lec13-09-global-energy - HAS222d 2009 Intro to Energy and...

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HAS222d 2009 Intro to Energy and Environment: Lecture 13: Global energy: national profiles, local solutions
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We want to look into the global use of energy by humans, estimated at 4 x 10 20 J/year. This is the number which, divided by the global population and the number of seconds per year gives about 2 kW of rate-of-use of energy per global citizen, with the US consumption being ¼ of this (10 or 11 kW per person, by only 1/20 of the global population). Contrasting national energy profiles: US and Tanzania . .next 2 slides.
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B. Lomborg, Skeptical Environmentalist We have talked about the 1/10 solution…living with 1/10 our present energy use in the US (thus, about 1.1 kilowatts per person rather than 11 kilowatts). It’s too radical perhaps for the near term but not out of the question in coming decades (when home heating and transportation could be vastly more efficient).
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The next figure looks frighteningly complex, yet it is a gold-mine of insight into US energy flow. The ‘pipes’ show many aspects of energy sources, consistent with the previous slide, and uses and losses. For example, electricity is not an energy ‘source’ but a mode of delivery; you can see it at roughly 40% of the energy stream, and largely generated by burning coal. The numbers are exaJoules…10 18 J, but note that our total energy use is close to 100 of these….that is, 10 20 J per year, about ¼ of the global energy use. So, you can read the numbers as % of the US energy flow as well. Knowing that energy is conserved among all its forms, it is useful to look at the ‘rejected’ energy losses and contemplate how much of this you might scavange and use; for example the enormous heat billowing into the atmosphere over an electrical power generating station, or the ‘waste’ natural gas burnt off at the head of an oil well. Energy losses amount poor ‘efficiency’ (just as in the Stirling heat engine, we get mechanical work out which is only a part of the throughflow of heat). We estimated the efficiency of the automobile at about 20% in converting gasoline to mechanical energy. But…is it useful energy that is produced? Amory Lovins suggests that as a people-mover it is much less efficient…most of the kinetic energy is in the car, not the solitary driver. So multipy 20% by mass of driver/mass of car and you get about 1% efficiency. This is useful when you then calulate
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lec13-09-global-energy - HAS222d 2009 Intro to Energy and...

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