per unit length of exposed coastline, and multiplying by the length of
coastline. We ignore the question of what mechanism could collect all this
power, and start by working out how much power it is.

The power of Atlantic waves has been measured: it’s about 40 kW per
metre of exposed coastline. That sounds like a lot of power! If every-
one owned a metre of coastline and could harness their whole 40 kW, that
would be plenty of power to cover modern consumption. However, our
population is too big
. There is not enough Atlantic-facing coastline for ev-
eryone to have their own metre.

As the map on p73 shows, Britannia rules about 1000 km of Atlantic
coastline (one million metres), which is 160 m per person. So the total
raw incoming power is 16 kWh per day per person. If we extracted all this
power, the Atlantic, at the seaside, would be as flat as a millpond. Practical
systems won’t manage to extract all the power, and some of the power will
inevitably be lost during conversion from mechanical energy to electricity.
Let’s assume that brilliant wave-machines are 50%-efficient at turning the
incoming wave power into electricity, and that we are able to pack wave-
machines along 500 km of Atlantic-facing coastline. That would mean we
could deliver 25% of this theoretical bound. That’s 4 kWh per day per
person
. As usual, I’m intentionally making pretty extreme assumptions
to boost the green stack – I expect the assumption that we could line half
of the Atlantic coastline
with wave absorbers will sound bananas to many

How do the numbers assumed in this calculation compare with today’s
technology? As I write, there are just three wave machines working in deep
water: three Pelamis wave energy collectors (figure 12.1) built in Scotland
and deployed off Portugal. No actual performance results have been pub-
lished, but the makers of the Pelamis (“designed with survival as the key
objective before power capture efficiency”) predict that a two-kilometre-
long wave-farm consisting of 40 of their sea-snakes would deliver 6 kW
per metre of wave-farm. Using this number in the previous calculation,
the power delivered by 500 kilometres of wave-farm is reduced to 1.2 kWh
per day per person
. While wave power may be useful for small commu-
nities on remote islands, I suspect it can’t play a significant role in the
solution to Britain’s sustainable energy problem.

What’s the weight of a Pelamis, and how much steel does it contain?
One snake with a maximum power of 750 kW weighs 700 tons, including
350 tons of ballast. So it has about 350 tons of steel. That’s a weight-to-
power ratio of roughly 500 kg per kW (peak). We can compare this with
the steel requirements for offshore wind: an offshore wind-turbine with
a maximum power of 3 MW weighs 500 tons, including its foundation.
That’s a weight-to-power ratio of about 170 kg per kW, one third of the
wave machine’s. The Pelamis is a first prototype; presumably with further
investment and development in wave technology, the weight-to-power ra-
tio would fall.

Figure 12.2. Wave.
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