Electric vehicles recharging at home will start competing with households cooking dinner and watching TV, creating strain on existing electricity networks and forcing change to the way power is currently priced, say two new reports on the issue.

Auckland-based network company Vector warns that the sheer volume of electricity required to recharge a car with a long-distance battery at a suburban location will place a strain on existing networks and force costly upgrades once EVs become popular.

The strain is likely to be greatest in the early evening, when EV owners come home and plug in their cars to recharge, coinciding with the time of day when electricity demand peaks because households start cooking dinner, turning on heaters and lights, and using electrical devices.

The other report, by Wellington firm Concept Consulting for network owners Powerco, Orion and Unison, suggests electricity pricing will need to change to encourage EV owners to charge cars after 9pm if unnecessary network upgrade costs to cope with the new peak load are to be avoided. Author Simon Coates estimates the cost at around $4 billion in net present value terms.


Both reports also warn that the new generation of EVs, with larger batteries and far greater driving ranges, will take more than two days to fully charge from a standard wall socket. To avoid that, they predict demand will rise swiftly for fast-charging technology, which will place many times more load on local networks than socket-charging.

Concept says any such costs should be borne by EV owners rather than all electricity users, and fears the "fantastic opportunity for New Zealand, both in terms of massive gains to the environment and delivering genuinely cheaper transport services" will be frustrated by current electricity supply arrangements.

"With mass EV uptake just around the corner and greenhouse (gas) reduction targets getting ever-more urgent, there is a real-time imperative to resolving this issue", says Coates. More than 6,000 EVs are now on New Zealand roads, with registrations more than doubling in 2017. The previous government targeted 64,000 EVs by 2021 and the new administration is, if anything, more enthusiastic about encouraging EV ownership. Reducing transport emissions represents one of the country's few easy wins as it seeks to meet emissions reductions targets set for 2030.

More than 6,000 EVs are now on New Zealand roads, with registrations more than doubling in 2017. Picture / Alan Gibson
More than 6,000 EVs are now on New Zealand roads, with registrations more than doubling in 2017. Picture / Alan Gibson

There is some hope. Concept says "these financial and environment costs are avoidable with smarter, more cost-effective electricity prices that encourage EV-owners to charge their vehicles smoothly overnight" and would use technology already embedded in the software of the vehicles themselves, allowing a system similar to, but more sophisticated than, hot water 'ripple control' to be deployed to manage network constraints caused by EVs.

The Vector 'green paper' says "the potential network impacts of changing customer behaviour or battery technology are most pronounced at the street level".

"This is where electricity networks have traditionally been sized according to the number of houses on a street, with little spare capacity. The local network was not designed for, or envisaged (sic), any significant uptake of EVs and the consequential demand for charging at home."

That created a risk not only of higher electricity prices, but also of being unable to rely on charging an EV at home.

However, use of smart metering, dynamic charging and carefully considering where to locate charging infrastructure also held out the prospect of benefits for EV owners, including being able to sell electricity from their car batteries back into the grid when market conditions favoured that.


While the average light vehicle travels only 29kms daily in New Zealand, EVs would theoretically only need a charge every three days or so, but 'range anxiety' and convenience were expected to make owners keen to keep their batteries topped up, the Vector paper says.