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

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 CO 2 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

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 (H 2 O) 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