The WilderHill New Energy Global Innovation Index, which tracks 94 clean-energy stocks, gained 4.8 percent since the start of the year after a worldwide slump in the solar industry pulled it down in 2012.

The NEX, as it’s called, rose 1.8 percent to $125.73 at 3:10 p.m. in New York Thursday, after a 2.9 percent increase Wednesday. It lost 5.5 percent of its market value in 2012, while the NYSE Arca Oil Index rose 1 percent and the Standard & Poor’s 500 Index climbed 13 percent.

Last year was marked by a risk-averse market, and speculative investments in renewable energy were “inherently out of favor,” said Pavel Molchanov, an analyst at Raymond James & Associates Inc. in Houston. Those sentiments are shifting, and the index may rise in 2013, he said.

“When risk appetite is stronger, such as the past two days, the stocks tend to act much better,” Molchanov said Thursday in an e-mail.

“If the macroeconomic situation gets better, which seems to be happening,” investors may show more interest in renewable energy and clean technology.

Falling Prices

Low margins and falling prices for solar companies, the end of some national stimulus programs and questions about the future of other incentives all slowed demand for renewable energy last year, dragging down many NEX companies, said Joseph Salvatore, an analyst at Bloomberg New Energy Finance in New York. The same issues may affect shares this year, he said.

“There is still a large degree of uncertainty out there, especially in Europe with what will happen with the evolution of renewable-energy policy,” Salvatore said in an interview Wednesday.

There were some bright spots among renewable energy and clean-technology companies last year. The smart-grid system maker Itron Inc. gained 25 percent and Tesla Motors Inc., which makes electric cars, increased 19 percent.

Those were the exceptions, Molchanov said. “The vast majority were down and solars in particular were down.”

Solar manufacturers Suntech Power Holdings Co., Trina Solar Ltd. and Yingli Green Energy Holding Co. all closed the year down more than 30 percent. Solar panel prices have plunged 60 percent since the start of 2011.

Some of the pessimism is evaporating with the Jan. 1 extension of the U.S. production tax credit that was sought by wind-energy companies, and “optimism that the solar market is at the bottom of the trough,” Salvatore said.

This year will be “a stock picker’s market,” Molchanov said. “There were be some great winners and some terrible losers.”