The experimental program — developed by BMW and Pacific Gas and Electric Co. — will test one way to ensure that electric vehicles don’t burden the grid as their popularity slowly grows. If it works well, it could lead to a future in which EV drivers get paid for helping to maintain the grid’s stability. And that money could, in turn, offset the price of electric cars, which still cost substantially more than their gasoline-burning brethren. “If they will provide us grid service, we can provide them some incentives that will help lower the cost of these vehicles,” said James Ellis, PG&E’s director of electric vehicle programs.