Global investment in clean energy capacity expanded by 5 percent in 2011 to $260 billion. The growth comes despite the considerable drag from economic crisis in Europe and weak growth in the U.S.

The new research, compiled by Bloomberg New Energy Finance, was announced yesterday in New York at United Nations headquarters building, site of the Investor Summit on Climate Risk & Energy Solutions.

Up from $247 billion in 2010, last year's rise in spending on clean energy capacity offered reasons for optimism along with rising cause for concern. Note that this data includes spending on renewable energy technologies, but not advanced coal, nuclear or conventional big hydro.

The good news: Spending has quintupled in the past seven years, with outlays for solar power leading the expansion -- soaring by 36 percent to $137.5 billion during 2011.

And in the global horse race for green energy leadership, the U.S. regained its lead over China for the first time since 2008. U.S. spending hit a record, at $55.4 billion, up 35 percent, as investment in China rose by just one percent to $48.9 billion.

"The performance of solar is even more remarkable when you consider that the price of photovoltaic modules fell by close to 50 percent during 2011, and now stands 75 percent lower than three years ago, in mid-2008," Michael Liebreich, chief executive of Bloomberg New Energy Finance, said in a statement.

But lurking behind those big numbers are worries that U.S.' resurgence in 2011 may turn out to be the lunge that precedes a stumble. Spending in the U.S. was buoyed by a big surge of stimulus funds, originally set aside in the 2008 stimulus bill, that will taper off sharply in the year ahead.

"The U.S. jumped back into the lead in clean energy investment last year," Liebreich added. "However before anyone in Washington celebrates too much, the U.S. figure was achieved thanks in large part to support initiatives which have now expired."

As those incentives shrink, the global wind and solar industries are set to consolidate. Supply in both the wind and solar markets exceeds demand significantly, leading to bankruptcies and pullbacks. In the solar space, Solyndra is the most visible, but one of a growing number of startups that crashed under pressure from falling solar cell prices.

Dominated by mature conglomerates such as GE and Siemens, the outlook for wind is dimmer than for solar: Global investment fell by 17 percent to $74.9 billion. To try to compete with lower-cost Chinese manufacturers Vestas, the world's largest producer of turbines, yesterday announced it was shuttering a factory, and cutting 2,335 jobs, or about 10 percent of its staff.

Of course, oversupply means lower-cost energy systems for buyers. And even as subsidies are declining in the wealthy West, non-financial policy support remains resilient. In the U.S., renewable portfolio standards in 29 U.S. states represent a $400 billion investment opportunity, as other states finalize similar commitments.

Meanwhile, stepped up subsidies in emerging markets -- especially Brazil and India -- are upgrading energy services to virgin markets. Spending in these areas will replace some of the investment that is retreating in North America and Europe, said Ethan Zindler, Head of Policy Analysis at Bloomberg New Energy Finance.

Financial innovation remains a weak spot, however, especially in the U.S., where clever capital solutions could help fill the gap left by shrinking federal subsidies. Given the multi-billion dollar scale of many clean-energy investment projects, there's been a dearth of the sorts of high-efficiency financial instruments that can bundle up batches of projects, and finance them at low cost in public markets, Zindler added.

There have been some promising precedents -- such as PACE loans and solar lease-to-own programs. But nothing has yet emerged to substitute for large-scale, multi-billion federal subsidy programs. Proposals such as green bonds or a national infrastructure bank are stuck in the starting gate, said Zindler.

Institutional investors, meanwhile, are hungry for more diversified ways to put money into greener projects. "Investors need diversified, sustainable strategies that maximize risk-adjusted returns in a volatile investment environment," said Ceres head Mindy Lubber, which directs the Investor Network on Climate Risk, a network of 100 institutional investors with collective assets totaling about $10 trillion.

The retreat of subsidies may enhance the competitiveness of products and strategies already honed to deliver higher efficiency and energy savings, said Marc Vachon, vice president of ecomagination at GE. He added that GE's ecomagination product line is growing at twice the rate of the rest of the company, having already generated $85 billion in revenues to date.