Shares were down 6.9% at $185.99 in after-market trade.
Residential installations have fallen sharply this year, and utility-scale projects face challenges including long waits to connect to the grid and a shortage of skilled labor.
The company lowered its full-year 2024 sales forecast to between $4.10 billion and $4.25 billion, from its previous expectation of between $4.4 billion to $4.6 billion.
The company reported a sequential decline in quarterly sales, hurt by a decrease in the volume of megawatt (MW) sold.
However, the company reported a 16.6% rise in net profit for the quarter ended Sept. 30, at $313 million, or $2.91 per share, compared with a year earlier.
The Biden administration imposed new tariffs on foreign-made solar modules in May, benefiting U.S. companies like First Solar that produce domestically.
