Wave Energy

The ocean is never still. Waves break and retreat every second of the day, all around the world – much to the delight of surfers and dolphins.

Did you know that waves transmitenergy, not water? Energy is transferred in different ways through waves. For example, vibrations and magnetic fields in electromagnetic waves or vibrations of particles in sound. In water waves, the energy is transferred through vibration of water particles.

Wind blows over oceans, transferring its energy to the water and causing the particles to move in acircular motion. The rise and fall of water particles creates a wave, travelling in the direction of the wind. When we see waves coming into shore, it's easy to believe that the individual water particles are getting closer to us. However, the particles that move back and forth perpendicularly aren'tactually moving significantlyin terms of the wave's direction.

Have you ever done a Mexican wave at school, or a sports event? This works in a similar way. The wave moves around the whole area, but the people participating don't move at all.

Humans have been harnessing the power of the waves for centuries. The first patent for wave energy was filed in 1799, but it took many years to catch on. Let'sseawhat the technology is like nowadays…

New Wave Energy

Let's begin with a definition.

Wave energy is a newrenewable energy technology.

Wave energy is mostly used for:

• Pumping water

• Electricity generation

• Desalination plants

Wave Energy: Technology and Diagrams

There are five main types of technology used to generate energy from waves.

• Absorbers:floating structures thatabsorb energy through its movementsat the water surface. Once extracted, the energy is converted to electricity using a linear or rotary generator.

• Oscillating Water Columns (OWC):partially submerged enclosed structures. The upper part is filled with air, and remains above the surface of the water. Incoming waves are funnelled into the lower, submerged part of the structure. Waves entering causes the air in the top part topressurise and depressurise. This pushes and pulls air through aconnected air turbineabove it, which drives a generator.

• Attenuators:floatingdevices with two 'arms' attached on a hinge. They operate parallel to the wave direction, effectively 'riding' the waves. Attenuators capture energy from therelative movementof the arms as the wave passes, converting it to electricity using a hydraulic pump.

• Overtopping devices:'dams' thatcapture wateras waves break into a reservoir. The water is then returned to the sea, passing through a turbine that powers a generator.

Overtopping devices arevery similar到公司nventional hydroelectric dams.

• Oscillating Wave Surge Converters:hinged paddles on a mounted joint arepushed back and forth like a pendulumby the motion of the waves. The movement of the paddle drives ahydraulic pumpthat powers an electric generator.

Wave Energy: Locations

Wave power varies considerably around the world. It's only aneconomically feasibleenergy source in some regions of the world, depending onwind strength and access to coastlines.

• 地区之间30°60°N

• Southern latitudes that experience circumpolar storms

• Western coasts of temperate countries

Economically feasible areas for wave farms include Portugal, Australia, the US, and the UK.

Wave Energy in the UK

The windy coastlines of Scotland have excellent potential for wave energy generation. In fact, up to21.5 GWof wave and tidal energy could be generated annually from the Scottish coastlines.

苏格兰已经生产10%of Europe's total wave energy – and the Orkney Islands are one of the world's leading areas for wave energy.

Worked Example: What's the best site for harnessing wave power?

The energy of a wave depends on its:

• Height

• Wavelength

• Breaking distance

The energy (E) of the wave per square metre is proportional to the square of the height (H):

E∝H²

For example, Wave A istwice as tallas Wave B. Wave A will havefour timesthe energy per square metre of water as Wave B.

Fig. 3 - The stronger the wind, the taller the wave, so the more energy it has. Unsplash

During your A-Levels, you may be required to compare two potential sites for harnessing wave power, and work out which will generate more energy. This table shows wave height data from two different locations, Site A and Site B.

We can use at-testto see if there is astatistically significant differencebetween the means of two sites. If the difference is significant, it's unlikely to have occurred by chance.

To use a t-test, we need to know themeanof each data set, thestandard deviationof each data set, and thesample sizeof each data set.

Calculating Standard Deviation

• x̄: mean of the data set

• x: individual data measurement

• ∑: sum of

• 护士:年代ample size

• √: square root

Let's apply the information from Site A to this equation.

