Chinese solar-power equipment manufacturer Hanergy and the Audi unit of German automaker Volkswagen AG have unveiled plans to cooperatively develop a car energized by a solar film roof. In signing a memorandum of understanding at Hanergy’s headquarters in Beijing, the companies said their venture will mark the first step toward long-term cooperation in research and development, Caixin reports. Initially, the solar roof is expected to generate enough energy to power peripheral functions such air conditioning and seat heaters. The aim will be to improve the vehicle’s gas mileage. Later, the solar system could be improved to power the car’s battery. A prototype car with an integrated roof is expected to be available by the end of the year, the companies said. They did not offer a timetable for possible mass production, nor disclose the project’s financial details.