The advantages of tidal energy

Tidal energy is usually sold on being clean and renewable, which is true and is also
the least interesting thing about it. Solar and wind are both of those and are cheaper. The
advantages that matter are the ones nothing else in the renewable mix can offer.

It is predictable, not forecast

This is the whole case. Wind and solar output are predicted from weather models, and the
prediction degrades quickly past a few days. Tidal output is calculated from orbital mechanics,
and the timetable for a decade from now is already published.

For a grid operator that difference is worth more than raw capacity. Generation that can be
scheduled with confidence reduces the reserve that has to be held ready elsewhere.

Water is dense, so machines are small

Seawater is roughly eight hundred times denser than air. The energy carried by a moving fluid
scales with its density and with the cube of its speed, so a current of a few knots carries force
that would need a storm to match in air.

A tidal rotor of ten to twenty metres can therefore match a wind turbine several times its
diameter, and it turns slowly while doing it. See what a tidal
turbine is for how that changes the engineering.

It runs a large share of the time

Tidal stream sites generate through most of the flood and most of the ebb, pausing around
slack water. Capacity factors are high compared with wind, which matters more for the economics
than peak efficiency does. This is covered in tidal energy efficiency.

Nobody has to look at it

Tidal stream devices sit below the surface. The landscape objection that slows onshore wind
and the visual argument used against offshore wind simply do not apply.

The equipment lasts

Slow rotation in a dense, thermally stable medium produces gentler fatigue loading than
gusting air. Design lives of twenty five years and more are normal, and the resource itself does
not degrade.

What the advantages do not fix

None of this makes tidal power cheap today, and none of it creates suitable sites where the
geography does not provide them. Both are covered honestly in
the disadvantages.