Wave Power: Stealing the Juice?
Posted on February 01, 2007 @ 2:34 PM
COULD CLEAN, GREEN WAVE ENERGY DEVICES END UP KILLING OUR SURF?
This is the story about a cleaner future in which the waves we love give us more than just a few moments of pleasure. They’ll provide electricity, powering our homes and businesses, offering us a clean alternative to the oil addiction causing such havoc today.
This is also a story of surfers fighting against such a future because they’re worried their waves will get smaller. The events described below could happen anywhere in the world as the search for alternative energy gains pace and conflicts of interest emerge.
On 2nd of July 2006, the Sunday Times of London, England, published an article about a renewable energy project called the Wave Hub, soon to be installed off the coast of North Cornwall, UK. The article stated that some Cornish surfers were worried about the Wave Hub because its presence out there in the water might degrade the wave quality on local beaches.
It also pointed out that the presence of the device might not only ruin the waves for the surfers themselves, but also could mean the loss of hugely important tourist revenues that are loosely based around surfing.
The case of the Wave Hub is an environmental one. Environmental issues normally involve a conflict of interest; usually one group wants to alter the natural environment for their own benefit, but to the detriment of another group that wantsto preserve it for the greater good. But the Wave Hub turns this pattern on its head.
Suddenly surfers are being seen as the ones standing in the way of progress because they don’t want to give up their luxuries for the benefit of the rest of society. The luxuries in question aren’t cars, intercontinental flights or seaside properties, but the very waves we ride.
So now it’s not so clear who the ‘baddies’ really are. In general, surfers are normally the ones campaigning against environmental villains like polluters and coastal developers. Now, for this group of protestors, environmentalists are the ‘enemy’.
CLEAN ENERGY
For well-known reasons, we urgently need to cut down our use of fossil fuels. Not only are they a finite source of energy soon to run out, but they also emit greenhouse gases into the atmosphere, which a vast majority of climate experts now agree is already heating the planet up, which, in turn means that it might stop supporting us altogether sometime soon.
So, to motivate us into reducing our use of fossil fuels, the Kyoto Protocol was signed in 1997. It states that by the year 2012 the emission of greenhouse gases by 38 industrialised countries must be 5.2 % less than in 1990. Of course, the best way to do this would be to drastically reduce our energy consumption.
The classic non-renewable energy sources, coal and oil, took millions of years to form, but in just a few centuries we’re well on our way to burning them all up.
However in western culture people tend to think of this as a step backwards, and are therefore reluctant to do it. So another way to reduce greenhouse gas emissions is to find ways to generate electricity that don’t burn fossil fuels. These are called renewable energy sources.
The difference between non-renewable and renewable energy is basically the following. Non-renewable energy sources convert material into energy at a rate many times faster than that material can form, which means the material will inevitably run out. They also produce undesirable by-products, like greenhouse gases. The classic non-renewable energy sources, coal and oil, took millions of years to form, but in just a few centuries we’re well on our way to burning them all up.
On the other hand, renewable energy sources convert energy into energy. They don’t produce any direct forms of undesirable by-products, and they don’t deplete the energy source at a faster rate than it is produced. Along with wind farms, solar power and tidal power, wave power is one of the key renewable energy sources being heavily researched for a major worldwide increase in use. Now, with global warming becoming a very real threat, we are under more and more pressure to get these devices working, damn quick.
But of course it isn’t that simple. The advantages of a renewable energy device must of course outweigh the disadvantages. For example, a wave-energy converter might supply so many megawatts of electricity, which would otherwise have been supplied by a coalfired power station. It would therefore directly reduce the amount of greenhouse gases being pumped into the atmosphere. However, more greenhouse gases might actually be produced through factors associated with, say, the initial installation and ongoing maintenance of the device.
There are other aspects of these systems that might interfere negatively with the environment, but which are almost impossible to quantify. The recent Wave Hub controversy, and its possible effect on the waves for surfing, is a prime example.
WHAT IS THE ‘WAVE HUB’?
The Wave Hub is not a device for converting wave power into electricity, it is a central distribution point where wave energy converters are plugged in, hence the word ‘hub’. Think of it as a giant, multi-way adaptor.
