A Comparison of Energy Densities of Prevalent Energy Sources in Units of Joules Per Cubic Meter

Typically, the energy densities of solids or liquids such as coal and oil are measured in dimensions of energy per unit volume or energy per unit mass, whereas solar, wind, and hydroelectric sources are rated in dimensions of power per unit area. This article provides a unifying framework for comparing several prevalent energy sources on an energy-per-unit volume basis for the purpose of unifying conventional metrics. The energy density of oil is 35 to 45 gigajoules (10,000 kWh) per cubic meter∗ ∗One gigajoule equals one billion joules, and there are 3,600,000 joules in a kWh. A cubic meter is about half the volume of a kitchen refrigerator. . When measured using the methods presented, solar energy has a density of 1.5 microjoules per cubic meter, over twenty quadrillion times less than oil. Human energy density is approximately 1000 J/m3, while other inexhaustibles such as wind and tidal have energy densities of 0.5 to 50 J/m3. This article provides an educational engineering mathematics framework for calculating energy densities of prevalent energy sources. The goal is to provide a new perspective on how to compare energy sources on a more fundamental basis. Finally, the article provides a method of estimating the dollars-per-joule for natural resources versus human resources and concludes with commentary on how political decisions may be affected by energy densities and energy costs.