Plug-in electric vehicles (PEV) may not come fast enough to reach President’s Obama’s vision of One Million PEVs in the US by 2015, but they are coming. As of November 30 2013 accumulated since 2010 158 600 PEVs have been sold.  It is an impressive number but still just a fraction of the over 250 million registered passenger cars in the US.

At present numbers the impact of the PEVs on the electric grid is minimal except for some very local issues. However, it may not take long until the impact can be significant. An interesting indication of the potential growth of PEVs may be Norway, which has become a world leader in adopting PEVs. By the end of 2012 3.1 % of the registered passenger cars were PEVs. If the same adoption rate would happen here, there would be 7.7 million PEVs.

The reasons for the high adoption rate in Norway are several, e g high government subsidies, high gasoline prices, low electricity prices (predominantly by hydro power) and strong public environmental awareness. But even if we would not see the same adoption rate here, it is a fair guess that in 5 – 10 years there could be well over a million PEVs.

At 1 million PEVs the impact on the electric grid is still small, but not insignificant. If the average PEV has a 20 kWh battery, then 1 million of them will need 20 GWh to be fully charged!

Whether this amount of energy will be a blessing or curse for the electric grid will depend on when (at what time of the day) and how fast the charging will be.

For the sake of illustration one extreme would be if all of the 1 million PEVs have a fast charge in 30 minutes at the same time in the middle of the day. It would require 40 GW of power, which is almost as much as the net summer power generation capacity in Pennsylvania! 40 GW of power would not be available without a substantial build out of new power plants and most likely reinforcements of the transmission and distribution system. This scenario would be the “curse scenario”.

On the other hand if all the 1 million PEVs would recharge between 9 p m and 6 a m, it would only require 2.2 GW of power. During the night that amount of power is available without the need for any new power plants. Further allowing 9 hours for the charging would also enable the grid operator to use the fleet of cars for ancillary services such as grid balancing and frequency control. This scenario would be the “blessing scenario”, also providing the generators with an additional revenue stream for low extra costs.

The examples above are the polarized extremes. Not all cars will need to be fully recharged every day. Not all cars will demand or need a fast charge at the same time. Not all cars will be available for the 9 hour night time charge. Reality will be somewhere between the extremes. Nevertheless, it highlights that the difference can be most significant and it makes a lot of sense to early structure price/rate designs to stimulate desired behavior.  Nothing wrong in having a fast charge 2 p m on hot August afternoon, but it should reasonably cost more than having the car plugged in between 9 p m and 6 a m to be charged and providing ancillary services to the grid.