Tidal Energy

The main method of utilization of tidal energy is to generate electricity. Through reservoir, seawater will be stored by the form of potential energy in the reservoir during the floor tide; and will be discharged during the ebb tide. The rotation of hydro turbine will be propelled by use of hydraulic head between the highest and lowest tide, to drive the engine to generate the electricity. The power of tidal power stations is direct proportion to the hydraulic head and water flow rate. The tidal power stations are always operating under the different working condition, due to the reason that the water level of the reservoir in operation and of the ocean are likely to be changeable, when seawater is discharging from the reservoir, the water level is decreasing, and at the same time, the water level of the ocean is likely to change because of the function of tide. Therefore, the factors i.e. the differential working condition, lower water head, large flow rate and anticorrosive to seawater, should be considered during the design of turbine power generator sets and power stations system. The tidal power stations are more comparative complex than the conventional hydropower stations, the same in the power.

The tidal power stations can be divided into three types according to its operation method and requirement upon equipment, which are single-reservoir and single-direction type, single-reservoir and two-direction type and the two-reservoir and single-direction type.

a)        Single-Reservoir and Single-Direction Type

For single-reservoir and single-direction type tidal power stations, the penstock will be opened during the floor tide to fill water to the reservoir; be closed during the slack tide. After the ebb tide and while there is a certain water head between the reservoir and the open sea, the penstock will be opened to drive the turbine hydraulic power generator for electricity

The advantage of such kind of tidal power stations is its simple structure of the equipment and cost-efficient investment. The disadvantage is its intermittent operation. More than 65% of the time in a day is in the position of storage of water and shutdown state.

b)        Single-Reservoir and Two-Direction Type

There are two plan designed for single-reservoir and two-direction type tidal power station. The first plan is to utilize 2 sets of single-direction valve to control 2 pipelines for conducting water to water turbine. During the floor tide and ebb tide, seawater will be flowed to water turbine from respective conducting channel, making the single direction of rotating of water turbine to drive the engine. The second plan is to adopt two direction water turbine generation sets.

c)        Two-Reservoir and Single-Direction Type.

For this program, the continuous power generation by tidal energy can be realized in two reservoirs, which are associative in hydraulics. During the floor tide, the reservoir with higher level will be filled with water; while during the ebb tide, water will be discharged to the reservoir with lower level. The water head between these two reservoirs makes water turbine continuously generating the electricity in one direction rotation. The disadvantage is to build up two reservoirs, which may be heavy in investment and may decrease working water head.

The key technology for tidal power generation include design and manufacturing of water turbine generation sets featured with lower water head, large flow rate and different working condition; operation management of power stations; the interaction of power station and marine environment including the impact of power stations on environment and impact of marine environment on power stations, in particular the accumulation of mud; system optimization on power stations; coordination the relationship between the generation amount, intermittent generation, equipment cost and the reliability; anticorrosive of equipment in seawater.