By Charlie Zhu

HONG KONG, April 19 (Reuters) - The green energy potential of thin-film solar panels has propelled Li Hejun to the top of China's rich-list, but his Hanergy Holdings has yet to prove it can turn impressive laboratory research into commercially successful products.

Hanergy Thin Film Power, a Hong Kong-listed unit, has seen its value soar six-fold in the past year to $37 billion - more than its nearest two dozen rivals combined.

Hanergy and some analysts say the meteoric rise has been fuelled in part by Beijing's efforts to promote solar energy. But some industry insiders say it has more to do with the firm's own bullish proclamations on thin-film solar panels and the competitiveness of its products.

Some experts, including a Hanergy sales executive, say the firm's products are not efficient or cheap enough and are far from ready to take any major market share from conventional panels made with crystalline silicons.

"There's no real reason to switch to thin film unless the learning curve for thin film goes steeper," Christoph Flink, a solar specialist and senior director of JA Solar, a major U.S.-listed Chinese maker of conventional panels, told Reuters. "But I don't see it happening," he said, echoing views of a number of experts interviewed by Reuters in the past month.

Thin-film solar panels account for only about a tenth of the global solar panel industry, and many non-Chinese thin-film panel makers have gone out of business due to the technical challenges and sharp falls in silicon prices. U.S.-based First Solar and Japan's Solar Frontier K.K. are among few big solar companies still pursuing thin-film technology, and are widely regarded as industry leaders.

CONVERSION RATE

Light and flexible thin-film panels are potentially adaptable to a wide range of applications, including rooftop power generation, and for charging cars and mobile phones. But they have failed to make big inroads into solar markets partly because their efficiency in converting sunlight into electricity, at up to around 15 percent in utility projects, lags the 17-18 percent performance of traditional units.

Still, the flamboyant billionaire Li remains confident that Hanergy has mastered the technology. Sporting a pinstripe suit and gold tie, Li last month told the annual meeting of the Chinese People's Political Consultative Conference (CPPCC) in Beijing that Hanergy was ready for a mass roll-out of its products.

"Thin film technology is already mature. The core technology of portable energy is thin-film," Li said, noting Hanergy panels had topped 30 percent conversion efficiency.