Unit 8.2

Unit 8.2 - Unit 8.2 Notes What is renewable energy? o...

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Unit 8.2 Notes What is renewable energy? o Fossil fuels are nonrenewable: they draw on finite resources that will eventually dwindle, becoming too expensive or too environmentally damaging to retrieve o Renewable energy resources: are constantly replenished and will never run out. Most renewable energy comes either directly or indirectly from the sun Solar Energy (Photovoltaics) o Each day the earth receives more energy from the Sun than is consumed by our planet’s six billion inhabitants in 27 years o What are the most efficient solar energy-harvesting “devices” on Earth? Plants and photosynthetic organisms o How do humans harvest solar energy? Photovoltaic Cells turn light directly into energy using semi- conductors which are minerals that conduct electricity under certain conditions: Silicon is the most common o Doped n-types conductor: Silicon crystals form covalent bonds with each other to complete octet rule (tetrahedral) grown in 3 dimensions. Four single covalent bonds each, therefore will not conduct electricity as is. To make it a conductor, change one with an element that has more electrons than Si (ex. As). Anti semiconductor because an extra electron needs energy to move, gains energy from sunlight and becomes a semi-conductor when exposed to sunlight o This process is called doping. One electron not participating in bond and can move to turn crystal into semi-conductor o Doped p-type semiconductor: One covalent bond will have a “hole”. Creates conduction by moving electron around to try and fill the hole. Need to provide energy to move electrons, which makes it a semi-conductor. P-Type (fewer electrons) N-Type (more electrons) o How a solar panel works: Provides energy that allows electrons to move which is an electrical current and is a cycle with an external circuit o Photovoltaics Benefits: High reliability with virtually no maintenance Low Operating Costs- The fuel (sunlight) is free Environmental Benefits (clean and silent) Modularity: Can be constructed to any size Low Construction Costs Hydroelectric Power o They hydrologic cycle: Water constantly moves through a vast global cycle Evaporates from lakes and oceans forms clouds precipitates as rain or snow flows back to the ocean The energy of this water cycle is driven by the Sun. About 25% of the solar radiation reaching the earth powers the water cycle o Large Hydropower
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Reservoirs are created by damming streams and rivers in specific areas such as canyons and small valleys Using gravity, the trapped water is allowed to fall onto the blades of
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This note was uploaded on 02/04/2011 for the course CHEM 003 taught by Professor Marting.zysmilich during the Fall '06 term at GWU.

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Unit 8.2 - Unit 8.2 Notes What is renewable energy? o...

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