The solar power industry is booming and that growth helps the world meet its climate goals by replacing fossil fuels. But an emerging problem in the U.S. solar business that installs panels on homes risks slowing the effort to cut the country’s emissions.

Customer complaints against the country’s residential rooftop solar industry have increased dramatically in recent years. One-star ratings on Solar Reviews increased more than 1,000 percent since 2018. Across the country, prosecutors are investigating high-pressure sales tactics and misleading financing arrangements. Some customers say they were victims of fraud and forgery. This…