Can prime-time charging of EVs reduce smart grid crunch?

December 23, 2015 // By Paul Buckley
Researchers at the Norwegian University of Science and Technology (NTNU) are helping to develop smart grid solutions that aim to ease the crunch caused by powering our transportation with electricity.

When people with EVs come home from work in the afternoon, they plug in their cars to charge them. That results in an extra peak in electricity consumption in the afternoon.

“We’re moving towards a different kind of power use,” suggested Professor Olav B. Fosso, professor and director of the Energy strategic research area at the Norwegian University of Science and Technology (NTNU).

This peak may eventually become a major challenge for the electrical grid.

“We could have big voltage problems, with limited transmission capacity within the distribution system,” explained Fosso.

Capacity could also become a problem. Large variations in consumption throughout the day are challenging. Electrical power is perishable which means it is an advantage to have relatively stable power use over a 24-hour period. Renewable energy from the wind and sun has to be used immediately.

Fosso admits Norway is lucky to be able to regulate its hydropower.  Water reservoirs allow adjustments in the power supply, but few countries have that ability, and even in Norway high consumption at certain times of the day poses a challenge.

Afternoon charging of electric cars is not a problem — yet. But the orders for electric cars in Norway show that growth will not stop with the almost 75,000 EVs already on the road, including hybrids.

“Nothing suggests that this development won’t continue,” said Fosso.

Cars have different charging power and storage capacities. Storage capacity is related to the car’s range. Mitsubishi’s capacity is around 16 kWh, while the Nissan Leaf has a capacity of around 20 kWh and Tesla, 85 kWh. Battery size determines the charging time for a given amperage, with typical charging efficiency ranging from 4-8 kW. Home chargers provide long charging times, but that may become problematic when a lot of people charge their cars at the same time in residential areas. Quick charger installations require a higher current feed and thus a stronger electrical grid.

Fast chargers of around 20 kW are now available for home use in the United States. If this type of rapid charger becomes more common in Norway, so will problems.

Afternoon peaks in power use are common, because people come home and turn on heaters and appliances. But this peak will also be increased when people come home and plug in their EVs.

That is when people have to get smart in how they use the power. A Smart Grid - which uses new technology to better leverage the electrical grid - will likely be an essential part of the solution.

NTNU’s Faculty of Information Technology, Mathematics and Electrical Engineering (IME) is involved in developing a Smart Grid in Norway and its research will have a direct effect on consumers' electricity bills.

At the moment, when consumers get an electricity bill, they pay it and probably do not think about it again, since they might have used the power they have paid for several months previously.

But a Smart Grid gives consumers the potential to save both energy and money. For instance, you can adjust your consumption so some of it happens when electricity is cheaper. The goal is to be able to see when the price is at its lowest.

“Then you’ll notice a difference immediately,” said Fosso, who says he thinks this feature will make it easier to save, too.

If electricity is much cheaper at 10 pm, maybe you’ll time your car charging for then instead. Or maybe you’ll wait a few hours to turn on the washing machine.