Engineer paper：最强大的能源

Engineer paper：最强大的能源
Most Powerful Energy Source Nuclear 

 

有三种方法可以使太阳变为能源。 他们是太阳能电池或光伏电池,太阳能热水,太阳能炉。 普通人知道的主要方式,是太阳能电池的太阳能电池板。 “在1839年,法国科学家埃德蒙·贝克勒尔发现了(太阳能) 光电效应。 它被用于1800年代末由组成的“原始太阳能电池 ”。 后来在1950年代,贝尔实验室回做这个技术,使用硅代替了硒，它可以直接将在阳光下百分之四的能量转化为电能(太阳能)。 几年后，这种技术开始被用于推动飞船和卫星。

 

太阳能发电可以进一步分类，而不仅仅是太阳能发电。第一，有直接和间接的太阳能。直接太阳能中将其转化为可用的能源只有一个步骤。而间接太阳能发电需要多步转化为可用的能源。 例如生物燃料,化石燃料,水电站和风力涡轮机，从太阳能引起的风、雨其他气候相互作用,和海洋热能得到能量，从太阳引起的温度差异形成不同深度和波的风上得到能量。也有两个太阳能发电系统的分类。 第一个是被动的太阳能发电系统。 这种系统只需要阳光直射的帮助没有任何其他能源(基础)。 第二个是活跃的太阳能系统。 他们“利用太阳的能源与除此之外其他能源使其工作(基础)。 “太阳能在不同的群体中应用程序也有所不同。第一个是点聚焦抛物面碟”用于把分散阳光转化为集中的太阳辐射(基础)。

 

There are three ways to use solar power for energy. They are solar cells, or photovoltaic cells, solar water heating, and solar furnaces (Darvill-S). The main way that the common person knows of, though, is through solar cells which are in solar panels. "In 1839, French scientist Edmund Becquerel discovered (How Solar)" the photoelectric effect. This was used for "primitive solar cells (How Solar)" in the late 1800s made out of selenium. Later in the 1950s, Bell Labs looked back into this technology, and instead of selenium, used silicon which "could convert four percent of the energy in sunlight directly to electricity (How Solar)." After a few years, this technology started to be used for powering spaceships and satellites (How Solar).

 

Solar power can be further classified than just plain solar power. First, there is direct and indirect solar power. Direct solar power "involves only one step in transforming it to useable energy (All The Basics)." Indirect solar power requires more than one step to transform it into useable energy. Some examples are biofuel, fossil fuels, hydroelectric dams and wind turbines which get their energy from "solar-caused wind, rain other climatic interactions (All The Basics), and ocean thermal energy which gets its energy from "solar-caused differences in temperatures at various depths and wave movement by the wind (All The Basics)." Also, there are two classifications for solar power systems. The first one is a passive solar power system. This "only requires direct sunlight without the aid of any other energy (All The Basics)." The second one is an active solar power system. They "use the aid of energy besides that of the sun to make them work (All The Basics)." Solar power applications also have different groups within them. The first one is point focus which is a parabolic dish "used to focus diffuse sunlight into a concentrated point of solar radiation (All The Basics)." #p#分页标题#e#

 

At the point they are concentrated on there is a cluster of solar cells which then converts that radiation into electricity. The next one is line focus which is a "trough shaped parabolic dish or line of mirrors concentrate the sun's light which is then converted into electricity (All The Basics)." The last group is non-focus which is the ones that most people think of. These include solar thermal panels and solar cell panels (All The Basics).

 

The process for a solar cell to convert photons to electricity is actually relatively simple. First, a "thin semiconductor wafer is specially treated to form an electric field (Knier)." On one side there is a positive field and on the other side there is a negative field. When photons hit the solar cell, electrons are knocked loose "from the atoms in the semiconductor material. If electrical conductors are attached to the positive and negative sides (Knier)" they form an electrical current. This then captures the electrons in the form of an electric current creating electricity. These solar cells can be combined together to create a photovoltaic module. Then photovoltaic modules can be combined together to create an array (Knier).

 

Almost all solar cells are created out of silicon because of its chemical properties in its crystalline form. "The only problem is that pure crystalline silicon is a poor conductor of electricity (Aldous-2)." The only way to fix this problem is to have impurities in a solar cell. Impurities are "other atoms purposefully mixed in with the silicon atoms (Aldous-2)." One of the most common atoms for the impurity is phosphorous because it has five electrons in its outer shell instead of four like silicon. This leaves one electron open to break free of its bonds and become a free carrier. These free carriers leave behind a hole, and then they go seek out another hole to fill in, "carrying an electrical current (Aldous-2)." This process of adding impurities is called doping. The silicon that results from being doped by phosphorous is called N-type "because of the prevalence of free electrons (Aldous-2)." For a typical solar cell there is another impurity in the silicon. This impurity is boron. Boron has three electrons which leaves a hole open for the free carriers to find. Since there are no free electrons, the silicon with boron is called P-type (Aldous-2).

