Tidal energy advantages and disadvantages
Tidal power is predictable, dense, invisible and long lived. It is also expensive, limited to a few coasts, ecologically sensitive and hard to maintain. None of the drawbacks is a physics problem, which is the interesting part.
Most lists of tidal energy advantages and disadvantages read as though the writer had already decided. Here is the balance with the reasoning attached, because the interesting question is not the list, it is why the advantages have not yet won.
The balance
In favour
- It is predictable, not forecast. Output can be scheduled years ahead because it depends on orbits, not weather. For a grid this is worth more than raw capacity.
- The energy is dense, so machines are compact for their output.
- It is almost invisible, sitting below the surface, which removes the landscape objection.
- The equipment lasts, with design lives of 25 years and more in a stable medium.
Against
- It costs more per unit than offshore wind today, mostly because of work at sea rather than the machine.
- Very few places work, needing strong currents or a large range, which is a short list of coasts.
- The best sites are sensitive, the same channels that concentrate flow also matter for marine life.
- Maintenance is hard, access means recovery or diving in the short slack window.
Why the advantages have not won yet
Nothing on the against side is a physics problem. Every one is a cost or scale problem, and cost falls with volume. Offshore wind was in exactly this position twenty years ago and is now among the cheapest generation available.
The open question is whether the small number of good sites limits the industry before it reaches the volume that would make it cheap. That is covered in why tidal energy is not widely used, and the money in what it costs.