Will EVs disrupt the power grid?

On a quiet suburban residential street in Ostfildern, a town a few miles southeast of Stuttgart, 10 households are participating in an experiment that will help shape the future of e-mobility in Germany.

Netze BW, a company that maintains and runs part of the electricity grid in the southern German state of Baden-Württemberg, is running the experiment, which is called E-Mobility Alley.

The point of the 18-month experiment is to find out what happens when all the households on a typical German street, all of them on the same electricity circuit, drive electric cars. It's a model of the future. How do e-car recharging patterns typically unfold over the course of a week? When do peak loads occur? What kinds of battery storage solutions might be useful for stabilizing grid supply and demand?

A 22-kW peak-capacity EV recharging unit was installed in a wall box at each house, and each household was given an e-car for the test's duration, with five VW e-Golf, two BMW i3, and three Renault Zoe e-cars in the mix. In addition, there's a Tesla Model S 75D, which each household will drive for three weeks.

Engineers rub their hands in glee

Martin Braun is head of Electricity Grid Planning and Operation at Fraunhofer IEE, the Fraunhofer Institute for Energy Economics and Energy System Technology in Kassel. His team provides grid modeling studies, consulting, measurement, and testing services to the grid industry, and it's helping Netze BW with the E-Mobility Alley experiment.

"We're actively working on how future e-mobility demand can be cost-effectively integrated into electricity grids, and a stable, reliable electricity supply ensured," Braun told DW, referring to a time, just a few years from now, when first millions, then tens of millions of electric cars and trucks are supposed to be rolling quietly along Germany's roads.

What will happen when commuters returning home in the evening all plug in their EVs (electric vehicles) at more or less the same time? Could the sudden spike in power demand cause overloads, leading local transformers in villages or suburbs to overheat and blow out?

The engineers are confident

The short answer, according to both Braun and professor Oliver Brückl of the East Bavarian Technical University in Regensburg, is "no," everything will be fine — as long as appropriate grid upgrades are made in time.

"Our studies show that in many local electricity distribution grids, no adjustments will be required," Braun told DW.

"They're strong enough already. About 80% of the required upgrades for the state of Hesse will be needed in a subset comprising about 20% of local, low-voltage grids." Those are the neighborhood grids that deliver electricity to end users.

Oliver Brückl is director of a research project called "neos," whose mission is to figure out exactly what upgrades will be necessary to ensure a stable and secure grid in Bavaria, in a future buzzing with ever more EVs.

Braun and Brückl both emphasized that e-cars weren't the only reason grid upgrades were necessary. On the demand side, local grids will also have to integrate a rising number of electrically powered heat pumps and electric heaters, which will increasingly be used to substitute for natural gas fired heating of buildings.

On the supply side, grids will have to deal with the fact that the proportion of Germany's electricity supply derived from variable solar and wind power is rising year on year, and will eventually go to nearly 100%.

They're not worried. "The grid operators already have technical solutions in hand; the toolkit is extensive and it keeps getting bigger and better," Brückl said. "A lot has happened in this area over the past few years."

But what will it all cost? Will the required grid upgrades be affordable?

The price is right

"For Germany as a whole, we've estimated a cost of €20 billion [$21.9 billion] to €25 billion for the upgrades needed," Brückl said. "That money will be spent over a number of years, and in relation to the total volume of end-user electricity sales" — €60 to €70 billion a year — "it's not an unreasonable amount of money."

A study by Braun's institute estimated that in Hesse the grid upgrade cost will amount to about 1 euro per month per resident, and it will be offset by declining electricity costs in coming years.

Brückl cited automated digital load-balancing systems, responding to differential electricity prices designed to incentivize EV owners to charge their cars when demand is lower — something that can be looked after automatically by software built into recharging equipment as one of the key tools for adapting the grid to an e-mobility future.

On the hardware side, larger-diameter electricity cables will be required in local grids in some cases, as well as local power transformers that respond dynamically to changes in load. Such transformers have been commercially available for the past three years, Brückl said, and further improvements to their design can be expected.

Work continues

Fraunhofer IEE, Braun's employer, is now working on a project called Charging Infrastructure 2.0, in cooperation with grid operating companies, equipment suppliers, and carmaker Volkswagen, which has recently shifted into high gear in terms of its e-car model rollout.

The project's goal is to develop engineering solutions for the cost-effective integration of the coming e-mobility surge, including development of an innovative charging system with an optimal combination of network compatibility and user-friendly functionality.

The participation of carmakers is key, because "the charging converters built into EVs can be configured so that cars can act as network stabilizers," Braun said. Such e-cars can adjust their recharging rates to dynamically match the fluctuating availability of power in the grid.

Two things became apparent in DW's interviews with Braun and Brückl: First, Germany's engineering community is confident it can cost-effectively deal with the grid upgrades needed. And second, they're enjoying the challenge. It's just the kind of complex systems with multiple moving parts involved that gets engineers up in the morning.