by Michael Sivak.
This analysis compares the costs of usable energy when we buy gasoline and electricity for driving and natural gas for keeping warm. The unifying approach in this comparison involves the use of Btu (British thermal units), coupled with the costs of gasoline, electricity, and natural gas, and the energy efficiencies of light-duty vehicles (cars and light trucks) and furnaces.
Combustion of a gallon of gasoline (that includes ethanol) releases 120,333 Btu of energy.
The average retail cost of regular gasoline in 2018 was $2.719 per gallon.
Consequently, the average cost of the available energy from gasoline is $0.226 per 10,000 Btu.
The energy efficiency of conventional gasoline-powered vehicles ranges from 17% to 21%.
Assuming the energy efficiency of gasoline-powered vehicles of 19%, the cost of the usable energy from gasoline in vehicles is $1.189 per 10,000 Btu.
One kWh of electricity corresponds to 3,412 Btu.
The average residential cost of electricity in 2018 was $12.87 per 100 kWh.
Consequently, the average cost of the available energy from electricity is $0.377 per 10,000 Btu.
The energy efficiency of all-electric vehicles ranges from 59% to 62%.
Assuming the energy efficiency of all-electric vehicles of 61%, the cost of the usable energy from electricity in vehicles is $0.618 per 10,000 Btu.
Combustion of 100 cubic feet of natural gas releases 103,600 Btu of energy.
The average residential cost of natural gas in 2018 was $1.052 per 100 cubic feet.
Consequently, the average cost of the available energy from natural gas is $0.102 per 10,000 Btu.
The energy efficiency of the currently available natural-gas furnaces ranges from 80% to 98.7%, with a majority of the furnaces at or near the lower efficiency end.
Assuming the energy efficiency of natural-gas furnaces of 85%, the cost of the usable energy from natural gas in furnaces is $0.120 per 10,000 Btu.
The heat generated by furnaces needs to be distributed, typically with air handlers. According to the 2015 Residential Energy Consumption Survey, the additional expenditure for the electricity to power air handlers used with natural-gas furnaces averages about 9% of the expenditure for the natural gas used to fuel those furnaces (personal communication from James Berry, the U.S. Energy Information Administration).
Consequently, the cost of the usable energy from natural gas in furnaces, taking into account the cost of the electricity for air handlers, is $0.131 per 10,000 Btu.
Typical heat losses through ductwork range from 25% to 40%.
Assuming a heat loss of 33%, the cost of the usable energy from natural gas in furnaces, taking into account both the cost of the electricity for air handlers and the heat losses through ductwork, is $0.196 per 10,000 Btu.
The table below presents the findings in terms of the usable energy purchased for one dollar for average scenarios.
The main findings are as follows:
We purchase substantially more usable energy when we buy natural gas for our furnaces than gasoline or electricity for our vehicles. This is the case even after taking into account the cost of the electricity to power air handlers for natural-gas furnaces and the heat losses through ductwork. In average scenarios, one dollar of natural gas buys about six times the amount of usable energy than does one dollar of gasoline and about three times than does one dollar of electricity.
In average vehicle scenarios, one dollar of electricity buys about two times the amount of usable energy than does one dollar of gasoline.
Michael Sivak is the managing director of Sivak Applied Research and the former director of Sustainable Worldwide Transportation at the University of Michigan.