Question

The average US citizen consumes 12000 kWh of electric energy per year an ‘ end use’ number and does not include the energy lost in converting other energy sources, e.g. fossil fuels to electricity. Note also that a kWh (kilowatt hour) is a unit of energy (not power) but a ‘kWh per year’ is a unit of power. The average electric bill indicates that a consumer pays about $0.12 per kWh of electric energy.

1. Your Uncle Joe wants to get off the grid and save money. Using Craigslist to its fullest potential Joe purchases a collection of old exercise bikes, wires those bikes into his home circuitry as generators, and hires a group of laborers to work out on these bikes for 8 hour periods (three eight hour shifts per day). To satisfy his electrical power need (which is very average) how many exercise bikes would Joe need to buy and how many laborers would he need to hire?

2. Recognizing the futility of his exercise bike plan but remaining reluctant to admit defeat, Joe next purchases a handful of portable gasoline-powered generators to power his average lifestyle. How much money will Joe spend per day on gasoline?

   1. The energy density of gasoline is about 44 MJ/kg; Typical gasoline has a density of about 800 kg/m^3; 1 cubic foot holds 7.5 gallons. Assume that about 30% of the energy released from burning gasoline is converted to electricity (i.e. the efficiency of the generators is about 0.3). The US average gasoline price on 2/4/19 is about $2.25 per gallon.

Answer 1