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