The pump circulates a fluid, called a heat transfer fluid, through the collector for heating. The heated fluid then goes to a storage tank where it heats water. The hot water may then be piped to a faucet or showerhead. Most solar water heaters that operate in winter use a heat transfer fluid, similar to antifreeze, that will not freeze when the weather turns cold.
Today over 1. Solar Electricity. Besides heating homes and water, solar energy also can be used to produce electricity. Two ways to generate electricity from solar energy are photovoltaics and solar thermal systems. Photovoltaic comes from the words photo meaning "light" and volt , a measurement of electricity. Sometimes photovoltaic cells are called PV cells or solar cells for short.
You are probably already familiar with solar cells. Solar-powered calculators, toys, and telephone call boxes all, use solar cells to convert light into electricity. A photovoltaic cell is made of two thin slices of silicon sandwiched together and attached to metal wires.
The top slice of silicon, called the N-layer, is very thin and has a chemical added to it that provides the layer with an excess of free electrons. The bottom slice, or P-layer, is much thicker and has a chemical added to it so that it has very few free electrons. When the two layers are placed together, an interesting thing happens-an electric field is produced that prevents the electrons from traveling from the top layer to the bottom layer.
This one-way junction with its electric field becomes the central part of the PV cell. When the PV cell is exposed to sunlight, bundles of light energy known as photons can knock some of the electrons from the bottom P-layer out of their orbits through the electric field set up at the P-N junction and into the N-layer. The N-layer, with its abundance of electrons, develops an excess of negatively charged electrons. This excess of electrons produces an electric force to push the additional electrons away.
These excess electrons are pushed into the metal wire back to the bottom P-layer, which has lost some of its electrons. This electrical current will continue flowing as long as radiant energy in the form of light strikes the cell and the pathway, or circuit, remains closed.
Current PV cell technology is not very efficient. Today's PV cells convert only about 10 to 14 percent of the radiant energy into electrical energy. Fossil fuel plants, on the other hand, convert from percent of their fuel's chemical energy into electrical energy.
The cost per kilowatt-hour to produce electricity from PV cells is presently three to four times as expensive as from conventional sources.
However, PV cells make sense for many uses today, such as providing power in remote areas or other areas where electricity is difficult to provide. Scientists are researching ways to improve PV cell technology to make it more competitive with conventional sources.
Like solar cells, solar thermal systems use solar energy to make electricity. But as the name suggests, solar thermal systems use the sun's heat to do it. Most solar thermal systems use solar collectors with mirrored surfaces to concentrate sunlight onto a receiver that heats a liquid.
The super-heated liquid is used to make steam that drives a turbine to produce electricity in the same way that coal, oil, or nuclear power plants do. Solar thermal systems may be one of three types: central receiver, dish, or trough. A central receiver system uses large mirrors on top of a high tower to reflect sunlight onto a receiver.
This system has been dubbed a "solar power tower. This system resembles a television satellite dish. A third system uses mirrored troughs to collect sunlight. Until recently, trough systems seemed the most promising. The world's first solar electric plant used mirrored troughs. LUZ, as the plant was called, was perfectly situated in the sunny Mojave desert of California.
LUZ was the only solar plant to generate electricity economically. Dollar for dollar, it had always been cheaper to use conventional sources of energy coal, oil, nuclear to generate electricity. But the LUZ solar plant turned that around, producing electricity as cheaply as many new coal plants, and with no hidden pollution costs. The future looked bright for this pioneering solar plant and then the dream cracked.
LUZ closed its doors at the end of because of a drop in oil prices and an over-budget construction project at LUZ's home-base. LUZ may be gone, but most solar energy engineers believe solar power towers will be ready to take the place of trough systems very soon. Solar Energy and the Environment. There are many different types of solar furnaces, including solar power towers, parabolic troughs, and Fresnel reflectors. They use the same general method to capture and convert energy.
In previous designs of solar power towers, the concentrated sunlight heated a container of water, which produced steam that powered a turbine. More recently, some solar power towers use liquid sodium, which has a higher heat capacity and retains heat for a longer period of time. Parabolic troughs and Fresnel reflectors also use CSP, but their mirrors are shaped differently. Parabolic mirrors are curved, with a shape similar to a saddle.
Fresnel reflectors use flat, thin strips of mirror to capture sunlight and direct it onto a tube of liquid. Concentrated solar power plants were first developed in the s. Other large and effective plants have been developed in Spain and India. Concentrated solar power can also be used on a smaller scale. It can generate heat for solar cooker s, for instance.
People in villages all over the world use solar cookers to boil water for sanitation and to cook food. Solar cookers provide many advantages over wood-burning stoves: They are not a fire hazard, do not produce smoke, do not require fuel, and reduce habitat loss in forests where trees would be harvested for fuel. Solar cookers also allow villagers to pursue time for education, business, health, or family during time that was previously used for gathering firewood. Solar cookers are used in areas as diverse as Chad, Israel, India, and Peru.
Solar Architecture Throughout the course of a day, solar energy is part of the process of thermal convection , or the movement of heat from a warmer space to a cooler one.
When the sun rises, it begins to warm objects and material on Earth. Throughout the day, these materials absorb heat from solar radiation. At night, when the sun sets and the atmosphere has cooled, the materials release their heat back into the atmosphere. Passive solar energy techniques take advantage of this natural heating and cooling process.