The mean of Site A is4.58, and the sample size is10.

The standard deviation of Site A is0.776.

Now let's do the same for Site B.

The mean of Site B is2.58, and the sample size is10.

The standard deviation of Site B is0.898.

Calculating t

Now that we've calculated the standard deviation, we're going to work out our t-value.

• x₁is the mean of sample 1

• s₁is the standard deviation of sample 1

• n₁is the sample size of sample 1

• x₂is the mean of sample 2

• s₂is the standard deviation of sample 2

• n₂is the sample size of sample 2

Let's put this equation to use.

So, our calculated t-value is 5.329. What's next?

Critical t-value

To see if our calculated t-value is significant, we need to find out thecritical t-value.

We do this by working out ourdegrees of freedom(total sample size minus 2), which equals 18.

Then, we take our degrees of freedom and apply it to asignificance tableto find our the critical t-value. In environmental sciences, we use a significance level of0.05. This means that there is a 95% chance that these results didn't occur by chance.

• If your calculated t-value isgreaterthan the critical t-value, you can conclude that the difference between the means for the two groupsis significantly different.

• If your calculated t-value islowerthan the critical t-value you can conclude that the difference between the means for the two groupsis not significantly different.

For 18 degrees of freedom, the critical T-value is2.101. Our calculated t-value is5.329, which isgreaterthan 2.101. So, we can conclude that the difference between the meansis significantly different.

Which site, A or B, is a better site for harnessing wave power?

Advantages of Wave Energy

What are the main advantages of wave energy?

• Renewable:waves are driven by wind, which move solar energy around the Earth. As long as the Sun is a part of our solar system, wave energy will be a renewable source of power.

• Reliable:waves are always in motion. They aren't dependent on the season or the weather.

• Accessible:approximately 72% of the Earth is covered by water – and 2.4 billion people live within 100 kilometres of the coastline. Wave energy has the potential to become an important energy resource for billions of people worldwide.

• High-energy:it's estimated that harnessing the movement of the oceans could produce up to 80,00 TWh (terawatt hours) of electricity – four times the world's current energy usage!

• Clean:wave energy produces nogreenhouse gasesor harmfulpollutants.

• No Land Damage:generating energy from waves has no impact on terrestrial ecosystems.

Disadvantages of Wave Energy

What are the main disadvantages of wave energy?

• Visually Unappealing:wave energy technology could be considered an eyesore, and may impact tourism in coastal areas, causing a knock-on effect on the local economy.

• Damage to Marine Life:wave energy technology is relatively new, so scientists are unsure of the impacts on marine life. Concerns include disturbance to the sea floor, damage to benthic habitats (affecting animals such as crabs and starfish),noisepollution, and a danger of toxic chemical leaks into the water.

• Ship Disturbance:wave technology may impact the passage of ships and other vessels.

• Initial Cost:most wave technology is still in the early stages of development, so it's expensive to build and install. However, it's expected that construction costs will fall as wave technology becomes more common.

• Maintenance:inspecting and repairing wave energy technology is difficult, time-consuming, and expensive.

I hope that this article has explained wave energy for you. To recap: it's a clean, carbon-free source of renewable energy. Harnessing wave energy is most suitable in windy coastal areas. The energy produced is proportional to the square of their height – the higher the wave, the more energy is produced.

^{1. Aberdeen Renewable Energy Group,Wave Energy, 2021}

^{2. Gretel von Bargen, Independent T-test,Biology for Life, 2022}

^{3. GRID-Arendal, Spots of potential for wave energy harvest,Green Economy in a Blue World - Full Report, 2013}

^{4. National Renewable Energy Laboratory,Wave Energy, 2015}

^{5. Renee Cho, Tapping into Ocean Power,Columbia Climate School, 2017}

^{6. United Nations, Factsheet: People and Oceans,The Ocean Conference, 2017}

^{7. University of Hawaii, Wave Energy and Wave Changes with Depth,Exploring Our Fluid Earth, 2022}