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Reading about energy sources - To prepare speaking activities

Source: US Energy Information Administration. Kids

How we use energy

There are four major sectors that consume energy:

• The industrial sector includes facilities and equipment used for manufacturing, agriculture, mining, and construction.

• The transportation sector includes vehicles that transport people or goods. Cars, trucks, buses, motorcycles, trains, aircraft, boats, and ships are included in the transportation sector.

• The residential sector consists of homes and apartments.

• The commercial sector includes offices, malls, stores, schools, hospitals, hotels, warehouses, restaurants, etc.

Each sector consumes electricity produced by the electric power sector.

Energy and the Environment Basics

The use of energy sources has an effect on the environment. The type and size of the effects vary.

Did You Know? Most of our carbon dioxide emissions come from using coal and petroleum fuels.

|Overviews of each major energy source's impact on the environment |

|Nonrenewable Energy Sources |Renewable Energy Sources |Secondary Energy Sources |

|Oil and Petroleum Products |Hydropower |Electricity |

|Gasoline |Biomass | |

|Diesel Fuel |Ethanol | |

|Natural Gas |Biodiesel | |

|Coal |Wind | |

|Nuclear |Geothermal | |

| |Solar | |

Fire was civilization's first great energy invention, and wood was the main fuel for a long time. Learn how these different energy sources and technologies evolved….

• Coal

• Electricity

• Ethanol

• Geothermal

• Hydropower

• Municipal Solid Waste

• Natural Gas

• Nuclear

• Oil (petroleum)

• Photovoltaic

• Solar Thermal

• Transportation

• Wind

• Wood

Renewable Basics. Renewable energy sources can be replenished. There are 5 commonly used renewable energy sources:

• Biomass—includes:

• Wood & wood waste

• Municipal solid waste

• Landfill gas and biogas

• Ethanol

• Biodiesel

• Hydropower

• Geothermal

• Wind

• Solar

Nonrenewable Basics. There are four major nonrenewable energy sources Crude oil, - Natural gas, - Coal, - Uranium (nuclear energy)

Nonrenewable energy sources come out of the ground as liquids, gases, and solids. Crude oil (petroleum) is the only commercial nonrenewable fuel that is naturally in liquid form. Crude oil is used to make liquid petroleum products like gasoline, diesel fuel, and heating oil. Propane and other gases such as butane and ethane are found in natural gas and crude oil. They are extracted and stored as liquids and are called liquid petroleum gases.

All fossil fuels are nonrenewable, but not all nonren. energy sources are fossil fuels

Coal, crude oil, and natural gas are all considered fossil fuels because they were formed from the buried remains of plants and animals that lived millions of years ago.

Uranium ore, a solid, is mined and converted to a fuel used at nuclear power plants. Uranium is not a fossil fuel, but it is classified as a nonrenewable fuel.

Saving energy

People use energy each day for transportation, cooking, heating and cooling rooms, manufacturing, lighting, entertainment, and many other uses. The choices people make about how they use energy—turning machines off when they're not using them or choosing to buy fuel-efficient vehicles and energy-efficient appliances—affects the environment and everyone's lives.

The terms energy conservation and energy efficiency have two distinct meanings. There are many ways people can use less energy (conservation) and many ways people can use energy more wisely (efficiency).

Energy conservation is any behavior that results in the use of less energy. Turning the lights off when leaving the room and recycling aluminum cans are both ways of conserving energy.

Energy efficiency is the use of technology that requires less energy to perform the same function. Using a compact fluorescent light bulb that requires less energy is an example of energy efficiency.

Recycling is the act of converting waste into reusable material. Recycling often saves energy and natural resources.

Natural resources include land, plants, minerals, and water. By using materials more than once, we conserve natural resources.

Making a product from recycled materials almost always requires less energy than it does to make the product using new materials. For example, using recycled aluminum scrap to make new aluminum cans uses 95% less energy than making aluminum cans from bauxite ore, the raw material used to make aluminum.

