energy

Defining Energy and Power

Energy is the fundamental driver of most of the processes we care about. It drives photosynthesis to make plants grow, it powers cellular functions, and its modern forms make today’s societies different from those of antiquity.

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A New Definition of Humanity

Manipulating forms of energy distinguishes humans from other species; humans are the only species that deliberately converts energy from one form to another

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Modern Thermodynamics

Before the energy in fuels can be harnessed, it must be transformed. These transformations are governed by the laws of thermodynamics.

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The Steam-Powered Revolution

The relationship between energy and water has been important since the dawn of the Industrial Revolution.

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The First Law of Thermodynamics

The total amount of energy in a closed system remains constant. It can only be changed from one form to another or transferred from one body to another.

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Types of Energy

Energy—the ability to do work—can be divided into six different forms.

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Entropy: The Second Law of Thermodynamics

The second law of thermodynamics manifests as inefficiencies, losses, and waste streams during energy conversion, such as waste heat, lost fuel, or suboptimal operation of systems.

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Turning On the Lights: Conversions and Efficiencies

Flipping a light switch begins a sequence of energy conversions before you ever see the light.

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Primary Resources and Secondary Energy

Primary energy resources are those found in nature. Secondary energy resources are those forms that must be produced by conversion of primary resources.

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Global Energy Flows and Reservoirs

The earth and its atmosphere have flows and reservoirs of energy sources that are converted into useful energy services such as heating and motion.

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Fossil Fuels

Conventional fossil fuels include coal, natural gas, and liquid petroleum that has accumulated in Earth’s crust. The geologic time scale over which fossil fuels form—hundreds of millions of years—lies outside human time horizons, so these resources are considered for practical purposes to be finite and exhaustible.

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Renewable Energy

Renewable energy sources replenish continually or annually. Wind, solar, and hydro can never deplete, as meteorological, astronomical, and geological forces are not anticipated to end on any timeline that is relevant to human planning purposes.

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Energy Transitions

The historical transitions from wood to coal to oil reveal three very important aspects: transitions take a long time; transitions have a distinct trend towards decarbonization; and there has been an unmistakable pattern of growth in energy consumption ever since the Second Industrial Revolution.

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End Uses of Energy

There are four different end-use sectors responsible for energy consumption: transportation, residential, commercial and industrial. In addition, the electric power sector consumers a lot of primary energy that is subsequently used in the other four sectors.

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The Kaya Identity

Japanese energy economist Yoichi Kaya developed the Kaya identity as a function relating factors that determine the level of human impact on climate, in the form of emissions of the greenhouse gas, carbon dioxide.

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Carrying Capacity

As absolute energy and water use increases due to population growth and economic growth, it is worth considering what the ultimate carrying capacity of the earth is. That determination depends on factors such as how many people inhabit the earth and the quantity of resources they use for their existence.

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