When SolarCity, the fast-growing provider of rooftop solar electricity systems, announced last year that it would begin making its own equipment, executives said they would focus on creating high-efficiency panels in an effort to reduce the cost of the electricity they sell. They announced on Friday that they had done just that, with a panel that converts more of the sun’s energy into electricity than competing products.

The company plans to start making the panel — whose output has been measured at more than 22 percent — this month at a small plant in Silicon Valley, said Peter Rive, a founder, but will eventually produce it at the enormous factory it is building in Buffalo.

The move into manufacturing, a business that has proved deadly for many other upstart American solar companies, came with the acquisition of a start-up, Silevo, and is intended to help the company compete with conventional energy sources once generous federal subsidies begin to phase out at the end of next year.

Although 22 percent may not seem like a tremendous level of efficiency, the breakthrough for SolarCity is that it can produce the panels at a lower cost than it pays to buy standard models but get more electricity out of the same square footage, Mr. Rive said.