Recycling paper saves trees & water. Making a ton of paper from recycled paper saves up to 17 trees and uses 50% less water.

The Energy [R]evolution 2015



The Energy [R]evolution Scenario has become a well known and well respected energy analysis since it was first published for Europe in 2005. In 2015, the fifth Global Energy [R]evolution scenario was published; earlier editions were published in 2007, 2008, 2010, and 2012.

This is the year when the fight against climate change could take a dramatic turn. The conference in Paris in December presents political and business leaders with the opportunity to take the critical decisions needed if we are to keep average temperature rises to no more than 1.5 or 2 degrees Celsius. According to the IPCC, humankind cannot emit more than 1,000 giga-tonnes of CO2 from now, if we are to stay within this limit. At the current and projected rate of consumption, this entire carbon budget will be used by 2040.

Dynamic change is happening in energy supply, but the change needs to happen faster. this Energy [R]evolution scenario proposes a pathway to a 100% sustainable energy supply, ending CO2 emissions and phasing out nuclear energy, and making redundant new oil exploration in the arctic and deep sea waters such as off the coast of Brazil. It also demonstrates that this transformation increases employment in the energy sector.

What is required is for the political will to be there.

Greenpeace has been publishing its Energy [R]evolution scenarios since 2005, more recently in collaboration with the scientific community, in particular the German Aerospace Centre (DLr). While our predictions on the potential and market growth of renewable energy may once have seemed fanciful or unrealistic, they have proved to be accurate. the US-based Meister Consultants Group concluded earlier this year that "the world's biggest energy agencies, financial institutions and fossil fuel companies for the most part seriously under-estimated just how fast the clean power sector could and would grow". It wasn't the IEA, Goldman Sachs or the US Department of Energy who got it right. It was Greenpeace's market scenario which was the most accurate.

COP21: shows the end of fossil fuels is near, we must speed its coming

Posted by Kumi Naidoo — 14 December 2015

Credit: Yann Arthus-Bertrand/Spectral Q

The wheel of climate action turns slowly, but in Paris it has turned. There’s much in this deal that frustrates & disappoints me, but it still puts the fossil fuel industry squarely on the wrong side of history.

Parts of this deal have been diluted and polluted by the people who despoil our planet, but it contains a new temperature limit of 1.5 degrees. That single number, and the new goal of net zero emissions by the second half of this century, will cause consternation in the boardrooms of coal companies and the palaces of oil-exporting states and that is a very good thing. The transition away from fossil fuels is inevitable.

Now comes our great task of this century. How do we meet this new goal? The measures outlined simply do not get us there. When it comes to forcing real, meaningful action, Paris fails to meet the moment. We have a 1.5 degree wall to climb, but the ladder isn’t long enough. The emissions targets outlined in this agreement are simply not big enough to get us to where we need to be.

There is also not enough in this deal for the nations and people on the frontlines of climate change. It contains an inherent, ingrained injustice. The nations which caused this problem have promised too little to help the people on the frontlines of this crisis who are already losing their lives and livelihoods for problems they did not create.

This deal won’t dig us out the hole we’re in, but it makes the sides less steep. To pull us free of fossil fuels we are going to need to mobilise in ever greater numbers. This year the climate movement beat the Keystone XL tar sands pipeline, we kicked Shell out of the Arctic and put coal into terminal decline. We stand for a future powered by renewable energy, and it is a future we will win.

 

This is why our efforts have never been confined to these conference halls. Just as we've carried our messages of justice, equity, and environmental protection into the venues of the climate negotiations, and echoed the collective demand to speed the end of fossil fuels to the faces of our leaders, we will continue to raise our voices long after these talks are over.

We came to the COP with hope. Not a hope based on the commitments we wished our leaders would make, but a hope built on a movements that we have built together with many others. Together we are challenging the fossil fuel oligarchy, we are ushering in the era of solutions, and we are moving the political benchmark of what is possible.

