DAYTON — As many as 20,000 electric cars are expected on Miami Valley roadways in the next decade, something that could cause problems if utility companies are not prepared for the increased demand.

The vehicles plug into a socket and draw as much power as a small house or as little as a hair dryer.

Dayton Power & Light is in a good position, said director of operations Bruce Coppock, because the vehicles will arrive in other states first, so the utility can learn valuable lessons from experiences there.

The utility company has an electric-powered Chevy Equinox to test how the vehicles will tax neighborhood transformers and other equipment and is developing scenarios to accommodate them.

While the cars won’t be for sale in large numbers in Ohio for a year, in other parts of the nation, the first mass-market electric cars will roll out this month and throughout 2011. Utility companies are scrambling to upgrade transformers in parts of California, Texas and North Carolina, where the Nissan Leaf and Chevrolet Volt are expected to be in high demand. The utilities want to be certain that the extra electric draws don’t blow out power systems.