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.