1. Introduction


How is a solar powered car applicable to the real world? Solar cars are cars that use the sun for energy. Solar powered car has solar cells that is also known as photovoltaic. Photovoltaic cells are made of special materials called semiconductors such as silicon, which is currently used most commonly. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely. (Jessika Toothman, 2000) A semiconductor mixed, or "doped," with phosphorous develops an excess of free electrons. This is known as an n-type semiconductor. A semiconductor doped with other materials, such as boron, develops an excess of "holes," spaces that accept electrons. This is known as a p-type semiconductor. A PV cell joins n-type and p-type materials, with a layer in between known as a junction. Even in the absence of light, a small number of electrons move across the junction from the n-type to the p-type semiconductor, producing a small voltage. In the presence of light, photons dislodge a large number of electrons, which flow across the junction to create a current. This current can be used to power electrical devices, from light bulbs to cell phone chargers. The flow of electrons in the current can be used for external uses such as powering a calculator too. (William Harris, 2008) If building a solar powered car, the electrical system is the significant system of the car, because it is what converts sunlight to energy. The mechanical system is important because it needs to be strong yet lightweight. This is now achieved with composite materials. The weight is not the only factor, the price is also costly. Solar cars are beneficial because they do not use fossil fuels and they reduce pollution. But, they are limited in speed and power, and are only practical in areas with a lot of sunlight. We believe solar cars can be a big help for the environment. They create less pollution and reduce the amount of oil drilling needed. Most important is the battery. Since batteries only have a limited life it will reduce how much people want them. However, people who live in areas with a lot of sunlight will find them very useful. It is only a matter of time before a way is found to store other form of energies other than chemical potential energy for longer and make it easier for everyone to use them. We also think that things are advancing much quicker and now that people see pollution as a problem more money will be spent to improve the technology. Besides, people are learning how bad pollution is, so they want to fix it and these cars could help.(Abu Faisal, 2010) Solar energy is also the best energy solution. The amount of energy the sun sends towards our planet is 35,000 times more than what we currently produce and consume. Some part of this energy also known as solar radiation, is reflected back into space but a lot of it is absorbed by the atmosphere and other elements surrounding the inner atmosphere. This energy can be easily harnessed for practical purposes such as heating homes, lighting bulbs and running automobiles and even airplanes. The uses can be as varied as the uses of energy itself. And the great thing is that we are never going to run out of this massive energy resource even for thousands and thousands of years. Photovoltaic systems release no greenhouse gases into the atmosphere and they do not even need direct sunlight to produce energy, they just need daylight and this means they can operate even during cloudy and less bright days. Electricity is generated indirectly too by first generating heat from solar energy and then using the steam produced in the process to run power generators. Here too, since no fossil fuels are being burned to produce heat, the resultant energy to 100% eco-friendly. Although the oil lobby does its best to throttle endeavors to tap into renewable energy resources like solar energy, many countries are taking proactive strides towards setting up solar-energy generation plants. (Alternative Energy Foundation, 2008)
So our hypothesis is that the higher the light intensity and volt of the solar panel, the faster the toy car will go. We believe this is because the higher the light intensity, the more energy will be generated as more energy will be absorbed by the solar panel. We also believe that the higher the volt of the solar panel, the faster the current would flow thus this will make the vehicle travel faster. Even though real life solar powered car is somehow related to this investigation and development, the future of solar powered cars still has a long route to go. There are a number of practical problems with solar-powered cars. Most importantly, it's difficult for the car's solar array to gather enough power to move the car. That's why most solar race cars only carry one person -- the extra weight of a passenger would tax the car's power. With that said, all of the hard work that's gone into solar-powered cars hasn't been a waste. The information that engineers have learned from building solar-powered cars has guided their work in other areas. This includes aiding in the development of smaller, more efficient solar arrays, as well as the development of solar panels that can be attached to gasoline-powered cars to increase their efficiency and decrease their fuel consumption. While solar-powered cars really aren't a possibility in the near future, there's no reason to completely write off the idea. With continued research, they may eventually become a more practical solution.(Jamie Page Deaton, 2008) 

1.1 Background Research  

The solar cells that we see on calculators and satellites are also called photovoltaic (PV) cells, which as the name implies (photo meaning "light" and voltaic meaning "electricity"), convert sunlight directly into electricity. 

Photovoltaic cells are made of special materials called semiconductors such as silicon, which is currently used most commonly. When light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely.

PV cells also all have one or more electric field that acts to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off for external use, say, to power a calculator. This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce.

Silicon has some special chemical properties, especially in its crystalline form. An atom of sili­con has 14 electrons, arranged in three different shells. The first two shells -- which hold two and eight electrons respectively -- are completely full. The outer shell, however, is only half full with just four electrons.

 What forms the crystalline structure (turns out to be important to this type of PV cell) when a silicon atom will look for ways to fill up its last shell, and to do this, it will share electrons with four nearby atoms. It's like each atom holds hands with its neighbors, except that in this case, each atom has four hands joined to four neighbors. 

