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Energy Systems &Climate Change
Thursday 21 Jan. 2010
Ch.10: Wind, Water, BiomassIndirect from the Sun
Dr. E.J. [email protected]
http://academic.evergreen.edu/curricular/energy/0910
Overview
Questions? Announcements? Logistics …
Wind, Water, Biomass (Wolfson Ch.10 & Gore Ch.4, 6)
2:30: Brief Reports: Laura, Crystal, Torie
3:15: Seminar on 1st half of Laboratory Earth (upstairs)
Wind, Water, Biomass
• Hydropower and hydrologic cycle
• Wind power– How the sun drives winds– Coriolus force– Theoretical maxiumum
• Biomass and biofuels
US net energy production
Hydrologic cycle
Hydro systems
212E mv
U=mgh
Hydropower
23% of incoming solar energy goes to evaporating water on Earth
Hydropower is up to 90% efficient, very high energy quality – essentially no thermodynamic limit
Hydropower is nearly fully developed in industrialized nations
Potential for development x 5 worldwide – but it produces more GHG in tropical areas.
+ Clean, quiet, “non-polluting”
+ Pump water up high to store energy
- DISCUSS environmental and human impacts
Power from Niagara falls3. The average flow rate in the Niagara River is 6.0×106 kg/s, and the water drops 50 m over the Falls.If all this energy could be harnessed to generate hydro- electric power at 90 percent efficiency (e), what would be the electric power output?
Solution: Power = e • Energy/time and Energy = mgh:
Wind power
1% of solar energy drives global winds via
Temperature and pressure gradients
Surface directions steered by Coriolus force
Uneven insolation causes…
→ Warmer tropics …
Warmer tropics → lower pressure air
by Sanjay Limaye and Rosalyn Pertzborn, University of Wisconsin (http://www.earthscape.org/t1/lis01/lis01aa.html)
Low pressure → rising air cools →
condensation → precipitation
Hadley cells – atmospheric circulation
Coriolus force – winds deflect over rotating Earth
Total circulation pattern (play ≥)
Power in wind
2 31 12 2
3 31 12 2
2 2 3
3
3132 1
23
1
dE dx dE mv mvPower v
dt dt dx s s
Power Power mv mv
area s s s smass m
densityvolume s
Power mvv
area s
Windpower across the US
Wind Speed and Power
31300 2 1
023
mvPPowerv
area area s
6. By what factor must the wind speed increase in order for the power carried in the wind to double?
Let the initial
What happens to the velocity v if you double the power P? Solve for v/v0:
0
3 31 102 2
2
2
P P
v v
Optimal turbine speed
10. (a) Estimate the total energy produced by a wind turbine with the power curve shown in Fig.10.15 during a day when the wind blows at 2 m/s for six hours, at 10m/s for six hours, at 15 m/s for six hours, and at 25 m/s for six hours.
(b) What’s the turbine’s average power output over this day?
Wind power is rapidly growing
Discuss other considerations regarding windpower…
Energy payback time
• Solar PV: 2 years
• Wind: 2-3 months
Biomass and biofuelsBiomass: wood, waste, plant-derived fuel …
Photosynthesis:
6 H2O + 6 CO2 + energy → glucose + 6 O2
• less than 0.1% efficient, but stores 133 TW solar power in plant growth
• Plants use half of gross: net primary productivity• Humans use 40% of net pp – too much already.
Carbon neutrality requires: • Sustainable production/ harvest• No fossil fuel use (equivalent)
Environmental impacts of biofuels WVO?
Brief Reports
Laura
Crystal
Torie
Ch. 10 HW for next week
Questions 1, 2, 3, 5
Exercises 1, 2, 5, 6, 10, 12, 14
Research Problems: 1, 3
Please do Q and RP with your team, and turn in online in WinterWolfson forum.
Turn in individual hardcopy exercises before class.
Office hours next Wednesday: 3:15 in 3270 Lab II as usual
Break time
See you at 3:15 upstairs
Wolfson Research Problems
