1. Tidal action caused by gravitational effects of moon and sun on earth’s oceans.

2. Common tidal energy system is a barrage system as shown in the following slide.

4. 200 m
Top view
250 m
barrage

5. High tide Low tide Front view 200 m 6 m 3 m 8 m 12 m 4 m
turbine blades
4 m
20 m
200 m
3 m
8 m
4 m

6. High tide depth (h) = 6 m Width = 200 m Length = 250 m
Depth of water at low tide = 12 m
Seawater r = 1027 kg/m3
Tidal period = 12 hrs
Area behind barrage (A) = 200 m x 250 m = 50,000 m2
Estimate of total energy stored at high tide (assuming all mass is located at mid- high tide depth (11 m):

7. Assume power generated only during ebb tide (flow out)
Assume power generated only during ebb tide (flow out). Time of flow out = 6 hrs.
Assume all water stored during flow in is discharged during ebb tide
Volume of water stored during inflow:
V = 6 m (250 m x 200 m) = 3 x 105 m3

8. Assume average flow rate out of barrage is given by:
Assume all of this flow passes through the barrage opening of 20m by 4 m. Let a = 20m x 4 m = 80 m2

9. Average fluid velocity through this opening is given by:
v = F/a = (5 x 104 m3/hr)/80 m2 = 625 m/hr
In this opening there will be 5 turbine generators with blade radius equal to 2 ft.

10. Turbine power equation (same as for wind turbine) for each turbine generator is:

20. Power calculations for tidal currents and underwater turbine generators:
Assumptions:

21. Fairly low power output, but can run 24 hrs a day in all weather (tidal currents are reasonably constant)

22. For comparison a person riding a bicycle with the rear wheel linked to a generator can produce about 75 watts of electricity. The problem is that most people can’t keep this up for more than an hour.
(A possibility for Appledore is to open a recreation/fitness center with 10 or 15 bikes connected to generators).
By contrast Lance Armstrong can generate 500 watts --- but only for 20 minutes

23. In all of these options energy is lost in the transfer from mechanical to electrical energy. Typical efficiency of the overall processes is 40 – 50%.

24. Other “ocean – power” options include capturing wave energy
Other “ocean – power” options include capturing wave energy. Some of these options are shown in the following slides.
There are only a few of these schemes in actual operation so there is not sufficient data to assess their effectiveness – plus Appledore Island generally doesn’t experience significant wave action.

25. Ocean
Shore