Wave Power: Stealing the Juice?

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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THE POWER BUOY

Similar to a wavebuoy that measures wave height and direction, the Power Buoy converts wave power to electrical power by utilising the vertical motion of the buoy. It does this via a piston connected to an electrical generator. An interesting feature is that it has sensors to continuously monitor the performance of the system and the surrounding wave conditions, with the data transmitted in real time to a shoreline receiving station – again, very much like a wavebuoy. In the event of very large waves, the system automatically shuts down to avoid damage.

The type of device likely to be installed on the Wave Hub will have a large ‘collar’ to keep the thing afloat; but apart from that, most of the workings will be beneath the surface. There is also another type, fixed to the seabed, which the manufacturers are presently testing in Hawaii: this has virtually nothing showing above the surface apart from an antenna and some lights. Although this type won’t be attached to the Wave Hub, it’s worth mentioning because of an environmental impact assessment done by the US Office of Naval Research, whose overall conclusion was: “No Significant Impact”. And: “Minimal impacts on shoreline conditions, no alteration to currents of wave directions and no adverse effects on shoreline erosion or change in sand deposition patterns”.

THE FRED OLSEN FO3

This floating structure, looking rather like a miniature oil platform, consists of a series of vertical hydraulic cylinders containing piston-like ‘point absorbers’ whose up and down movement is transformed into electrical energy. Working in both directions, the absorbers pump hydraulic fluid into electrical generators.

The structure is made from modern composite materials, and the design is based on well-proven technologies. The mechanical and electrical characteristics can be tuned according to variations in the wave climate. Physical models of the device have been tested in a wave tank with equivalent wave heights of 14 metres (46ft), and a 1:3 scale model has been tested in the sea.

WILL IT AFFECT THE WAVES?

We all know that, if we put a wall or any other structure directly in the path of the oncoming waves, it will either block them off or cause some sort of interference as they refract around it. This is what seawalls, groynes, piers and breakwaters are designed to do. By the same logic, the presence of the Wave Hub and its associated wave-energy devices is bound to affect the waves in some way or other. After all, the whole idea is to extract energy from the waves.

The question is – and this is what all the fuss is about – whether the effect will be significant enough to reduce the quality of the waves that break on the shore, and hence make them less suitable for surfing. And, if the effect does turn out to be significant, whether the loss or degradation of our surfing waves is too much of a price to pay for a step towards meeting the need
for renewable energy.

In most western countries, before a large project such as the Wave Hub can be put into practice, a proper environmental impact assessment needs to be carried out. In order to pre-empt any complaints and fears based on lack of information, the results of this study should be published and made available to the public. At the time of writing, the possible effects of the Wave Hub on Cornwall’s coastal hydrodynamics and morphology have been assessed by two different groups, with a third study possibly underway. The results of these studies are directly relevant to how the surfing waves along the North Cornish coast might or might not be affected.

First, a comprehensive independent study was done by Dean Millar and colleagues from the University of Exeter, using a mathematical model to simulate waves propagating towards the coast. The model was run first with, and then without, the Wave Hub in place. A paper describing the results of this study has been published in the peer-reviewed journal Ocean Engineering.

The Hub and its attached devices were represented by a single object 4km (2.5 miles) wide, which absorbed some or all of the wave energy. Since the authors didn’t know which devices will be deployed on the hub, or how much energy each one absorbs, they repeated the tests with different absorption coefficients. These were: 100, 60, 30 and 10%. The last example, with one-tenth of the energy being extracted, was estimated to be the most likely, based on calculations on the efficiency and physical characteristics of the devices themselves. Nevertheless, to highlight and make easily identifiable any shoreline effects, they published all the results including those assuming a total, 100% block of wave energy. It must be stressed that this is assuming all incoming energy across the entire 4km is absorbed, which is clearly impossible.

The wave characteristics between the Hub and the coast were calculated over an 11-month period using a model called SWAN (Simulating WAves Nearshore). The inputs to this model were from ‘real’ offshore waves obtained from the NOAA WaveWatch III model every 12 hours between December 2002 and November 2003. Using data covering almost a whole year would give a good spread of different wave conditions. The difference between the wave height with the Hub and without it was then calculated for a number of points all along the coast, and for the four different absorption coefficients.

