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Chapter 1 Introduction Problem Solutions1 VerSp21/l (Fundamentals of Renewable Energy Processes, 4e Aldo Vieira da Rosa, Juan Carlos Ordonez) (Solution Manual all Chapters) 1 / 4
Fund. of Renewable Energy ProcessesProb. Sol. c..1Page 1 of 1 Question c. 1 If you eat 2000 kcal in a day, what is your power intake in W, hp, eV/s, and kWh/day?
We can use the conversion table in chapter 1:
2000 kcal day
= 2000
kcal day
1day (24)(3600) s
4184 J
- kcal
= 96:9 W (1)
96:9 W = 96:9 W
- hp
745:7 W
= 0:13 hp(2)
96:9 W = 96:9
J s
- eV
1:60210
19 J
= 6:05 10
20 eV s (3)
96:9 W = 96:9
J s
- kWh
3:610
6 J
(24)(3600) s
- day
= 2:33
kWh day (4) Beyond these simple unit conversions, you should try to get a feeling for these units.SolutionofQuestionc. 12 VerSp21/j 2 / 4
Fund. of Renewable Energy ProcessesProb. Sol. c..2Page 1 of 1 Question c. 2 Suppose you are participating in an endurance race lasting 4 hours (e.g a stage of the Tour de France) and that, be- ing an elite cyclist, you average 300 W during the race. What is your energy output during the stage in J and in kWh? If you were to sell this energy but had to price it at15 cent=kWh in order to be compet- itive with electricity available from other sources, how much money would you make in this stage from this sale?With a power output of 300W, the energy output in 4 hours would be
4 h300 W = 1200 Wh = 1:2 kWh.
Now, 1:2 kWh = 1:2kWh (3:610 6
J=kWh) = 4:32 10
6 J (1) At 15 cents/kWh, the 1.2kWh would be priced at 18 cents. You immediately can see that human powered generation systems have no chance to compete with established methods. You may also gain some admiration for the contraptions that have been developed for the purpose of power generation.Notice that the 300W is the power output and should not be confused with the "calories burned" during this event. The rate at which energy is depleted from the body will signicantly exceed the 300 W. If you measured it you could get an idea of the energy conversion eciency for these elite athletes.SolutionofQuestionc. 23 VerSp21/j 3 / 4
Fund. of Renewable Energy ProcessesProb. Sol. c..3Page 1 of 1 Question c. 3 The Raramuris (Tarahumaras) are a group of indige- nous people in Mexico's Copper Canyon. Running makes part of their daily life, from childhood to old age. If a Raramuri runs 4 hours a day, estimate the extra energy intake that he or she will need be- cause of this physical activity over the course of 30 years. Estimate the distance traveled and the fuel that would be needed to travel that distance by car. You will have to make a lot of assumptions, but this is true for most energy estimates.Answers will vary according to your assumptions. The main objective of the question is to get you to state and justify those assumptions.One approach, further expanded in Problem 1.20, relies on a simple rule of
thumb in sport physiology: any healthy person uses about 1 kcal per kilometer
per kilogram of body weight when running.
- kcal km
- / 4
1 kg 1 4000 J km 1 kg 1 (1) Assuming an average 70 kg person. Thus a 70 kg person will use some 280 kJ/km. You can continue from here by estimating the distance covered in 30 years running 4 hours a day. To estimate the fuel consumed by a car, you could rely on average kilometers per gallon (or miles per gallon) for a typical car.A good nal step would be to estimate the impact of some of the assumptions on the answers by varying the assumed values within their expected ranges.You could also rene your model and assume that the person is growing up (increasing his/her weight and maybe even his/her ability to run) during the 30 year period and compare with the simplied initial approach. This last step can give you some insight in regards to transient vs time averaged estimates.SolutionofQuestionc. 34 VerSp21/j
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