Physics 11IB �Energy Production III
Goals: Describing the basic features of hydroelectric systems and wind generators
Hydroelectric Energy:
Water is stored in a dam at some potential energy.
When it falls some height h, it will convert that to kinetic energy in a turbine which then works a generator.
Power Demand
- What does this graph look like?
Most people start sleeping
Start waking up!
It’s dark but we’re not sleeping!
You’re still gaming aren’t you?
HydroElectric Energy 3
How can a hydro plant put out more or less energy to meet the changes in demand?
Water flow rate!
How is volume flow rate Q = ΔV/Δt related to Power output?
P = Δmgh/Δt
P = ρΔVgh/Δt = P = ρQgh
Issues with HydroElectric Energy (nothing is free)
- water quality: siltation (silt builds up in reservoir)
- aquatic life: Salmon migrate upstream to spawn every year. Now they’re blocked!
- habitat destruction: some areas flooded, other experience drought
Issues with HydroElectric Energy 2
- displaced people: ex. China’s Three Gorges Dam, (~ 1.4 million people displaced, 13 cities, 140 towns and 1,350 villages were submerged )
- In BC: Site C
On First Nations �Territory�Interferes with �hunting/ fishing
Wind Energy
150,000 wind turbines operating around the world in over 90 countries
Three main variables determine how much energy a turbine can produce
1. Wind speed - 12-50 km/h
2. Blade radius
3. Air Density
depends on altitude, temperature and pressure. Better at sea level.
Wind Power
What is the maximum power wind can produce?
Power = Kinetic energy / time
= ½mv2 /Δt let m = ρAvΔt where A is the cross sectional area of the fan. ρ is air density.
= ½(ρAvΔt)v2 /Δt P = ½ρAv3
This of course is the theoretical max. To get this the wind would stop! Also each turbine near by produces turbulence and has frictional effects.
Thus wind energy is only ~30% efficient.
Assignment
Tsokos p328�#17-25
Listen to:
Boyz II Men - Water runs dry (1994)