While our political leaders walk, our movements run, and we must keep running.

From the High Arctic to Brazil, from the Alberta tar sands to Indonesia’s peatlands, from the Gulf of Mexico to the Mediterranean we will stand against those faceless corporations and regressive governments that would risk our childrens future.

We will push our beautifully simple solution to climate change - 100% renewable energy for all - and make sure it is heard and embraced. From schoolyards in Greece, to the streetlights of India, to small Arctic communities like Clyde River in Canada, we will showcase the clean, renewable solutions that are already here, and pressure our governments to make them available for everyone, fast.

Finally, we will stand with those communities on the front lines of this struggle. They are the leaders of this movement. They are the ones facing the rising seas, the superstorms, and the direct effects of our governments’ collective inaction. We will amplify their voices so the world is forced to hear our call for change.

In 2016 we - the entire climate movement - will escalate the fight. Together we will show the world that if our governments won’t act to stop the carbon bullies, then we will.

History is waiting in the wings, and we’re standing on the right side of it.

When fossil fuels become extinct



Sep 1, 2001 Jodie Wehrspann | Farm Industry News

As supplies of coal, oil and gas continue to dwindle, generator manufacturers are planning for the day we run out. They are investigating alternative, renewable fuels that can power on-site generators traditionally powered by natural gas, propane and diesel fuel.

Manufacturers say most of these technologies are still years away from being viable alternatives on farms. The holdup on most of these is cost. “All of these things cost more money than it does to hook up to an electrical power line, so that is why you don't see a big rush for it,” says Greg McFarland, marketing manager with Federated Rural Electric in Jackson, MN. However, cost may come down as more products are marketed and mass produced.

Here is a look at the alternative energies that may soon be viable for Midwest farms.

Wind

Wind turbines that generate electricity are here now. And although they are still expensive, their cost is coming down, approaching that of electricity. New wind systems 39 kW or less (enough to power a typical farm) cost between $100,000 and $115,000, according to McFarland. To reduce that initial capital cost, farmers can buy retired or reconditioned windmills for $45,000 to $60,000, he says.

Another limitation of wind is that it does not blow all of the time. “Because wind is unpredictable, it can't be used as a reliable backup, but can be used as a second or third cash crop if installed correctly,” McFarland says. Also, you need to be in a windy location, such as on a hill. For every 10 ft. of height over 80 ft. on the tower, you will pick up another 1.5% in efficiency, he says.

Most of the wind turbines used today are installed to generate electricity for the grid, not as an on-site source of backup power.

Visit the Web site of American Wind Energy Association () for a listing of wind turbine manufacturers.

Solar

The cost of solar energy is coming down, but it is a niche market, according to John Holt, manager of generation and fuels at the National Rural Electric Cooperative Association (NRECA). “It is a lot more expensive than traditional electricity unless you are far from the grid and need power for a well to pump water for cattle or for a residence,” he says.

What's more, some areas of the Midwest may get only six hours of peak sunlight in which to charge a battery, which in turn will allow you to have power to operate some small motors or lights, according to Federated's McFarland.

“With solar you can preheat or heat some or all of your hot water needs with the right equipment,” he says. “It may be a good second solution in areas like Montana, the western Dakotas and Colorado where there are long distances between lines and where a line extension would be cost prohibitive.”

Biomass

NRECA's Holt says changing biomass to usable energy is doable, but high priced. “There are a few farms that are using cow manure to produce methane and using it for either heating or for electricity,” Holt says. “So technically, it is available, just not economical.” He rates its viability as equal to that of solar energy.

Microturbines

Microturbines, which operate like a jet engine and are about the size of a refrigerator, are reliable, affordable and available now. But they are still in the early stages of commercial use.

They are capable of producing large amounts of power. However, one of their biggest drawbacks is that they are inefficient unless you can find an application for the exhaust heat, Holt says.

