Sunlight is an energy source that is available to varying degrees every single day. Sunlight has been used in various ways since the beginning of human history. Today, advanced technologies are used to deliver the power generated from sunlight through small-scale solar power collection sites, as well as through power-generating plants that serve large populations. Solar power technology is still developing and has also met with strong resistance by the government and large oil companies. Despite these obstacles this technology holds great potential for generating nonpolluting energy for the world.
Humans have attempted to use solar power for their own benefit throughout history. Native Americans of the Southwest chose to build their homes into the south-facing sides of cliffs to capture the sun's warmth. They observed that the sun was in the southern sky during the coldest months of the year and positioned their dwellings to trap the heat from the sun. The Romans took a similar approach, only they also developed and installed glass in their windows, which allowed light in but kept heat from escaping.
Using the sun's energy in this way is called passive heating and is only one of the many ways solar power can be harnessed. It is called passive because there is no expenditure of energy in trapping the power from the sun. This technique is still applied today. Like the cliff dwellers of the Southwest, people living in a community called Esperanza del Sol (Hope for the Sun) in Dallas, Texas, are using these same techniques. All of the people in this community live in homes with large roof overhangs. These overhangs block the hot summer sun and keep the air inside the home cool. The sun travels much lower in the winter and so the sunlight is then able to come through the windows and warm the air inside the home. This simple construction feature allows the people of Esperanza del Sol to feel much more comfortable in their homes regardless of what season it is. In addition, because they are not relying on fossil fuels to create electricity to power an air conditioner or heating system, they pay much less in energy bills and are helping to reduce the damage being done to the environment.
Flat Plate Collectors
Flat plate collectors, a form of passive heating that uses sunlight to heat water, work in much the same way as using sunlight to heat a home. By running water through a glass-topped box, black inside, and installed on the roof of a home, the energy from the sun can be used to heat the water. This technology was used in an informal way during the pioneer days and was later developed into a more formal system in the 1970s.
Flat plate collectors can be built in a variety of ways and range anywhere from about four feet square to the size of the entire roof. A common design includes a series of black tubes, filled with water or antifreeze, that run through the box. The water or antifreeze in these
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tubes can heat up to more than 160 degrees Fahrenheit in less than an hour under direct sunlight. With a flat plate collector that holds water, the homeowner can shower, bathe, wash clothes, or do dishes using the heated water directly from the flat plate collector. If the tubes hold antifreeze, then the heated antifreeze fluid can be pumped through tubes in a water storage tank, heating the water in the tank for use in the home.
Solar Trough Collectors
Although there are over eight hundred thousand solar water heaters, such as flat plate collectors, in operation in America today, most of these serve only the needs of individual homes or small businesses. Scientists have been working hard to find ways to make solar heating more applicable to large populations. Solar trough collectors are one solution scientists in the Mojave Desert of California have been examining as a way to serve large numbers of people at once. At this site, nine sets of sixty-four curved mirrors (which are about 2 ½ feet by just over 4 feet) are used to focus sunlight onto tubes that run along the center of the curved mirrors. Synthetic oils in the tubes, which are about 150 feet long, absorb the solar energy and heat up, reaching temperatures around 735 degrees Fahrenheit. Because the fluid inside the tubes is so hot, merely running the tube through a large vat of water causes the water to boil. The steam from the boiling water is then used to drive a turbogenerator, which creates electricity. This site in California is currently generating about a third of the energy production of a large nuclear plant, or enough energy to power 350,000 homes.
The power generated in this fashion is not yet efficient, costing more than twice as much as fossil fuels at about twelve cents per kilowatt. However, scientists are researching how to improve this type of solar energy collection and decrease the cost of the materials.
The Solar Furnace
In the Pyrenees mountains of France is another large-scale experimental solar power system. In the 1970s scientists constructed a solar furnace capable of reaching temperatures so high that it can melt metal. The builders of the furnace chose a location at about five thousand feet up in the mountains to guarantee clear skies for their project.
The solar furnace is much larger than a solar trough, mainly because it uses hundreds of flat mirrors, called heliostats, to collect sunlight over a much larger area. This sunlight is bounced onto a single curved mirror the size of a ten-story building. Since the mirror is curved, the sunlight can be focused onto one central tower opposite it. Like the solar trough collector, this central tower, which looks somewhat like a large water tower, uses the sunlight to create electricity by heating fluids to create steam to run through a turbogenerator.
The solar furnace effectively generates about one thousand kw of energy, enough to power more than six hundred homes. However, it is still used as a research site, as duplicates of the furnace are still too expensive to build and operate competitively.
