That’s the rating at capacity though, which barely ever happens. The ocean current will never stop, so over the course of it’s life the ocean turbine might well beat out a wind turbine (ok, I consider that mildly unlikely, but it’s nice to have power generation that’s less susceptible to suddenly not producing anything).
Also note they say it produced 100kw, not what it was rated for.
The turbine capacity is reached quite regularly, particularly during windy days.
UK Crown Estate have a map of current renewable generation (https://www.thecrownestate.co.uk/en-gb/what-we-do/asset-map/) and right now the Hornsea 1 field is generating nearly 900MW (~90% capacity) on not a particularly windy day for the North Sea. The capacity factors you read are averaged over a year.
I'm not good at nautics, but in my understanding currents slowly stop and later turn around. Most tide charts are more or less a sine wave, with different highs and lows.
So it's interesting how this 100kw was produced.
The article only says: "The business was able to generate roughly 100 kilowatts of steady electricity during demonstrations earlier this year."
So is this over a few days or just a few hours while peak flow? While currents change, their change is highly forseeable - unlike wind.
Currents are relatively unrelated to tides, and are fairly consistent over time (with some seasonal variation due to differences in hemispheric temperatures).
From [1], "the large scale prevailing winds drive major persistent ocean currents..." Keyword is persistent.
I imagine that's one goal of the project? I can't imagine that there hasn't been a shit ton of experiments with "deep" sea currents before this power experiment. I mean it's dead obvious and they wouldn't have ponied up the cash for this if ocean currents were all over the place.
