What mainly drives the tidal currents that tidal power plants harness?

The gravitational pull of the Moon and Sun mainly drives the tidal currents that tidal power plants harness, with the Moon's gravity playing the dominant role since it is so much closer to Earth, while the Sun's gravity adds a smaller but still meaningful contribution. Because these celestial bodies move in highly predictable orbital patterns, the resulting tides can be charted with precision years in advance, unlike weather-dependent wind or solar power.

Underwater volcanic heat drives geothermal activity, not the rise and fall of ocean tides. Sudden shifts in ocean salinity are a separate, smaller-scale phenomenon unrelated to the massive, predictable gravitational forces that generate tidal movement worldwide.

Tidal turbines essentially work like underwater wind turbines, spun by the powerful currents created as tides rise and fall, making tidal energy one of the most reliably forecastable renewable resources available anywhere on Earth.