The Electrical Side of Solar Power
Using sunlight to heat fluids to run turbogenerators is not the only way energy can be harnessed from the sun to create electricity. Sunlight can also be captured in photovoltaic (PV) cells, which make up the common solar panel seen on everything from calculators to rooftops. A PV cell is constructed of a thin, small wafer of silicon that is about two inches square. One side of the wafer is dipped in a boron solution. This is a solution that contains atoms that want to give up electrons. The other side of the wafer is dipped in a phosphorus solution that has atoms that want to take electrons. When sunlight strikes the top side of the wafer, it gives boron atoms a lot of energy. This burst of energy causes the boron atoms to give up their additional electrons. A thin metal wire is attached to both sides of a PV cell. Because metal is composed of atoms that attract electrons, the electrons that were given up by the boron atoms move toward the wire and travel down it in the form of electricity. An appliance or machine plugged into the wire can then use the electricity. When the electricity has run through the appliance or machine, it returns via the wire to the phosphorus side of the PV cell. Eventually these electrons pass through the silicon wafer back to the boron side of the PV cell. These electrons can be used over and over to create electricity. One or two small PV cells are commonly used to power such items as small calculators and watches.
PV Cell Modules
Many of these PV cells must be linked together to create enough electricity to power most electrical motors. For instance, a solar-powered car would need about 375 PV cells to run efficiently. When PV cells are linked together by running a wire from one PV cell to the next, they are called modules. The more cells collecting energy and funneling it to one destination, such as an electric motor, the more power that motor receives. The National Aeronautics and Space Administration (NASA) first used solar modules in 1959 to power the Vanguard 1 satellite. This was a perfect solution to the power needs of space exploration, as solar modules are lightweight, durable, and require little-to-no maintenance. Sunlight is also in constant abundance in space.
Today, people are finding that solar modules are an excellent option when they do not have immediate access to electricity through conventional power lines. Owners
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of recreational vehicles and boats can place solar modules on the roof of an RV or on the deck of a boat to capture energy. This energy can then be used to power small appliances on board, such as stoves, refrigerators, and radios.
More commonly seen, perhaps, is the use of solar modules to power traffic signals, road signs, and streetlights. The signs and road signals are often in remote areas where it would be far too expensive to run electrical lines to the site. Instead, road departments choose to use solar modules to generate electricity from the sun to power the equipment.
For people who live far away from any source of electricity to power their homes or businesses, solar modules are sometimes a solution. These solar modules may be attached to the roof of a home or may be on freestanding bases. In either case, the modules are angled toward the sun to capture the most energy. As the sun's angle to the earth varies throughout the year, the owners often reset the angle of the modules to capture the most energy from the sun. Depending on the size and number of modules, a home can be powered solely by solar modules. For example, the typical homeowner could meet his or her energy needs with an array of eight standard 120-watt PV cell modules. Counts of current solar power usage are difficult to make due to their rural distribution. The most recent count to date was released in a CNN report in late 1997, showing that over ten thousand homes in the United States were entirely powered by solar energy.
Scientists are also applying solar energy techniques to cars. Solar-powered cars, first built in Chicago in 1955, may become the wave of the future, but for now they are used mostly for competitions instead of the public market. The main barrier is the price of construction, which can run as much as $80,000 to $120,000. This high cost comes from the fact that the parts and energy collection and storage systems are expensive and not made on a production-level scale, which would greatly reduce the price.
Another type of solar-powered car being actively developed is actually an electric car that is primarily charged by solar panels while it is parked and runs off of a battery while in use. "The typical car is charged up via an electrical outlet, which could be powered by solar-powered carports and parking garages," explains Jennifer Carless, author of Renewable Energy: A Concise Guide to Green Alternatives. "PV panels in the roofs would provide enough energy to charge cars on sunny days, which would be more energy-efficient than refining petroleum."10
Another version is the fuel cell car which runs off of hydrogen. Solar energy is used to generate hydrogen at a station where a car can fill up, similar to existing gas stations. The way this works is that solar energy is collected from the sun to generate electricity. The electricity is then applied to water, breaking it into its parts, hydrogen and oxygen. The hydrogen, which is flammable, is used as a combustible gas while the oxygen is released harmlessly into the atmosphere. Hydrogen fuel cells can be used again and again.
Currently, there are hydrogen filling stations in use in Germany and Japan, as well as a display model built by the Ford Motor Company in Dearborn, Michigan, in 1999. Scientists project a massive reduction—about 16.4 percent in the United States—in the use of fossil fuels if solar power technology is applied to the automobile industry.
Sunlight: Free and Nonpolluting
There are many benefits to using solar power. First and foremost, solar power is available wherever the sun shines—which is, for the most part, anywhere on the planet. People living in developing countries are using more and more solar power as they begin to establish cities and towns. Up to 80 percent of the solar modules created in the United States are exported to third world countries. These countries are using solar energy to power everything from village wells to the first solar-powered hospital, as is being done in Mali, Africa.
