Tesla Chief Executive Elon Musk stands on the podium as he attends a forum on startups in Hong Kong Reuters/Bobby Yip Hydrogen-powered cars have come back into focus as more automakers explore cleaner, more efficient alternatives to gas.

Honda will begin sellings its hydrogen-powered sedan, the Honda Clarity, in California by the end of 2016. Toyota is gearing up production of its own hydrogen-powered car, the Toyota Mirai.

And they aren't the only automakers exploring fuel cell technology.

But Tesla CEO Elon Musk thinks hydrogen-powered cars are a bad move. Specifically, he thinks the technology is "incredibly dumb."

"If you're going to pick an energy storage mechanism, hydrogen is an incredibly dumb one to pick — you should just pick methane, that's much much easier, or propane," Musk said.

Musk made those remarks during the Automotive World News Congress in Detroit in early 2015. He said the issue with hydrogen is how difficult it is to produce.

"I just think that they're extremely silly... it's just very difficult to make hydrogen and store it and use it in a car," Musk said at the time. "If you, say, took a solar panel and use that... to just charge a battery pack directly, compared to split water, take hydrogen, dump oxygen, compress hydrogen... it is about half the efficiency."

The debate over whether hydrogen-powered cars or battery-powered ones are better has valid points on both sides, and you can read more about that here.

But if you'd like to hear Musk's thoughts, watch the video below starting at the 10:20 mark: