30-06-2012, 11:52 AM
Solar energy
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Abstract
The increase in passenger and freight traffic represents a great challenge for transport infrastructures, logistics and technology. The new technologies are necessary to meet increased transport demands in future and satisfy the need for the safer, faster and more sustainable mobility of persons and goods. Automobile is one of the key sectors in the country. The early history of the automobile can be divided into a number of eras, based on the prevalent means of propulsion during that time. Later periods were defined by trends in exterior styling, and size and utility preferences. But today, transport is responsible for about 20 percent of all CO2 emissions and about 70 percent of mineral oil consumption. It also causes noise which is harmful to health. The climate protection objectives therefore begin with transport, like lower emissions of greenhouse gases, greater energy efficiency and a higher percentage of renewable energies.
For years the vision for futuristic vehicles has being in the mind of many engineers. Nonetheless, the combination of many old thoughts and ideas has played a significant role to modern day vehicles as well a major foundation to futuristic vehicles. Improvements to the early vehicle are what will create the futuristic vehicle. Solar energy is the one of the renewable energy resources, which can be used for Futuristic cars to achieve the above mentioned objectives.
Given the abundance and the appeal of solar energy, this resource is poised to play a prominent role in our energy future.
In the broadest sense, solar energy supports all life on Earth and is the basis for almost every form of energy we use. The sun makes plants grow, which can be burned as "biomass" fuel or, if left to rot in swamps and compressed underground for millions of years, in the form of coal and oil. Heat from the sun causes temperature differences between areas, producing wind that can power turbines. Water evaporates because of the sun, falls on high elevations, and rushes down to the sea, spinning hydroelectric turbines as it passes. But solar energy usually refers to ways the sun's energy can be used to directly generate heat, lighting, and electricity.
The Solar Resource
The amount of energy from the sun that falls on Earth's surface is enormous. All the energy stored in Earth's reserves of coal, oil, and natural gas is matched by the energy from just 20 days of sunshine. Outside Earth's atmosphere, the sun's energy contains about 1,300 watts per square meter. About one-third of this light is reflected back into space, and some is absorbed by Solar energy—power from the sun—is a vast and inexhaustible resource. Once a system is in place to convert it into useful energy, the fuel is free and will never be subject to the ups and downs of energy markets. Furthermore, it represents a clean alternative to the fossil fuels that currently pollute our air and water, threaten our public health, and contribute to global warming. the atmosphere (in part causing winds to blow).
By the time it reaches Earth's surface, the energy in sunlight has fallen to about 1,000 watts per square meter at noon on a cloudless day. Averaged over the entire surface of the planet, 24 hours per day for a year, each square meter collects the approximate energy equivalent of almost a barrel of oil each year, or 4.2 kilowatt-hours of energy every day. Deserts, with very dry air and little cloud cover, receive the most sun—more than six kilowatt-hours per day per square meter. Northern climates, such as Boston, get closer to 3.6 kilowatt-hours. Sunlight varies by season as well, with some areas receiving very little sunshine in the winter. Seattle in December, for example, gets only about 0.7 kilowatt-hours per day. It should also be noted that these figures represent the maximum available solar energy that can be captured and used, but solar collectors capture only a portion of this, depending on their efficiency. For example, a one square meter solar electric panel with an efficiency of 15 percent would produce about one kilowatt-hour of electricity per day in Arizona.
Solar Thermal Concentrating Systems
By using mirrors and lenses to concentrate the rays of the sun, solar thermal systems can produce very high temperatures—as high as 3,000 degrees Celsius. This intense heat can be used in industrial applications or to produce electricity. One of the greatest benefits of large scale solar thermal systems is the possibility of storing the sun’s heat energy for later use, which allows the production of electricity even when the sun is no longer shining. Properly sized storage systems, commonly consisting of molten salts, can transform a solar plant into a supplier of continuous baseload electricity. Solar thermal systems now in development will be able to compete in output and reliability with large coal and nuclear plants.
Solar concentrators come in three main designs: parabolic troughs, parabolic dishes, and central receivers. The most common is parabolic troughs—long, curved mirrors that concentrate sunlight on a liquid inside a tube that runs parallel to the mirror. The liquid, at about 300 degrees Celsius, runs to a central collector, where it produces steam that drives an electric turbine.
Solar energy is not available at night, and energy storage is an important issue because modern energy systems usually assume continuous availability of energy.[101]
Thermal mass systems can store solar energy in the form of heat at domestically useful temperatures for daily or seasonal durations. Thermal storage systems generally use readily available materials with high specific heat capacities such as water, earth and stone. Well-designed systems can lower peak demand, shift time-of-use to off-peak hours and reduce overall heating and cooling requirements.[102][103]
Phase change materials such as paraffin wax and Glauber's salt are another thermal storage media. These materials are inexpensive, readily available, and can deliver domestically useful temperatures (approximately 64 °C). The "Dover House" (in Dover, Massachusetts) was the first to use a Glauber's salt heating system, in 1948
Solar energy can be stored at high temperatures using molten salts. Salts are an effective storage medium because they are low-cost, have a high specific heat capacity and can deliver heat at temperatures compatible with conventional power systems. The Solar Two used this method of energy storage, allowing it to store 1.44 TJ in its 68 m3 storage tank with an annual storage efficiency of about 99%
Pumped-storage hydroelectricity stores energy in the form of water pumped when energy is available from a lower elevation reservoir to a higher elevation one. The energy is recovered when demand is high by releasing the water to run through a hydroelectric power generator
DevelopThe Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth's surface is mostly spread across the visible andnear-infrared ranges with a small part in the near-ultraviolet.[3]
Earth's land surface, oceans and atmosphere absorb solar radiation, and this raises their temperature. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth's surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as wind, cyclones and anti-cyclones.[4] Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C.By photosynthesis green plants convert solar energy into chemical energy, which produces food, wood and the biomass from which fossil fuels are derived.
Parabolic dish concentrators are similar to trough concentrators, but focus the sunlight on a single point. Dishes can produce much higher temperatures, and so, in principle, should produce electricity more efficiently.
A promising variation on dish concentrating technology uses a stirling engine to produce power. Unlike a car's internal combustion engine, in which gasoline exploding inside the engine produces heat that causes the air inside the engine to expand and push out on the pistons, a stirling engine produces heat by way of mirrors that reflect sunlight on the outside of the engine. These dish-stirling generators produce about 30 kilowatts of power, and can be used to replace diesel generators in remote locations.
The third type of concentrator system is a central receiver. One such plant in California features a "power tower" design in which a 17-acre field of mirrors concentrates sunlight on the top of an 80-meter tower. The intense heat boils water, producing steam that drives a 10-megawatt generator at the base of the tower. The first version of this facility, Solar One, operated from 1982 to 1988 but had a number of problems. Reconfigured as Solar Two during the early to mid-1990s, the facility is successfully demonstrating the ability to collect and store solar energy efficiently.4 Solar Two's success has opened the door fHybrid cars are recently becoming more and more popular, especially as gas prices seem to be going up all the time, and as climate change problem is becoming more and more serious. The basic definition of hybrid cars would be the car that uses two or more distinct power sources to move the vehicle, mostly the combination of an internal combustion engine and one or more electric motors. Such combination enables hybrid cars to have higher fuel efficiency and lower emissions compared to traditional gas-powered cars.
There are two main advantages of hybrid cars compared to traditional cars, one is lower CO2 emissions, and therefore less impact to global warming (the environmental advantage of hybrid cars), and the other is higher fuel efficiency that can save you sufficient amount of money over the years (economic advantage of hybrid cars). In times when gasoline was fairly cheap improving mileage wasn't something many people were worried with, but at these uncertain economic times, when almost any dollar matters fuel efficiency has become rather important advantage that hybrid cars have over traditional cars.
Currently there are some strong efforts in United States to improve mileage of cars. If you look at the Corporate Average Fuel Economy (CAFE) standards then you can see that the current standards require that the average mileage of all the new cars sold by an auto maker should be 27.5 mpg (8.55 liters per 100 km). These standards were also meant to increase the production of hybrid cars in the United States because the more hybrid cars certain auto maker sells, the more highly expensive luxury cars can be sold too, for instance if an auto maker sells one hybrid car that use 3.92 liters per 100 km, it can then sell four expensive luxury cars that use 11.76 liters per 100 km.
The biggest disadvantage of hybrid cars is that they are still fairly expensive, namely the production of hybrid cars still has relatively high costs. Hybrid cars therefore usually cost in range from $2,000 to $5,000 more than their non-Hybrid versions. The high costs of hybrid cars are usually the results of using very rare materials in their production (for instance dysprosium used to fabricate many of the advanced electric motors and battery systems in hybrid propulsion systems, and neodymium used as a crucial ingredient in high-strength magnets that are found in permanent magnet electric motors).