John Schaeffer, president and founder of Real Goods, states, "There are still 2 billion of the world's 6 billion people who have no electricity. Bringing them electricity from solar instead of fossil fuels makes more sense."11
Indeed, if these countries can plan how they want to develop, they may be able to create systems that are entirely self-sustaining through the use of solar power. This would mean that they would not have to rely on other countries for energy. They would also be able to step away from all of the pollution problems industrialized nations now face through the abundant use of fossil fuels.
Economically speaking, solar energy is a wise choice. According to Carless, "The cost of running a PV system reduces to zero after buying and installing it."12 A solar power system has a high initial investment cost, but once it is paid for there is little-to-no maintenance cost. The savings from not having energy bills to pay will cover the cost in five to ten years. After that, energy is free for the lifetime of the solar modules, which are usually guaranteed for at least twenty-five years. Considering how the cost of electrical bills can add up over time, this is quite an attractive aspect of solar energy. In many cases, using solar energy not only frees people of monthly energy bills, but local power companies will buy the excess power generated by solar power systems if the homes are connected to the utility company through their power lines. Unused electricity can then be of financial benefit to the solar power system owner and can be made available for use by other customers.
Overall, solar power has a lot to offer, as the authors of The Almanac of Renewable Energy assert. "PV technology is an inherently clean source of electricity. During power generation, PV arrays produce no noise, acid rain, smog, carbon dioxide, water pollutants, or nuclear wastes."13
The Limitations of Solar Power
Although solar power could be seen as the answer to the world's energy needs, it does have some significant drawbacks. Some of these drawbacks are inherent in the use of any energy source. Other drawbacks are unique to solar power.
It is true that solar power is available for use wherever the sun is shining. One major problem, however, is that the sun only shines during daylight hours. Cloudy days also reduce the effectiveness of solar modules. Unfortunately, the evening hours and cloudy days are the times when energy needs are at their highest. During the evening people are home from work and are busy making dinner, watching television, and taking baths. On a cloudy day people use a lot of energy to heat their homes. This means another source of energy needs to be used in the evening hours or during a particularly cloudy day.
For people currently using solar power, these secondary sources of energy are often generators. Generators cause noise pollution and emit many gases that contribute to the greenhouse effect and global warming. Many of the environmental benefits of solar power are lost when generators are used as a secondary source of power.
Some people circumvent the need for a generator by storing the energy generated by their solar modules during the day in a series of deep cell batteries. These batteries are designed to have a long life of ten to twenty years and to not be damaged by daily recharging. Yet once these batteries have expired, they too become a source of pollution that needs to be carefully disposed of.
Another reason solar power is not widely used is because it often is greatly misunderstood by members of the general public. During the energy crisis of the 1970s many people became interested in alternative energy sources. One of the main sources explored was solar power. At the time, much was still unknown about solar power, and scientists were still discovering the best ways for this energy to be utilized. Yet some solar energy companies attempted to make a quick profit in the budding market, making extreme claims about their products, which were often shoddy and had less than one-tenth the operating power of the modules made today. As these solar panels failed to deliver the energy promised by the companies, many people became dissatisfied with solar power as a whole. This has led to a long-lasting mistrust of solar power. Today, most people do not realize how simple a solar power system is to install and operate and the energy potential it can offer.
A Bright Future
Even though many people know little about solar power technology, the general population is becoming educated about the environmental degradation of the planet and the long-term effects this will have. Many understand why global warming is occurring and what role their energy use choices play in it. International relationships are becoming strained because of a dependence on oil. All of these factors have led to many people wanting better energy alternatives to be available for use. "Interest in PV power remains high and appears to be growing," states the Almanac of RenewableEnergy. "Policy makers and the public alike have become increasingly concerned about the environmental impacts of fossil fuels and nuclear energy. In addition, the Gulf War, like the energy crises of the 1970s, demonstrated the economic and political costs of the world's heavy dependence on oil."14
Scientists are now exploring better methods of collecting and storing solar power. From the 1970s to now, PV cells have become 40 percent more effective in collecting sunlight. This means people using solar power today require roughly half the number of solar modules as they did thirty years ago to create the same amount of electricity. This also means consumers have to spend less to get the same result and need less room for mounting the panels. Due to these changes the future for solar power appears bright, although it will require government, public, and financial backing to become a reality.
Many power companies are also eager to explore other methods for creating electricity so they can more consistently supply power to their customers, avoiding rolling blackouts and sometimes frequent brownouts. Environmentalists, many scientists, and conscientious consumers are holding out for the day when solar power is used consistently by utilities as a standard source of their energy supply. "Then," says author Jennifer Carless, "we will be making practical and widespread use of a free, environmentally benign energy source."15