 

To make the solar cell work, both types of silicon must be put together. This results in an electric field. All of the free electrons on the N side try to fill in all the holes on the P side. In between the two sides there is a junction which as the electrons try to get through, they create a barrier making it harder for the electrons to get to the other side. "Eventually, equilibrium is reached, and we have an electric field separating the two sides (Aldous-3)." The electric field starts to only let electrons to come from the P side to the N side, not the other way around. Now, when photons start to hit the solar cell, each one usually has the energy to break apart one "electron-hole pair (Aldous-3)", but if this photon is in range of the electric field it will send the electron to the N side and the hole to the P side. If there is an external current path, the "electrons will flow through the path to the P side to unite with holes that the electric field sent there (Aldous-3)." This electron flow causes a current and the electric field causes voltage, and when combined they provide power. The only bad part is that silicon is very reflective, so many photons are reflected away before they can do anything. An antireflective coating is put on to lessen this effect. The last step to creating a solar cell to put on a glass plate to protect it (Aldous-3).#p#分页标题#e#

 

There are three types of solar cells. They are single-crystal, polycrystalline, and amorphous. The singe-crystal cells "are made in long cylinders and sliced into round or hexagonal wafers (How Solar)." This process produces the highest efficiency cells, but they are wasteful of materials. Because they are expensive, they are usually sold with concentrators that boost their efficiency to thirty percent. They account for about 29 percent of the global market of solar cells. Polycrystalline cells are "made of molten silicon cast into ingots or drawn into sheets, then sliced into squares (How Solar)." The production costs may be lower than single-crystal, so is their efficiency at 15 percent. These cells make up about 62 percent of the global market. Lastly, there are amorphous silicon cells. These cells created in a very different way than the other two. It is made in one step by having silicon "sprayed onto a glass or metal surface in thin films (How Solar)." It is the least expensive procedure, but has a very low efficiency at about 5 percent (How Solar).

 

There are many new things being researched to help improve solar power. "A number of exotic materials other than silicon are under development (How Solar)." Some are gallium arsenide, copper-indium-deselenide, and cadmium-telluride. The reason these are under development is that they could have higher efficiencies, "and other interesting properties, including the ability to manufacture amorphous cells that are sensitive to different parts of the light spectrum (How Solar)." There is also research being done in silicon processing, thin-film processing, metamorphic multijunction solar cells, polymer processing, nanoparticle processing, transparent conductors, silicon wafer-based solar cells, infrared solar cells, UV solar cells, 3D solar cells, metamaterials, and photovoltaic thermal hybrids (Solar cell).

 

With solar power, there are advantages and disadvantages to it. The first major advantage of solar power is that it is a renewable resource and it causes no pollution. Since it causes no pollution, it does not contribute to global warming, acid rain or smog. Instead, it does the opposite; it decreases the green house gas emissions since it causes no pollution. Another advantage is that it can save you money. Once the initial cost has been paid for, "the energy from the sun is practically (Solar Energy)" free. There are financial incentives from the government to reduce the cost of it. You can gain money back, if the system produces more energy that you actually use. The company will buy it back from you. This process is called net-metering. It saves money on people's electricity bill. There is no fuel required for solar power. Solar power systems require little to maintenance which means they will last for a very long time. They make no noise, as there are no moving parts in it (Solar Energy).

 

The major disadvantage of solar energy is the initial cost of solar panels and cells. Another is that solar power systems can only generate power during the daytime, so during about half the day they are not producing any energy. Weather can also affect the efficiency of solar cells. This can be cloudy days, rain, thunderstorms, snow, or fog. Pollution can also affect a solar cell's efficiency, which means that businesses or industries in highly polluted areas that want solar power would be in a bad situation (Pros).

 

Wind energy has been used for centuries from "the sailing ships of the ancient Greeks, to the grain mills of pre-industrial Holland, to the latest high-tech wind turbines rising over the Minnesota prairie (How Wind)." The beginning of the use of wind energy in the United States began between 1870 and 1930. Many farmers used wind to pump their water with windmills. When the New Deal brought electricity to the countryside, the windmills died out. However, the interest in wind energy was reborn in the 1970s during the energy crises. In the 1970s, the DOE researched large turbine designs, although the result ultimately failed, it provided a basis for the research that was to come. "The modern wind era began in California in the 1980s (How Wind)." 15000 medium wind turbines were installed by small companies and entrepreneurs between 1981 and 1986. The state provided tax incentives to promote wind energy during this time and with the help of federal tax incentives helped the wind energy industry rise. The tax incentives expired in 1985 which caused the industry to slow, but it was also because of the decline in fossil fuel prices. Improvements in technology created increased turbine reliability and lower costs of production in the early 1990s. Congress passed the Energy Policy Act of 1992 which gave a new production tax credit for wind and biomass electricity. There was a massive slowdown for all alternative energy sources which caused investment in new power plants to fall. In 1998, the wind industry started to pick up again due to federal tax incentives, state level renewable energy requirements and incentives and rising fossil fuels which began in 2001. While it has grown very much, it has suffered from the off and on support of federal tax incentives in the early 2000s, but in 2006 "a period of uninterrupted federal support for wind began (How Wind)."

