Tesla has blamed the previous delays on the complexity of the solar roof, which looks like a conventional roof but has solar cells inside, and the need to do intensive testing on the new product, for the delay.

While Tesla keeps working on the solar roof that it unveiled in a Hollywood event in October 2016, its conventional solar energy business continues to shrink.

Tesla installed 73 megawatts of solar energy generating capacity during the third quarter, down from 17 percent from a year ago. It was the worst quarter for solar energy deployments in at least five years, dating back to before Tesla acquired the solar energy business from SolarCity.

Tesla’s solar deployments have plunged by 38 percent during each of the last two years, and were 61 percent lower than the all-time high set in 2016.

Since then, Tesla has moved aggressively to stem losses in the solar energy business. Tesla said it now gets most of its solar sales from its own website and its network of 378 stores.

That shift has resulted in “significantly lower” customer acquisition costs, which had remained stubbornly high when the solar business was operated by SolarCity before Tesla acquired it in November 2016.