Phosphorous has five electrons in its outer shell, not four. It still bonds with its silicon neighbor atoms, but in a sense, the phosphorous has one electron that doesn't have anyone to hold hands with. It doesn't form part of a bond, but there is a positive proton in the phosphorous nucleus holding it in place. When energy is added to pure silicon, in the form of heat for example, it can cause a few electrons to break free of their bonds and leave their atoms. A hole is left behind in each case. These electrons, called free carriers, then wander randomly around the crystalline lattice looking for another hole to fall into and carrying an electrical current. However in the case of impure silicon with phosphorous atoms mixed, it takes a lot less energy to knock loose one of our "extra" phosphorous electrons because they aren't tied up in a bond with any neighboring atoms. As a result, most of these electrons do break free, and we have a lot more free carriers than we would have in pure silicon.

When light, in the form of photons, hits our solar cell, its energy breaks apart electron-hole pairs. Each photon with enough energy will normally free exactly one electron, resulting in a free hole as well. If this happens close enough to the electric field, or if free electron and free hole happen to wander into its range of influence, the field will send the electron to the N side and the hole to the P side. This causes further disruption of electrical neutrality, and if we provide an external current path, electrons will flow through the path to the P side to unite with holes that the electric field sent there, doing work for us along the way. The electron flow provides the current, and the cell's electric field causes a voltage. With both current and voltage, we have power, which is the product of the two. 

Silicon happens to be a very shiny material, which can send photons bouncing away before they've done their job, so an antireflective coating is applied to reduce those losses. The final step is to install something that will protect the cell from the elements -- often a glass cover plate. (Scott Aldous, 2008)

Traditional solar cells use silicon in the n-type and p-type layers. The newest generation of thin-film solar cells uses thin layers of either cadmium telluride (CdTe) or copper indium gallium deselenide (CIGS) instead. One company, Nanosolar, based in San Jose, Calif., has developed a way to make the CIGS material as an ink containing nanoparticles. A nanoparticle is a particle with at least one dimension less than 100 nanometers (one-billionth of a meter, or 1/1,000,000,000 m). Existing as nanoparticles, the four elements self-assemble in a uniform distribution, ensuring that the atomic ratio of the elements is always correct.
The layers that make up the two non-silicon thin film solar cells are shown below. Notice that there are two basic configurations of the CIGS solar cell. The CIGS-on-glass cell requires a layer of molybdenum to create an effective electrode. This extra layer isn't necessary in the CIGS-on-foil cell because the metal foil acts as the electrode. A layer of zinc oxide (ZnO) plays the role of the other electrode in the CIGS cell. Sandwiched in between are two more layers -- the semiconductor material and cadmium sulfide (CdS). These two layers act as the n-type and p-type materials, which are necessary to create a current of electrons.

The CdTe solar cell has a similar structure. One electrode is made from a layer of carbon paste infused with copper, the other from tin oxide (SnO2) or cadmium stannate (Cd2SnO4). The semiconductor in this case is cadmium telluride (CdTe), which, along with cadmium sulfide (CdS), creates the n-type and p-type layers required for the PV cell to function. (William Harris,2008)

Some people have a flawed concept of solar energy. While it's true that sunlight is free, the electricity generated by PV systems is not. There are lots of factors involved in determining whether installing a PV system is worth the price.

People living in sunny parts of the world start out with a greater advantage than those settled in less sun-drenched locations, since their PV systems are generally able to generate more electricity. The cost of utilities in an area should be factored in on top of that. Electricity rates vary greatly from place to place, so someone living farther north may still want to consider going solar if their rates are particularly high. Next, there's the installation cost; as you probably noticed from our discussion of a household PV system, quite a bit of hardware is needed. As of 2009, a residential solar panel setup averaged somewhere between $8 and $10 per watt to install [source: National Renewable Energy Laboratory]. The larger the system, the less it typically costs per watt. It's also important to remember that many solar power systems don't completely cover the electricity load 100 percent of the time. Chances are, you'll still have a power bill, although it'll certainly be lower than if there were no solar panels in place. Despite the sticker price, there are several potential ways to defray the cost of a PV system for both residents and corporations willing to upgrade and go solar. These can come in the form of federal and state tax incentives, utility company rebates and other financing opportunities. Plus, depending on how large the solar panel setup is -- and how well it performs -- it could help pay itself off faster by creating the occasional surplus of power. Finally, it's also important to factor in home value estimates. Installing a PV system is expected to add thousands of dollars to the value of a home. Right now, solar power still has some difficulty competing with the utilities, but costs are coming down as research improves the technology. Advocates are confident that PV will one day be cost-effective in urban areas as well as remote ones. Part of the problem is that manufacturing needs to be done on a large scale to reduce costs as much as possible. That kind of demand for PV, however, won't exist until prices fall to competitive levels. It's a catch-22. Even so, as demand and module efficiencies rise constantly, prices fall, and the world becomes increasingly aware of the environmental concerns associated with conventional power sources, it's likely photovoltaics will have a promising future. (Scott Aldous 2008)

1.2 Research Question 

An Investigation And Development of A Solar Powered Toy Car

1.3 Hypothesis 

Our goal is to develop a solar powered toy car that can travel the fastest using the least amount of energy. We will also investigate the amount of light energy needed to power the car and the speed it is traveling at. Our hypotheses it that the higher the light intensity and volt of the solar panel, the faster the toy car will go.

1.3.1 Independent variable(s) 

The surface area of the solar panel

1.3.2 Dependent variable 

The speed of the car.

1.3.3 Constants 

The type of wheels, the type of toy car chassis, the type of solar panel used for each car design, the type of light powering the toy car, the light intensity when carrying out experiment, type of DC Motor

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