Fuel cells

Of all of these technologies, Holt rates fuel cells as the most viable alternative in the future. And the future could be very close. “A number of manufacturers are putting out their beta models and hoping to put out commercial units next year,” he says.

They offer the potential of being efficient, quiet and reliable. And the byproduct emission is just heat, which can be used to heat water.

“A number of farms have these test units right now,” Holt says. “Cost is high, but the hope is by going to mass production, it will bring that down to an affordable cost and offer superb opportunities.” He predicts that farmers will be able to buy them in about three years.

Biomass Energy Basics



We have used biomass energy, or "bioenergy"—the energy from plants and plant-derived materials—since people began burning wood to cook food and keep warm. Wood is still the largest biomass energy resource today, but other sources of biomass can also be used. These include food crops, grassy and woody plants, residues from agriculture or forestry, oil-rich algae, and the organic component of municipal and industrial wastes. Even the fumes from landfills (which are methane, the main component in natural gas) can be used as a biomass energy source.

Benefits of Using Biomass

Biomass can be used for fuels, power production, and products that would otherwise be made from fossil fuels. In such scenarios, biomass can provide an array of benefits. For example:

• The use of biomass energy has the potential to greatly reduce greenhouse gas emissions. Burning biomass releases about the same amount of carbon dioxide as burning fossil fuels. However, fossil fuels release carbon dioxide captured by photosynthesis millions of years ago—an essentially "new" greenhouse gas. Biomass, on the other hand, releases carbon dioxide that is largely balanced by the carbon dioxide captured in its own growth (depending how much energy was used to grow, harvest, and process the fuel). However, recent studies have found that clearing forests to grow biomass results in a carbon penalty that takes decades to recoup, so it is best if biomass is grown on previously cleared land, such as under-utilized farm land.

• The use of biomass can reduce dependence on foreign oil because biofuels are the only renewable liquid transportation fuels available.

• Biomass energy supports U.S. agricultural and forest-product industries. The main biomass feedstocks for power are paper mill residue, lumber mill scrap, and municipal waste. For biomass fuels, the most common feedstocks used today are corn grain (for ethanol) and soybeans (for biodiesel). In the near future—and with NREL-developed technology—agricultural residues such as corn stover (the stalks, leaves, and husks of the plant) and wheat straw will also be used. Long-term plans include growing and using dedicated energy crops, such as fast-growing trees and grasses, and algae. These feedstocks can grow sustainably on land that will not support intensive food crops.

NREL's vision is to develop technology for biorefineries that will convert biomass into a range of valuable fuels, chemicals, materials, and products—much like oil refineries and petrochemical plants do.

NREL performs research to develop and advance technologies for the following biomass energy applications:

• Biofuels — Converting biomass into liquid fuels for transportation

• Biopower — Burning biomass directly, or converting it into gaseous or liquid fuels that burn more efficiently, to generate electricity

• Bioproducts — Converting biomass into chemicals for making plastics and other products that typically are made from petroleum.

Biofuels Basics

This video provides an overview of NREL research on converting biomass to liquid fuels.

Text Version

Unlike other renewable energy sources, biomass can be converted directly into liquid fuels, called "biofuels," to help meet transportation fuel needs. The two most common types of biofuels in use today are ethanol and biodiesel. Ethanol is an alcohol, the same as in beer and wine (although ethanol used as a fuel is modified to make it undrinkable). It is most commonly made by fermenting any biomass high in carbohydrates through a process similar to beer brewing. Today, ethanol is made from starches and sugars, but NREL scientists are developing technology to allow it to be made from cellulose and hemicellulose, the fibrous material that makes up the bulk of most plant matter.

Ethanol can also be produced by a process called gasification. Gasification systems use high temperatures and a low-oxygen environment to convert biomass into synthesis gas, a mixture of hydrogen and carbon monoxide. The synthesis gas, or "syngas," can then be chemically converted into ethanol and other fuels.

