Prime-time charging of EVs could cause power crunch

December 22, 2015

By eeNews Europe

Power Management Batteries / Power Supplies

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, above and beyond the usual peaks caused by people coming home and turning on heaters and appliances.

"We’re moving towards a different kind of power use," says 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. According to Fosso, "We could have big voltage problems, with limited transmission capacity within the distribution system.

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," says 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.

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," says Fosso, who says he thinks this feature will make it easier to save, too.

If electricity is much cheaper at 10 PM, maybe consumers will time their car charging for then instead. Or maybe they will wait a few hours to turn on the washing machine.

Developing a smart grid is a task with many variables. In the future, private households will produce more of their own electricity, which complicates the picture further. Then it will be all the more important for the power grid to be used more efficiently.

There is not much that needs to be done to reduce consumption. Preliminary experiments show that a smart grid helps save around 10% on energy costs, and reduce peaks loads by around 15%.

"One kWh saved is as good as one kWh produced. We need to bring the end users on board," says Fosso.

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