Energy Sciences

How Do We Get the Energy We Need?

We owe the sun for most of our energy here on Earth.  Without it, well, there wouldn’t be much here for us.  The energy radiating from the sun has enriched our planet by providing conditions possible to support life.  That energy is abundant, and a great deal has been stored and can be harvested as fuel. 

Human technology for harvesting energy likely evolved when early mankind burned wood (or another fuel source) for heat and light.  In a modern region with electric power, a power plant produces electricity by changing the chemical energy in fuel into electrical energy. First, fuel is burned within the plant, converting its chemical energy into heat. Next, the heat turns water into steam, which moves a turbine motor or generator. Finally, the generator produces electricity which then either needs to be stored or transmitted and used.

This steam-based technology was first discovered in the early 1700s when engineers began to figure out ways to use the energy in steam released by boiling water. They developed engines that converted steam energy into mechanical energy for use in farm and factory machinery, and later for trains and cars. The development of the steam engine sparked the period in modern history called the industrial revolution “A typical American family from the time our country was founded used wood (a renewable energy source) as its primary energy source until the mid- to late-1800s. Early industrial growth was powered by water mills. Coal became dominant in the late 19th century before being overtaken by petroleum products in the middle of the last century, a time when natural gas usage also rose quickly.

Since the mid 20th century, the use of coal has again increased (mainly as a primary energy source for electric power generation), and a new form of energy—nuclear electric power—emerged. After a pause in the 1970s, the use of petroleum and natural gas resumed growth, and the overall pattern of energy use since the late 20th century has remained fairly stable.”³

Source: U.S. Energy Information Administration⁴

Energy consumption patterns have changed significantly over the history of the United States as new energy sources have been developed and as uses of energy changed.

Nonrenewable Energy Sources

Nonrenewable energy sources are classified as nonrenewable because they can not be replenished in a short time.  Most nonrenewable energy sources are based on crude oil (petroleum), natural gas, and coal.  These are known as fossil fuels.  Uranium is also considered a nonrenewable resource because it has to be mined or harvested from seawater. 

Crude Oil: “Crude oil is a mixture of hydrocarbons that formed from plants and animals that lived millions of years ago. Crude oil is a fossil fuel, and it exists in liquid form in underground pools or reservoirs, in tiny spaces within sedimentary rocks, and near the surface in tar or oil sands. Petroleum products are fuels made from crude oil and other hydrocarbons contained in natural gas. Petroleum products can also be made from coal, natural gas, and biomass. After crude oil is removed from the ground, it is sent to a refinery where different parts of the crude oil are separated into useable petroleum products. These petroleum products include gasoline, distillates such as diesel fuel and heating oil, jet fuel, petrochemical feedstocks, waxes, lubricating oils, and asphalt.” ⁵

About 100 countries produce crude oil. However, in 2018, five countries accounted for about half of the world's total crude oil production. The top five crude oil producers and their shares of world crude oil production in 2018 were:

• United States—13.2%
• Russia—13.0%
• Saudi Arabia—12.6%
• Iraq—5.6%
• Canada—5.2% ⁶

Natural Gas: Odorless, invisible, and tasteless natural gas is made of many different compounds, with the largest component methane, a compound with one carbon atom and four hydrogen atoms (CH₄).  The chemical methyl mercaptan is added to give it a sulfur odor to help detect leaks.  Like crude oil, natural gas is a fossil fuel and a product of millions of years worth of plants and animals, including diatoms, that decomposed and were buried in the crust of the earth.  Some of this carbon and hydrogen-rich material, over time and pressure and heat, formed into either coal, natural gas, or crude oil.  When burned, it is an energy source.  There are several sources of natural gas, including on-shore and off-shore oil wells and coal beds.  However, “during the 1980s and 1990s, Mitchell Energy experimented with alternative methods of hydraulically fracturing the Barnett Shale (a geological formation in northern Texas). By 2000, the company had developed a hydraulic fracturing technique that produced commercial volumes of shale gas. As the commercial success of the Barnett Shale became apparent, other companies started drilling wells in this formation, and by 2005, the Barnett Shale was producing almost half a trillion cubic feet (Tcf) of natural gas per year.”⁷ This technology continues to evolve, with horizontal drilling allowing even greater access to previously hard to reach reserves.  Fracking technology, while greatly increasing our national supply of energy resources, also has environmental concerns.  Fracking requires high-pressure water and chemicals injected into the ground, which introduces a concern over triggering earthquakes and storage of wastewater, in addition to how much freshwater is contaminated in the process.  “One of the main chemicals released in the fracking process is methane, and it is estimated that 4% of it escapes into the atmosphere during extraction. Because methane is 25 times stronger than carbon dioxide in terms of trapping heat, the release of this gas is detrimental to the air quality of surrounding fracking sites.”⁸ Most of the methane is burned off, and large sites like North Dakota’s Bakken Shale look as bright as a large city at night due to the flaring of methane gas. Similar sites in New Mexico and Texas are also flaring large amounts of methane as a waste byproduct of fracking. 

