The lesson, one previously taught by Apple, is that so goes a stock that accounts for 10%, 15% or more of an ETF, so goes that ETF. [Apple’s Rise not Luring ETF Investors]

With controversy starting to swirl around Hanergy Thin Film, solar investors could be forced to relearn that lesson the hard way. The stock plunged 8.5% during Asian trading Friday, leading to TAN’s heavy volume loss of 2.9% during Friday’s U.S. session.

“Questions have been circling in recent months over Hanergy’s business. Roughly 62% of last year’s sales were made to its privately held parent company, Hanergy Holding Group, according to The Wall Street Journal, Barron’s reports.

Guggenheim Solar ETF