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Unformatted text preview: ENV221, Fall Semester 2010 Sept. 30 th Lecture #5: ENERGY 1. Energy definitions • First law of thermodynamics: conservation of energy- Energy is n either creat ed, n either d estroyed- Energy doesn’t disapp e ar when we us e it, it chang es from a form to another but the a mount of en in the universe stays the sa m e Where does it com e from? • Energy sources:- Non-renewable: Resources that are used faster than they can be replenished and often also finite o Fossil fuel o Nuclear: using uranium, which is not reusable- Renewable: e n ergies that are gen erat ed from resources that are naturally replenished o Sun = ultimat e source of en ergy o Wind o Tides • Net useful e n ergy:- Usable a mount of e n ergy available from a n e n ergy source over its lifetime- Calculated by subtracting all losses, including those a uto m atically wasted and those wasted in the discovery, processing and transportation, transfer of this e n ergy • Energy Return On Invest m ent (EROI) = - Ration of the a mount of us able e n ergy acquired from a particular e n ergy resource to the a mount o e n ergy expend ed to obtain that e n ergy resource = EROI Energy ReturnedEnergy Invested- Examples: o Oil a nd n atural g as: from 100/1 to 15/1 -> before oil was abund ant, it was e asy to extract it without spending a lot of e n ergy; nowadays is it h arder and harder to s e arch for it -> increas e of invest m...
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- Fall '10