Shock Wave: Electricity From The Ocean

First published in UCD College Tribune

Even in this futuristic world of ours, all our electricity is generated by simply spinning a turbine. The fossil fuels which are bringing us ever closer to a complete climate catastrophe are not just used to power our cars, but also to create steam which generates the electricity needed for everything from phones to lightbulbs. This is exactly the same principle employed by nuclear power plants. In both cases, fuel is used to create heat, which is used to generate electricity. There are ways, however, to generate electricity which do not require heat at all. Some renewable technologies harness the vast mechanical power available from a planet that is in constant motion. Wave power generators (WPGs) are a possible energy source of the future, but how do they compare with their rivals?

It is worth quickly comparing ocean energy and wind energy since the two are similar in a number of ways. This is why underwater turbines closely resemble those of wind farms. A major difference between the two is the potential energy contained within. Water is nearly 800 times denser than air, meaning that the same volume, travelling at the same speed, contains much more power. What this means on the practical side is that much smaller devices can produce the same yield of energy.

A major difference between WPGs and tidal power is the source of energy. Tides result from the gravitational pull of the moon dragging water up and down our shores as it passes by above us. WPGs, alternatively, find their energy source in the sun. Solar radiation does not heat the earth evenly. The air in places which receive more heat rises upwards, allowing colder air to rush in to take its place. That rushing of air is what we call wind. Since wind is the driving force behind waves, any energy that we harvest from waves comes indirectly from the heat of the sun. It is for this reason that WPGs are considered a renewable technology.

Tidal power is perhaps the most reliable source of energy on earth. Twice a day like clockwork, unimaginably vast quantities of water rush in and out of our coasts. Globally, there is as much power available from tides alone as there would be from nearly 5 and a half billion coal-burning plants. One of the problems, however, is that only a very small fraction of this energy could actually be harvested. There are only 40 or so places in the world where the difference between low and high tide is great enough to produce a worthwhile amount of power. One way that the power of the tides can be harnessed in such places is by building tidal ‘barrages’. These consist of huge dams which trap water from the rising tide, then release it slowly when the tide is low. As the water passes through the dam back into the sea, it spins a series of turbines to generate electricity.

WPGs come in a variety of forms. One very cool design that was deployed in the ocean as far back as 2004 resembles a giant sea-snake. Each segment of the snake is attached to the next by hinge joints which are connected to hydraulic rams. As the sections of the snake move back and forth over the waves, the hydraulic rams drive a series of electrical generators.

Another simple yet ingenious way of harnessing the power of waves is by using a device known as an oscillating water column (OWC). These machines consist of a hollow cylinder containing a turbine which is attached to a buoy. As the waves pass by underneath, air is forced up through the cylinder, spinning a turbine. What makes these devices truly remarkable is the special kind of turbine contained within. The so-called ‘Well’s Turbine’ is shaped in such a way that it can generate electricity regardless of which way the air is flowing. This means that power can be harnessed when the device is rising to the crest of a wave and also when it is falling to a trough, doubling the overall efficiency.

The final method for generating electricity from the ocean is called ocean thermal energy conversion (OTEC). This is another way we can indirectly generate solar energy using the ocean as a middle man. The way OTEC works is that a liquid with a low boiling point (like ammonia) is evaporated by the warm surface water of the ocean and expands, spinning a turbine. The ammonia vapour is then condensed using cold seawater and returned to the evaporation chamber to start the process over again.  The technology required for this method is simple and rapidly improving, meaning that OTEC is very much one to watch out for in the coming years.

So, which is better, WPGs or tidal barrages? WPGs hold greater promise in my view, largely because tidal barrages can be devastating to already strained marine ecosystems. Think about it; much of the ocean’s life is concentrated close to the shore. As the tide rises, both water and marine life can pass freely through the dam. Once that waterway is shut, however, the only way back to the sea is through a series of rotating blades. Many barrages are built on estuaries where rivers meet the sea. By preventing free movement through these estuaries, barrages can also seriously disrupt the spawning patterns of fish like salmon. WPGs, floating on the surface in open water, are much easier to build in a way that’s hospitable to marine life.

This is of vital importance; through plastic pollution, overfishing and ghost fishing, we have already utterly decimated almost all marine life. With plastic pollution and ocean acidification set to get much worse, we simply cannot afford to do any more harm to the beautiful animals that reside beneath the waves. If a plan is to be truly environmentally friendly, it must consider not only the CO2 it will emit, but also the effects it will have on our fellow animals. It is this major issue, coupled with the location problem mentioned earlier, which means that WPGs hold more promise than tidal barrages. In any case, it is clear that as both the financial and environmental costs of fossil fuels rise in the coming decades, blue power will assume an increasingly important position in the global energy industry.