Question

A bay, which is considered for hydropower generation has an area of 70 km and is characterized by ocean tides with an average monthly tidal range of 5 m. Assume that a tidal period is 24 hours and 50 minutes and the generator(s) for the hydropower scheme has 36 pole pairs to deliver electrical power at 50 Hz. (a) Assess the potential for monthly power generation of a tidal barrage scheme for the bay. Consider two options, the first with two-way (bi-directional) generation on the ebb and flood tide, and second, one-directional generation during ebb tide only. (10 marks) (b) Suggest suitable turbine type(s) for the tidal power generation for both one- and two-way generation. (5 marks) (c) List two advantages and two disadvantages of each: two-way generation and one-way generation hydropower schemes. (4 marks) (d) Calculate specific speed, Kn, of a single turbine if the total number of turbines are 10 using the one-way ebb tide power generation option. Comment on the suitability of the proposed turbines in part (b) based on the specific speed calculations in part (d) (6 marks)

Answer 1

a. The power generation for two way as well as one way generation scheme is outlined below. The energy from tide is calculated using the given parameters and then the calculated energy is divided by the tidal period to give the power generation. Power generation is in MW. For two tidal plants, energy will be harnessed in both the wave motion of tide and thus, it will be twice the energy generated in one way generation.

b. For one way generation, axial flow type ducted turbine would be preferred while for two way generation, cross flow type ducted turbine should be preferred.

c. Advantages of the two way turbine is that the power generation for the same tidal period/cycle is more as compared to one way. The disadvantage of two way turbine is the complex system and the installation of that system beneath the sea for harnessing power.

The advantage of one way system is its simplicity. The system consist of a duct with turbine in that duct and the turbine harnesses the energy from the movement of tides. The disadvantage of one way system is the area requirements for setting up plant for power generation in the coastal area.

d. The specific speed is calculated from a relation obtained through dimensional analysis. The Power in the relation of specific speed is in kW and height is in metres. N is given as 10.