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most all biofuels used today cause more greenhouse gas emissions than conventional fuels if the pollution caused by producing these "green" fuels is taken into account, two studies published Thursday have concluded.

The benefits of biofuels have come under increasing attack in recent months as scientists have evaluated the global environmental cost of their production. The new studies, published by the journal Science, are likely to add to the controversy.

When you take this into account, most of the biofuel that people are using or planning to use would probably increase greenhouse gasses substantially," sai

The major challenge to using wind as a source of power is that it is intermittent and does not always blow when electricity is needed. Wind cannot be stored (although wind-generated electricity can be stored, if batteries are used), and not all winds can be harnessed to meet the timing of electricity demands. Further, good wind sites are often located in remote locations far from areas of electric power demand (such as cities).

Although wind power plants have relatively little impact on the environment compared to fossil fuel power plants, there is some concern over the noise produced by the rotor blades, aesthetic (visual) impacts, and birds and bats having been killed (avian/bat mortality) by flying into the rotors. Most of these problems have been resolved or greatly reduced through technological development or by properly siting wind plants.

A Renewable Non-Polluting Resource Wind energy is a free, renewable resource, so no matter how much is used today, there will still be the same supply in the future. Wind energy is also a source of clean, non-polluting, electricity. Unlike conventional power plants, wind plants emit no air pollutants or greenhouse gases. According to the U.S. Department of Energy, in 1990, California's wind power plants offset the emission of more than 2.5 billion pounds of carbon dioxide, and 15 million pounds of other pollutants that would have otherwise been produced. It would take a forest of 90 million to 175 million trees to provide the same air quality.

There are many uses for fuel cells — right now, all of the major automakers are working to commercialize a fuel cell car. Fuel cells are powering buses, boats, trains, planes, scooters, forklifts, even bicycles. There are fuel cell-powered vending machines, vacuum cleaners and highway road signs. Miniature fuel cells for cellular phones, laptop computers and portable electronics are on their way to market. Hospitals, credit card centers, police stations, and banks are all using fuel cells to provide power to their facilities. Wastewater treatment plants and landfills are using fuel cells to convert the methane gas they produce into electricity. Telecommunications companies are installing fuel cells at cell phone, radio and 911 towers. The possibilities are endless.

Stationary

More than 2500 fuel cell systems have been installed all over the world

Through the use of hydrogen together with fuel cell technology it is possible to achieve a radical decrease in local pollution of carbon dioxide, nitrogen oxides and particles from the transportation sector. Although the production of hydrogen from fossil fuels affects the environment it is an advantage that the carbon dioxide emissions can be separated already on the production site. This becomes evident when hydrogen is used as vehicle fuel, avoiding pollution from every individual vehicle.The only emission from a fuel cell reacting with hydrogen is pure water. The environmental gains are high, provided that pollution in the hydrogen production process is kept low. A fuel cell is approximately twice as energy efficient as a combustion engine if used in a regular car. The effect is that, using the same amount of energy, a fuel cell car can drive twice as far as a car with a combustion engine can.

The U.S. consumes a little more than 20 million barrels of oil a day. The largest end uses are motor gasoline (9 million barrels) and diesel (4 million barrels). That works out to about 140 billion gallons of gasoline and 60 billion gallons of diesel a year. In 2006, the U.S. consumed nearly 5.4 billion gallons of ethanol, 12 percent of which was imported. Adjusting for its lower energy content, that amounted to about 2.5% of the total U.S. demand for gasoline. Biodiesel consumption was much lower, about 250 million gallons in 2006.

The U.S. consumes a little more than 20 million barrels of oil a day. The largest end uses are motor gasoline (9 million barrels) and diesel (4 million barrels). That works out to about 140 billion gallons of gasoline and 60 billion gallons of diesel a year. In 2006, the U.S. consumed nearly 5.4 billion gallons of ethanol, 12 percent of which was imported. Adjusting for its lower energy content, that amounted to about 2.5% of the total U.S. demand for gasoline. Biodiesel consumption was much lower, about 250 million gallons in 2006. In the Energy

The U.S. consumes a little more than 20 million barrels of oil a day. The largest end uses are motor gasoline (9 million barrels) and diesel (4 million barrels). That works out to about 140 billion gallons of gasoline and 60 billion gallons of diesel a year. In 2006, the U.S. consumed nearly 5.4 billion gallons of ethanol, 12 percent of which was imported. Adjusting for its lower energy content, that amounted to about 2.5% of the total U.S. demand for gasoline. Biodiesel consumption was much lower, about 250 million gallons in 2006. In the Energy Policy Act of 2005, Congress enacted the Renewable Fuels Standard, which requires an annual increase in biofuels use to 7.5 billion gallons by 2012. The chart above details past levels of U.S. ethanol production and the minimum levels set by the Renewable Fuels Standard. In the 2006 State of the Union address, President Bush announced a goal of replacing “more than 75% of our oil imports from the Middle East by 2025.” According to the Department of Energy, meeting that goal will require 60 billion gallons of biofuels a year. A year later, the President accelerated the timetable and called for “20 in 10.”

Biofuels have been around as long as cars have. At the start of the 20th century, Henry Ford planned to fuel his Model Ts with ethanol, and early diesel engines were shown to run on peanut oil.

