The solar industry is facing a looming shortage of photovoltaic panels, reversing a two-year slump triggered by a global glut.

The oversupply pushed prices through the floor, making solar power more competitive and driving up demand. It also dragged dozens of manufacturers into bankruptcy, and slowed capital investment at the survivors. With installations expected to swell as much as 29 percent this year, executives are bracing for the first shortfall since 2006.