Transcript SU-Hydro-Electric_Dams_Lecture_Notes

Renewable
& Clean
Energy
Hydro-Electric Dams
Lecture Notes
Physics and Astronomy Outreach Program at the University of British Columbia
Hydro-Electric
Dams
• Hydro-electricity can be generated in
numerous ways: dams, rivers, tides
and waves.
• Here we describe the simplest and
oldest method, the dam.
• The analysis can easily be applied to
run-of-the-river power generation.
Physics and Astronomy Outreach Program at the University of British Columbia
Hydro-Electric
Dams
• The energy transformations are:
• Solar radiation evaporates water
from the ocean
• Rain falls on mountains, and runs
into lakes
• The runoff is interrupted by a
reservoir and dam
• Water is extracted at the base of
the dam to turn generators
Physics and Astronomy Outreach Program at the University of British Columbia
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
Physics and Astronomy Outreach Program at the University of British Columbia
Hydro-Electric
Dams
• In principle, one can calculate a
maximum value of Q from h and the
size of the hole using Bernoulli’s
principle.
• In real hydro-electric dams Q is
determined by the amount of rainfall
landing on the catchment area A of
the lake.
Physics and Astronomy Outreach Program at the University of British Columbia
Hdro-Electric
Dams
• Let’s look at the W.A.C. Bennett Dam
in north-eastern BC.
• A = 70 000 km2
• Rainfall = 600 mm/year
2
m
m
1 year
2
6
Q  (70,000km )(10
)(0.6
)(
)
2
7
km
year 3.15x10 s
 1300m3 /s
Physics and Astronomy Outreach Program at the University of British Columbia
Hydro-Electric
Dams
• Potential energy per unit volume at
the surface is ρgh (in J/m3)
• Potential energy at the turbines
is ρghQ
• ρ = density of the water = 1000 kg/m3
• h = 186 m
• Efficiency = η
Pturbines= ηρghQ
Physics and Astronomy Outreach Program at the University of British Columbia
Hydro-Electric
Dams
• Assuming ηgenerators = 1
• The calculated maximum available
power is 2.4 GW
• The maximum power rating of the
dam 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
Hydro-Electric
Dams
• The annual average power generated
is given to be 13 100 GWh per year.
13,100GWh 1 year
(
)(
)  1.5 GW
1 year
8760h
• 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
Hydro-Electric
Dams
• GHG emissions from hydro-electric
dams are small to other means of
electricity generation, but not negligible
• They arise from the construction and
decay of biomass in the flooded valley
(if that is how the project is constructed)
Physics and Astronomy Outreach Program at the University of British Columbia
Hydro-Electric
Dams
• The proposed “Site-C” dam is just
downstream of the Bennett Dam
• This project has a rated power of ~1
GW and flood 10 000 hectares
• A 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 plants
Physics and Astronomy Outreach Program at the University of British Columbia
Home
Heating
1. BC Hydro. The Peace/Williston Fish and Wildlife Compensation
Program (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, Critics
Say (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].
Physics and Astronomy Outreach Program at the University of British Columbia