The coal powder mixes with hot air, which helps the coal burn more efficiently, and the mixture moves to the furnace. The burning coal heats water in a boiler, creating steam. Steam released from the boiler powers an engine called a turbine, transforming heat energy from burning coal into mechanical energy that spins the turbine engine. The spinning turbine is used to power a generator, a machine that turns mechanical energy into electric energy. This happens when magnets inside a copper coil in the generator spin.

Electricity-generating plants send out electricity using a transformer, which increases the voltage of the electricity based on the amount required and the distance it must travel. Voltages are often as high as 500,000 volts at this point.  Electricity flows along transmission lines to substation transformers. These transformers reduce the voltage for use in the local areas to be served.  From the substation transformers, electricity travels along distribution lines, which can be either above or below the ground, to cities and towns. Transformers once again reduce the voltage—this time to about 120 to 140 volts—for safe use inside homes and businesses. The delivery process is instantaneous. By the time you have flipped a switch to turn on a light, electricity has been delivered.

In the hydrogen economy, there is no storehouse to tap into. We have to actually create the e­nergy in real-time.

There are two possible sources for the hydrogen: Electrolysis of water - Using electricity, it is easy to split water molecules to create pure hydrogen and oxygen. One big advantage of this process is that you can do it anywhere. For example, you could have a box in your garage producing hydrogen from tap water, and you could fuel your car with that hydrogen. Reforming fossil fuels - Oil and natural gas contain hydrocarbons -- molecules consisting of hydrogen and carbon. Using a device called a fuel processor or a reformer, you can split the hydrogen off the carbon in a hydrocarbon relatively easily and then use the hydrogen. You discard the leftover carbon to the atmosphere as carbon dioxide.

To have a pure hydrogen economy, the hydrogen must be derived from renewable sources rather than fossil fuels so that we stop releasing carbon into the atmosphere. Having enough electricity to separate hydrogen from water, and generating that electricity without using fossil fuels, will be the biggest change that we see in creating the hydrogen economy.

Advantages by Application Telecoms CHP Fuel Cell Generators Electric Vehicles - APU's and Range Extenders Fuel Cell Forklifts Marine Power Portable Power

The PV effect was discovered in 1954, when scientists at Bell Telephone discovered that silicon (an element found in sand) created an electric charge when exposed to sunlight.

The Life-cycle greenhouse-gas emissions of solar power are in the range of 22 to 46  g/kWh depending on if solar thermal or solar PV is being analyzed, respectively. With this potentially being decreased to 15 g/kWh in the future.[71] For comparison (of weighted averages), a combined cycle gas-fired power plant emits some 400-599 g/kWh,

The wind turns the blades, which spin a shaft connected to the generator and produces electricity. Turbine blades are designed in such a way that wind causes them to rotate, which rotates the shaft at low speed, with a gear at the end that itself is connected to small gear on high speed shaft that runs through alternator housing.

he generator produces electricity using the same principle as a generator of your car (depending on the turbine). Magnetic Rotor inside the generator on high speed shaft spins inside loops of copper wire that are wound around an iron core. The rotor creates “electromagnetic induction” as it spins around the inside of the core through the coils, which generates electrical power. The current is regulated and transmission network (or home network system connection), after some changes, so it can use in our homes or sent to a battery bank for storage.

They may also reduce the amount of electricity generated from fossil fuels and therefore reduce the amount of air pollution, carbon dioxide emissions, and water use of fossil fuel power plants.

Modern wind turbines are very large machines, and some people do not like their visual impact on the landscape. A few wind turbines have caught on fire, and some have leaked lubricating fluids, though this is relatively rare. Some people do not like the sound that wind turbine blades make. Some types of wind turbines and wind projects cause bird and bat deaths. These deaths may contribute to declines in species that are also being affected by other human-related impacts. Many birds are killed from collisions with vehicles and buildings, by house cats and hunters, and by pesticides. Their natural habitats may be altered or destroyed by human development and by the changes in the climate that most scientists believe are caused by greenhouse gases emissions from human activities (which wind energy use can help reduce).

Making the metals and other materials in wind turbines and the concrete for their foundations requires the use of energy, which may be from fossil fuels.

3,816,000 Gigawatts of Electricity is used in the United states each year

Archaeological evidence shows that the first human use of geothermal resources in North America occurred more than 10,000 years ago with the settlement of Paleo-Indians at hot springs

Today, most hydrogen in the United States, and about half of the world's hydrogen supply, is produced through the steam reforming of natural gas. The U.S. demand for hydrogen currently is about 9 million tons per year. Of this amount, about 1.5 million tons is merchant hydrogen production that is sold to refineries and chemical plants. In refineries, hydrogen is produced as a by-product of naphtha reforming, and any supplemental hydrogen is produced from steam reforming of natural gas. The chemical industry also uses hydrogen, mostly to manufacture ammonia and other nitrogen-based fertilizers. Hydrogen for the chemical industry is also produced from steam reforming of natural gas, although some chemical plants use coal gasification (i.e., partial oxidation) to produce hydrogen. In total, about 95 percent of U.S. hydrogen production for supplemental refinery needs and the chemical industry is produced from natural gas using steam reforming technology.

It depends what you mean by "solar energy." Humans have always used solar energy in some sense: to warm themselves, to grow food, etc. However, I'm assuming that's not really what you mean (although it is important to realize that all energy on earth, with the exception of nuclear fission and geothermal, is ultimately driven by the sun's energy -- even fossil fuels, which after all were plants that grew with sunlight millions of years ago). Solar power has been used directly in various forms for over 100 years.