Automotive works in a highly planned, agile and efficient manner to deliver products to market, whereas DNOs work on much longer timescales largely on a fit-for-life basis.In essence, to really succeed, the My Electric Avenue project shows that perhaps the DNOs will need to work a little faster and the automotive industry slower than each of them are comfortable with, in order to accommodate the widespread adoption of plug-in vehicles that the public may well demand in our larger towns and cities.”

From a current running total of just 1.7 percent of new car sales in the UK represented by plug-in vehicles, the threshold levels of around 40 percent penetration before which network problems will become apparent may seem a remote prospect.Step changes can happen quickly, however, and with the next generation of plug-in vehicles boasting larger battery capacities, an increasing number of potential customers may start to think electric for their next purchase without any range anxiety over their daily commute.And if the increasing popularity of higher capacity charging than the 3.5 kW considered by My Electric Avenue is also taken into account, the urgency for collaboration between the power and automotive industries has never been more apparent.

This article is an edited version of a feature 'Electric Future' published in RQ magazine, Q1, 2016 - click on the magazine cover below to go to the magazine version: