General Motors has installed 401 electric vehicle charging stations at its U.S. production and business facilities, the automaker has announced.

More than 20 percent of the stations use electricity generated from solar canopies to help charge employee vehicles.

The majority of the stations are located at GM’s large engineering and corporate facilities in Michigan, where employee ownership of battery-electric vehicles is growing steadily. All charge stations are available free of charge to GM employees and visitors.

In addition to workplace charging, GM has another 400 charge spots dedicated exclusively to vehicle development and testing. Chevrolet and Cadillac dealers have installed approximately 5,900 charge stations at their locations for owner use; 17 of these dealerships use solar charging canopies.