# 7: Energy

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Energy for lighting, heating and cooling our buildings, manufacturing products, and powering our transportation systems comes from a variety of natural sources. The earth’s core provides geothermal energy. The gravitational pull of moon and sun create tides. The sun emits light (electromagnetic radiation), which creates wind, powers the water (hydrologic) cycle, and enables photosynthesis. Plants, algae, and cyanobacteria utilize solar energy to grow and create biomass that can be burned and used for biofuels, such as wood, biodiesel, bioethanol. Over the course of millions of years, biomass from photosynthetic organisms can create energy-rich fossil fuels through the geologic process of burial and transformation through heat and pressure.

Each of these types of energy can be defined as renewable or non-renewable. Renewable energy sources can be replenished within human lifespans. Examples include solar, wind, and biomass energy. Nonrenewable energy is finite and cannot be replenished within a human timescale. Examples include nuclear energy and fossil fuels, which take millions of years to form. All energy sources have some environmental and health costs, and the distribution of energy is not equally distributed among all nations. The environmental impacts of energy use on humans and the planet can happen anywhere during the life cycle of the energy source. The impacts begin with the extraction of the resource. They continue with the processing, purification or manufacture of the source; its transportation to place of energy generation, and ends with the disposal of waste generated during use.

Figure $$\PageIndex{a}$$: How much of the worlds energy comes from renewable sources. Graph by Our World in Data (CC-BY)

Modified by Kyle Whittinghill, Melissa Ha and Rachel Schleiger from the following sources:

• 7.1: Energy from Fossil Fuels
We are heavily dependent on fossil fuels, which comprise 62.6% of electricity generation in the United States and 84.3% of global energy consumption. Coal reserves are abundant in the United States, but globally, proven oil and natural gas reserves are projected to last another 50 years.
• 7.2: Nuclear Energy
The nuclear fuel cycle describes the mining, milling, and enrichment of uranium ore to produce nuclear fuel as well as disposal of wastes. Nuclear reactors contain reactor cores, where nuclear fission takes place, and the machinery needed to generate electricity. Nuclear fission releases heat, which produces high-pressure steam to turn a turbine and power a generator.
• 7.3: Solar Energy
Solar energy comes from the sun and can be used for lighting, heating, and electricity. Advantages of using solar energy are that it generates few air pollutants and contributes little to climate change; however, cost and limitations in battery capacity are disadvantages.
• 7.4: Hydropower
Hydropower (hydroelectric energy) is the energy of movement in water. Dams and reservoirs are a common use of hydropower. The filling of reservoirs destroys terrestrial habitat, which decompose to release methane. However, the operation of hydroelectric power plants does not release air pollutants. Smaller run-of-the-river hydroelectric plants have minimal environmental impact.
• 7.5: Geothermal Energy
Geothermal energy refers to heat from deep within the Earth. It can be used to generate electricity. Additionally, cool temperatures underground (close to the surface) can directly to heat or cool buildings. While it is reliable and generates minimal air pollution, building geothermal power plants is costly and limited to specific locations.
• 7.6: Wind Energy
Wind energy is harnessed into electricity when wind spins the blades of a wind turbine, powering a generator. While wind energy creates jobs, is relatively inexpensive, and generates minimal pollution, it is intermittent. Additionally, some find the the sight and sound of them off-putting.
• 7.7: Biofuels (Biomass Energy)
Biofuels contain energy from organisms. There are many forms of biofuels, including trash, animal waste, plants and their products, and wood. Some biofuel uses are more sustainable than others, particularly those that use materials that would otherwise be discarded. Biofuels are carbon neutral, but burning them does pollute the air.
• 7.8: The Electrical Grid, Battery Challenges, and Energy Conservation
Energy conservation refers to reducing energy waste and increasing efficiency. This can involve behaviors or technologies. Some have no cost, but others require financial investment.

Thumbnail image - "Renewable energy on the grid" is in the Public Domain

This page titled 7: Energy is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Melissa Ha and Rachel Schleiger (ASCCC Open Educational Resources Initiative) .