Tuesday, February 22, 2011
Tuesday, November 23, 2010
Energy sources
Energy sources
What is an energy-source, which kinds of energy are there and why are energy sources so important? At this place you learn about sources of energy.
An energy source is a system which makes energy in a certain way, for instance a hydro-electric station. A hydro-electric station uses the current of the river for the making of electricity.
Nowadays we need energy-sources for electricity. Without electricity no computers, no television, no washers. A lot of apparatus would not work without electricity.
Which different sources of energy do we know?
How many energy-sources do we know, below are the most important sources.
The three different kinds of energy-sources have their own pros and cons. In this part we give a few of them.
What is an energy-source, which kinds of energy are there and why are energy sources so important? At this place you learn about sources of energy.
- What are sources of energy and where are they used for?
- Which different sources of energy do we know?
- What are the pros and cons of different sources of energy?
An energy source is a system which makes energy in a certain way, for instance a hydro-electric station. A hydro-electric station uses the current of the river for the making of electricity.
Nowadays we need energy-sources for electricity. Without electricity no computers, no television, no washers. A lot of apparatus would not work without electricity.
Which different sources of energy do we know?
How many energy-sources do we know, below are the most important sources.
- Nuclear power
Nuclear power is a form of energy which arise from a reaction between atomic nucleï. Mostly this form of energy comes out of nuclear fission. To explain how this process works, we give a little explanation about the structure of atomic nucleï. Atomic nucleï excist out of neutrons and protons. these little parts (neutrons and protons) are held together in the center of the atomic nucleus through a special energy, called binding-energy. In a process in which the atomic nucleï collide whith eachother, they fall apart and the loose parts come out of the atomic nucleus. The energy which kept the parts together is not necessary anymore and this energy comes 'free'. At the technique of nuclear fission, atomic nucleï collide with eachother in a central boiler to become as much energy out of it as possible. The so called 'binding-energy' falls apart and this energy comes out of the atomic nucleus. This energy is used for heating up water and this water becomes steam. Through the steam a turbine can be driven and so electricity is a fact. The speed in which the atomic nucleï collide is controlled by special rods. These rods can pull atomic nucleï towards them and so there become less atomic nucleï which can collid and then there is less binding-energy to come 'free'.
- Fossil energy
Fossil energy is generated through the burning of fossil remains. At this burning the fossil fuel is used as a source of heat to make steam out of water. This steam is used for the working of a turbine. With the help of a generator, this turbine can make electricity. Examples of fossil fuels are oil, natural gas and coal. These fossil fuels are remains of dead materials of plants and animals. These plants and animals died over a million years ago and under the pressure of the earth's surface and through the decay of this material their came a process of compression. Carbon is the main part of these fossile fuels, the more carbon, the heavier the fuel.
- Alternative energy
Alternative energy is a form of energy without waste-matters. It is also a form where the source, which delivers the energy, is endless. Some alternative energy-sources are sun-, water- and windenergy. By al these forms of alternative energy, excisting energy (like water, wind and sun) is used for the making of electric energy. For instance, a hydro-electric station makes use of the fall between a lake and a river. They build a flood control dam between the lake and the river. And in the one outlet of the dam they build a turbine. This turbine activates a generator and the water energy is transformed into electric energy. More information about alternative energy you can find in the article about green energy.
The three different kinds of energy-sources have their own pros and cons. In this part we give a few of them.
- Nuclear power
For the generation of nuclear power little raw material is needed to generate a lot of electric energy. This is an advantage, because the supply of the raw material will be enough for quite a time. A very big disadvantage is that the raw material for nuclear power, uranium, is very radio-active. Also the used rods en other used materials stay radio-active for ages. at a nuclear power plant as Tsjernobyl we have seen how dangerous this type of energy-generation can be. This is the major reason why environmental groups (like Greenpeace) are against this form of energy-winning.
