Energy from the Sun

Basics

Energy from the sun

The sun has produced energy for billions of years and is the ultimate source for all of the energy sources and fuels that we use today. People have used the sun's rays (solar radiation) for thousands of years for warmth and to dry meat, fruit, and grains. Over time, people developed devices (technologies) to collect solar energy for heat and to convert it into electricity.

Radiant energy from the sun has powered life on earth for many millions of years.

Source: NASA

Collecting and using solar thermal (heat) energy

An example of an early solar energy collection device is the solar oven (a box for collecting and absorbing sunlight). In the 1830's, British astronomer John Herschel used a solar oven to cook food during an expedition to Africa. People now use many different technologies for collecting and converting solar radiation into useful heat energy for a variety of purposes.

We use solar thermal energy systems to

● heat water for use in homes, buildings, or swimming pools

● heat the inside of homes, greenhouses, and other buildings

● heat fluids to high temperatures in solar thermal power plants

Solar photovoltaic systems convert sunlight into electricity

Solar photovoltaic (PV) devices, or solar cells, change sunlight directly into electricity. Small PV cells can power calculators, watches, and other small electronic devices. Arrangements of many solar cells in PV panels and arrangements of multiple PV panels in PV arrays can produce electricity for an entire house. Some PV power plants have large arrays that cover many acres to produce electricity for thousands of homes.

Solar energy has benefits and some limitations

The two main benefits of using solar energy are

● Solar energy systems do not produce air pollutants or carbon dioxide.

● Solar energy systems on buildings have minimal impact on the environment.

The main limitations of solar energy are

● The amount of sunlight that arrives at the earth's surface is not constant. The amount of sunlight varies depending on location, time of day, season of the year, and weather conditions.

● The amount of sunlight reaching a square foot of the earth's surface is relatively small, so a large surface area is necessary to absorb or collect a useful amount of energy.

Solar Energy and the Environment – Basics

An array of solar photovoltaic panels supplies electricity for use at Marine Corps Air Ground Combat Center in Twentynine Palms, California

Source: U.S. Marine Corps photo by Pfc. Jeremiah Handeland/Released (public domain)

Solar energy does not produce air or water pollution or greenhouse gases. However, using solar energy may have some indirect negative impacts on the environment. For example, some toxic materials and chemicals are used to make the photovoltaic (PV) cells that convert sunlight into electricity. Some solar thermal systems use potentially hazardous fluids to transfer heat. U.S. environmental laws regulate the use and disposal of these types of materials.

As with any type of power plant, large solar power plants can affect the environment near their locations. Clearing land for construction and the placement of the power plant may have long-term affects on habitat areas for native plants and animals. Some solar power plants may require water for cleaning solar collectors and concentrators or for cooling turbine generators. Using large volumes of ground water or surface water in some arid locations may affect the ecosystems that depend on these water resources. In addition, the beam of sunlight a solar power tower creates can kill birds and insects that fly into the beam.

Wind – Basics

Energy from moving air

How uneven heating of water and land causes wind

Source: Adapted from National Energy Education Development Project (public domain)

Wind is caused by uneven heating of the earth's surface by the sun. Because the earth's surface is made up of different types of land and water, it absorbs the sun's heat at different rates. One example of this uneven heating is the daily wind cycle.

The daily wind cycle

During the day, air above the land heats up faster than air over water. Warm air over land expands and rises, and heavier, cooler air rushes in to take its place, creating wind. At night, the winds are reversed because air cools more rapidly over land than it does over water.

In the same way, the atmospheric winds that circle the earth are created because the land near the earth's equator is hotter than the land near the North Pole and the South Pole.

Wind energy for electricity generation

Today, wind energy is mainly used to generate electricity, although water pumping windmills were once used throughout the United States.

Electricity Generation from Wind – Basics

How wind turbines work

Diagram of wind turbine components

Source: National Renewable Energy Laboratory, U.S. Department of Energy (public domain)

Wind turbines use blades to collect the wind’s kinetic energy. Wind flows over the blades creating lift (similar to the effect on airplane wings), which causes the blades to turn. The blades are connected to a drive shaft that turns an electric generator that produces the electricity.

