Tide turns for wave power

From The Sunday Times
August 3, 2008
Ocean Power Technologies believes that it has found the next big thing in carbon-neutral energy
Ben Laurance

WIND POWER faces difficult obstacles, but its supporters can at least point to wind farms already in operation. By contrast, tidal power, often touted as an environmentally friendly alternative, has struggled.
A firm quoted on London’s Alternative Investment Market believes it is on to the next big thing in carbon-neutral energy — wave power.
Ocean Power Technologies (OPT) is one of four companies whose hardware is to be tried out in a wave-power project off the coast of Cornwall. Electricity should start coming ashore in 2010.
Over several decades, a range of technologies have been used to capture wave power. The Cornwall project, called Wavehub, will experiment with four approaches.
One involves a floating platform in which waves push air through turbines. A second exploits tidal flow rather than waves. The third system — from Scotland’s Pelamis — uses a series of floating tubes joined by hinges: as they move relative to one another, power is generated.
Then there is OPT’s system. It consists of a steel column that sits vertically in the water. A collar like a huge doughnut moves up and down the column as waves pass. That movement drives a generator and electricity is then taken ashore.
OPT is also supplying one of its buoys for a trial off Orkney. The hardware should be in place in a year.
Until now, the cost of the hardware has made wave power uneconomic: it has struggled to compete with wind generation, let alone power stations burning fossil fuels such as coal and gas.
However, OPT insists that if it can start volume production of large versions of its buoys, the cost of producing electricity could be lower than with wind turbines.
There are three practical problems. First, the sea is a hostile environment for anything involving moving parts, and in particular for electrical equipment. OPT reckons that the simplicity of the design of its generating buoys and the effectiveness of seals to keep water out should ensure reliability. “Our first experimental unit went into the sea in 1997,” said company founder George Taylor. “Two of our units have operated for more than a year.”
The second challenge is that waves are erratic — they are either too small to generate power or so large that they threaten to destroy the equipment. The OPT system deals with this by shutting down when waves become too big. One of the company’s buoys off the coast of New Jersey survived Hurricane Wilma in 2005.
The third issue is the rhythm of waves: a basic power-generating buoy has a natural frequency and will work most effectively only when waves arrive at that frequency. OPT’s buoy has a device that can detect within a split second the size and speed of waves and adjust itself to make the most of the available energy.
Wave power has some advantages over other types of carbon-neutral electricity generation. A wave farm covering 300 square miles of the Pacific could supply electricity for all of California’s homes. To do the same with wind farms would require 15 times as much space.
Furthermore, wave-power generators can produce electricity 30% to 45% of the time — when waves are neither too big nor too small. Solar and wind generators manage to produce useable amounts of power only between 10% and 35% of the time.
The first test of the commercial viability of OPT’s system will come this month when one of the company’s buoys will go into the sea off Spain, where it will supply electricity as part of a project headed by Iberdrola.
And then there are the economics of the whole idea: do they really stack up?
OPT estimates that electricity from large wave-power buoys should be cheaper than that from solar panels or wind turbines. And it should at least be within striking distance of the cost of generation by natural gas and coal-fired plants.
There is room for dispute, though, over the true cost of producing electricity from different sources. “This is an issue of great controversy,” said Jim Skea, at the UK Energy Research Centre.
The future cost of coal and gas for plants using fossil fuels can only be guessed at. Also, “wind turbines are much more expensive than they were just two or three years ago”, said Skea. This reflects the simple fact that demand has vastly outstripped supply. Estimates of the total cost of electricity from nuclear power vary enormously according to what cost is put on waste disposal and the decommissioning of old power stations.
And crucially, the economics of different types of plant depend on what discount rate is applied over the lifetime of a project. With coal and gas, most of the cost is in buying the raw materials to burn. But with wind, solar and wave power plants, nearly all the cost is incurred upfront: once in place, the only significant cost is maintenance — wind and waves are free.
Will wave power make a big short-term contribution to electricity generation? No. “And there are bound to be problems as we develop prototypes and learn from our mistakes,” said OPT’s Taylor. “But long term this looks like a viable technology.”