Introduction to Renewable Energy for Engineers By Kirk D. Hagen
Email: Richard@qwconsultancy.com
Chapter 1 Introduction to Renewable Energy
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1.1
Problem statement Calculate the kinetic energy of a 0.145-kg baseball with a velocity of 80 milh. Express the answer in units ofkJ. Diagram
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v = 80 mi/h
Assumptions 1. Mass and velocity are constant. Governing equations
Calculations Converting 80 milh to rnls, we have 80 milh x
1 rnls = 35.76 rnls 2.2369 milh
KE= V2 (0.145 kg)(35.76 m/s) 2 = 92.7 J = 0.0927 kJ
Solution check No errors are detected. Discussion A Major League pitcher can throw a fast ball 100 milh.
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1.2
Problem statement A satellite in orbit about the earth has a photovoltaic solar panel that faces directly into the sun for 10 hours per day. How much solar energy is incident on the panel during this period of time if the panel's surface area is 5m2? Diagram
]solar= 1366 W/m2
Assumptions 1. Solar heat flux is1366 W/m 2• Governing equations £solar = ]solar A /).(
Calculations Esolar =
(1366 W/m2)(5 m 2)(10 h X 3600 s!h)
= 2.46 X 108 J = 246 MJ
Solution check No errors are detected. Discussion Only a small fraction of this energy is absorbed by the solar panel, so the electrical output energy would be much less than 246 MJ.
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1.3
Problem statement The sun radiates energy at a rate of3.9 x 1026 W. How much energy has the sun radiated since the beginning of the Common Era? Diagram
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I
psolar
= 3.9 X 1026 W
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Assumptions 1. Sun's radiation has been constant since the beginning of the Common Era. 2. About 2016 years have passed since the beginning of the Common Era. Governing equations £solar
= psolar /).f
Calculations Esolar
= (3.9 X 1026 W)(2016 y X 365 day/y X 24 hlday X 3600 slh) =2.5 X 10 37 J
Solution check No errors are detected. Discussion Scientists estimate that the sun has around 6 billion years oflife left before it becomes a white dwarf star. The sun's radiative power will not change significantly for a very long time.
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