What happened 

Shares of clean energy companies Bloom Energy (NYSE:BE) and FuelCell Energy (NASDAQ:FCEL) jumped as much as 8.7% and 15.8%, respectively, as investors bid up renewable energy stocks on Monday. Shares closed the day up 5.7% and 11.7%, respectively. 

So what

Neither company was connected to any specific news that came out on Monday, but there was a lot of movement in the energy sector overall. West Texas Intermediate crude oil traded 2.9% higher and Henry Hub natural gas prices rose a whopping 15.6% on the day. Investors were betting that fuel demand will keep rising despite a growing outbreak of COVID-19, and that has pushed energy prices higher overall.

Dice with fossil being flipped to H2, followed by dice spelling fuel.

Image source: Getty Images.

Oil is often seen as a proxy for energy stocks, but it's really natural gas that investors should be looking at here. It's the leading fuel source for electricity generating, and that's where Bloom Energy and FuelCell Energy are competing. 

Now what

This was unquestionably a speculative day for investors, but it will be worth watching what fossil fuel prices do from here. Natural gas has been beaten up in 2020, which has made it more difficult for cleaner fuel companies to compete. But if prices continue to rise that trend may be broken. I wouldn't buy these stocks based on Monday's move alone, but this is the kind of volatility investors in speculative energy stocks should expect, and right now, that's playing in investors' favor.