Ethanol is mostly used as blending agent with gasoline to increase octane and cut down carbon monoxide and other smog-causing emissions. Some vehicles, called Flexible Fuel Vehicles, are designed to run on E85, an alternative fuel with much higher ethanol content than regular gasoline.

Biodiesel is made by combining alcohol (usually methanol) with vegetable oil, animal fat, or recycled cooking grease. It can be used as an additive (typically 20%) to reduce vehicle emissions or in its pure form as a renewable alternative fuel for diesel engines. Research into the production of liquid transportation fuels from microscopic algae, or microalgae, is reemerging at NREL. These microorganisms use the sun's energy to combine carbon dioxide with water to create biomass more efficiently and rapidly than terrestrial plants. Oil-rich microalgae strains are capable of producing the feedstock for a number of transportation fuels—biodiesel, "green" diesel and gasoline, and jet fuel—while mitigating the effects of carbon dioxide released from sources such as power plants.

Hydrogen Basics

Hydrogen is a clean-burning fuel, and when combined with oxygen in a fuel cell, it produces heat and electricity with only water vapor as a by-product. But hydrogen does not exist freely in nature: it is only produced from other sources of energy, so it is often referred to as an energy carrier, that is, an efficient way to store and transport energy.

Hydrogen can be made directly from fossil fuels or biomass, or it can be produced by passing electricity through water, breaking the water into its constituent components of hydrogen and oxygen. Some envision a future "hydrogen economy," where hydrogen is produced from a variety of energy sources, stored for later use, piped to where it is needed, and then converted cleanly into heat and electricity.

Most hydrogen production today is by steam reforming natural gas. But natural gas is already a good fuel and one that is rapidly becoming scarcer and more expensive. It is also a fossil fuel, so the carbon dioxide released in the reformation process adds to the greenhouse effect. Hydrogen has very high energy for its weight, but very low energy for its volume, so new technology is needed to store and transport it. And fuel cell technology is still in early development, needing improvements in efficiency and durability. The challenges NREL researchers are working on to help make a hydrogen economy a reality include:

• Fuel Cells — Improving fuel cell technology and materials needed for fuel cells.

• Production — Developing technology to efficiently and cost-effectively make hydrogen from renewable energy sources.

• Storage — Developing technology to efficiently and cost-effectively store and transport hydrogen.

Advanced Vehicles and Fuels Basics

We can improve the fuel economy of our cars, trucks, and buses by designing them to use the energy in fuels more efficiently. And we can help to reduce our nation's growing reliance on imported oil by running our vehicles on renewable and alternative fuels. Advanced vehicles and fuels can also put the brakes on air pollution and improve our environment.

At least 250 million vehicles are in use in the United States today. They include all kinds of passenger cars, trucks, vans, buses, and large commercial vehicles. It takes an enormous amount of fuel to operate these vehicles every year.

Because the nation's oil supplies are limited, we import more than half of the petroleum that we use for transportation and other important needs. To reduce the costs and risks of these imports and improve the environment, researchers are developing newer, more energy-efficient fuels and vehicles and finding ways to make fossil fuels like gasoline and diesel fuel last longer.

We can reduce the amount of transportation fuel we use in many different ways. For example, we can create designs that will lower a vehicle's weight and aerodynamic drag to make it "slip" through the air more easily. We can reduce the rolling resistance of tires. We can improve the combustion efficiency of the engine. And we can use a different propulsion system, such as a hybrid electric system.

Researchers at NREL are helping the nation achieve these goals by developing transportation technologies like these:

• Fuel cell vehicles

• Hybrid electric vehicles

• Plug-in hybrid vehicles

• Advanced vehicle systems and components.

In addition, NREL's specialists in vehicle testing and analysis contribute information, test results, and research studies that manufacturers can use to produce energy-efficient new vehicles and cleaner burning alternative fuels.

