SU-Hydro-Electric Dams Lecture Notes

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Physics and Astronomy Outreach Program at the University of British Columbia

Renewable

& CleanEnergy

Hydro-Electric Dams

Lecture Notes

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Hydro-Electric

Dams

Hydro-electricity can be generated innumerous ways: dams, rivers, tides

and waves.

Here we describe the simplest andoldest method, the dam.

The analysis can easily be applied to

run-of-the-river power generation.

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Hydro-Electric

Dams

The energy transformations are: Solar radiation evaporates water

from the ocean

Rain falls on mountains, and runsinto lakes

The runoff is interrupted by a

reservoir and dam

Water is extracted at the base of

the dam to turn generators

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Hydro-Electric

Dams

A reservoir (may be a natural lake): h height below water level the

water is extracted

Q flow rate (in m3

/s)A - surface area

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Hydro-Electric

Dams

In principle, one can calculate amaximum value ofQ from h and the

size of the hole using Bernoullis

principle. In real hydro-electric dams Q is

determined by the amount of rainfall

landing on the catchment areaA of

the lake.

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Hdro-Electric

Dams

Lets look at the W.A.C. Bennett Damin north-eastern BC.

A = 70 000 km2

Rainfall = 600 mm/year

Physics and Astronomy Outreach Program at the University of British Columbia

/sm1300

)s3.15x10

year1)(

year

m0.6)(

km

m(10)km70,000(

3

72

262

Q

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Hydro-Electric

Dams

Potential energy per unit volume atthe surface isgh (in J/m3)

Potential energy at the turbines

isghQ = density of the water = 1000 kg/m3

h = 186 m

Efficiency =

Pturbines=ghQ

Physics and Astronomy Outreach Program at the University of British Columbia

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Hydro-Electric

Dams

Assuming generators = 1 The calculated maximum available

power is 2.4 GW

The maximum powerrating of thedam and its 10 turbines is 2.73 GW

The maximum power cannot be

sustained as it is greater than the

calculated value when assuming

100% efficiency and no evaporation

Physics and Astronomy Outreach Program at the University of British Columbia

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Hydro-Electric

Dams

The annual average powergeneratedis given to be 13 100 GWh per year.

This is of the same order as, but

comfortably less than, our ideal

maximum value of 2.4 GW

Physics and Astronomy Outreach Program at the University of British Columbia

GW1.5)h8760

year1

)(year1

GWh13,100

(

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Hydro-Electric

Dams

GHG emissions from hydro-electricdams are small to other means of

electricity generation, but not negligible

They arise from the construction anddecay of biomass in the flooded valley

(if that is how the project is constructed)

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Hydro-Electric

Dams

The proposed Site-C dam is justdownstream of the Bennett Dam

This project has a rated power of ~1

GW and flood 10 000 hectaresA study predicts ~150 000 tonnes of

CO2 will be emitted for the first 20

years, half from construction and half

from biomass decay in the artificial lake.

10 000 000 tonnes/GWh of electricity is

produced by coal-fired plantsPhysics and Astronomy Outreach Program at the University of British Columbia

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Physics and Astronomy Outreach Program at the University of British Columbia

1. BC Hydro. The Peace/Williston Fish and Wildlife CompensationProgram (PWFWCP) (online).

http://www.bchydro.com/pwcp/program.html [12 May 2010].

2. Natural Resources Canada. The Atlas of

Canada (online). http://atlas.nrcan.gc.ca/site/english/maps/environme

nt/climate/precipitation/precip [12 May 2010].

3. The Vancouver Sun. Site C Dam No Green Power Project, CriticsSay (online).

http://www.canada.com/vancouversun/news/business/story.html?id=2

97338f7-f072-47d5-babb-1a20e58664ab&k=49198 [9 April 2010].

4. MacKay DJC. Sustainable Energy - Without the Hot Air (online). UIT

Cambridge.http://www.inference.phy.cam.ac.uk/sustainable/book/tex/p

s/1.112.pdf[12 May 2010].

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