Microsoft Corp co-founder and Chairman Bill Gates said that expanding nuclear power and making it safer was the most economic way to ward off climate change.

In an address to the IHS CERAWeek conference of international energy company executives, he said safe and reliable reactors were the best option and dismissed wind and solar energy as less practical.

“The only way to solve the climate challenge is have some source of energy that’s economic,” Gates told the gathering on Thursday evening.

Expanding the nuclear option, he said, outweighed any notion of wind or solar energy as large-scale storage systems for both remained unproven.

“You can site it where the power is needed,” Gates said. “Unless you think there is a miracle hidden in storage.”

Gates is a primary investor in Terra Power, a company working to create an improved, safer reactor intended to reduce waste and avoid creation of any fuel that could be used in nuclear weapons.

But technology, he said, had to meet new, worldwide demands for safety and reliability arising from the meltdowns at Japan’s Fukushima Daiichi nuclear plant after the March 2011 earthquake and tsunami - the worst civil nuclear accident in 25 years.

“Post-Fukushima, people are expecting to take some of the instabilities out of the design of nuclear reactors,” Gates said.

He also called on the U.S. Energy Department to increase its investment in energy technology research and development.

“We should put a lot more into innovation. When we get a carbon tax we should put some of that into innovation,” he said, without elaborating.

According to the U.S. Congressional Budget Office, the U.S. Energy Department’s investment in research and development in 2012 was $3.4 billion, down from $10 billion (in 2011 dollars) in 1980.