What happened

Well, that certainly got ugly in a hurry. For most of Wednesday trading, the Nasdaq composite index was in the red a bit -- down 1%, which isn't great, but isn't horrible in the context of some of the larger declines we've seen these past few months. Then, all of a sudden, around 1:30 p.m. EDT today, the index fell off a cliff, eventually closing down 3%.

Hydrogen fuel-cell stocks suffered much of the damage, with shares of Plug Power (PLUG 4.78%) closing 6.6% lower, FuelCell Energy (FCEL 7.00%) falling 9.7%, and Bloom Energy (BE 4.49%) wilting 9.8%.

3 red arrows going down and crashing through the floor

Image source: Getty Images.

So what

Broadly speaking, tech investors appear to have been disappointed with Tesla (TSLA 2.99%) and its Battery Day revelations, and that seems to have cast a pall over the entire renewable energy industry, from materials suppliers such as lithium stocks, to the hydrogen fuel-cell stocks named above.

If anyone can electrify energy tech investors, after all, it's Elon Musk -- but if even Elon Musk falls flat, then what hope is there for anyone else?

Now what

The day wasn't a total loss. One of the three stocks named above, Plug Power, actually had some positive news. In the morning, Plug announced a new partnership with Universal Hydrogen, a fuel logistics company that Plug says is working to make it possible to power aircraft with hydrogen fuel cells.

Plug Power says the two companies intend to cooperate "to develop, build, and certify a commercially viable hydrogen fuel cell-based propulsion system designed to power commercial regional aircraft," by developing a two-megawatt hydrogen-electric aircraft powertrain incorporating Plug's Pro-Gen hydrogen fuel-cell stack and Universal Hydrogen's fuel delivery system.

If successful, Plug Power says the new powertrain could permit airplane trips of up to 1,000 kilometers (620 miles) without jet fuel, and they hope to have a prototype ready to test fly by 2024.