America’s rooftop solar installers are stockpiling massive volumes of panels and other equipment before a key federal tax credit for the industry starts shrinking next year.

On Tuesday, Sunrun Inc.—the nation’s largest rooftop solar installer—said it’s collecting enough equipment to help qualify 500 megawatts worth of planned installations for the full investment tax credit, which currently covers 30% of a project’s costs. For comparison, Sunrun deployed 373 megawatts in 2018.

Support is growing for an extension of renewable energy tax credits “as the single highest-impact, actionable policy opportunity to combat climate change,” Sunrun Executive Chairman Ed Fenster told analysts in a call Tuesday. But “the chance of passage in any specific moment in time is difficult.”

Sunrun isn’t the only one amassing inventories. Solar company SunPower Corp. told investors during a recent earnings call that it was sourcing enough equipment to help qualify 200 megawatts worth of projects. The company said it expects to do this again next year.

While rival Vivint Solar Inc. said it was “cautiously optimistic” that the federal government would extend the credit, the company has placed orders for 115 megawatts worth of panels that will allow it to take advantage of the full credit for some of the installations it does next year.