Introduction

• The word "tides" is a generic term used to define the alternating rise and fall in sea level with respect to the land, produced by the gravitational attraction of the moon and the sun.

• One of the oldest forms of energy, tide mills in use on the Spanish, French and British coasts

• The first tidal power station began working in France in 1965

Why there are tides?

Different types of TidesSpring Tides

When the moon is full or new, the gravitational pull of the moon and sun are combined. At these times, the high

tides are very high and the low tides are very low. This is known as a spring high tide. Spring tides are especially

strong tides (they do not have anything to do with the season Spring). They occur when the Earth, the Sun, and the

Moon are in a line. The gravitational forces of the Moon and the Sun both contribute to the tides. Spring tides occur

during the full moon and the new moon. 

Neap Tides

During the moon's quarter phases the sun and moon work at right angles, causing the bulges to cancel each other.

The result is a smaller difference between high and low tides and is known as a neap tide. Neap tides are especially

weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another

(with respect to the Earth). Neap tides occur during quarter moons.

The Proxigean Spring Tide

 It is a rare, unusually high tide. This very high tide occurs when the moon is both unusually close to the Earth (at its

closest perigee, called the proxigee) and in the New Moon phase (when the Moon is between the Sun and the Earth).

The proxigean spring tide occurs at most once every 1.5 years.

Tides in physics

• Motions of Earth, Moon and Sun• Renewable resource• Contains extreme amounts of potential energy• Requires large tidal difference for generating power• Affects environment less than other fuels and gasses• Might be a solution of current energy problems

Energy form tides…

• Tidal power generators derive their energy from movement of the tides.• Obviously requires large bodies of water nearby. Not viable on the

prairies.• Has potential for generation of very large amounts of electricity, or

can be used in smaller scale. • Tidal power is not a new concept and has been used since at least the

11th Century in Britain and France. • There are a number of places around the world that have adopted

pilot projects for different types of tidal generators

How do tides changing = Electricity?• As usual, the electricity is provided by spinning turbines.

• Two types of tidal energy can be extracted: kinetic energy of currents between ebbing and surging tides and potential energy from the difference in height (or head) between high and low tides.

• The potential energy contained in a volume of water is E = xMgwhere x is the height of the tide, M is the mass of water and g is the acceleration due to

gravity.

• Therefore, a tidal energy generator must be placed in a location with very high-amplitude tides. Suitable locations are found in the former USSR, USA, Canada, Australia, Korea, the UK and other countries

Methods• The generation of electricity from tides is very similar to hydroelectric

generation, except that water is able to flow in both directions and this must be taken into account in the development of the generators.

• The simplest generating system for tidal plants, known as an ebb generating system, involves a dam, known as a barrage across an estuary.

• Sluice gates on the barrage allow the tidal basin to fill on the incoming high tides and to exit through the turbine system on the outgoing tide (known as the ebb tide).

• Alternatively, flood-generating systems, which generate power from the incoming tide are possible, but are less favored than ebb generating systems.

Category of generation • Ebb generation Generation occurs as the tidal ebbs

• Flood generation Generation occurs as the tidal floods

• Two-way generation Generation occurs both as the tidal ebbs and floods

Ebb Generation

• The basin is filled through the sluices and freewheeling turbines until high tide. Then the sluice gates and turbine gates are closed. • They are kept closed until the sea level falls

to create sufficient head across the barrage and the turbines generate until the head is again low. Then the sluices are opened, turbines disconnected and the basin is filled again. • The cycle repeats itself. • Ebb generation (also known as outflow

generation) takes its name because generation occurs as the tide ebbs.

Some Turbine Types• In systems with a bulb turbine, water flows

around the turbine, making access for maintenance difficult, as the water must be prevented from flowing past the turbine. • Rim turbines reduce these problems as the

generator is mounted in the barrage, at right angles to the turbine blades. Unfortunately, it is difficult to regulate the performance of these turbines and it is unsuitable for use in pumping. • Tubular turbines have been proposed for use

some UK projects. In this configuration, the blades are connected to a long shaft and orientated at an angle so that the generator is sitting on top of the barrage.

Flood generation

Flood Generation

• Tidal Fences

• Tidal Lagoons

• Tidal Turbines

Tidal Fences• Tidal fences are composed of individual,

vertical axis turbines which are mounted within the fence structure, known as a caisson.

• Kind of like giant turn styles which completely block a channel, forcing all of the water through them.

• Unlike barrage tidal power stations, tidal fences can also be used in unconfined basins, such as in the channel between the mainland and a nearby off shore island, or between two islands.

Tidal Lagoons

• Tidal lagoons are an adaptation of the barrage system. Similar to standard barrage models, tidal lagoons retain a head pond and generate power via conventional hydro-turbines. • The difference is that the conventional

barrage designs exploit the natural coast line to minimize barrage length. • However, a lagoon, for a low cost can pretty

much be built anywhere that there is a high tidal range.• The lagoon has relatively little visual impact,

as it is below the high water tide mark and appears like a normal sea wall at low tide

Tidal Turbines • Tidal turbines offer significant advantages over

barrage and fence tidal systems (and other renewable energy sources):

• High energy intensity: A 1MW tidal turbine can access five to ten times as much energy per square meter of rotor than a 1MW wind turbine, resulting in a smaller and potentially lower cost machine.

• Minimal environmental impact: tidal turbines are visible enough to be avoided by mariners but they have a low visual impact on the seascape, they produce no pollution or noise and their slow moving rotors which turn at less than one revolution in four seconds (15 rpm) are considered unlikely to harm marine life.

• High energy return on energy invested: tidal turbines should offer faster energy payback than most other renewables.

Tidal Turbines...

• Tidal turbines utilize tidal currents that are moving with velocities of between 2 and 3 m/s (4 to 6 knots) to generate between 4 and 13 kW/m2. • Fast moving current (>3 m/s) can cause

undue stress on the blades in a similar way that very strong gale force winds can damage traditional wind turbine generators, whilst lower velocities are uneconomic.

Calculations: Tidal Stream Generators

P = the power generated (in watts)

ξ = the turbine efficiency

ρ = the density of the water (seawater is 1025 kg/m³)

A = the sweep area of the turbine (in m²)

V = the velocity of the flow

*Power equation is based on the kinetic energy of the moving water*

Calculation: Barrage Tidal Power

• E = energy• ρ = the density of the water (seawater is 1025

kg/m³) • A = horizontal area of the barrage basin • G = Gravity (9.81m/s2)• H = Vertical Tide Range* The potential energy available from a barrage is dependent on * the

volume of water.

Advantages and Disadvantages

• Advantages• The energy is free – no fuel needed, no waste produced• Not expensive to operate and maintain• Can produce a great deal of energy

• Disadvantages• Depends on the waves – sometimes you’ll get loads of energy, sometimes

almost nothing• Needs a suitable site, where waves are consistently strong• Some designs are noisy. But then again, so are waves, so any noise is

unlikely to be a problem• Must be able to withstand

Environmental Impact

• Noise pollution• Displace productive fishing sites• Change the pattern of beach sand nourishment• Alter food chains and disrupt migration patterns• Offshore devices will displace bottom-dwelling organisms where they

connect into the

Representative tidal projects

Annapolis Royal

(Canada)

Representative tidal projects

• La Rance• (France)

Representative tidal projects

• • Jiangxia• (China)

Conclusion & discussion

• Comparing with wind power energy and solar energy, tidal power seems not a big sustainable resource

• We have to make the cost lower, so that it can be built in a large scale

• Turbine has to be more effective, technology of its working process should be fully developed

• We should never neglect the environment impacts of tidal power, we do need a way to solve the current problems.