The plan is for it to sit on the seabed about 12 miles off the north coast of Cornwall, UK. Different wave energy converters, most of which will sit on or near the surface, will be plugged into the Hub and be tested by the different companies that have designed them. While these devices will already have been through various testing stages, the versions deployed on the Hub will not yet be commercially viable, but nor will they be primitive prototypes. At the shore, the Hub will be connected directly to the electricity network, so designers can perform extensive testing of their efficiency and performance in real time and in a real environment. This should greatly speed up the process of deciding which configurations work and which don’t.
The Hub will have four ‘slots’, each to be allocated to a separate company to allow them to test their particular apparatus. Each company is only allowed one slot, but the number of devices they can actually connect will depend on the physical size of the device and the amount of power it produces. Installation of the entire Wave Hub system (still subject to planning permission) will take place between around mid-2007 and mid-2008, with the thing envisaged to be up and running before the end of 2008.
DEVICES ON THE HUB
The devices likely to be connected to the Wave Hub are being developed independently by several different companies. They differ considerably from each other, not only in the way they produce electricity, but also in the way their physical presence feeds back to affect the environment, which it inevitably will, no matter how unobtrusive they are. At the time of writing, only the Pelamis, the PowerBuoy and the Fred Olsen FO3 have been offered positions on the Wave Hub, so there is one more slot available – which another system, the Wave Dragon, is aiming to fill. Despite not being ready to roll yet, the Wave Dragon needs to be taken seriously particularly because it is likely to be of most concern to surfers.
THE WAVE DRAGON
The Wave Dragon is proposed to work through the principle of overtopping. Overtopping is normally an undesirable effect that occurs on seawalls and breakwaters, where the water sloshes over the top after the wave hits the structure. The Wave Dragon is designed to purposely induce overtopping. It first focuses the waves onto a steep ramp in the centre of two large, parabolic-shaped reflector arms. The water from the magnified wave then runs up the ramp, over the top and into a reservoir and thereby turning turbines connected to electrical generators.
The principle is remarkably simple, with few moving parts, and it produces a very reasonable amount of electrical power. However, the most worrying feature of the Wave Dragon is its size and shape. The arm-span of the proposed commercial version of the Wave Dragon would be some 300 metres (c.900ft) wide, with the arms sticking out of the sea surface by up to seven metres (c21ft), so it would be a ‘barrier’ of sorts, and thereby potentially blocking the swell. Furthermore, the designers envisage waveenergy ‘farms’, a bit like offshore wind farms, but consisting of several Wave Dragons strung out in a line perpendicular to the prevailing wave direction. The anufacturers seem to be aware that this might interfere with the waves and currents on the shoreward side of the structures, leading to possible unpredictable morphological effects on nearby coastlines. They state that:
“DESPITE NOT BEING READY TO ROLL YET, THE WAVE DRAGON NEEDS TO BE TAKEN SERIOUSLY ... BECAUSE IT IS LIKELY TO BE OF MOST CONCERN TO SURFERS.”
“Wave Dragon farms will extract energy from waves and to some extent change the hydrodynamics behind a farm. Effects will be subject to generic and site-specific hydrodynamic studies and the results from these will act as guidance in the site selection process.”
THE PELAMIS
This is a series of giant floating tubes, linked end-to-end by hinged joints, very much like a huge string of floating sausages. The commercial version is 150 metres (490ft) long by 3.5 metres (11.5ft) in diameter and weighs 700 tonnes. It is designed to lie semi-submerged in the water and go up and down with each swell. To allow it to function properly, it orientates itself perpendicular to the waves. As the sections move, each one independent of the other, hydraulic rams inside the tubes pump hydraulic fluid into electrical generators.
The basic idea is beautifully simple and the technology has already been tried and tested on other marine structures like oil rigs. One interesting feature of the Pelamis is its ability to be ‘tuned’ to the characteristics of the waves, helping to enhance the power extracted in small seas. It can also be ‘de-tuned’ out of phase with the waves to avoid damage in large swells. The combined effect is to make the overall power output more constant over long periods of time, especially in places where the wave height varies greatly throughout the year.
Again, for the Pelamis to produce a practical amount of power, the designers are proposing ‘farms’ consisting of about 40 devices, installed in an array covering about one square kilometre of sea surface. Any such array would clearly reduce the power of the waves inshore of it, and therefore must have some potential to cause hydrodynamic, and hence morphological, effects at some nearby coast. However, since these devices are semisubmerged and do actually move up and down with the waves, the effect ought to be somewhat less than a barrier-like structure like the Wave Dragon.
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