Tidal energy, explained: how it works, what it costs, where it runs

Every other renewable is a forecast. Tidal power is a timetable: it is set by the moon, and the schedule for 2035 is already written.

This is how tidal turbines work, what tidal power costs per kWh, and why, with everything in its favour, there is still so little of it.

Two highs and two lows a day, 12h 25m apart. The turbine earns on the shaded rush between them, not at the peaks. Every one of those moments is known years ahead.

12h 25mbetween one high tide and the next

~800xdenser than air, so a slow current still carries force

<1%of world electricity, and that is the puzzle

Start where your question is

the most asked questionAdvantages and disadvantagesPredictable, dense and invisible. Also expensive, limited and hard to maintain. Both halves, without the marketing.Read the balance sheet how it worksHow a tidal turbine worksA wind turbine underwater, until you reach the numbers.With diagrams the moneyWhat it costs per kWhSet against offshore wind and nuclear, on the same basis.See the table typesStream, barrage, lagoonThree ways to take the same tide.Compare the puzzleWhy is it still rare?Everything about it is attractive.The honest answer the basicsWhat tidal energy isGravitational, not solar. That is the whole trick.Start here

Why the tide is different

Every other renewable is a forecast. Tidal power is a timetable. The moon pulls the ocean into a bulge, the earth turns under it, and any coast passes through that bulge twice a day. None of it depends on weather.

The practical consequence is that a grid planner can write tidal generation into a schedule years ahead and be right to the minute. Water is also about eight hundred times denser than air, so a tidal rotor is small and slow next to a wind turbine of the same output. From there the two technologies stop resembling each other, which is the subject of how a tidal turbine works.