Renewable-energy Use in the United States

Solar Energy

Principles of Solar Energy

•Constant•Abundant•Free•Everlasting•Drawback

•Dilute

Using Solar Energy

• Collection

• Conversion

• Storage

• Cost-effectiveness

Solar Heating Systems

• Active: moves water or air with pumps and blowers

• Passive: moves water or air with natural convection currents or gravity

Solar Heating of Water: Flat-plate Solar Collector

• Acts like a greenhouse

1. Light energy goes in

2. Converted into heat energy (infrared)

3. Heat energy is trapped

4. Heat is transferred to circulating water

Solar Water Heaters

Passive Solar Space Heating

Solar Production of Electricity

Photovoltaic Cell

Photovoltaic Cell (PV)

• Mostly made of silicon– Silicon form 4-bonds with other atoms– Silicon crystal is a poor conductor

Silicon Crystal

• All electrons are fixed in bonds– Poor conductor

• “Doping” silicon crystals with impurities makes silicon a better conductor– Semiconductor

Silicon Doping• N-type

– Add phosphorus• Has extra electron in outer orbit

• Donates electrons easily

– Negatively charged

• P-type– Add Boron

• Has one less electron in outer orbit

• Accepts electrons easily

– Positively charged

PV Cell• Electric field (electrical potential or voltage) is generated when N and P

silicon are in contact• Electrons move from N to P silicon at contact point• Electric field is generated• Once electric field is produced electrons cannot pass from N to P silicon

– Acts like a diode (electrical one-way valve)

N-type

P-type

PV cell in Action• Photons (packets of light energy) are absorbed cause

electrons to be freed• Electrons move from P to N but cannot go back to the

P side directly• Electrons flow through the wire back to the P side

N-type

P-type

What about at night?

• Energy stored in batteries

• Net metering– Special meter that can run backwards– Generate energy “currency” during the day

and use the it at night

Efficiency

• Only 15-25% efficient– All or nothing effect

• Threshold amount on energy required to knock off an electron

– Reflection at surface– Resistance generated on N-side– DC current must be converted to AC

current

Concentrating Solar Power

• PV power plants• Solar-trough

collectors• Power towers• Dish-engine

system

The Solar-trough Collector

How the Solar-trough Collector Works

• The curved reflector focuses sunlight on and heats oil in the pipe.

• Heated oil used to boil water and generate steam for driving a conventional turbogenerator.

Power Tower

Solar Dish Engine System

Disadvantages of Solar Energy Technologies

• Expense

• Only works during the day

• Requires backup energy sources, e.g., batteries

• Some climates not sunny enough

Indirect Solar Energy

• Hydropower

• Wind power

• Biomass energy

Hydropower: Drawbacks

• Limited to certain geographical areas

• Ecological impacts above and below dam

• Disruption of communities

Wind Power

Wind Power

• Pros– Small environmental degradation– Clean energy

• Cons– Limited to certain geographical areas– Aesthetics– Low megawatt output– Noise

Long Island Wind Park

• South shore off Jones Beach and Robert Moses Park

• Proposed 1999

View from Robert Moses Park

View from Jones Beach

Benefits

• Provide electricity to 44,000 homes

• Saves 13.5 million barrels yearly

Ecological Impact?• Disruption of benthic environment

– 2.7 acres support base– 14.3 acres cable– Small area effected

• Migratory Birds– Multiple European studies – safe to migrating

birds

Biomass Energy – All produce CO2

• Burning firewood• Burning wood/corn

pellets• Burning wastes• Burning biogas

(methane)

Geothermal Energy: Benefits or Drawbacks?• Pros

– Consistent source– No pollution

• Cons– Limited to certain

geographical area

Geothermal Heat Pump System

Tidal Power• Pros

– Consistent source– No pollution

• Cons– Very expensive– Effects ecology of

shoreline

Rance river in France

Tidal Power

Wave Power

• Pros– No pollution– Consistent source– Minimal environmental impact

• Cons– Expensive to install and connect to power grid

Shoreline Devices

Shoreline Device

Shoreline Device

Offshore Device

Offshore Device

Offshore Device

Renewable Energy and Transportation

• Biofuels: ethanol and biodiesel

• Hydrogen: the fuel for the future

Hydrogen–Oxygen Fuel Cell

• Electrophoresis– Produces hydrogen and

oxygen gas– Electric field passed

through water splits water (H2O) into hydrogen and oxygen

• Fuel Cell– Electrophoresis run in

reverse

Fuel Cells: Benefits or Drawbacks?

• Pros– Substitute for fossil fuels

– No pollution!!!

• Cons– Production

– Portability

– Distribution system