Biomass Basics

Biomass—renewable energy from plants and animals

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

Biomass is organic material that comes 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 is passed to animals and people after the plants are consumed.

Biomass is a renewable energy source. Some examples of biomass fuels are wood, crops, animal manure, and human sewage.

The chemical energy in biomass is released as heat when it is burned. The wood burned in a fireplace is a biomass fuel. Wood and waste materials made from wood and garbage are burned to produce steam for making electricity or heat for industries.

Converting biomass to other forms of energy

Burning biomass is not the only 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 the main component of natural gas. Garbage, agricultural waste, 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 vegetable oils and animal fats.

Solar Energy

Here's what you need to know about ​the warming planet, ho​​w it's affecting us, and what's at stake.

By National Geographic at

Every hour the sun beams onto Earth more than enough energy to satisfy global energy needs for an entire year. Solar energy is the technology used to harness the sun's energy and make it useable. Today, the technology produces less than one tenth of one percent of global energy demand.

Many people are familiar with so-called photovoltaic cells, or solar panels, found on things like spacecraft, rooftops, and handheld calculators. The cells are made of semiconductor materials like those found in computer chips. When sunlight hits the cells, it knocks electrons loose from their atoms. As the electrons flow through the cell, they generate electricity.

On a much larger scale, solar thermal power plants employ various techniques to concentrate the sun's energy as a heat source. The heat is then used to boil water to drive a steam turbine that generates electricity in much the same fashion as coal and nuclear power plants, supplying electricity for thousands of people.

In one technique, long troughs of U-shaped mirrors focus sunlight on a pipe of oil that runs through the middle. The hot oil then boils water for electricity generation. Another technique uses moveable mirrors to focus the sun's rays on a collector tower, where a receiver sits. Molten salt flowing through the receiver is heated to run a generator.

Other solar technologies are passive. For example, big windows placed on the sunny side of a building allow sunlight to heat-absorbent materials on the floor and walls. These surfaces then release the heat at night to keep the building warm. Similarly, absorbent plates on a roof can heat liquid in tubes that supply a house with hot water.

Solar energy is lauded as an inexhaustible fuel source that is pollution and often noise free. The technology is also versatile. For example, solar cells generate energy for far-out places like satellites in Earth orbit and cabins deep in the Rocky Mountains as easily as they can power downtown buildings and futuristic cars.

But solar energy doesn't work at night without a storage device such as a battery, and cloudy weather can make the technology unreliable during the day. Solar technologies are also very expensive and require a lot of land area to collect the sun's energy at rates useful to lots of people.

Despite the drawbacks, solar energy use has surged at about 20% a year over the past 15 years, thanks to rapidly falling prices and gains in efficiency. Japan, Germany, and the United States are major markets for solar cells. With tax incentives, solar electricity can often pay for itself in five to ten years.

Wind Power

Here's what you need to know about ​the warming planet, ho​​w it's affecting us, and what's at stake.

By National Geography at

Wind is the movement of air from an area of high pressure to an area of low pressure. In fact, wind exists because the sun unevenly heats the surface of the Earth. As hot air rises, cooler air moves in to fill the void. As long as the sun shines, the wind will blow. And as long as the wind blows, people will harness it to power their lives.

Ancient mariners used sails to capture the wind and explore the world. Farmers once used windmills to grind their grains and pump water. Today, more and more people are using wind turbines to wring electricity from the breeze. Over the past decade, wind turbine use has increased at more than 25 percent a year. Still, it only provides a small fraction of the world's energy.

Most wind energy comes from turbines that can be as tall as a 20-story building and have 3 200-foot-long (60-mt-long) blades. These contraptions look like giant airplane propellers on a stick. The wind spins the blades, which turn a shaft connected to a generator that produces electricity. Other turbines work the same way, but the turbine is on a vertical axis & the blades look like a giant egg beater.

