Tidal power

Introduction to Tidal Power

Key word Tidal Power

Tidal power is fundamentally the same source of electricity as hydroelectric but with a twist. Traditional hydroelectric converts the gravitational pull of the Earth into usable energy by harnessing the energy inherent in the motion of water falling to Earth. Tidal power systems convert gravitational pull both upwards and downwards.

How tidal power works

How tidal power works

When the tide is coming in the tide captures the energy present in the gravitational pull of the Moon (and to a much lesser extent the Sun), and when the Earth rotates away from these massive objects, the Earth’s own gravitational pull overcomes the upward force and the water falls. The movement of the water back into place can be harnesses as usable tidal power. Thus gravity has been converted into electricity through the medium of moving water. Tidal power is not to be confused with wave power. Wave power represents the transference of energy from the wind through waves. The medium for energy transfer however is the same in both cases, movement of water up and down. But the source of the energy which moves the water is different in the case of tidal power to that of wave power. With tidal power it’s gravity and in the case of waves it’s wind.

Tidal Power Depletion and Environmental Impact

So owing to the fact that tidal power derives from the ocean’s gravitational interaction with the celestial bodies and the Earth (and the Earth’ rotation), itself, tidal power is for practical purposes inexhaustible. But conversion of gravity into tidal power does slow the Earth down. Movements of the tides cause the Earth and Moon to lose mechanical energy. Over the last 650 million years the duration of an Earth day has risen from 22 hours to 24 hours. And over that period the Earth has lost 18% of its rotational energy. So strictly speaking human exploitation of tidal power by creating further friction in the surface movement of the water will slow the Earth down further but the effect involved is so negligible as to be academic. It is however a concept to be taken on board because it illustrates that all energy comes from somewhere. But tidal power arguably has the lowest cost in terms of depletion of its originating source.

Underwater turbines

Underwater turbines

Environmental issues arising from tidal power are minimal but not be ignored. Tidal power exploitation has virtually no global environmental impact but can be enormously damaging to the micro environments and local marine habitats in which any tidal power facility is located. Rotating blades required for tidal power electricity generation kill sea life and fish might abandon the area altogether with a knock on effect into to the associated ecology of the location. Essential mechanical fluids like lubricants used in tidal power facilities are also liable to leak into the sea water.

Tidal power will be available as long as the Earth and moon exist and there’s water available on the Earth to move up and down. In fact tidal power is the only energy force which does not depend directly or indirectly on the Sun. Tidal power depends on the availability of large oceans of water on the Earth for gravity to move, and the gravitational pull of the moon to move it. And gravity doesn’t get depleted like the Sun’s hydrogen resources eventually will. Unfortunately that is cold comfort for all of us because when the Sun finally runs out of hydrogen the Earth will be incinerated.

Potential for Tidal Power

Harnessing wave energy

Harnessing wave energy

During the coming several billion years before that happens however tidal power although not yet widely used is a good prospect as a reliable renewable energy source for electricity generation. Tides are 100% predictable. To date the difficulty with tidal power has been its capital cost and the relatively small number of locations where it can be harnessed easily with the tidal power conversion technology available.. Recently however design of tidal power harvesting equipment, in the form of, tidal lagoons, axial turbines, dynamic tidal power, and cross flow turbines, have advanced in leaps and bounds, making tidal power a much better prospect in the future.. But as long as oil remains affordable tidal power exploitation will be less attractive.

But the possibilities for tidal power and the various other alternatives to oil, gas and coal are reassuring. In the decades to come fossil fuels will become more expensive as their supply diminishes. Renewables will take over slowly and without the massive dislocation which some predict.  The world will not run out of oil overnight. The oil crises of the past have arisen because of sudden human induced disruptions to supply or to sudden price rises imposed by the OPEC Oil Cartel. Tidal power will assume a place in the energy mix if required and depending on its cost.

History of Tidal Power

Tidal power has been going since as far back as medieval and even Roman times. Large storage ponds were built to trap the water when the tide came in and to release it to power water wheels when the tide went out. The world’s first large tidal power station however arrived in the form of the Rance Tidal Power Station in Brittany (France) in 1966 and further tidal power stations have followed since. Rance Tidal Power Station remains operational today.

Three basic methods are used to harness tidal power.

Tidal Stream Generators use the kinetic energy of moving water to run electricity turbines and some can even be built into the structure of existing constructions or into new ones. A bridge for example may have a turbine built into it capable of harnesses the tidal power of the water flowing under it. So a new bridge can also be a tidal power station and the economics of tidal power in such circumstances changes in its favour dramatically

Tidal Barrages capture the potential energy present in the difference between the water height at low and high tides. Dams are placed to ensure that when the tide starts coming in the tidal power in the form of the transitory rise in sea level is directed into a basin located behind the dam. When the tide goes out the water is released into turbines converting the potential energy into mechanical energy and tidal power becomes electricity. The Estuary in effect becomes a tidal power station

Dynamic Tidal Power

Dynamic Tidal Power is very new. It’s untried to date but appears to have promise. Dynamic Tidal Power would exploit the interaction between kinetic energy and potential energy present in the flow of the tides. Dams, as long as 50km with built in ‘tidal phase differences’ are built straight out to sea with no enclosure. The tidal phase differences provide for differential water levels where the coast is shallow and where ‘coast parallel oscillating tidal currents’ are present. The UK benefits from these types of currents in abundance but they are also present off the coast of China and elsewhere.