Delegates listen as Christiana Figueres, the executive secretary of the U.N. Framework Convention on Climate Change speaks during the opening session of the Climate Summit on November 30, 2015 in Paris, France.
Delegates listen as Christiana Figueres, the executive secretary of the U.N. Framework Convention on Climate Change speaks during the opening session of the Climate Summit on November 30, 2015 in Paris, France. - 
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On the first day of the 2015 climate summit in Paris, nearly 50 heads of state and billionaire entrepreneurs gathered to announce a joint push for an energy breakthrough. They pledged tens of billions of dollars in investments to push low-carbon technologies out of the lab and into the market.

The investments target an early stage in energy technologies. The stage where money runs out.

"They can get lost in what's called the Valley of Death," said Jessika Trancik of the MIT Institute for Data Systems and Society, "which is basically this valley between public sector investment and research, and uptake by the private sector."

So to build a bridge across the valley, 20 governments on one side of that valley pledged to double energy investments. And on the other side, private investors with names like Gates and Branson promised to put in their money.

The challenge is, with clean energy, the valley is deep. Dan Reicher at Stanford's Center for Energy Policy and Finance used to work at Google, where new energy teams competed for money against smartphone app developers.

"The folks inside the company pitching the next information technology product would often measure time frames in months and millions of dollars," Reicher said. "We'd measure ours in the energy context in decades and billions of dollars. And that's a big problem. This is not creating the next app."

Renewable energy can require expensive build-outs, like power plants. Often investment returns are long. And the competition – that is fossil fuels – is convenient and cheap. Energy game changers are not simple garage projects.

Still, the market may be changing. Renewables including solar and wind power are now cost-competitive in many markets, and demand for them is global.

"If you believe that the world of energy is changing and that it is no longer a question but an inevitability," said Ethan Zindler of Bloomberg New Energy Finance, "then these are the kinds of technologies that inevitably you are going to want to be supportive of in the long term.

This is what brings billionaires to Paris: a collective peek across the clean energy valley, and a piece of the action.

Follow Scott Tong at @tongscott