Electricity generation with wind

In 2015, wind turbines in the United States were the source of nearly 5% of total U.S. electricity generation. Although wind's share of the country's total electricity production is small, it was equal to the electricity use of about 17.5 million U.S. households in 2014.

The amount of electricity generated from wind has grown significantly over the past 15 years. Electricity generation from wind in the United States increased from about 6 billion kilowatthours (kWh) in 2000 to about 191 billion kWh in 2015.

New technologies have decreased the cost of producing electricity from wind, and growth in wind power has been encouraged by government and industry incentives.

Wind Energy and the Environment – Basics

Wind is an emissions-free source of energy

Wind turbines at the Cerro Gordo Project, west of Mason City, Iowa

Source: National Renewable Energy Laboratory (public domain)

Wind is a renewable energy source. Overall, using wind to produce energy has fewer environmental impacts than many other energy sources. Wind turbines do not release emissions that can pollute the air or water (with rare exceptions), and they do not require water for cooling. Wind turbines may also reduce the amount of electricity generated from fossil fuels, which reduces total air pollution and carbon dioxide emissions.

An individual wind turbine has a relatively small physical footprint. Groups of wind turbines, sometimes called wind farms, are located on open land, on mountain ranges, or offshore in lakes or the ocean.

Wind turbines have some negative impacts on the environment

Modern wind turbines are large machines, and they have a visual impact on the landscape. A small number of wind turbines have also caught fire, and some have leaked lubricating fluids, but these occurrences are rare. Some people do not like the sound that wind turbine blades make as they turn in the wind. Some types of wind turbines and wind projects cause bird and bat deaths. These deaths may contribute to declines in the population of species also affected by other human-related impacts. The wind energy industry and the U.S. government are researching ways to reduce the impact of wind turbines on birds and bats.

Most wind power projects on land also require service roads that add to the physical impact on the environment. Wind turbines also require the use of rare earth minerals. These minerals are often located in countries with less stringent environmental standards than the United States, and mining these minerals can have negative impacts on the environment. Producing the metals and other materials used to make wind turbines and the concrete used for their foundations requires energy that may have been produced by fossil fuels.

Basics

Energy from moving water

Source: Adapted from National Energy Education Development Project (public domain)

Hydropower generates electricity

Hydropower is the largest renewable energy source for electricity generation in the United States. In 2015, hydropower accounted for about 6% of total U.S. electricity generation and 46% of electricity generation from all renewables.

Because the source of hydroelectric power is water, hydroelectric power plants are usually located on or near a water source.

Hydropower relies on the water cycle

Understanding the water cycle is important to understanding hydropower. The water cycle has three steps:

● Solar energy heats water on the surface of rivers, lakes, and oceans, which causes the water to evaporate.

● Water vapor condenses into clouds and falls as precipitation (rain, snow, etc.).

● Precipitation collects in streams and rivers, which empty into oceans and lakes, where it evaporates and begins the cycle again.

The amount of precipitation that drains into rivers and streams in a geographical area determines the amount of water available for producing hydropower. Seasonal variations in precipitation and long-term changes in precipitation patterns, such as droughts, have a big impact on hydropower production.

Hydroelectric power is produced from moving water

The volume of the water flow and the change in elevation (or fall) from one point to another determine the amount of available energy in moving water. Swiftly flowing water in a big river, like the Columbia River that forms the border between Oregon and Washington, carries a great deal of energy in its flow. Water descending rapidly from a high point, like Niagara Falls in New York, also has substantial energy in its flow.

At both Niagara Falls and the Columbia River, water flows through a pipe, or penstock, then pushes against and turns blades in a turbine to spin a generator to produce electricity. In a run-of-the-river system, the force of the current applies pressure on a turbine. In a storage system, water accumulates in reservoirs created by dams and is released as needed to generate electricity.