They found that, over the entire 11-month period, the maximum reduction in wave height at the shoreline due to the presence of the Wave Hub, assuming the most realistic scenario of 10% absorption, was 4cm (1.5in), and the average reduction was less than 1cm (0.3in).

In their conclusions, the authors state that: “The results suggest that any signal could easily be swamped by natural wave climate variability year-to-year”; and: “It also appears unlikely that the effects of the Wave Hub will be felt by shoreline sea users”.

Another consultancy, called Halcrow, some more simulations. Again, they used a mathematical model to estimate the changes
in wave height between the Hub and the shoreline. This time, however, they were more specific about the devices deployed on the Hub. They repeated their tests with two different layouts: (a) One Wave Dragon, two Fred Olsens, 30 Power Buoys and six Pelamis, and;
(b) Four west-facing Wave Dragons. (This was considered the ‘worst-case scenario’.)

Rather than using ‘real’ wave data, Halcrow mathematically ‘generated’ various different types of waves and ‘propagated’ them in. These included large, long-period waves, small shortperiod ones, very large waves and what they considered typical waves for surfing. Heights ranged from 1-4m (3-13ft) and periods ranged from 4-16secs.

The results showed an absolute maximum reduction at the shore of between 5% (long-period waves, with layout ‘a’) and 13% (short-period waves, with layout ‘b’). Note that the main difference in the height-reduction figures between layouts ‘a’ and ‘b’ is due
to the number of Wave Dragons, suggesting that this is the device producing the most effect. Travelling along the coast, the effect
will range from zero to the maximum then back to zero again, depending on your position relative to the wave shadow. While not
shown on the model, it is worth remembering that the position of the wave shadow (and therefore the area of maximum reduction)
will ‘sweep’ up and down the coast in accordance with the swell direction and period. This means that one single beach will not be
directly in the lee of the hub all the time.

“ONCE THE TESTS HAVE BEEN CARRIED OUT, THE INTENTION IS TO DEPLOY THEM
IN GREATER NUMBERS SOMEWHERE ALONG THE COAST OF THE UK, EUROPE,
OR THE REST OF THE WORLD. IN THIS CASE, THE EFFECTS ON THE COASTAL
HYDRODYNAMICS AND MORPHOLOGY MIGHT BE MORE SERIOUS.” – TIM NUNN

Halcrow then went on to model a typical sea state consisting of many waves of different periods and directions, all mixed up together, which is more characteristic of a stormy sea than of a clean groundswell. In this case, the attenuation in wave height at the shore was only around 3%.

Finally, to see if the devices would cause any morphological changes to the shore, they did simulations on the effects on shore sediment regimes using a simple mathematical model that predicts the sediment transport in response to the waves and currents. They ran the model for 48 hours using the same ‘storm’ wave conditions as above. This was repeated first with four Wave Dragons in place, and then without them. The results showed a difference in sediment transport virtually undetectable against the normal background variations.

As I have already mentioned, there are no Wave Dragons actually planned to be plugged in to the Wave Hub. So, why did Halcrow decide to model the waves using four Wave Dragons? Well, it is envisaged that, over the years, several different devices will be plugged into the hub, each one having a different effect on the waves. Halcrow, not knowing which devices might be on the Hub in the future, just assumed that nothing could be worse than a Wave Dragon. In reality, since each company is only allocated one slot, there couldn’t ever actually be four Wave Dragons.

If the manufacturers of the Wave Dragon want to connect in the future, they will only be allocated one of the four spaces available, just like any other company. Also, because of the large size of the Dragon (both physically and in terms of power production), they will only be able to put one device in. Therefore, the maximum number of Wave Dragons on the hub can only ever be one. The equivalent effect of four Wave Dragons would only occur if four separate companies each connected a device with the equivalent effect of a Wave Dragon, and then all tested them at the same time. The chances of this occurring are very slim.

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WHAT DOES THAT MEAN TO US?

According to the results from the two studies undertaken so far, one of which has already been published in an international peerreviewed scientific journal, it seems likely that any changes in the wave height at the shoreline due to the presence of the Wave Hub will be unnoticeable.