Coal: Coal is a dark-colored sedimentary rock heavy in carbon and hydrocarbons that accumulated over millions of years as energy stored in swampy plants became buried and exposed to long term heat and pressure.  There are several different types of coal, categorized by carbon content.  About half of the coal produced in the coal mining regions around West Virginia, Kentucky, Indiana, and Pennsylvania contain bituminous coal, which is abundant and has a high enough carbon content to generate electricity or to be used as a raw material for making metals such as iron and steel.  Coal mining has environmental impacts, such as above-ground environmental destruction, water pollution, and the venting of methane gas.  Burning coal releases several compounds that have harmful effects.  Nitrogen oxides, sulfur dioxides, and particulate matter contribute to a hazy smog and can trigger respiratory illnesses and acid rain.  The release of carbon dioxide is another huge detriment to the burning of coal.  Carbon dioxide is a greenhouse gas, and the world has seen historic concentrations of it in our atmosphere on a growing trend over the past 100 years. The effects of a warmer climate are predicted to have rippling effects throughout the world, including climate and ocean shifts that can have a devastating impact on world economies and populations.  While coal may be an abundant and currently inexpensive resource, we must live through whatever happens as a result of its use and it is time for an energy dependence shift.

Nuclear: Nuclear fission of uranium atoms produces a large amount of heat and radiation.  The nuclear reaction is controlled within a nuclear power plant and the resulting energy is used for the generation of electricity. Uranium is more abundant than silver, but nuclear power plants require a rarer form known as U-235 because its atoms are easier to split.  While nuclear power plants do not produce direct carbon dioxide emissions, radioactive waste needs to be contained and either disposed of or stored away.  The cost of constructing and maintaining a nuclear power plant, obtaining and processing U-235, and taking care of waste by-products are all concerns related to the continued use of nuclear energy. 

Renewable Energy Resources

Renewable energy sources are sustainable alternatives to fossil fuels because are constantly renewed by natural means.  Several of the top sources are biomass, geothermal, hydrogen, hydropower, solar, ocean thermal, and wind.  Although these alternatives do pose some environmental concerns, they are a much cleaner source of energy if the means of production and storage or transmission are practical and the challenges of any environmental impact can be mediated. The reduction of carbon dioxide should be a priority, as this will have the most global impact.  Regional availability of resources, energy production and storage technology, governmental policy, financial interests, and worldwide collaboration are all factors in making an energy resource shift.

Biomass: Biomass fuels are produced from organic materials such as wood, waste, ethanol, biodiesel, and landfill gas. These fuels can either be burned directly or converted to liquid biofuels such as ethanol.  These organic materials are formed via solar energy through the process of photosynthesis. 

Geothermal: Geothermal energy is the result of the slow decay of radioactive particles in the earth's core.  The earth has four major parts or layers: an inner core of iron, an outer core of molten rock, a mantle of magma and rock surrounding the outer core, and a crust of solid rock that is between 15 to 35 miles thick under the continents and 3 to 5 miles thick under the oceans. “Scientists have discovered that the temperature of the earth's inner core is about 10,800 degrees Fahrenheit (°F), which is as hot as the surface of the sun.”⁹ Water heated by a geothermal process is at the surface in the form of hot springs.  Regions with easy access to this natural resource can use it as a source of heating and cooling, or electricity production.  In Iceland, they use geothermal heating in most of their public buildings.  Geothermal reserves can also be found by drilling into the crust.  “The United States leads the world in the amount of electricity generated with geothermal energy. In 2018, there were geothermal power plants in seven states, which produced about 16.7 billion kilowatt-hours (kWh), equal to 0.4% of total U.S. utility-scale electricity generation.” ¹⁰

