Solar cell producers and related exchange traded funds that track the sub-sector have been one of this year’s worst performers as the lower energy prices and heavy Chinese subsidies weigh on the global solar industry.

Guggenheim Solar ETF (NYSEArca: TAN) and Market Vectors Solar Energy ETF (NYSEArca: KWT) are down more than 35% year to date.

Both funds fell to new all-time lows Monday while the larger KWT saw heavy trading volume.

Solar energy made sense before the recent financial shock when oil prices were knocking on $150 and natural gas was $13. However, with energy prices falling, especially natural gas, we are thinking less about alternative energy.

“Perhaps clean energy’s biggest problem is this: because natural gas has gotten so cheap, there is no longer a financial incentive to go with renewables,” Juliet Eilperin wrote for Wired.

Austin Hatley for StreetAuthority calculates that at today’s prices, it costs about $0.04 to generate one kilowatt hour of energy from natural gas. On the other hand, it costs over $0.20 to generate a kWh from solar, $0.10 from biomass and $0.08 from wind.

Moreover, the solar industry has suffered as prices for solar cells plummeted 66% since the third quarter of 2010, reports Lou Kilzer for TribLIVE.