For several decades there has been quite a bit of discussion about the damage caused to the environment by littering and pumping harmful gases into the atmosphere. Many ideas on how to protect the environment have been put into place, either by social consciousness or by law, to help clean up the earth and reduce future pollution. These range from recycling, to picking up trash, to using alternative energy sources. We're going to focus on the benefits, possibilities, and barriers that come with the use of alternative energy.
Alternative energy is best defined as the use of energy sources other than traditional fossil fuels, which are considered environmentally harmful and are in short supply. Fossil fuels consist of natural gas, coal, and oil. Currently, fossil fuels are the most used energy source to heat our homes and power our cars. To use these fuels as energy they must be burned, and burning of these fuels releases harmful gases into the atmosphere, causing pollution. Another problem associated with fossil fuels is their supply: it is unclear how long oil and coal reserves will last with our current rate of consumption or if new reserves will be found before current reserves run out. Estimates on how long current reserves will last run anywhere from 20 to 400 years. Because of these concerns with fossil fuels, more people are beginning to use alternative energy sources. Some popular alternative energy sources are wind power, hydroelectricity (water power), solar power, biofuels, and hydrogen. These fuels all have two things in common: their small environmental impact on the earth and their sustainability (never ending supply) as an energy source.
So if alternative energy sources are supposed to fix our environmental and supply problems, why have we not switched to using alternative energy sources solely? The simple answer is that alternative energy sources also tend to have common barriers to their use as widespread energy sources. These include location, storage, high cost to produce and use, and inconsistent energy supply.
Wind power is not a new source of energy. For hundreds of years, people have used the power of the wind to send ships across the oceans and used windmills to grind grain, pump water, and saw wood. The power of the wind can most easily be seen by using a child's pinwheel. The basic concept is that when the windmill is held up in oncoming wind currents, the wind catches in the curve of the blades, causing the windmill to rotate. This is the wind's energy at work.
A wind turbine works much like an old-fashioned windmill in that it also uses the wind's kinetic energy (energy caused by motion) to turn the blades. The blades spin a shaft that is connected to a generator. A generator is a device that converts mechanical energy into electrical energy. Inside the generator, a copper coil is moved through a magnetic field by the shaft that is connected to the moving blades. This movement causes an electric current to flow through the copper coil. When the generator is mechanically powered by the wind via a wind turbine, it can make electricity.
Wind power is consider a clean energy source because there are no chemical processes involved in wind power generation. No by-products are made, such as carbon dioxide, to pollute the air or water. Wind generation is a renewable resource that will never run out, and it is a great energy source for people who live in remote areas where it may be difficult to supply power by use of wires connected to a power plant that is far away. The actual space taken up by a wind turbine is relatively small compared to other alternative energy sources. A diameter of only about six feet is needed at the base, making the real estate cost for a wind turbine relatively cheap.
A problem with using wind power is that it is not always a guaranteed energy source. When the wind isn't blowing, no electricity is generated, and a back up energy source must be used. Wind farms are needed for commercial generation, which raises the issue of scenery obstruction caused by many wind turbines lined up next to each other. Many people don't want to see multiple wind turbines outside their kitchen windows. Another problem is the hazard these moving blades cause for birds flying through the area. New construction of wind turbines have larger blades that rotate at slower speeds so birds may see them and not get caught in the blades.
The term hydroelectricity refers to the generation of electricity through the power of water. "Hydro" comes from the Greek word hydra which means water. Like wind power, using water for power also has earlier roots than modern times. Water wheels were first used to capture water's energy and mechanically grind grain. They were later used for pumping water, crop irrigation, driving sawmills, and powering textile mills. Today we use water turbines much like wind turbines to generate electricity.
The most common source for capturing the power of water today is the hydroelectric power plant. Hydroelectric power plants usually require a dam built on a river that creates a reservoir of water. The dam holds the water back until gates open to allow the water to run through. With the help of gravity, the water runs through a pipeline, called a penstock, to the turbine. The elevation change through the penstock helps the water to build up pressure as it approaches the turbine. The moving water reaches the turbine and spins the turbine's blades. Above the turbine is a generator, which is connected to the turbine by a shaft. Like the generator in a wind turbine, the generator in a water turbine also produces electricity by moving a series of copper coils past magnets. A transformer then takes the electricity produced by the generator and converts it to a higher voltage current. The electricity is now ready to power businesses and homes via power lines.
