Net Energy

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= “The true value of energy to society is the net energy, which is what’s left after the energy costs of getting and concentrating that energy are subtracted". [1]


Mary Odum:

"All processes in the world involve energy, materials, and information. Materials are transformed through energy, which drives the process of creating every good, service, and environmental process. Information guides the process of transformation. Energy has different qualities, so a calorie of one form of energy is not the same in quality as a calorie of another form, as certain forms of energy are not substitutable, depending on the situation. A calorie of sunlight may not be substituted for a calorie of oil or of food. In order to compare apples and oranges, we need to create a common denominator. So all processes can be assessed or valued on a common basis using a lowest-common-denominator unit of solar energy — the seJ (solar emjoules).

The science of Emergy accounting places values on the energy, information, and materials in the processes, allowing us to choose more efficient policies. Emergy is defined as the available energy of one kind that is used up in transformations directly and indirectly to make a product or service. Real wealth, then, can be measured as the emergy memory that exists in human goods and services, and in non-human environmental goods and services. Odum’s updated term for net energy is net emergy or net empower. The true cost of a process to society is the net emergy, which is the emergy delivered after the emergy costs of getting and concentrating that energy are subtracted.

Net emergy contribution of any process within the economy including energy production can be calculated using an Emergy Yield Ratio, which is the net energy yield of a process expressed in emergy, divided by the purchased goods and services, which are also expressed in emergy. The EYR includes the contributions for renewable and non-renewable sources, and inputs such as human labor/services and environmental contributions, using a quality correction factor for energies of different qualities. Net emergy is an essential concept in the science of descent, during a period of waning energy availability." (