- Fossil energy
The big advantage of fossil energy is that, to generate the energy from the raw material is easy and cheap. Disadvantage is that during the process of combustion a lot of toxic materials comes into the air which causes extra pollution of the atmosphere, these materials also increase the effect of global warming. Another disadvantage of fossil energy is that the supply of fossil fuels is not endless. The current supply is for approximately 50 years. That is why the USA wants to trail for oil and natural gas in Alaska. If the USA do this, there are big consequences for the environment. For more information about this subject, go to the article about exhaustion.
- Alternative energy
The advantage of alternative energy is that the energy source is endless and doesn't give any pollution. Still, there are not many alternative energy forms, because for instance the technique to transform sun-beams into electric energy is very expensive. For more information about alternative forms of energy-winning, go to the article about green energy
Friday, November 19, 2010
Fuel Cell Basics
Fuel Cell Basics
Through this website we are seeking historical materials relating to fuel cells. We have constructed the site to gather information from people already familiar with the technology–people such as inventors, researchers, manufacturers, electricians, and marketers. This Basics section presents a general overview of fuel cells for casual visitors.
| What is a fuel cell? | How do fuel cells work? |
| Why can’t I go out and buy a fuel cell? | |
| Different types of fuel cells. | |
What is a fuel cell?
A fuel cell is a device that generates electricity by a chemical reaction. Every fuel cell has two electrodes, one positive and one negative, called, respectively, the anode and cathode. The reactions that produce electricity take place at the electrodes.
Every fuel cell also has an electrolyte, which carries electrically charged particles from one electrode to the other, and a catalyst, which speeds the reactions at the electrodes.
Hydrogen is the basic fuel, but fuel cells also require oxygen. One great appeal of fuel cells is that they generate electricity with very little pollution—much of the hydrogen and oxygen used in generating electricity ultimately combine to form a harmless byproduct, namely water.
One detail of terminology: a single fuel cell generates a tiny amount of direct current (DC) electricity. In practice, many fuel cells are usually assembled into a stack. Cell or stack, the principles are the same.
How do fuel cells work?
The purpose of a fuel cell is to produce an electrical current that can be directed outside the cell to do work, such as powering an electric motor or illuminating a light bulb or a city. Because of the way electricity behaves, this current returns to the fuel cell, completing an electrical circuit. (To learn more about electricity and electric power, visit “Throw The Switch” on the Smithsonian website Powering a Generation of Chang) The chemical reactions that produce this current are the key to how a fuel cell works.
There are several kinds of fuel cells, and each operates a bit differently. But in general terms, hydrogen atoms enter a fuel cell at the anode where a chemical reaction strips them of their electrons. The hydrogen atoms are now “ionized,” and carry a positive electrical charge. The negatively charged electrons provide the current through wires to do work. If alternating current (AC) is needed, the DC output of the fuel cell must be routed through a conversion device called an inverter.
 Graphic by Marc Marshall, Schatz Energy Research Center |
Oxygen enters the fuel cell at the cathode and, in some cell types (like the one illustrated above), it there combines with electrons returning from the electrical circuit and hydrogen ions that have traveled through the electrolyte from the anode. In other cell types the oxygen picks up electrons and then travels through the electrolyte to the anode, where it combines with hydrogen ions.
The electrolyte plays a key role. It must permit only the appropriate ions to pass between the anode and cathode. If free electrons or other substances could travel through the electrolyte, they would disrupt the chemical reaction.
Whether they combine at anode or cathode, together hydrogen and oxygen form water, which drains from the cell. As long as a fuel cell is supplied with hydrogen and oxygen, it will generate electricity.
Even better, since fuel cells create electricity chemically, rather than by combustion, they are not subject to the thermodynamic laws that limit a conventional power plant (see “Carnot Limit” in the glossary). Therefore, fuel cells are more efficient in extracting energy from a fuel. Waste heat from some cells can also be harnessed, boosting system efficiency still further.
So why can’t I go out and buy a fuel cell?
The basic workings of a fuel cell may not be difficult to illustrate. But building inexpensive, efficient, reliable fuel cells is a far more complicated business.
Scientists and inventors have designed many different types and sizes of fuel cells in the search for greater efficiency, and the technical details of each kind vary. Many of the choices facing fuel cell developers are constrained by the choice of electrolyte. The design of electrodes, for example, and the materials used to make them depend on the electrolyte. Today, the main electrolyte types are alkali, molten carbonate, phosphoric acid, proton exchange membrane (PEM) and solid oxide. The first three are liquid electrolytes; the last two are solids.