Hydropower and the Environment – Basics

Hydropower generators produce clean electricity, but hydropower does have environmental impacts

Most dams in the United States were built mainly to control floods and to help supply water for cities and irrigation. Although many of these dams have hydroelectric generators, only a small number of dams were built specifically for hydropower generation. Although hydropower generators do not directly produce emissions of air pollutants, dams, reservoirs, and the operation of hydropower electric generators can affect the environment.

Fish ladder at the Bonneville Dam on the Columbia River separating Washington and Oregon

Source: Stock photography (copyrighted)

Did you know?

The Safe Harbor Dam on the Susquehanna River in Pennsylvania has elevators that lift migrating shad from the base of the dam to the top of the reservoir.

A dam that creates a reservoir (or a dam that diverts water to a run-of-river hydropower plant) may obstruct fish migration. A reservoir and dam can also change natural water temperatures, water chemistry, river flow characteristics, and silt loads. All of these changes can affect the ecology and the physical characteristics of the river. These changes may have negative impacts on native plants and on animals in and around the river. Reservoirs may cover important natural areas, agricultural land, or archeological sites. A reservoir and the operation of the dam may also result in the relocation of people. The physical impacts of a dam and reservoir, the operation of the dam, and the use of the water can change the environment over a much larger area than the area covered by a reservoir.

Although no new hydropower dams have been built recently in the United States, they are being built in other countries like China. Manufacturing the concrete and steel used to construct these dams requires equipment that may produce emissions. If fossil fuels are used as the energy source to make these materials, then the emissions from the equipment could be associated with the electricity that hydropower facilities generate. However, given the long operating lifetime of a hydropower plant (50 years to 100 years) these emissions are offset by the emissions-free electricity that is generated.

Carbon dioxide and methane may also form in reservoirs and be emitted into the atmosphere. The exact amount of greenhouse gases produced in hydropower reservoirs is uncertain. The emissions from reservoirs in tropical and temperate regions, including the United States, may be equal to or greater than the greenhouse effect of the carbon dioxide emissions from an equivalent amount of electricity generated with fossil fuels. Scientists at Brazil's National Institute for Space Research designed a system to capture methane in a reservoir and burn it to produce electricity.

Fish ladders help salmon reach their spawning grounds

Hydropower turbines kill and injure some of the fish that pass through the turbine. The U.S. Department of Energy has sponsored the research and development of turbines that could reduce fish deaths to lower than 2%, in comparison to fish kills of 5% to 10% for the best existing turbines.

There are many species of fish, such as salmon, that swim from the sea up rivers and streams to reproduce in their spawning grounds in the beds of rivers and streams. Dams block their way. Different approaches to fixing this problem have been used, including the construction of fish ladders and elevators that help fish move through or around dams to the spawning grounds upstream.

Basics

Biomass—renewable energy from plants and animals

Source: Adapted from The National Energy Education Project (public domain)

Source: Adapted from The National Energy Education Project (public domain)

Biomass is organic material that comes from plants and animals, and it is a renewable source of energy.

Biomass contains stored energy from the sun. Plants absorb the sun's energy in a process called photosynthesis. When biomass is burned, the chemical energy in biomass is released as heat. Biomass can be burned directly or converted to liquid biofuels and biogas that are burned as fuels. Examples of biomass and their uses for energy:

● wood and wood processing wastes—burned to heat buildings, to produce process heat in industry, and to generate electricity

● agricultural crops and waste materials—burned as a fuel or converted to liquid biofuels

● food, yard, and wood waste in garbage—burned to generate electricity in power plants or converted to biogas in landfills

● animal manure and human sewage—converted to biogas, which can be burned as a fuel

Converting biomass to other forms of energy

Burning biomass is only one way to release its energy. Biomass can be converted to other useable forms of energy like methane gas or transportation fuels like ethanol and biodiesel.

Methane gas is a component of landfill gas or biogas that forms when garbage, agricultural waste, and human waste decompose in landfills or in special containers called digesters.