Hydroelectric power is a renewable source that causes no waste or pollution. Unlike wind power, however, hydroelectricity is reliable. The energy can be stored up for use by the dam holding back water until more energy is needed. However, hydroelectricity requires a large power plant, which is very expensive to build. These power plants also require building dams on rivers, changing the ecosystem of the area. Instead of a river in the area above the dam, there is now a large lake that expands over the habitats of land animals. The amount and quality of water running out of the dam can have a negative effect on the plants living on the land and in the water below.
Solar power is simply using the sun's light as energy. This can be done by using a solar cell to convert the sun's light into electricity, using solar thermal panels that use sunlight to heat air and water, or passively using the sun's energy by letting sunlight enter through windows to heat a building. The total energy received from the sun each year is about 35,000 times greater than what people use, which means this power source may be among the best sources for the future. The challenge lies in harnessing and storing this energy in a cost effective way.
One of the most popular ways of harnessing the sun's energy is by using photovoltaic (PV) cells, which are also known as solar cells. PV cells work by absorbing the particles of solar energy that make up sunlight. These particles are called photons. The absorbed photons are transferred to a semiconductor material, usually silicon. (Semiconductors are substances that conduct electricity more easily than insulators but not as easily as conductors like copper.) Electrons in the semiconductor are knocked loose by the incoming photons, leaving spaces in between the bonds of the atoms. Both the loose electrons and the open spaces can carry an electrical current. PV cells are built with one or more electric fields to control the flow of the electrons, thus controlling the flow of the current. When metal contacts are placed on the top and the bottom of a PV cell (much like a battery), we can extract this electrical current to use it in our everyday lives.
Like the above alternative energy sources, solar power is renewable and nonpolluting. Unlike wind turbines and hydroelectricity, photovoltaic conversion to electricity is direct, meaning an expensive, bulky generator is not required. Like wind turbines, solar power can also be used in remote locations where it would be economically impossible to provide power from a far away power plant. Solar power can also be very efficient in providing heat and light through the use of solar ovens, solar water heaters, solar home heaters, and the use of skylights.
Solar power shares a common drawback with wind turbines: their unpredictability. Solar power only works when the sun is out, making a PV cell ineffectual at night and hit or miss during a cloudy day. For these times, power storage needs to be implemented in order to make solar power the main power source. Many forms of solar power are still not economically practical. Photovoltaic power stations are expensive to build and are only about 10% efficient in producing energy. It takes about five years for a power station to produce the same amount of energy that went in to the initial building of the power station. With current technology, solar power is best used on a smaller scale, such as individual homes.
There are many energy sources that fall under the category of biofuels: biomass, biodiesel, ethanol, and methanol are just a few. The basic idea here is to use organic matter (usually plant derived) as a fuel source. Biomass refers to using garbage and vegetation as a fuel source. When garbage is decomposing (breaks down) it produces a gas called methane that can be captured and later burned to produce energy that can be turned into electricity. Vegetation can be burned directly, much like fossil fuels, to generate energy. While these methods do help in the cost and sustainability areas, they still cause a significant environmental impact much like fossil fuels.
Ethanol and methanol are two alcohols that are made from biomass. Ethanol is usually made from corn, but can also be made from agricultural, logging, and paper wastes. Methanol is also known as wood alcohol because it can be made from wood; however, most methanol is produced using natural gas because it is cheaper. Whereas biodiesel is the alternative for diesel engines, ethanol and methanol are the alternatives for gasoline engines. Most private vehicles have gasoline engines and can use ethanol blends with little or no modification of the engine. Ethanol also burns cleaner and produces lower greenhouse emissions than gasoline. However, comparing the price of ethanol with the price of gasoline is a bit tricky. One gallon of pure ethanol contains 34% less energy than one gallon of pure gasoline. A common ethanol blend, E85, is a mixture of 85% ethanol and 15% gasoline and produces 27% less fuel economy than 100% gasoline. So in order for E85 to cost less than gasoline, it must have more than a 27% price reduction than gasoline. Gasoline that costs $3.00 a gallon has the same fuel economy as E85 that costs $2.19 a gallon.
Biodiesel is made by combining a vegetable oil, such as canola or soy oil, and an alcohol such as methanol or ethanol. A catalyst is often added to increase the rate of the reaction between the vegetable oil and alcohol. This process to make biodiesel is called transesterification(for more information on transesterification, click here). This chemical process causes the glycerin to separate from the fat in the vegetable oil, leaving behind two products: methyl ester or ethyl ester (the chemical name for biodiesel) and glycerin. Glycerin is a valuable byproduct often used to make soaps and other products.
