Give us a wave!

David Ross
says that the immense potential of wave power is on its way to being realized.

Wave energy has been hailed as the most promising renewable source for maritime countries. It does no environmental damage and is inexhaustible – the waves go on for ever. It is invariably popular with the public, which has a sentimental love of the sea.

The potential resource is vast. It is usually estimated as being of the order of 2,000 gigawatts (GW), though UNESCO has put it at roughly double that amount. But what we need to estimate is how much can be gathered and delivered at an economic price. Getting energy from the waves has been studied since the time of the French Revolution when the first patent was filed in Paris by a father and son named Girard. They noted that ‘the enormous mass of a ship of the line, which no other known force is capable of lifting, responds to the slightest wave motions’.

There was little progress in turning those motions into useful energy until the last quarter century, mainly through lack of scientific knowledge of what a wave was, how it travelled and how it could be converted. There was also a well-deserved respect for the formidable nature of the task, and the considerable capital needed was not available.

Unlike hydro-electric power it cannot draw on the flow of water running in one direction. You cannot put a water wheel in the sea and leave it to revolve and generate electricity, even though, to the watcher on the shore, it appears that the waves are advancing towards the beach in a straight line. Leonardo da Vinci noted that when the wind blew across a field of corn, it looked as though waves of corn ran across the field – whereas, in fact, the individual heads were only moving slightly. So it is with waves in the sea, which can also be compared with the movement of a skipping rope. As one end is waggled, a wave form travels to the other – but the rope itself does not advance.

A wave travels forward in an elusive, up-and-down motion. Its height is the key indication of its power. So the rougher the sea, the more potentially fruitful it is – but also the harder it is to harvest. So wave energy engineers have to design a power station that can absorb the power of the most ferocious waves without being wrecked. Two, in Scotland and Norway, have already been victims of the sea.

Yoshio Masuda, from Japan, invented the oscillating water column (OWC) – effectively a chimney which stands on the seabed and admits the waves through an opening near to its base. As they rise and fall in the open sea outside, the height of the column of water inside rises and falls too. As the water level rises, air is forced up and out through a turbine which spins and drives the generator. As it falls again, air is sucked back in from the atmosphere to fill the resulting vacuum and once again the turbo-generator is activated.

Professor Alan Wells of Queen’s University, Belfast, greatly improved the efficiency of the invention by devising a turbine which spins in the same direction regardless of whether the air is being pushed out or sucked back into the chimney.

Norway launched a wave energy station on the coast close to Bergen in 1985, which combines an OWC standing facing the waves, with a Norwegian invention called a Tapchan (from the words tapered channel). The waves ride up a concrete slope to a point 3 metres above sea level, where they splash into a reservoir. The water flows back to the ocean through a turbine which drives a generator.

Professor Stephen Salter of Edinburgh University has contributed the most intellectual invention. Salter’s Duck, as it is called, looks charming and popularized the idea of wave power. It is also a potential world-beater. The ducks are cones, filled with sophisticated electronic equipment, built around a spine, which bob up and down on the waves driving a generator. Salter will not let the system go to sea until he feels it is ready.

Small-scale wave power initiatives – from 100 kilowatts (kW) to 2 megawatts (MW) – are now going ahead in more than a dozen countries. Scotland had an experimental 75kW OWC on the shore of the island of Islay for 11 years: this has now been replaced by a 500kW model, named the Limpet, clinging to rocks facing waves sweeping in from 3,000 miles of the Atlantic.

The same group of researchers plans a 2MW seagoing device called the Osprey. Another Scottish model, called Pelamis, is a series of cylinders linked by hinged joints and hydraulic motors driving generators.

Portugal has been working for several years on an OWC on the island of Pico in the Azores. The Netherlands has invented the Archimedes Wave Swing, an air-filled ‘floater’ which moves up and down while its ‘ground floor’ sits on the seabed. An American company is working on a 10MW scheme based on buoys 3 kilometres off the south coast of Australia. India, China, Sweden and Japan are among other countries where wave energy is burgeoning.

The technical problems have been steadily overcome but the only practical applications have been on a small scale. Wave energy is crying out for 2,000MW power stations in the deep ocean.

The big hurdle is financial. Wave energy was not devised to save money but to save the world. Early researchers used to say optimistically that the energy was free because the gods provided the waves. Others swung to the opposite extreme by using high discount rates, which hit wave energy unfairly because it is a capital-intensive technology, where most of the expenditure is during construction. The simple way to change the costing is to change the discount rate.

The energy establishment has not been helpful; it naturally did not welcome a new rival for its markets. Governments and companies emphasized conventional costing. A leading Netherlands inventor commented: ‘The financial engineering is even more difficult than the technical engineering. In our team, we call it emotional engineering.’ But, for the first time for 30 years, the breakthrough is now in sight. Wave-electricity will be on the grid in many countries before long

David Ross is author of Energy from the Waves (Pergamon, 1979), Power from the Waves (Oxford University Press, 1995) and Scuppering the Waves (Open University Network for Alternative Technology, 2001).

PHOTOGRAPH: Denjiro Sato/UNEP/Still Pictures

This issue:
Contents | Editorial K. Toepfer | Secure and sustainable | Fuelling multilateralism | Meeting growing needs | Make way for the zero-litre car | Power sharing | Oil and rising water | Energetic challenges | At a glance: Energy | Competition | Power to the people | Cutting carbon | Winds of change | Power and choice | Rising sun | Give us a wave! | Less energy, more wealth

Complementary articles in other issues:
Issue on Climate and Action December 1998
Issue on Climate change December 1997
Issue on Oceans June 1998

AAAS Atlas of Population and Environment:
Climate change
Air pollution