WAVE POWER

But supplemental energy sources are still needed and are under investigation. What more often than not stretches over England's green and pleasant lands is a leaden sky, so solar energy is even less of a salvation there than it is in California. On the other hand, though Britannia no longer rules the waves, she does seek to extract their energy.

Most of the energy of sea waves is in the up and down motion of the water as the wave passes by, but there is also some kinetic energy in the motion along the direction of travel of the wave. Most schemes convert the up and down motion of the water to rotational motion that drives an electric generator. The mechanism that accomplishes this is usually something that floats on the wave and works a ratchet or pump as the wave lifts and drops it. This seems to be the most successful class of mechanisms.

Typical representatives of this group are "Salter's Ducks" and "Cockerell Rafts," the latter shown in the photo above.

Salter's ducks are tear drop shaped tanks that float on the water, pivoting about a fixed horizontal axis. The tanks will bob up and down like nodding ducks as the crest of a wave moves past them. Inside the tanks, along the horizontal axis, there are ratchet driven hydraulic pumps which in turn drive electric generators. The ducks might extract as much as 90% of the waves' energy, and many of them could be strung together side by side, nodding about the same horizontal axis.

Another variant was invented by Sir Christopher Cockerell the rafts shown above. A string of such rafts would flex with the waves and turn hydraulic generators in the hinges joining the rafts, each hinge driving about 1 kW of electric output power.

Many more such schemes exist, some of them only on paper. A somewhat different idea is to make the waves compress air - for example, by a column of water rising and falling in a vertical pipe which then drives an air turbine attached to a generator. This class again has several variants.

The trouble with all these schemes is the same as with solar energy (in fact, via sun, wind and waves, all of this is solar energy): The energy is very dilute. Even the most optimistic estimates put the capacity of rafts 55 yards wide and 110 yards long at a mere 2 MW (which, incidentally, is of the same order as the solar energy that could be harnessable from the raft's area when the sun is out). That means that a belt of rafts 32 miles long would be needed for 1,000 MW of electric power (with nothing to spare for periods of smaller waves).

A 300 mile chain of Salter's ducks would supply the present British consumption of electric power, it is claimed. That is reminiscent of the claim (in itself also almost correct) that all of the US power consumption could be supplied with solar power if all the US roads were roofed over with solar collectors.

No more than that! A cinch.

All of which goes to show that like direct solar energy, wave power may be a good supplement, but it can never be a substitute for the concentrated energy of fossil and nuclear fuels. [More: "How waves package solar power," Electr. Rev. Internatnl., 9/9/77 and 4/2/78; "Power from the sea," Popular Mechanics, 3/77; "Wave power: contouring rafts bob into the lead," New Scientist (London), 4/27/78.]