This article discusses the types of tidal energy forms and power plants, as follows;
-Types of Tidal Energy Forms
The types of tidal energy forms are; potential tidal energy and kinetic tidal energy.
1). Potential Tidal Energy (as one of the Types of Tidal Energy Forms)
Potential tidal energy is a type of tidal energy form that is accumulates when tide-powered sea water is retained or stored by any retention mechanism like a barrage (which is similar to a water dam), tidal lagoon, or tidal stream.
This form of tidal energy comes from the interaction between sea water in oceans, solar radiation, and gravitational influence of terrestrial and extraterrestrial bodies like the Moon.
Tidal potential energy is directly proportional to the volume of water being driven by tidal processes. This means that the amount of tidal potential energy in seawater at high levels (flooding) is larger than the amount at lower levels (ebbing).
Tidal potential energy magnitude may also vary as a result of factors like sea basin geometry and geographic location.
The amount of tidal potential energy that can be extracted from sea water undergoing tidal processes, depends on the nature of technology being used (the design and components of the tidal power plant)
It must be noted that tidal potential energy or potential tidal energy, is different from tidal energy potential; where the former is an energy form and the latter is an estimate of global output capacity.
The potential of tidal energy on a global scale is at least 500 GW . There have been several different estimates of tidal energy potential, some reaching over 3,000 GW. The exact value is yet to be ascertained, mainly due to the limited exploration and development of tidal energy resources so far.
2). Kinetic Tidal Energy (as one of the Types of Tidal Energy Forms)
Kinetic tidal energy or tidal kinetic energy is the more common form of tidal energy.
Unlike tidal potential energy that is proportional to water level and volume, tidal kinetic energy depends on mass movement water during tidal floods and ebbs.
What this means is that tidal kinetic energy is higher in cases where water movement is more rapid or significant .
It must be noted that, in its natural form, tidal energy occurs as a combination of potential and kinetic forms . This is the same for other water-based renewable energy types like wave energy and conventional hydro energy.
However, the kinetic form of tidal energy is easier to use for electricity generator, because the turbine and electric generator in a tidal power plant both require rotation (mechanical energy).that is derived from direct conversion and kinetic energy, to operate.
For this reason, tidal energy systems are generally designed to convert most of the tidal energy in water into its kinetic form, by creating a water level gradient that allows water to fall from a height or flow rapidly, and gain kinetic energy in the process.
-Types of Tidal Power Plants
The three types of tidal power plants are; single-basin, double-basin, and double-basin pumped tidal power plants.
1). Single-basin Tidal Power Plant (as one of the Types of Tidal Power Plants)
The single basin tidal power plant is a type of tidal power plant which retains water and tidal energy in a single reservoir or basin.
Stored water may be released from the basin onto the tidal turbine, to induce rotation and generate electricity.
For a single-basin tidal power plant, regardless of design, the principle of operation is summarized as follows;
1). Tide-driven water flows into a retention area (basin) where it is retained
2). In high-tide, the retained water overflows and collides with the blades of a turbine installed underwater, causing the turbine to rotate
3). The rotation of the turbine is used to activate a generator and produce electricity
4). Water flows backward in a receding fashion as the tide falls, and this may be harnessed to rotate the turbine in an opposite direction
Based on design and working principle, there are three subtypes of single basin tidal turbine; the single basin one-way plant, single basin two-way cycle plant, and single basin-pumped storage plant.
1(a). Single basin one-way plant stores water in the reservoir during high tide or flooding, and releases the water during low tide or ebbing. This creates a unidirectional trend of power generation where electricity is produced as the tide falls and energy is stored as the tide rises.
1(b). Single basin two-way cycle plant is designed such that it can generate electricity in both flood and ebb tide conditions.
This possible due to the presence of a water reversal mechanism that uses some of the tidal energy stored in high tide to increase the level of water in the basin during low tide.
The result of this is a system in which water flows out from the reservoir and back toward the reservoir in flood and ebb conditions respectively. On both occasions, the turbine is rotated by the flowing, tide-driven water.
To harness the kinetic energy under both conditions, a bi-directional turbine is usually installed.
Single basin two-way cycle plant produces more overall power than one-way plant, although there are usually significant differences between the amount of power generated in flood and ebb tide conditions.
1(c). Single basin-pumped storage plant is a modified form of the single basin two-way cycle plant, which replaces the manual mechanism of water-level increase in ebb tide, with the use of hydraulic pumps (which are often powered by tidal electricity).
While it is more energy-intensive to operate, this type of tidal power plant is also capable of generating relatively-larger amount of power, and is more consistent and reliable, than other types.
2). Double-basin Tidal Power Plant (as one of the Types of Tidal Power Plants)
A double basin tidal power plant is a type of tidal energy system that comprises of two adjacent basins or reservoirs installed at different hydrological levels, with a reversible or bi-directional turbine and a dam between them.
The basin in a tidal power plant is any system or mechanism that effectively retains water in a manner that creates a water level gradient which can be used to produce tidal kinetic energy for driving a turbine.
Double basin tidal power plant works in a manner that is similar to that of the single basin two-way cycle plant, but it is more efficient at reversing water levels during low tide.
In the upper basin (at higher hydrological level) of a double basin tidal plant, water level rises in high tide as the basin is filled by tidal water currents that flow into it. This accumulated water overflows, rotates the turbine, and flows across the turbine into the adjacent lower basin where it now accumulates
(The dam between the two basins usually has sluices or aperture to allow water flow freely between both of them).
In low tide, the water that has accumulated in the lower basin flows backward through the turbine system, rotates the turbine, then accumulates in the upper basin, from which it will overflow again when it has filled the basin.
The mechanism explained above is driven by water-level differences between both basins at different times, and ensures that the turbine is rotated under all tidal conditions.
The advantage of using two basins in a tidal power plant is that it is much more reliable and consistent in generating electricity, than the single basin power plant.
Differences in water head between the basins is maintained at all times, and this allows the system to generate power for as long as significant volume of water is available.
However, the double-basin model is more complex and expensive both to install and maintain, than single-basin model.
3). Double-basin Pumped Tidal Power Plant (as one of the Types of Tidal Power Plants)
The double basin pumped tidal power plant is a modified form of the double basin power plant.
It is different from the latter by being equipped with a hydraulic pump system that helps to drive water from one basin to another.
The types of tidal energy forms are;
1. Potential Tidal Energy
2. Kinetic Tidal Energy
Types of tidal power plants are;
1. Single-basin Tidal Power Plant
2. Double-basin Tidal Power Plant
3. Double-basin Pumped Tidal Power Plant
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