The biggest wind turbines generate enough electricity to supply about 600 U.S. homes. Wind farms have tens and sometimes hundreds of these turbines lined up together in particularly windy spots, like along a ridge. Smaller turbines erected in a backyard can produce enough electricity for a single home or small business.

Wind is a clean source of renewable energy that produces no air or water pollution. And since the wind is free, operational costs are nearly zero once a turbine is erected. Mass production and technology advances are making turbines cheaper, and many governments offer tax incentives to spur wind-energy development.

Some people think wind turbines are ugly and complain about the noise the machines make. The slowly rotating blades can also kill birds and bats, but not nearly as many as cars, power lines, and high-rise buildings do. The wind is also variable: If it's not blowing, there's no electricity generated.

Nevertheless, the wind energy industry is booming. Globally, generation more than quadrupled between 2000 and 2006. At the end of last year, global capacity was more than 70,000 megawatts. In the energy-hungry United States, a single megawatt is enough electricity to power about 250 homes. Germany has the most installed wind energy capacity, followed by Spain, the United States, India, and Denmark. Development is also fast growing in France and China.

Industry experts predict that if this pace of growth continues, by 2050 the answer to one third of the world's electricity needs will be found blowing in the wind.

Geothermal Energy. Tapping the Earth's Heat

Here's what you need to know about ​the warming planet, ho​​w it's affecting us, and what's at stake.

By National Geographic

Geothermal energy has been used for thousands of years in some countries for cooking and heating. It is simply power derived from the Earth's internal heat.This thermal energy is contained in the rock and fluids beneath Earth's crust. It can be found from shallow ground to several miles below the surface, and even farther down to the extremely hot molten rock called magma.

These underground reservoirs of steam and hot water can be tapped to generate electricity or to heat and cool buildings directly.

A geothermal heat pump system can take advantage of the constant temperature of the upper ten feet (three meters) of the Earth's surface to heat a home in the winter, while extracting heat from the building and transferring it back to the relatively cooler ground in the summer.

Geothermal water from deeper in the Earth can be used directly for heating homes and offices, or for growing plants in greenhouses. Some U.S. cities pipe geothermal hot water under roads and sidewalks to melt snow.

To produce geothermal-generated electricity, wells, sometimes a mile (1.6 kilometers) deep or more, are drilled into underground reservoirs to tap steam and very hot water that drive turbines linked to electricity generators. The first geothermally generated electricity was produced in Larderello, Italy, in 1904.

There are three types of geothermal power plants: dry steam, flash, and binary. Dry steam, the oldest geothermal technology, takes steam out of fractures in the ground and uses it to directly drive a turbine. Flash plants pull deep, high-pressure hot water into cooler, low-pressure water. The steam that results from this process is used to drive the turbine. In binary plants, the hot water is passed by a secondary fluid with a much lower boiling point than water. This causes the secondary fluid to turn to vapor, which then drives a turbine. Most geothermal power plants in the future will be binary plants.

Geothermal energy is generated in over 20 countries. The United States is the world's largest producer, and the largest geothermal development in the world is The Geysers north of San Francisco in California. In Iceland, many of the buildings and even swimming pools are heated with geothermal hot water. Iceland has at least 25 active volcanoes and many hot springs and geysers.

There are many advantages of geothermal energy. It can be extracted without burning a fossil fuel such as coal, gas, or oil. Geothermal fields produce only about one-sixth of the carbon dioxide that a relatively clean natural-gas-fueled power plant produces. Binary plants release essentially no emissions. Unlike solar and wind energy, geothermal energy is always available, 365 days a year. It's also relatively inexpensive; savings from direct use can be as much as 80 percent over fossil fuels.

But it has some environmental problems. The main concern is the release of hydrogen sulfide, a gas that smells like rotten egg at low concentrations. Another concern is the disposal of some geothermal fluids, which may contain low levels of toxic materials. Although geothermal sites are capable of providing heat for many decades, eventually specific locations may cool down.

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