This invention relates to tidal power plants. More specifically, the invention relates to two-way generation tidal power plants with a barrage. The barrage separates the basin from the rest of bay (outer bay).
Any tidal power plant with a barrage has a power house with hydraulic turbines and electric generators. The power house itself is a part of the barrage. If the hydraulic turbines can work with flow passing in both directions, then the plant generates power during high tide with water passing through the turbines to the basin and during low tide with the water passing from the basin to the outer bay (two-way generation). If the hydraulic turbines can work with the flow passing in only one direction the tidal power plant generates power either during high tide (flood generation) or during low tide (ebb generation), but not both.
Power output of a tidal power plant turbine Pt (kW) is given by the following formula:
Pt=gηQtHt (1)
where:
A two-way generation tidal power plant is clearly more attractive, because potentially it could produce twice the energy than either ebb generation or flood generation plants using the same barrage. Current technology offers only two possible scenarios:
Case 1: Tidal power plant turbines similar to those normally used for a low head hydro electric plant.
Such turbines have adjustable blade runners and diagonal wicket gates. However, in a two-way generation tidal power plant the turbines must work with flow moving in both directions, so their blades must rotate through the range of angles between optimum positions for opposite flow directions. This range may even exceed 180°, though for conventional adjustable blade runners the range is bounded above by 50°. This makes two-way runners more expensive and less reliable.
The efficiency of this kind of two-way turbine is not the same for each direction. If the turbine is designed to work with high efficiency, say around 90%, in one direction, then it exhibits much lower efficiency in the other direction.
One example of deployment of such turbines, is the largest operating tidal power plant in La Rance, France, with adjustable blade runners and peak power of Pp=240 MW. It is equipped with ALSTOM bulb turbines originally designed and built for two-way generation. However, due to mechanical problems they allow only ebb generation.
Case 2: Orthogonal tidal power plant turbines, similar to Darrieus turbines for wind power plants (an experimental section of a power house with an orthogonal turbine with diameter 2.5 m is being constructed at Kislaya Guba, Russia).
These turbines have the same efficiency in both directions, however it is about 65%. Also they rotate very slowly and can work only with direct current generators. Thus, such turbines require the installation of converters from direct to alternating current. The use of converters decreases the overall efficiency of the plant and increases the cost of equipment.
In either case, two-way tidal power generation with barrage presents a need for an economically attractive technical solution.
The present invention discloses a two-way generation tidal power plant with a barrage in which the water flow moves through the hydraulic turbines in the same direction for both ebb and flood generation. In oder to maintain the same flow direction in the turbines for ebb and flood generation, the tidal power plant has two additional barrages separating its power house from the basin and the outer bay. These two additional barrages form the head and tail reservoirs for the power house. Each reservoir can be connected to the basin and the outer bay by means of sluices with gates. During ebb the head reservoir is connected to the basin and the tail reservoir is connected to the outer bay. During flood the head reservoir is connected to the outer bay and the tail reservoir is connected to the basin. There are two possible arrangements for the head and tail reservoirs. In one arrangement the head reservoir is located in the outer bay and the tail reservoir in the basin. In the alternative arrangement the head reservoir is located in the basin and the tail reservoir in the outer bay.
The power house is the same as in a conventional low head hydro power plant and can be fitted with conventional bulb turbines with the electrical generator located in the bulb. The turbine runner could be a Kaplan runner or an axial propeller. An ideal turbine for such a power house would be a bulb turbine with an axial propeller and an exit stay apparatus (see Hydraulic Trbine and Exit Stay Apparatus therefor, U.S. Pat. No. 6,918,744 B2, Jul. 19, 2005). A bulb turbine with an axial propeller and an exit stay apparatus has almost the same overall efficiency as a bulb turbine with a Kaplan runner, but is more reliable, less expensive, and fish friendly.
A two-way generation tidal power plant with one-way turbines and with head and tail reservoirs is the most advantageous economically in the case of a tidal power plant with a barrage much longer than the power house. In this case the construction of two additional barrages forming the reservoirs will increase the cost of the plant construction much less than by a factor of two compared to a one-way generation plant, whereas the yearly energy production will increase two-fold and the time to recoup the capital will substantially decrease. The proposed tidal power plant for Fundy bay is the best application for a two-way generation tidal power plant with one-way turbines and with head and tail reservoirs, since its total length from shore to shore is 7.91 km and the power house length (along the barrage) is only 2.34 km.
Referring now to
Sluices 11, 12, 13 and 14 shown in
A bulb hydraulic turbine presented in
When the head reservoir level is equal to [Zhr]min and the tail reservoir level is equal to [Ztr]max the sluice gates 17, 18, 19, and 20 of
Due to the fact that in the power house of a two-way generation tidal power plant with head and tail reservoirs the water flows in the same direction during both web and flood generations, it can be fitted with one-way conventional bulb turbines and electrical generators located in the bulbs. The turbine runner could be a Kaplan runner or an axial propeller. An ideal turbine for such a power house is a bulb turbine with an axial propeller and an exit stay apparatus (see Hydraulic Turbine and Exit Stay Apparatus therefor, U.S. Pat. No. 6,918,744 B2, Jul. 19, 2005). A bulb turbine with an axial propeller and an exit stay apparatus has almost the same overall efficiency as a bulb turbine with a Kaplan runner, but it is more reliable, less expensive, and fish friendly. A bulb turbine with an axial propeller without an exit stay apparatus can be used only with direct current electrical generators, because otherwise it has low overall efficiency and high pulsations in the draft tube.
A two-way generation tidal power plant with one-way turbines presented in