In 2016, Tesla CEO Elon Musk unveiled one of the innovative products for which he’s become famous: roof tiles that incorporate solar panels. The resulting solar roof, as Musk called it, would be beautiful, environmentally beneficial—and cheaper than a conventional roof with separate solar panels, he said. That summer, Musk published a second “master plan” for Tesla on the internet that listed the solar roof among his top priorities, saying it would “accelerate a sustainable future.”

Almost seven years later, Tesla has realized little of Musk’s vision. The roof has proved difficult to manufacture and expensive to install, topping $100,000 for some customers—more than five times the cost of covering the same roof with conventional solar panels. Tesla increasingly markets the roof as a luxury product. Despite the high costs, the company still loses money on the roofs, and executives are discussing raising the price, according to a person close to the project.