Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Lecture Notes

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 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 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 m 3 /s) A - surface area Physics and Astronomy Outreach Program at the University of British Columbia 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 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 = km 2 Rainfall = 600 mm/year Physics and Astronomy Outreach Program at the University of British Columbia 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/m 3 ) Potential energy at the turbines is ρghQ ρ = density of the water = 1000 kg/m 3 h = 186 m Efficiency = η P turbines = ηρghQ Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia

Hydro-Electric Dams Assuming η generators = 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 Physics and Astronomy Outreach Program at the University of British Columbia

Hydro-Electric Dams The annual average power generated is given to be 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 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 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 hectares A study predicts ~ tonnes of CO 2 will be emitted for the first 20 years, half from construction and half from biomass decay in the artificial lake tonnes/GWh of electricity is produced by coal-fired plants Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia

1.BC Hydro. The Peace/Williston Fish and Wildlife Compensation Program (PWFWCP) (online). [12 May 2010]. 2.Natural Resources Canada. The Atlas of Canada (online). nt/climate/precipitation/precip [12 May 2010]. nt/climate/precipitation/precip 3. The Vancouver Sun. Site C Dam No Green Power Project, Critics Say (online) f7-f072-47d5-babb-1a20e58664ab&k=49198 [9 April 2010] f7-f072-47d5-babb-1a20e58664ab&k= MacKay DJC. Sustainable Energy - Without the Hot Air (online). UIT Cambridge. s/1.112.pdf [12 May 2010]. s/1.112.pdf Home Heating