Hydrogen: The combination of hydrogen and oxygen molecules in a fuel cell produces an electric current and zero carbon dioxide emissions. Liquid hydrogen is currently used as rocket fuel, and gaseous hydrogen is used for treating metals and processing petroleum.  It can be used as a more efficient fuel source than fossil fuels for powering an internal combustion engine.  A major obstacle to the adoption of hydrogen-based transportation is the availability of fueling stations within our current infrastructure, although many large cities are using hydrogen to power public transportation.

Hydropower: Hydropower relies on the process of the water cycle.  Flowing water is used to spin a turbine or turn a wheel, resulting in kinetic energy.  This kinetic energy is converted to electrical energy which can then be stored or transmitted.  In most cases, hydropower is a practical resource if located near the source of water due to the expense of transportation or limitations of storage technology.

Ocean Thermal and Tidal: Ocean thermal conversion uses the temperature differences between deep, cool water and warm, shallow water to run a heat engine and produce electricity.  A tidal barrage system, which uses sluice gates to control water levels, is a potential energy resource in regions that have the necessary topography.  Tidal turbines, which need to be resistant to corrosion and ocean elements, can be placed on the seafloor in strong tidal zones.  “The United States does not have any tidal power plants, and it only has a few sites where tidal energy could be economical to produce. France, England, Canada, and Russia have much more potential to use tidal power.” ¹¹

Solar: The sun has been producing energy for billions of years and it is the root source of most of the energy on Earth.  We can also directly collect solar energy for electricity using photovoltaic cells. “Sunlight is composed of photons, which are particles of solar energy. These photons contain varying amounts of energy that correspond to the different wavelengths of the solar spectrum. A PV cell is made of semiconductor material. When photons strike a PV cell, they may reflect off the cell, pass through the cell, or be absorbed by the semiconductor material. Only the absorbed photons provide energy to generate electricity. When the semiconductor material absorbs enough sunlight (solar energy), electrons are dislodged from the material's atoms. Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to the dislodged, or free, electrons, so the electrons naturally migrate to the surface of the cell.”¹² Solar cells are easy to add to the tops of buildings and in open areas that receive a lot of direct sunlight.  Solar energy does not release additional carbon into the air as a result of the energy conversion, so it is a suitable alternative source of fuel only limited by the amount of available sunlight.  Photovoltaic cells can be small and generate enough electricity to power a watch or calculator.  Larger cells can be used to heat or cool homes and water.  Even larger installations can be used to power big areas.  Current photovoltaic cells are about 18% efficient at absorbing and converting solar energy.  The main obstacles to solar energy usage are the cost to generate and store electricity and the availability of enough sunlight to meet the energy demand.  Dr. Brudvig, the Yale seminar leader for the seminar sessions from which this unit was created, is currently researching artificial photosynthesis and methods of storing and releasing energy held in chemical bonds, similar to the process used by all of the green plants on Earth.  Current solar energy technologies also use solar energy to heat molten salt (which can store that heat for several hours after sunset).  In other areas, solar energy is distributed to other regions or stored in advanced, large capacity batteries. 

Wind: As the sun shines down on the land and water, various areas absorb and reflect solar energy at different rates.  This uneven heating and cooling process drives the movement of large air masses.  This energy can be collected through spinning turbines and transferred to an electrical generator to convert mechanical energy to electrical energy using the principle of electromagnetic induction.  “In 2018, wind turbines in the United States were the source of about 6.6% of total U.S. utility-scale electricity generation.

The amount of electricity generated from wind has grown significantly since 2000. Electricity generation from wind in the United States increased from about 6 billion kilowatt-hours (kWh) in 2000 to about 275 billion kWh in 2018. New technologies have decreased the cost of producing electricity from wind, and growth in wind power has been encouraged by government and industry incentives.”  ¹³