Biodiesel is considered an ideal fuel because it is clean burning and can be used in any diesel engine. It is often mixed with regular petroleum diesel to avoid complications with cold weather usage. Pure biodiesel gels at a higher temperature than petroleum diesel. (Soy biodiesel bought in the U.S. begins to gel up at about 40 °F.) This means that it is harder to start a truck in sub-zero temperatures that runs on biodiesel than a truck that runs on petroleum diesel. Biodiesel costs more to produce and therefore costs more to buy than petroleum diesel. Otherwise, biodiesel tends to work as well as petroleum diesel. Pure biodiesel and biodiesel blends release fewer greenhouse gases, are biodegradable (able to decompose by natural processes), and can extend the life of diesel engines. Some filling stations that provide diesel also provide biodiesel. These retailers are more prevalent in the Midwestern states. Here is a map of retailers who sell biodiesel in the United States.
One of the most promising alternative fuels of the future is hydrogen. Its large supply and clean burning properties have many scientists and environmentally conscious citizens looking to it as the solution to replacing fossil fuels without drastically changing our current lifestyles and dependency on personal vehicles. Unlike fossil fuels, it is a non-carbon fuel so when it is burned it does not produce more carbon dioxide. Hydrogen is the simplest and most abundant element found on earth and is found in water, air, and all organic matter. However, even with these all these positives, two major problems stand in the way of using hydrogen as a main fuel source: its production and its storage.
There are two main ways to produce hydrogen: electrolysis and reforming natural gas. Electrolysis involves using an electric current to split the water molecule into hydrogen and oxygen. (To separate hydrogen at home using electrolysis, click here.) In the process of reforming natural gas, methane (which is a principal component in the natural gas used to produce hydrogen) is heated using steam, causing a reaction between the methane and water vapor that produces hydrogen, carbon dioxide, and trace amounts of carbon monoxide. Currently, both methods use natural gas to produce hydrogen. Reforming methane requires splitting the hydrogen from the carbon in methane, but electrolysis requires a power source to produce electricity to split the water molecule. Natural gas is most often used as the fuel source to produce this electricity. Since both of these methods require the consumption of natural gas to produce hydrogen, hydrogen costs more to use than natural gas.
Hydrogen can be used to power vehicles in two ways: to produce electricity in a fuel cell or be used directly in an internal combustion engine. Using hydrogen in a fuel cell is the cleaner method. A fuel cell is an electrochemical device that combines hydrogen and oxygen to produce electricity. Its only by-products are heat and water, which do not pollute the environment. When using hydrogen directly in an internal combustion engine, the hydrogen is burned with the ou side air (which is about two-thirds nitrogen) producing nitrogen based oxide gases, which cause some pollution, and water vapor. Whether hydrogen is used directly in an internal combustion engine or in a fuel cell, both methods require the storage of hydrogen for use as the vehicle is driven. On a weight basis, hydrogen produces the most energy when burned compared to any other fuel - one pound of hydrogen produces 2.6 times more energy than one pound of gasoline. However, hydrogen is a gas so one pound of hydrogen takes up four times the amount of space as does one pound of gasoline. For example, a vehicle that holds 15 gallons of gasoline would need to hold 60 gallons equivalent value of hydrogen to produce the same amount of energy. The tank in the vehicle would have to be the size of two average bathtubs to hold the hydrogen needed in order to drive a reasonable distance without refueling. However, the 15 gallons of gasoline would weigh 90 pounds whereas the 60 gallons of hydrogen would only weigh 34 pounds.
To solve this space problem, hydrogen can be turned into a liquid which takes up less space than hydrogen as a gas, but in order to turn hydrogen into a liquid, it must be cooled and kept to -423.2 ° Fahrenheit. Storing hydrogen as a gas or a liquid is very expensive and cumbersome. Still, there is hope on the horizon. The United States Department of Energy has offered grants to scientists to find ways to improve the storage of hydrogen on small vehicles by improving compression and liquefaction of hydrogen, using metal hydrides to store more hydrogen without adding too much weight to the vehicle, and improving the use of adsorbent materials to collect and hold hydrogen gas on the surface of a solid. However, even if we overcome the storage problem, we still face the hurdle and expense of replacing all gasoline-powered cars with hydrogen-powered cars and replacing gasoline-filling stations with hydrogen-filling stations to become a hydrogen-based America.