The type of fuel also depends on the electrolyte. Some cells need pure hydrogen, and therefore demand extra equipment such as a “reformer” to purify the fuel. Other cells can tolerate some impurities, but might need higher temperatures to run efficiently. Liquid electrolytes circulate in some cells, which requires pumps. The type of electrolyte also dictates a cell’s operating temperature–“molten” carbonate cells run hot, just as the name implies.
Each type of fuel cell has advantages and drawbacks compared to the others, and none is yet cheap and efficient enough to widely replace traditional ways of generating power, such coal-fired, hydroelectric, or even nuclear power plants.
The following list describes the five main types of fuel cells. More detailed information can be found in those specific areas of this site.
Different types of fuel cells.
 Drawing of an alkali cell. |
 Drawing of a molten carbonate cell |
Phosphoric Acid fuel cells (PAFC) use phosphoric acid as the electrolyte. Efficiency ranges from 40 to 80 percent, and operating temperature is between 150 to 200 degrees C (about 300 to 400 degrees F). Existing phosphoric acid cells have outputs up to 200 kW, and 11 MW units have been tested. PAFCs tolerate a carbon monoxide concentration of about 1.5 percent, which broadens the choice of fuels they can use. If gasoline is used, the sulfur must be removed. Platinum electrode-catalysts are needed, and internal parts must be able to withstand the corrosive acid.
 Drawing of how both phosphoric acid and PEM fuel cells operate. |
Proton Exchange Membrane (PEM) fuel cells work with a polymer electrolyte in the form of a thin, permeable sheet. Efficiency is about 40 to 50 percent, and operating temperature is about 80 degrees C (about 175 degrees F). Cell outputs generally range from 50 to 250 kW. The solid, flexible electrolyte will not leak or crack, and these cells operate at a low enough temperature to make them suitable for homes and cars. But their fuels must be purified, and a platinum catalyst is used on both sides of the membrane, raising costs.
 Drawing of a solid oxide cell |
More detailed information about each fuel cell type, including histories and current applications, can be found on their specific parts of this site. We have also provided a glossary of technical terms–a link is provided at the top of each technology page.
Thursday, November 18, 2010
Hydrogen
Hydrogen
Like electricity, hydrogen is a secondary source of energy. It stores and carries energy produced from other resources (fossil fuels, water, and biomass).
Hydrogen Basics
What Is Hydrogen?
The sun is basically a giant ball of hydrogen gas undergoing fusion into helium gas and giving off vast amounts of energy in the process.
Source: NASA (Public Domain)
Hydrogen is the simplest element. Each atom of hydrogen has only one proton. It is also the most plentiful gas in the universe. Stars like the sun are made primarily of hydrogen.
The sun is basically a giant ball of hydrogen and helium gases. In the sun's core, hydrogen atoms combine to form helium atoms. This process — called fusion — gives off radiant energy.
This radiant energy sustains life on Earth. It gives us light and makes plants grow. It makes the wind blow and rain fall. It is stored as chemical energy in fossil fuels. Most of the energy we use today originally came from the sun's radiant energy.
Hydrogen gas is so much lighter than air that it rises fast and is quickly ejected from the atmosphere. This is why hydrogen as a gas (H2) is not found by itself on Earth. It is found only in compound form with other elements. Hydrogen combined with oxygen, is water (H2O). Hydrogen combined with carbon forms different compounds, including methane (CH4), coal, and petroleum. Hydrogen is also found in all growing things — for example, biomass. It is also an abundant element in the Earth's crust.
Hydrogen has the highest energy content of any common fuel by weight (about three times more than gasoline), but the lowest energy content by volume (about four times less than gasoline).
Hydrogen Is an Energy Carrier
Energy carriers move energy in a useable form from one place to another. Electricity is the most well-known energy carrier. We use electricity to move the energy in coal, uranium, and other energy sources from power plants to homes and businesses. We also use electricity to move the energy in flowing water from hydropower dams to consumers. For many energy needs, it is much easier to use electricity than the energy sources themselves.
