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Convection currents (wind and ocean waves), 368 . 1012 W
Evaporation of water, heating of water & ice.40 . 1015 W
Photosynthesis on land and sea,98 . 1012 W
Direct conversion to heat, 82 . 1015 W
Long wave radiation to space122.5 . 1015 W
Tidal energy (moon and sun),3 . 1012 W
Geothermal energy,32 . 1012 W
Incoming solar energy, 175 . 1015 W
Reflected short wave radiation,52.5 . 1015 W
Formation of fossil fuels, 13 . 106 W
Surface of the earth
Atmospheric boundary
Energy from the sun
FOSSIL FUELS
NUCLEAR POWER
INDUSTRY
BUILT ENVIRONMENT
TRANSPORT
RENEWABLEENERGYSOURCES
ELECTRICITY
Hydro power systems
H
Power from water
If a mass M of water falls through a
distance H, its loss of potential energy
is MgH
As it falls, the water could be made to
do work, and in theory this work would
also equal MgH
In a hydro power plant, the water flows
continuously, and the rate of doing
work is
mHgmtime
MgH; is the mass flowrate
Hydro-electric power plant
Water collects in the
upper reservoir, flows
through the turbine and
is then discharged at low level.
The rate of power production is
ideally,
and in practice, where η is the efficiency
of the process. In a real system, energy will be dissipated as heat in
the generator, the turbine and in the connecting pipelines
Generator
Turbine
HgmP
HgmP
Loch Sloy dam: 290 m head, 130 MW rated output
Augst-Whylen power station, River Rhine: 13 Kaplan turbines
Kaplan turbine runner, 8.4 m diameter, 20.5 MW
Pelton Wheel rated at 117 MW under a head of 686 m
Large Francisrunner: hand
finishing priorto delivery
Sectional drawingof modern Francisturbine installationshowing the inletvalve and spiralcasing, guide vanes, runner and draft tube.
Direct shaftdrive to the
generatormounted above.
Underground powerstation: Ceannacroc,near Fort Augustus.90 m head, 20 MWtotal power outputfrom two turbines
Exposed pipework for hydro plant, Peru, S. America
Construction ofLongyang dam,China. 178 m
high, it willincorporate 3turbines each
rated at320 MW
Hydraulic pumped storage
In its generatingmode, the plantoperates as a conventionalhydro power plant.But the generator can function as a motor, and the turbineas a pump. When demand for electricity is low, power maybe taken from the grid to pump water into the upper reservoir, to act as an energy store for futureuse when demand for electricity is high.
Generator
Turbine
Motor
Pump
Cruachan pumped storage scheme, Argyll: 365 m head,400 MW rated output; 4 Francis pump/turbine units
Aerial view ofCruachan siteshowing upper
reservoir and dam.Administration and
visitor centre ison the shore of
Loch Awe below;power station isunderground,
some 400 m fromthe loch-side
Gravity and the tides
Earth Moon
Lunar cycle has a period of about 12h 25min
Tidal range would be very small (about 0.5 m) if the earth were covered in water. But the land masses interfere, and create very large ranges in some parts of the world.
Global tidal resource, exploitable ‘at reasonable cost’, measured in GW
5
20
5
33
5
8020
8
5
10
40
Single-effect barrage system with sluice gates (S) and turbines (T)
Sea Basin
T
S
DATUM
Sea Basin
z1 Z z2
Mean level
Operation of a single-effect tidal barrage
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 750
Standing
Filling
Pumping
Standing
Power generation
Standing
La Rance tidalbarrage system:
rated power240 MW
Proposed location for Severn barrage
Length of barrage 16 km
Peak tidal range exceeds
10 m
Rated power output
12 000 MW