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Home Green (Renewable) Energy


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Photosynthesis. In the process of photosynthesis, plants convert radiant energy from the sun into chemical energy in the form of glucose or sugar. Water plus carbon dioxide plus sunlight yields glucose plus oxygen. Six water plus six carbon dioxide plus radiant energy yields sugar plus six oxygen.Renewable Energy from Plants and Animals

Biomass is organic material made from plants and animals. Biomass contains stored energy from the sun. Plants absorb the sun's energy in a process called photosynthesis. The chemical energy in plants gets passed on to animals and people that eat them.

Biomass is a renewable energy source because we can always grow more trees and crops, and waste will always exist. Some examples of biomass fuels are wood, crops, manure, and some garbage.

When burned, the chemical energy in biomass is released as hyeat. If you have a fireplace, the wood you burn in it is a biomass fuel. Wood waste or garbage can be burned to produce steam for making electricity, or to provide heat to industries and homes.

Converting Biomass to Other Forms of Energy

Image with different kinds of biomass types: wood, crops, garbage, landfill gas, and alcohol fuelsBurning biomass is not the only way to release its energy. Biomass can be converted to other useable forms of energy, such as methane gas or transportation fuels, such as ethanol and biodiesel.

Methane gas is the main ingredient of natural gas. Smelly stuff, like rotting garbage, and agricultural and human waste, release methane gas — also called "landfill gas" or "biogas."

Crops like corn and sugar cane can be fermented to produce ethanol. Biodiesel, another transportation fuel, can be produced from left-over food products like vegetable oils and animal fats.

How Much Biomass Is Used for Fuel?

Biomass fuels provide about 4% of the energy used in the United States. Researchers are trying to develop ways to burn more biomass and less fossil fuels. Using biomass for energy may cut back on waste and greenhouse gas emissions.


Solar Energy

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Energy from the Sun

Solar EnergyThe sun has produced energy for billions of years.  Solar energy is the sun’s rays (solar radiation) that reach the Earth. This energy can be converted into other forms of energy, such as heat and electricity.


In the 1830s, the British astronomer John Herschel famously used a solar thermal collector box (a device that absorbs sunlight to collect heat) to cook food during an expedition to Africa. Today, people use the sun's energy for lots of things.

Solar Energy Can Be Used for Heat and Electricity

When converted to thermal (or heat) energy, solar energy can be used to:

  • Heat water — for use in homes, buildings, or swimming pools
  • Heat spaces — inside homes, greenhouses, and other buildings

Solar energy can be converted to electricity in two ways:

  • Photovoltaic (PV devices) or “solar cells” change sunlight directly into electricity. Individual PV cells are grouped into panels and arrays of panels that can be used in a wide range of applications ranging from single small cells that charge calculator and watch batteries, to systems that power single homes, to large power plants covering many acres.
  • Concentrating Solar Power Plants generate electricity by using the heat from solar thermal collectors to heat a fluid which produces steam that is used to power the generator. Out of the 11 known concentrating solar power generating units operating in the United States at the end of 2008, 9 of these are in California, 1 in Arizona, and 1 in Nevada.

Two drawbacks of solar energy are:

  • The amount of sunlight that arrives at the Earth's surface is not constant. It depends on location, time of day, time of year, and weather conditions.
  • Because the sun doesn't deliver that much energy to any one place at any one time, a large surface area is required to collect the energy at a useful rate.

Wind Energy

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Energy from Moving Air

How Uneven Heating of Water and Land Causes Wind
Image of how uneven heating of water and land causes wind.   Land heats up faster than water.  Warm air over the land rises.  Cool air over the water moves in.
Source: National Energy Education Development Project (Public Domain)

Wind is simply air in motion. It is caused by the uneven heating of the Earth's surface by the sun. Because the Earth's surface is made of very different types of land and water, it absorbs the sun's heat at different rates. One example of this uneven heating can be found in the daily wind cycle.

The Daily Wind Cycle

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

In the same way, the atmospheric winds that circle the earth are created because the land near the Earth's equator is heated more by the sun than the land near the North and South Poles.

Wind Energy for Electricity Generation

Today, wind energy is mainly used to generate electricity. Wind is a renewable energy source because the wind will blow as long as the sun shines.



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Energy From Moving Water

Image of the water cycle. Solar energy heats water on the surface, causing it to evaporate.  This water vapor condenses into clouds and falls back onto the surface as precipitation.  The water flows through rivers back into the oceans, where it can evaporate and begin the cycle over again.Hydropower Generates Electricity

Hydropower is the renewable energy source that produces the most electricity in the United States. It accounted for 6% of total U.S. electricity generation and 67% of generation from renewables in 2008.

Hydropower Relies on the Water Cycle

Understanding the water cycle is important to understanding hydropower. In the water cycle:

  • Solar energy heats water on the surface, causing it to evaporate.
  • This water vapor condenses into clouds and falls back onto the surface as precipitation (rain, snow, etc.).
  • The water flows through rivers back into the oceans, where it can evaporate and begin the cycle over again.


Mechanical Energy Is Harnessed from Moving Water

The amount of available energy in moving water is determined by its flow or fall. 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 very high point, like Niagara Falls in New York, also has lots of energy in its flow.

Image of how a hydropower plant works. The water flows from behind the dam through penstocks, turns the turbines, and causes the generators to generate electricity. The electricity is carried to users by a transmission line. Other water flows from behind the dam over spillways and into the river below.In either instance, the 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 the needed pressure, while in a storage system, water is accumulated in reservoirs created by dams, then released as needed to generate electricity.

History of Hydropower

Hydropower is one of the oldest sources of energy. It was used thousands of years ago to turn a paddle wheel for purposes such as grinding grain.  Our Nation's first industrial use of hydropower to generate electricity occurred in 1880, when 16 brush-arc lamps were powered using a water turbine at the Wolverine Chair Factory in Grand Rapids, Michigan.

The first U.S. hydroelectric power plant opened on the Fox River near Appleton, Wisconsin, on September 30, 1882.

Because the source of hydroelectric power is water, hydroelectric power plants must be located on a water source. Therefore, it wasn't until the technology to transmit electricity over long distances was developed that hydropower became widely used.


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