Renewable Energy

• Renewable Energy Sources


  -Lots of types being studied to help reduce fossil fuel use

  -General Points:

  1- Each has advantages and disadvantages No 'magic material' that comes without any drawbacks

  2- No one source will provide all our energy needs Need a varied approach
• Renewable Energy Advantages


  1- Abundant

  2- Produce little pollution

  3- Low maintenance

  4- Safe
• Disadvantages


  1-Technology still being developed

  2- Expensive

  3- Infrastructure compatibility

  4- Acceptance by society
• Solar


  Capture all the sunlight for 1 hour = a year's supply of energy

  -How can we harness solar energy?
• Solar Farms


  Use mirrors to focus/reflect sunlight onto a receiver
• Solar Electricity


  Photovoltaics (PV): a method of generating electricity by converting solar radiation (sunlight) into direct current electricity using semiconductors
• Photovoltaic Cells (PVCs)-


  converts sunlight directly into electricity

  -Constantly improving

  -New organic materials being studied
• Photovoltaics (PV)


  -Use ~ 7.5% of the Sahara desert as solar farms = provide half the world's energy needs

  -Assumes 10-15% PVC efficiency
• Solar Use


  Energy Payback (EPB): time it takes to generate enough energy to offset the energy used in system production

  -Since 2000 solar's EPB has dropped to 2-3 yrs
• Solar Disadvantages


  1- Insolation Variations

  2- Some pollution from making older PV cells

  -Ex- cadmium

  3- Where to put solar farms?
• Hydroelectric


  Flowing water used to turn turbines that generate electricity
• Hydroelectric Advantages


  1- Doesn't pollute the water

  2- Quick profit

  - ~ 5 years to recover plant construction costs via sale of electricity
• Hydroelectric Disadvantages


  1- Reservoir creation floods areas

  2- Dams alter downstream environments

  3- Site selection Efficiency

  4- Site Safety

  -Not in my Backyard effect affects some renewables

  Fear of dam failure
• Case Study: Banqiao Dam


  -Built to resist a 1,000 yr flood event

  -Aug 6-7 1975: 2,000 yr flood event.

  --41+ in rain fell in 24 hours (= a full year's worth in 1 day)

  -700 million tons H2O released in 6 hrs

  --wave 6+ mi wide, 20 ft high

  -171,000 died
• Hydroelectric: Tides & Waves

  -Convert kinetic energy into electricity

  -Old devices too complicated

  -New buoy system is just 2 components
• Specific Advantages:


  1- simple device

  2- very consistent
• Hydroelectric Buoys: Concerns


  1- Rough Environment

  2- Changes coastal environments

  -Reduces wave energy

  3- Some areas far from coasts

  4- Effects on wildlife
• Wind Power


  -Winds generate ~ 5x more power than total global energy consumption

  -N. Dakota could provide 1/3 of US electrical needs

  -2020: wind generates > 6% of global electrical supply

  --Up almost 5% in about 10 years
• Wind Advantages


  1- Cost down 80% in last 20 years (disputed)

  2- Energy Payback only ~ 1 yr
• Wind Disadvantages


  1- Not consistent in many areas

  -Areas defined by classes 1-7

  -Class 1 & 2 = wind energy not viable

  2- Best sites often far from population centers

  3- "Not in My backyard" syndrome

  -Home turbine = 30 ft tall, blades 7-25 ft long

  -Industrial turbine = 20 stories tall, blades about 100 ft long
• Case Study: Cape Cod, MA

  -People objecting to a windfarm that would be built 5.5 miles offshore

  -"Ruining our view"
• WARP Turbines


  Wind Amplified Rotor Platform: Stacking up a lot of little platforms and put up a bunch of small blades

  
  

  Just as powerful and maybe more powerful than conventional turbines
• Is it Safe?


  Concerns about birds being killed
• Biofuels


  -Use of biological materials as fuel

  Ex- wood

  -Renewable IF managed properly
• Algae


  -Grow algae, then convert their lipids into biofuel

  -Algae farms = oil crops
• Algae Advantages


  1- Doesn't need freshwater

  2- Doesn't need cropland/soil

  3- Waste is biodegradable

  4- Multiple harvests per year

  -Can yield 15-300x more energy per acre than other biofuel crops (ex: corn grown for ethanol)
• Algae Disadvantages


  1- Currently expensive

  -New technique published in Dec 2013

  2- Doesn't lower atmospheric CO2 levels as some claim
• Conclusions


  Every energy source will work well in some places but not in others

  Utilize several different ones

  -Wind turbines in North Dakota

  -Geothermal near Yellowstone

  -Tidal buoys on the West Coast

  Have to accept some drawbacks Weigh the pros and cons to decide what is best