RENEWABLE AND CLEAN ENERGY
Tidal Power
Problem Set
Problem 1: Severn Estuary Tidal Hydro Power Station. Since 1925 there has been talk surrounding the development of a tidal hydro power station in the Severn Estuary in SW England. A barrage would be constructed across the river with sluice gates or water channels which the tide is able to flow in through.
When the tide is fully in, the sluice gates would shut, forming a lake behind the barrage. The tide goes out and when the difference between the height of the water in the lake and the water in the river is maximized, the water is allowed to flow out of the lake through turbines, producing power.
Estimate how much power the proposed design could produce and compare it to the value the developers are suggesting. Comment on how this amount of power compares to the electricity demands of the UK and its current carbon emissions.
Problem 1 Solution: Severn Estuary Tidal Hydro Power Station.
Known Values:
Density of water (ρ) ~ 1000 kg/m 3
Acceleration due to gravity (g) ~ 10 m/s 2
Two tides a day  t ~ 12 h
Estimated/Researched Values:
Lake area: 480 km 2
Lake depth: 14 m
Average height of water above turbines: 7 m

 mgh

Vgh



Vgh
 t
V is the volume of the lake = (480 km 2 ) (14 m) = (480 x 10 6 m 2 ) (14 m) = 6.7 x 10 9 m 3

3
9
3
2

University of British Columbia Department of Physics and Astronomy

An average of 10 GW of power could be produced, but this is without taking into account the efficiency of this power station.
The developers are predicting 8.6 GW when the water is draining out of the lake, i.e. this would be the peak power not average power during the entire day.
The total power demand in the UK is about 50 GW, so this power station alone could produce between
10 and 20 percent of the power for the UK.
In regards to CO
2
emissions, in its 100 year lifetime the tidal powered station will emit 10 million tonnes of CO
2
. This is considerably low when comparing it to the CO
2
emissions there would be when generating the same amount of power using coal - a 1GW coal fired power station produces about 10 million tonnes of CO
2
each year (see article on “ Clean Coal ”).
References:
Renewable Energy UK. Severn Barrage Tidal Power (online). http://www.reuk.co.uk/Severn-Barrage-
Tidal-Power.htm
[21 June 2010].
Wikipedia. Severn Barrage (online). http://en.wikipedia.org/wiki/Severn_Barrage [21 June 2010].
Woollcombe-Adams, C., Watson, M., & Shaw, T. Severn Barrage Tidal Power Project: Implications for
Carbon Emissions. Water and Environment Journal 23: 63-68, 2009.
Brittany Tymos 2010/06/21
University of British Columbia Department of Physics and Astronomy