1) If energy was produced by human servants turning hand cranks at 100W each, it would cost $80/kWh compared to the typical $0.10/kWh cost of electricity. 2) For energy from servants to be competitive with conventional electricity, they would need to be paid $0.01/hour, which is 1/800 of what was calculated in the first example. 3) Nuclear power accounts for 9% of total US energy and 20% of electrical energy. This means that electricity accounts for 45% of total US energy supply.

1. AdityaWibawa
2ES16066W
Exercises2
1. Suppose yougotall your energyfromhumanservantsturninghand-crankedelectricgenerators,
each producingenergyatthe rate of 100W. if youpaidthose servants$8 perhour,a bitmore
than the US minimumwage,what wouldyoube yourcost for1 kWh of energy?(the typical cost
of 1 kWh of electrical energyisactuallyaround10 ¢.)
Firstconvertwatts to kilowatts.
100 watts*1kW/1000W = 0.10 kW
Since yourservantdoesworkat a rate of 0.1 kW,it wouldtake him/her10 hoursto produce
1kWh of energy(i.e.the amountwe want)
10kW* 10 hrs = 1 kWh
Nowsince we are paying$8 per hr for 10 hours,thismakes$80 per kWh.
The electricenergyactuallyonlycharges10 ¢ ($ 0.10) for the same amountenergy. That’sa
factor of $80/$0.10 = 800 more thanthe typical cost for a kWh.
2. What hourlywage wouldyouhave topay your servantsfromexercise1if the energythey
producedwere competitive withelectrical energytheyproducedbyconventional meanssuchas
fossil fuel?Use the typical costof 10ȼ/kWh.
To make the energyservants’powercompetitive withconventionallyproducedelectrical power,
I’dhave to pay them1/800 whatI paidthemin Exercise 1.Theirhourlywage wouldbe just
$8/800 = 1¢ perhour.
3. Figure 2.6a showthat 9% of US. Energycomesfrom nuclearpowerplants.The outputof those
plantsiselectricity,andthisnuclear-generatedelectricityrepresents20% of US electrical
energy.Use these factsto determinethe fractionof the total US energysupply thatisinthe
formof electricity.
Nuclearenergyconstitutes9%of total energy,and20% of electrical energy.Therefore,asthe
figure suggests,
nuclearelectricity
=
total electricity
=
9
= 45 %
total electricity total energy 20

2. 4. For the devicesidentify inquestion3,estimate the total time youuse eachdevice inaday, and
use thisquantityalongwiththe powerconsumptiontoestimatetotal energyeachdeviceusesin
a day. (youcan thinkof thisquantityas an average powerconsumptionforeachdevice.)
Power= rate of energyuse = energypertime,soenergyused= powerx time.
My dailyuses:
Device Power (W) Time (h) Energy (Wxh)
Lightbulb 100 4 400
Flourence Bulb 10 10 100
laptop 70 6 420
Refregirator 200 24 4800
Electrickettel 1000 0.2 200
Microwave 1000 0.1 100
Dishwasher 1300 0.5 650
VacumCleaner 1400 0.1 140
Rice cooker 600 0.5 300
Conventionalelectricoven 2000 1 2000
Cell phone 1 24 24
Subtotal formisc.devices 9134 W = 9.134 kWh
5. Your author’shome usesabout350 kWhof electrical energyeachmonth.Convertthistoan
average rate of electrical energyconsumptioninwatts.
Power =
Rate of energy
=
350 kWh
.
Mo
.
D
.
1000W
= 470 W
consumption mo 30 D 24 h kW
6. Findthe cost perkilowatt-hourof electricityinyourarea,andthe cost of a gallongasoline,
consideringthatgasoline containsabout40 kWh/gal, compare the price perkilowatt-hourfor
gasoline vselectrical energy.
Nuclear 9%
Gas 25%
Oil 37%
Coal 21%
other 1%
Biomass 4% Hydro3%

3. http://www.tepco.co.jp/en/index-e.html Live inJapanchargesalmost 19.43 ¥ per kWhand
gasoline costalmost500 ¥ pergallon (125¥/L):
Gas cost
=
500¥
.
Gal
= 12,5 ¥ / kWH
kWh gal 40kWh
It appearsto be abot as cheapto get electricityfromgasoline,butthisisassumingagas
poweredgeneratoroperatesat100% efficiency.Infact,itsefficientcyisfarless,soelectricity
fromPSE is a better deal-especiallybecausethatismostlyfromhydropowernotcoal.
7. What isthe approximate slope(vertical rise dividedbyhorizontalrun) of the straightline shown
infigure 2.7? to be sure to include units.Whatisthe meaningof thisquantity?
Using(0,0) and the endpointnearthe US, the slope isapproximately
39 k$/y
=
3.7 k$/y
10.5 kW kW
The slope representsthe ratioof percapitaGDP to per capitaenergyconsumption,orinverse
energyintensity.The energyintensityof the countriesnearthisslopeis0.27
𝑘𝑊
𝑘$/𝑦
8. A countryusesenergyat the rate of 3.5 kW percapita, andits citizensenjoyanannual per
capita GDP of $7500. Calculate the energyintensityof thiscountry,anddeterminewhetherit
usesenergymore orlesefficientlythanthe countriesonthe diagonal line infigure 2.7
A countryusing3.5 kW percapita, with$7500 GDR per capita,wouldbe below Polandandto
the right.This country’senergyintensityishigherthanthose onthe diagonal line.Ituses energy
lessefficiently.
3500 W
=
0.47 kW
, while the average energyintensity =
0.27 kW
$ 7500/ y K$/y K$/y