Shares of Clean Energy Fuels Corp. plunged 17% in morning trade Thursday, putting them on track for the biggest one-day loss in 20 months, after Raymond James analyst Pavel Molchanov turned bearish on the natural gas company, citing concerns over valuation after the "excessive euphoria" over the equity investment made by Total S.A. The stock had rocketed 94% since the companies announced a strategic partnership and equity investment before the May 10 open. Molchanov cut his rating to underperform from market perform, saying the rally has pushed the valuation to levels well above its peers, and that's assuming Congress revives the tax credit for natural gas fuels, which Molchanov said was far from certain. The stock has run up 86% year to date, while the S&P 500 has gained 1.9%. Separately, Molchanov downgraded NextEra Energy Partners LP to market perform from outperform, sending the stock down 2.1%. He also upgraded Advanced Energy Industries Inc. to outperform from market perform, helping send the stock up 4.2%, to bounce off Tuesday's 18-month closing low.