Deck 13: Tidal Energy

Question 1

has been suggested that tidal turbines could be used to generate power
from ocean currents. The Gulf Stream, for example, has a constant velocity of about 1.5
m/s. Discuss the advantages or disadvantages of this approach compared to the use of
turbines in a tidal current that varies from (in one direction) to +3.0 m/s (in the
other direction).

Answer 1

For the Gulf Stream, the velocity is constant so the power output will be constant.
This is advantageous compared to the tidal stream current which varies between 0 and a
maximum velocity. On the other hand, the total energy produced by the tidal stream
generator is greater than that produced by the Gulf Stream generator. This is because the
power is proportional to the cube of the velocity and the mean value of v3 for (e.g.) a

Question 2

Calculate the average current velocity that is necessary for an 8-m diameter
water turbine with a coefficient of performance of 0.3 to generate 1 MW.

Answer 2

Question 3

A 10 m diameter tidal turbine is placed in an inlet and operates with a

Answer 3

Since the velocity and hence the power varies over the tidal cycle, it is necessary

Question 4

What is the total tidal energy available (at 100% efficiency) during the
falling tide from a basin of area 100 km2 with a tidal range of 8 m?

Question 5

velocity variation of a tidal current through a tidal cycle is more
accurately described as sinusoidal (rather than linear as assumed in Problem 13.9).
Reconsider this previous problem using a sinusoidal variation. How does this new
assumption affect the result?

Question 6

(a) A tidal turbine has an efficiency of 40%. In a tidal stream with a
velocity of 7 m/s, what is the diameter of a turbine that is required to produce 1 MWe?
(b) A wind turbine has an efficiency of 40%. In a wind with a velocity of 7 m/s, what is the
diameter of a turbine that is required to produce 1 MWe?
(c) From the answers to parts (a) and (b), calculate the relative mass of water to air passing
through the rotor per second.

Question 7

Estimate the average velocity of water leaving the Gulf of Khambhat
during the falling tide cycle.

Question 8

Using the tidal range and basin area for Penzhinsk inlet given in the chapter,
estimate the monetary value of the electrical energy that can be generated (at 25%
efficiency) during one falling tide cycle. Assume electricity has a value of $0.10/kWh.

Question 9

Although the Gulf Stream is probably the best-known ocean current, the
Antarctic Circumpolar Current is the largest ocean current. This current circulates around

Question 10

What is the power available from an underwater turbine with a coefficient
of performance of 0.4 that is 10 m in diameter in a current of seawater traveling at a
velocity of 2.0 m/s?

Question 11

In some tidal areas, such as the Bay of Fundy, some smaller basins could
be used for tidal generation using barrage systems, while more open areas could be used
for in-stream tidal turbines. Discuss how the variations in power output from these two
approaches during the tidal cycle would (or would not) complement each other.

Question 12

A water turbine 15 m in diameter is placed in a channel with a tidal current
moving with a velocity of 3.5 m/s. Estimate the power produced by the turbine.

Question 13

Consider the four proposed tidal barrage generating facilities for Argentina
as described in Table 13.1. Calculate the average power available and compare with the
capacity as given in the table. Comment on any differences between these quantities.

Question 14

Based on a calculation of the total energy available and an assumed
capacity factor of 0.24, calculate the total annual energy production for tidal generating
stations at the three Canadian sites in Table 13.1. Estimate the number of homes that could
be supplied with electricity from these three sites.

Question 15

Consider the possibility of implementing either tidal or wave energy in

Question 16

Calculate the total kinetic energy seawater moving with a velocity of 1 m/s.

Question 17

A tidal inlet has an area of 32

Question 18

For the proposed tidal lagoon facility in Swansea, calculate the average
tidal power available during the tidal cycle. Are the proposed turbines appropriate for this
facility?

Question 19

tidal barrage system generates 15 MWe from 85% efficient
turbines/generators at the beginning of the power generation cycle. The mean head of
water above the turbines in 5.7 m and the water flows through the turbines with a velocity
of 6 m/s. What is the total turbine area?

Question 20

For a tidal current with a velocity of 1.5 m/s in a channel that is 0.5 km wide
and 28 m deep (on average), calculate the mass of water per unit time moving through the
channel.