Donald Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE bashed renewable energy sources Monday night, saying solar power doesn’t work well and wind turbines kill birds.

The GOP presidential nominee has stated his preference for coal and natural gas, and has previously said that solar power is unreliable and wind turbines are unsightly and harmful to wildlife.

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“It’s so expensive,” Trump said of alternative energy at a rally in Pennsylvania.

“And honestly, it’s not working so good. I know a lot about solar. I love solar. But the payback is what, 18 years? Oh great, let me do it. Eighteen years,” he said, turning to wind power. “The wind kills all your birds. All your birds, killed. You know, the environmentalists never talk about that.”

Solar power has historically been expensive, but its costs have fallen dramatically in recent years.

The Solar Energy Industries Association estimates that the cost to install solar panels has dropped by 70 percent since 2009 to just over $2 per watt for photovoltaic technology.

The wind industry has challenged Trump’s previous statements about wildlife deaths, including his contention earlier this year that turbines kill more than a million birds a year.

The U.S. Fish and Wildlife Service estimates that wind turbines kill about 500,000 birds annually in total, much less than other bird threats like cats and buildings.

Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonBiden leads Trump by 36 points nationally among Latinos: poll Democratic super PAC to hit Trump in battleground states over coronavirus deaths Battle lines drawn on precedent in Supreme Court fight MORE has set a goal to expand the country’s solar power capacity sevenfold and generate enough renewable electricity in the United States to power every home by 2027.

At the Pennsylvania rally Monday, Trump also promised to reduce the frequency of coal mine inspections.

“I have friends that own the mines. I mean, they can’t live,” he said.

“The restrictions environmentally are so unbelievable where inspectors come two and three times a day, and they can’t afford it any longer and they’re closing all the mines. … It’s not going to happen anymore, folks. We’re going to use our heads.”