Because the investigators were unsure which devices were going to be deployed on the Hub and how much energy each one would absorb, they have erred on the side of caution and considered virtually-impossible scenarios. While in any scientific study of this type it is usual to consider the full range of possibilities, the upper limits of wave-height reduction figures in both the Exeter and Halcrow results are truly unrealistic. Taking into account all the tests performed, a realistic average waveheight reduction over the range of beaches along the affected coastline, over a year, would be 1% or less.

So, how might this equate to any change in our surfing experience? Well, one might be able to measure the difference. For example, a swell that would normally produce 1-2m waves at the beach would now produce, with the Wave Hub in place, 0.99 to 1.98-metre waves. But would this actually be noticeable if we were surfing them? Would a 1% reduction in height really reduce the quality of your surfing experience?

Of course, there must be some threshold percentage waveheight reduction at which it does make a difference to our surfing. There are more than enough examples of man-made structures that have completely ruined a good surf spot. While this certainly won’t happen with the Wave Hub, things aren’t so clear when considering a much larger array of wave energy converters in the future. To generate a practical amount of electricity, these things might need to be deployed in large ‘farms’ covering wide areas of ocean. At the moment an uncontrolled proliferation of devices along the Cornish coast is impossible because the Wave Hub has only very limited facilities for connection. However, once the tests have been carried out, the intention is to deploy them in greater numbers somewhere along the coast of the UK, Europe, or the rest of the world. In this case, the effects on the coastal hydrodynamics and morphology might be more serious and they would certainly have to be studied in greater detail before allowing the installation to go ahead.

Alterations to the surfable waves from changes in coastal morphology are more difficult to predict than those solely due to changes in the waves themselves, but they are probably just as important. The waves and the coastal morphology are intimately linked and, in the case of sandy beaches, the breaking waves affect the shape of the beach just as much as the beach affects the shape of the breaking waves. So, the question is, will any changes in wave height at the shore due to the presence of the Wave Hub, affect the shape of the beach enough to affect the waves for surfing. For example, will good sandbars no longer form where they used to because of some change in the local hydrodynamics?

The changes in shoreline wave heights will be relatively insignificant – probably less than 1% on average, as I have already mentioned. Some results from coastal studies of sediment dynamics suggest that, during long periods of small-wave conditions, a slight bias in the sediment transport in one direction can cause large overall changes in morphology. The small difference in shoreline hydrodynamics due to the presence of the Wave Hub might just conceivably alter the dynamics enough to slowly start causing ‘anomalous’ morphological changes during periods of very low energy conditions. However, these changes would then be totally wiped out by episodic events containing larger waves.

Even if the waves for surfing were noticeably affected by the presence of the Wave Hub, it is difficult to see how this effect would be so great as to outweigh the advantages of having it there.

There is recent evidence that coastal morphodynamic systems are self-organising. Most of the time they exist in one of a number of
‘attractor states’ determined by the general, intrinsic characteristics of the system itself and not the size of the external forcing
mechanisms (in this case the waves). The system has a certain resilience to outside forcing and will only ‘flip’ to another attractor state if this external forcing reaches some threshold. So, if the changes in hydrodynamics and sediment transport are small enough to be swamped by natural variations (as concluded by both studies) they will probably be too small to allow the system to ‘flip’ into
another state.

Even if the waves for surfing were noticeably affected by the presence of the Wave Hub, it is difficult to see how this effect would be so great as to outweigh the advantages of having it there. Renewable-energy schemes such as the Wave Hub exist to reduce the effects of global warming which could, ultimately, be much more serious for us than the small impact resulting from the structures themselves.

Moreover, if the surf really were substantially affected, we would at least be sacrificing some of our waves for a good cause. Protesting against a renewable energy scheme is not the same as protesting against some concrete structure built by someone who simply wants to stop Nature eroding their beach in order for them to fit more money-spending tourists on it.

Lastly, if the scheme were actually stopped through the opposition of surfers, then how would the general public see us? Would they believe us in the future, for example, if we opposed some scheme that threatened our waves for the more usual reasons of greed and short-sightedness on the part of some selfish coastal developer or corrupt government?

Surfers of the world should keep an eye on this and any other wave power projects. We need to guard our coasts and waves from
exploitation by the greedy, but let’s not get greedy ourselves.

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