Energy and Environment, Class 16

1
Energy and Environment, Class 16

• Larger Scale Considerations of Alternative
  Sources of Energy

2
Land Use

• Hydropower
• Lake Powell produces 1250 MW continuously
• Surface area is 254 square miles
• Annually, this is about 44 GWh per square mile of
  disrupted land surface
• Solar Power
• In Prescott, a 10 acre facility produces a peak
  power of 1 MW.
• From the solar power calculator
  (http//rredc.nrel.gov/solar/codes_algs/PVWATTS/),
  a 1 MW solar array (single axis tracking) will
  produce 2830 MWh in a year.
• This equates to about 184 GWh per square mile

3
Land Use, Cont.

• Wind Power
• In the San Gorgonio wind fields in 1999, the
  energy production was 638,445,122 kWh
  (http//www.energy.ca.gov/wind/documents/1996-1999
  _wprs_report/1996-1999_report_excel_files/Page-27.
  xls). The total area of the field is 5487 acres
  (http//www.ca.blm.gov/palmsprings/windenergy.html
  )
• This equates to 74 GWh per square mile.
• Fossil Fuels
• At Black Mesa, about 80 square miles of land is
  being strip mined or disrupted during the life of
  the mine to produce about 3800 MW continuously.
• This equates to 420 GWh per square mile over the
  life of the mine
• Looking at it another way, if that entire 80
  square miles was used for solar power, it would
  produce about 1680 MW, on average.

4
Land Use, Cont.

• Biomass
• Corn cultivation uses about 1 acre to produce
  about 15 tons in a year.
• A ton of biomass produces about 4400 kWh of heat
  energy.
• If we produce electricity at an efficiency of
  35, that means that each square mile would
  produce 17.5 GWh.

5
Land Use Summary

• Land Area Comparisons
• Prescott National Forest 1933 sq. mi.
• 1002 area of Arctic Refuge 2340 sq. mi.
• Massachusetts 7838 sq. mi.
• Arizona 113642 sq. mi.

6
Intermittent Power

• Even in the best circumstances, wind and solar
  are intermittent and somewhat unpredictable.
• In the San Gorgonio pass area, the windmills
  typically operate for 6 to 8 hours per day.
• For a power grid that is required to operate
  24/7, this is a problem.
• In Europe, countries like Denmark are
  aggressively pursuing renewables for electricity,
  with a target (in Denmark) of about 20 of
  electricity from wind by 2010.
• If a country was to rely on intermittent
  renewables for much more than 20 of its
  electricity needs, it becomes problematic without
  some form of energy storage.

7
Energy Storage

• Batteries
• Used on small scale
• Expensive, need to be replace often,
  environmental costs
• Pumped water storage
• A different twist on hydropower
• Just as much land surface disruption as
  hydropower
• Expensive infrastructure
• Flywheels
• Using magnetically suspended wheels with very
  little friction, a spinning wheel can store
  energy for quite a while.
• Current systems are 10 to 250 kW in size

8
Energy Storage, Cont.

• Compressed Air Energy Storage
• Air is pumped into caves or mines and compressed
  to 1000 pounds per square inch.
• When power is needed, the air is released and the
  pressure is used to run a turbine
• In practice, natural gas is used to heat the gas
  increase the pressure before it gets to the
  turbine
• A plant in Ohio is designed to produce 2700 MW of
  peak power.

9
Compressed Air Energy Storage
10
Hydrogen

• Demonstration of small electrolysis unit and fuel
  cell
• Electricity can be used to split water into
  hydrogen and oxygen in the process of
  electrolysis
• 2H2O energy gt 2H2 O2
• This hydrogen can be stored and later used as a
  fuel
• It can be burned at high efficiency
• It can also be used to run a fuel cell that
  produces electricity in the reverse process of
  electrolysis.

11
Hydrogen, Cont.

• Downsides of hydrogen
• Lower energy density requires more storage volume
  compared to gasoline
• Ignites at a very low concentration, so leaks
  could be dangerous
• A recent report (T. K. Tromp Et Al, Science, June
  13, 2003) analyzed the possible impact of a leak
  rate of 10 to 20 would have on the environment
• Their modeling suggest that this could
  significantly deplete stratospheric ozone
• Very controversial
• (e.g. http//www.rmi.org/images/other/E03-07_SciFu
  tureH2Econ.pdf)