First Solar and Enphase Energy finished Friday's trading among the top three gainers on the S&P 500, +11% and +8.1% respectively, after the Trump administration released new guidance on eligibility requirements for federal tax credits that were less punitive than the industry had feared.

Residential solar systems will continue to qualify under prior guidance and the new rules will not be applied retroactively, and larger projects must meet a physical construction standard but will still have four years to complete their developments.

Sunrun, the biggest U.S. residential solar installer, closed +32.8% after soaring as much as 42%, home solar equipment provider SolarEdge ended +17.1% after rising as much as 28%, top large-scale solar and wind developer NextEra finished +4.4%.

Other big movers included Array Technologies Inc. +25.3%, FTC Solar, Inc. +17.7%, Shoals Technologies Group +13.1%, NEXTracker Inc +12.2%, Canadian Solar +7.4%, Fluence Energy, Inc. +5.1%, AES Corp +2.8%, Maxeon Solar Technologies Ltd +1.5%.

More than 2,500 announced wind and solar projects - with a combined generating capacity equivalent to 383 nuclear reactors - that have yet to begin construction could be affected by the decision, according to data from Bloomberg.

"What it is going to do is reward sophisticated companies that have projects that are further along in their development. The companies that are going to suffer are the smaller medium sized developers that aren’t going to be able to meet this time frame," Advanced Energy Advisors CEO Rhone Resch told Bloomberg.