After coming under significant pressure earlier this week, the Guggenheim Solar ETF (NYSEArca: TAN) and the Market Vectors Solar Energy ETF (NYSEArca: KWT) rebounded nicely Thursday, closing higher by 2.7% and 3.4%, respectively.

TAN may be able to extend Thursday’s gains after Guggenheim announced it is eliminating Hanergy Thin Film Power Group from the ETF. MAC Solar, the provider for TAN’s underlying index, will boot Hanergy Thin Film at the close on the date the embattled Chinese solar firm resumes trading, according to Investor’s Business Daily.

Shares of Hanergy plunged 47% in Hong Kong trading Wednesday before being halted. Controversy has been swirling around Hanergy, including the fact that its closely held parent company accounted for nearly two-thirds of last year’s revenue. [Reason for Caution With Solar ETFs]

As of May 19, Hanergy was TAN’s largest holding at a weight of 11.98%. That weight has since tumbled to 5.82%, making Hanergy TAN’s fifth-largest holding. Hanergy was almost 8.4% of KWT’s weight on that day, enough to make the stock the ETF’s second-largest holding, but that weight has since dipped to 4.66%, making Hanergy KWT’s seventh-largest holding.

Top-heavy sector and industry ETFs are not uncommon. Most cap-weighted technology ETFs feature allocations to Apple (NasdaqGS: AAPL) that are often 500 basis points or more above the funds’ second-largest holdings. Cap-weighted energy ETFs often sport massive combined weights to Exxon Mobil (NYSE: XOM) and Chevron (NYSE: CVX). [Hanergy Punishes Solar ETFs]

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