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Can the Electricity Grid Cope with Electric Vehicles?

Credit: Nischaporn/Adobe

Credit: Nischaporn/Adobe

By Sohaib Rafique & Graham Town

Electric vehicles are expected to take over our roads in the coming decade, but can our electricity infrastructure cope with the additional demands they will place on it?

Transport is expected to become electrified in coming decades, bringing new benefits, challenges and opportunities. As electric vehicles (EVs) displace internal combustion engine vehicles, a number of benefits are likely to follow: reduced costs for vehicle operation and maintenance, reduced greenhouse gas emissions, and use of the substantial battery storage present in EVs to compensate for variability in energy supply and demand.

However, there have also been some widespread concerns that are perhaps contributing to the slow uptake of electric vehicles in countries such as Australia. These include the up-front vehicle cost, a lower driving range before recharging is required, and the availability of fast-charging infrastructure. For the electricity distributors there are also questions about the impact of electric vehicles on the electricity grid.

We set out to investigate the validity of most of the latter concerns, and to quantify the potential benefits of transport electrification. Our study, which has been published in the Australian Journal of Electrical and Electronics Engineering (https://goo.gl/RtCFsq), used existing travel data from the NSW Household Travel Survey 2014/15.

We found that approximately 90% of vehicle commutes within most parts of Sydney are less than 40 km, so concerns about the limited range of EVs are largely unfounded. In fact, 88% of all vehicle commutes within Sydney could be serviced by existing low- to mid-range fully-electric vehicles costing up to $40,000. This result was surprisingly similar to a study published in Nature Energy which estimated that 87% of commutes across the United States could be provided by mid-range EVs (https://goo.gl/dggmPU).

The pattern of arrival times of vehicle trips shows that vehicles were parked at home for about 10 hours overnight, which was sufficient to recharge the EVs. More than 86% of weekday trips and 88% of weekend day trips would recharge in less than 3 hours.

Overnight charging will have minimal impact on the grid despite an increase in the overall electricity consumption. Overnight charging by the amount required to replenish daily commutes is easily coordinated and managed, similar to how heating of off-peak hot water systems are currently co­ordinated.

When considering EV usage, and hence the impact on the electricity grid, both the time and location of the vehicles must be taken into consideration. EVs have the potential to reduce power quality if a large proportion of EV charging is rapid or unscheduled.

We have calculated the aggregated rise in electric energy demand for 35 local government areas (LGA) in NSW based on EV recharging after a round trip commute for both an average weekday and weekend day. Our analysis indicated that energy demand would increase by more than 10% of current electric energy consumption (with 18% being maximum) in nine of the 35 LGAs. Based on our analysis of 35 LGAs it could be inferred that if 82% of the weekday and 81% of the weekend vehicle commute trips were conducted using commonly available EVs, there would be an 8% increase in electric energy demand, on average, compared with actual electric energy consumption.

It’s worth mentioning that the actual average energy consumption is usually 40–60% of the installed capacity. Our analysis indicated that in most LGAs the existing electricity infrastructure is (on average) adequate to meet the expected charging needs of the EVs. The results also showed that the rise in demand for electric energy is likely to be higher in regions where population density is low and vice-versa (with a few exceptions).

Alternatively, the batteries in EVs can serve as energy storage systems. We found that the energy stored in EV batteries is more than sufficient to meet the additional electricity demand. Thus, EV batteries can not only charge from grid to vehicle but also inject energy from vehicle to grid (V2G). Nissan, energy multinational Enel and V2G company NUUVE are currently running commercial trials of V2G technology in Denmark and the UK.

The electric energy from EV batteries could also be used to exchange energy from vehicle to vehicle (V2V), thus assisting long distance commutes and compensating for the intermittent nature of renewable energy sources. For example, electric energy from the sun is only available during the daytime, and any additional energy from solar panels that could not be used on-site is either wasted or transferred to the grid. This additional energy can be stored in EV batteries parked on-site during the day.

We also mapped the spatio-temporal distribution of the average state of charge of vehicles. This revealed that the concentration of energy available for EVs is higher in densely populated areas. At 9 am most cars will leave for work, but if all those cars recharged to make up for the energy they discharged during travel, the energy required to recharge would be far less than the energy available from the EV pool. Algorithms are being developed to enable optimal utilisation of available energy resources, including solar, wind, fuel cells and EV battery storages. Such systems need to be established so that irregular vehicle charging and usage needs are met.

Global sales of EVs nearly quadrupled between 2014 and 2017, and almost two million EVs expected to be sold this year. This growth trend in is likely to accelerate due to the declining cost of batteries, increasing battery energy densities, and the increasing viability of home storage and charging options. Furthermore, the purchase price of EVs are expected to reach price-party with internal combustion engine vehicles around 2025. Given the substantially cheaper running costs of EVs, demand is expected to increase to the point where half the world’s car sales are expected to be for EVs by 2027 (https://goo.gl/R8kuNi).

We found that fully electric mid-range EVs could service 88% of daily commutes in major NSW regions. Furthermore, as long as the vehicles are charged daily and the charging is scheduled, the electricity grid should, on average, be able to cope with the additional demand. However, we cannot rule out that some localities may experience substantial loads with a negative impact on power quality.

Our analysis showed that the energy available from EV batteries is not only sufficient to meet the additional energy demand but also has the potential for V2G and V2V to have a significant positive impact on the grid by reducing energy use at peak times and offsetting variability of renewable energy resources. Our results therefore demonstrated the potential for wide-scale adoption of EVs in Australia.


Sohaib Rafique is a PhD student and Graham Town (graham.town@mq.edu.au) is Professor in the School of Engineering at Macquarie University.