Homes and other buildings use passive solar energy to distribute heat efficiently and inexpensively. At night, the thermal mass releases its heat back into the room. Effective ventilation systems—hallways, windows, and air ducts—distribute the warmed air and maintain a moderate, consistent indoor temperature.
Passive solar technology is often involved in the design of a building. This method takes into account the latitude , altitude , and typical cloud cover of a specific area.
In addition, buildings can be constructed or retrofitted to have thermal insulation, thermal mass, or extra shading. Other examples of passive solar architecture are cool roofs, radiant barriers, and green roofs. The white surface reduces the amount of heat that reaches the interior of the building, which in turn reduces the amount of energy that is needed to cool the building. Radiant barrier s work similarly to cool roofs. They provide insulation with highly reflective materials, such as aluminum foil.
In addition to roofs and attics, radiant barriers may also be installed beneath floors. Green roof s are roofs that are completely covered with vegetation.
They require soil and irrigation to support the plants, and a waterproof layer beneath. Green roofs not only reduce the amount of heat that is absorbed or lost, but also provide vegetation. Through photosynthesis, the plants on green roofs absorb carbon dioxide and emit oxygen. They filter pollutant s out of rainwater and air, and offset some of the effects of energy use in that space. Green roofs have been a tradition in Scandinavia for centuries, and have recently become popular in Australia, Western Europe, Canada, and the United States.
For example, the Ford Motor Company covered 42, square meters , square feet of its assembly plant roofs in Dearborn, Michigan, with vegetation. In addition to reducing greenhouse gas emissions, the roofs reduce stormwater runoff by absorbing several centimeters of rainfall.
In busy cities, the temperature can be consistently higher than the surrounding areas. Many factors contribute to this: Cities are constructed of materials such as asphalt and concrete that absorb heat; tall buildings block wind and its cooling effects; and high amounts of waste heat is generated by industry, traffic, and high populations.
Using the available space on the roof to plant trees, or reflecting heat with white roofs, can partially alleviate local temperature increases in urban areas.
Solar Energy and People Since sunlight only shines for about half of the day in most parts of the world, solar energy technologies have to include methods of storing the energy during dark hours. Thermal mass systems use paraffin wax or various forms of salt to store the energy in the form of heat. Photovoltaic systems can send excess electricity to the local power grid , or store the energy in rechargeable batteries. There are many pros and cons to using solar energy.
Advantages A major advantage to using solar energy is that it is a renewable resource. We will have a steady, limitless supply of sunlight for another 5 billion years. Solar energy is clean. After the solar technology equipment is constructed and put in place, solar energy does not need fuel to work.
It also does not emit greenhouse gases or toxic materials. Using solar energy can drastically reduce the impact we have on the environment.
There are locations where solar energy is practical. Solar cookers provide an excellent alternative to cooking with wood-fired stoves—on which 2 billion people still rely. Solar cookers provide a cleaner and safer way to sanitize water and cook food.
Solar energy complements other renewable sources of energy, such as wind or hydroelectric energy. Homes or businesses that install successful solar panels can actually produce excess electricity. These homeowners or businessowners can sell energy back to the electric provider, reducing or even eliminating power bills.
Disadvantages The main deterrent to using solar energy is the required equipment. Solar technology equipment is expensive. Purchasing and installing the equipment can cost tens of thousands of dollars for individual homes.
Although the government often offers reduced tax es to people and businesses using solar energy, and the technology can eliminate electricity bills, the initial cost is too steep for many to consider. Solar energy equipment is also heavy. Both active and passive solar technology depend on factors that are out of our control, such as climate and cloud cover.
Local areas must be studied to determine whether or not solar power would be effective in that area. Sunlight must be abundant and consistent for solar energy to be an efficient choice. Agua Caliente has more than 5 million photovoltaic modules, and generates more than gigawatt-hours of electricity. Green Chicago Millennium Park in Chicago, Illinois, has one of the most expansive green roofs in the worldalmost , square meters more than a million square feet. Vegetation at ground level covers Department of Energy.
But how exactly does our Sun go about producing this energy? What steps are involved, and how does it get to us here on planet Earth? The simple answer is that the Sun, like all stars, is able to create energy because it is essentially a massive fusion reaction.
Scientists believe that this began when a huge cloud of gas and particles i. This not only created the big ball of light at the center of our Solar System, it also triggered a process whereby hydrogen, collected in the center, began fusing to create solar energy. Technically known as nuclear fusion, this process releases an incredible amount of energy in the form of light and heat. But getting that energy from the center of our Sun all the way out to planet Earth and beyond involves a couple of crucial steps.
It is here, in the core, where energy is produced by hydrogen atoms H being converted into molecules of helium He. This is possible thanks to the extreme pressure and temperature that exists within the core, which are estimated to be the equivalent of 2 50 billion atmospheres The net result is the fusion of four protons hydrogen molecules into one alpha particle — two protons and two neutrons bound together into a particle that is identical to a helium nucleus.
Two positrons are released from this process, as well as two neutrinos which changes two of the protons into neutrons , and energy. The core is the only part of the Sun that produces an appreciable amount of heat through fusion.
The rest of the Sun is heated by the energy that is transferred from the core through the successive layers, eventually reaching the solar photosphere and escaping into space as sunlight or the kinetic energy of particles. The Sun releases energy at a mass—energy conversion rate of 4. To put that in perspective, this is the equivalent of about 9.
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