The earnings surprised Wall Street, which had forecast a loss.
SunRun's earnings fell to $24.1 million, or 11 cents a share, from $37.4 million, or 28 cents a share, in the year-earlier quarter.
Revenue more than doubled to $438.7 million from $209.7 million.
Analysts surveyed by FactSet had forecast a loss of 5 cents a share on revenue of $413.7 million.
Shares of the San Francisco company at last check fell 2.7% to $56.17.
SunRun's customer count topped 600,000. As of Sept. 30, SunRun had 630,441 customers, including 545,727 subscribers.
“The Sunrun team continues to execute well, delivering robust growth in our customer base while also delivering a strong improvement in our customer margins during Q3, despite a dynamic supply chain and operating environment,” Chief Financial Officer Tom vonReichbauer said in a statement.
SunRun designs, develops, installs, sells and maintains residential solar energy systems.
By the end of 2021 SunRun expects cost synergies derived from the acquisition of Vivint Solar to total $120 million. SunRun acquired Vivint Solar in July 2020 and closed the transaction in October last year.
The company expects solar energy capacity installed growth to be 30% for full-year 2021.