Why is tidal energy not widely used?

Tidal power is predictable, dense, invisible and long lived, and it supplies well under
one percent of world electricity. That gap is the most interesting question in the subject, and
the answer is not that it does not work.

The technology is not the obstacle

Tidal barrages have generated reliably since the 1960s. Tidal stream turbines have run for
years in some of the most aggressive water on earth. Nothing here is waiting on a breakthrough.

There are not many places

A viable site needs a large tidal range or a strong reliable current, which requires geography
that funnels water. That is a short list of coasts worldwide, and several of them are remote from
the demand that would pay for the power.

This constraint does not improve with technology. It is the one disadvantage that scale cannot
fix.

Costs need volume, volume needs costs

Tidal stream is expensive largely because each project has been close to bespoke. Costs fall
when a supply chain exists, and a supply chain appears when there is a pipeline of projects. That
pipeline needs the costs to already be lower.

Offshore wind escaped exactly this trap, through sustained policy support that guaranteed a
market until volume arrived. Tidal has had far less of that, partly because it competed for the
same support against a technology that was already cheaper.

The good sites are contested

Narrow channels with strong flow are also important for marine life and often busy with
shipping and fishing. Consent takes years, and every project carries survey costs before it
generates anything.

What would change it

A committed pipeline at a handful of proven sites, long enough for a supply chain to form.
That is a policy decision rather than an engineering one, which is why the argument about tidal
power is mostly an argument about whether predictability is worth paying for. See
the balance sheet.