Like electricity, hydrogen is an energy carrier and must be produced from another substance. Hydrogen is not currently widely used, but it has potential as an energy carrier in the future. Hydrogen can be produced from a variety of resources (water, fossil fuels, or biomass) and is a byproduct of other chemical processes.
How Is Hydrogen Made?
Source: The National Energy Education Project (Public Domain)
Because hydrogen doesn't exist on Earth as a gas, it must be separated from other elements. Hydrogen atoms can be separated from water, biomass, or natural gas molecules. The two most common methods for producing hydrogen are steam reforming and electrolysis (water splitting). Scientists have discovered that even some algae and bacteria give off hydrogen.
Steam Reforming Is a Widely-Used Method of Hydrogen Production
Steam reforming is currently the least expensive method of producing hydrogen and accounts for about 95% of the hydrogen produced in the United States. This method is used in industries to separate hydrogen atoms from carbon atoms in methane (CH4). But the steam reforming process results in greenhouse gas emissions that are linked with global warming.1
Electrolysis Creates No Emissions but Is Costly
Electrolysis is a process that splits hydrogen from water. It results in no emissions, but it is currently an expensive process. New technologies are currently being developed.
Hydrogen can be produced at large central facilities or at small plants for local use.
How Much Hydrogen Is Produced in the United States?
About 9 million metric tons of hydrogen are produced in the United States annually, enough to power 20-30 million cars or 5-8 million homes. Most of this hydrogen is produced in three States: California, Louisiana, and Texas.
1. U.S. Environmental Protection Agency, Climate Change State of Knowledge.
The Space Shuttle
Source: NASA (Public Domain)
Hydrogen Fuel Cell Public Bus in Use in Perth, Western Australia
Source: Hax0rw4ng, Wikimedia Commons author (GNU Free Documentation License) (Public Domain)
Hydrogen Fuel Cell Hybrid Vehicle
Source: Gnsin, Wikimedia Commons author (GNU Free Documentation License) (Public Domain)
Most Hydrogen Is Used in Refining, Treating Metals, and Processing Foods
Nearly all of hydrogen consumed in the United States is used by industry for refining, treating metals, and processing foods.
The National Aeronautics and Space Administration (NASA) is the primary user of hydrogen as an energy fuel; it has used hydrogen for years in the space program. Liquid hydrogen fuel lifts NASA's space shuttles into orbit. Hydrogen batteries, called fuel cells, power the shuttle’s electrical systems. The only by-product is pure water, which the crew uses as drinking water.
Hydrogen Fuel Cells Produce Electricity
Hydrogen fuel cells make electricity. They are very efficient, but expensive to build. Small fuel cells can power electric cars. Large fuel cells can provide electricity in remote places with no power lines.
Because of the high cost to build fuel cells, large hydrogen power plants won't be built for a while. However, fuel cells are being used in some places as a source of emergency power, from hospitals to wilderness locations.
Portable fuel cells are being sold to provide longer power for laptop computers, cell phones, and military applications.
Hydrogen Use in Vehicles
Today, there are an estimated 200 to 300 hydrogen-fueled vehicles in the United States. Most of these vehicles are buses and automobiles powered by electric motors. They store hydrogen gas or liquid on board and convert the hydrogen into electricity for the motor using a fuel cell. Only a few of these vehicles burn the hydrogen directly (producing almost no pollution).
The present cost of fuel cell vehicles greatly exceeds that of conventional vehicles in large part due to the expense of producing fuel cells.
From the Laboratory to the Road
Hydrogen vehicles are starting to move from the laboratory to the road. Hydrogen vehicles are in use by a few state agencies and a few private entities.
The Refueling Challenge
Currently, there are 56 hydrogen refueling stations in the United States, about half of which are located in California. There are so-called “chicken and egg” questions that hydrogen developers are working hard to solve, including: who will buy hydrogen cars if there are no refueling stations? And who will pay to build a refueling station if there are no cars and customers?
Subscribe to:
Posts (Atom)