Wave power is more predictable than wind energy, with condition forecasts possible three days ahead.

It is also a more concentrated form of energy than most other renewable energy sources.

However, it is less predictable in the long term than tidal energy. Wave power is also seasonal and nearly half of the annual energy produced by it becomes available between December and February.

Since the water’s surface is sometimes calm, the variability of the energy is an important issue. As with wind and other energy sources, it is necessary to provide a “spinning reserve” – or back-up generation of energy, available when needed – to make up for lulls.

Moreover, there are environmental conditions to overcome. The Pelamis system must withstand the force of the elements at their worst.

Pelamis units are fixed by a system of weights and floats designed to keep the device facing oncoming waves. Each device is about the length of four train carriages and lies semi-submerged, partly visible on the water’s surface.

Its articulated structure is composed of cylindrical sections linked by hinged joints. The wave-induced motion of these joints is resisted by hydraulic rams, which pump oil through hydraulic motors which, in turn, drive generators to produce electricity.

Power is fed down a single cable to a junction on the seabed. Several devices can be connected together and linked to shore through a single seabed cable. The resistance of the rams can be varied according to the sea conditions to maximise generating capacity.

Ideally, the Pelamis system is moored in waters approximately 50m-60m in depth (often 5km-10km from the shore). This would allow access to the potential of larger swell waves, but avoid the costs involved in a longer submarine cable if the device was located further out to sea.

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