 

Wind energy is usually generated by wind turbines. The most common one is called "horizontal-axis wind turbines (HAWTs) (Layton-2)." There is another wind turbine called "vertical-axis wind turbines (VAWTs) (Layton-2)." For the simplest wind turbine, there are three necessary parts. They are the rotor blades, the shaft, and the generator. The rotor blades are "the sails of the system (Layton-1)." They act as a barrier to the wind, but more modern designs have gone beyond that initial method. The wind forces the blades to move which transfers some of its energy to the rotor. The shaft is connected to the center of the rotor. The shaft spins when the rotor spins, which transfers "its mechanical, rotational energy to the shaft, which enters an electrical generator on the other end (Layton-1)." The generator uses the properties of "electromagnetic induction to produce electrical voltage (Layton-1)." It usually consists of magnets and a conductor. The conductor is usually a coiled wire. The shaft connects with an "assembly of permanent magnets that surrounds the coil of wire (Layton-1)" inside the generator. Voltage is induced in the conductor when the conductor is surrounded by magnets and one is rotating relative to the other. The rotor spins the shaft which spins the magnets which induces a current in the coil of wire. The current then goes through power lines for distribution (Layton-1).#p#分页标题#e#

 

The two modern day wind turbines work slightly differently, but still work on those same principles. The VAWT in production is called the Darrieus turbine which slightly looks light an egg beater. Its shaft is mounted on a vertical axis. They are always aligned to the wind, so there is no need for adjustment when the wind changes direction. The only part is that it cannot start moving by itself, so it needs boost from its electrical system. For support it uses guy wires instead of a tower which means that the rotors are lower in elevation. This means that there are slower wind speeds due to ground interference which makes VAWTs less efficient than HAWTs. VAWTs are usually used for "small-scale turbines and for pumping water in rural areas (Layton-1)." The HAWT shaft is mounted horizontally on a tower. Unlike the VAWT, it needs to constantly adjust itself to the wind. To do this it uses a yaw-adjusting device. It usually consists of electric motors and gearboxes which move the entire rotor left or right in small increments. "The turbine's electronic controller reads the position of a wind van device and adjusts the position of the rotor to capture the most wind energy available (Layton-1)." The components of a large HAWT include the rotor blades, the shaft, the nacelle, the tower, and the electrical equipment. The nacelle is the part that connects the rotor blades and the tower and holds all the electrical equipment. The nacelle holds the gearbox, the generator, electrical control unit, yaw controller, and brakes (Layton-1).

 

For a large HAWT, the process of gaining electricity is slightly more complicated than the simplest design. It starts with the wind's energy being converted to rotational motion by the rotor. As the rotors turn they turn the shaft which then transfers that motion into the nacelle. The shaft enters the gearbox which greatly increases the rotational shaft speed. The gearbox is connected to the generator which converts the rotational motion into electricity at medium voltage which is hundreds of volts. The electricity then flows down the electric cables inside the tower to a transformer which then increases the voltage of the electric power to distribution voltage which is thousands of volts. This power then flows through underground lines to a collection point where the power is combined with the power of other wind turbines (Layton-1).

 

There are advantages and disadvantages to wind energy. One advantage is that wind turbines do not generate pollution or radioactive waste, and "their construction and installation has less environmental impact as well (Perry)." It can provide electricity to "individual homes or other facilities on a self-reliant basis (Perry)." They will not lose their power if power lines go out. It can also generate power for large amounts of people with larger turbines connected to the electrical grid. Wind energy does not "consume any non-renewable resources (Perry)." Wind energy also has the "potential of covering six times the world's electricity consumption, or one time the world's total energy consumption. The energy consumption for production, installation, operation and decommission of a wind turbine is usually earned back within 3 months of operation (Wind)." When wind turbines are decommissioned, everything, including the foundation, is removed. Due to improvements in blade design, it is now possible to hold a conversation directly underneath it as the modern designs are much quieter than their earlier counterparts. The amount of birds and bats that are killed by wind turbines "is negligible when compared with other human activities (Wind)."#p#分页标题#e#

 

There are also many disadvantages to wind energy. Many people believe that wind turbines are noisy and not very aesthetically pleasing. Wind turbines kill many birds and bats even though the "siting generally takes into account bird flight patterns, but most paths of migration, birds that fly at night, are unknown (Wind)." Another disadvantage is that the construction of a "large wind energy facility is also far from ecologically benign in previously undeveloped locations. It requires wide straight flat roads, a large hole filled with tons of steel and concrete to secure each giant assembly, clearing of trees in wooded areas and a transformer and power lines for each turbine (Wind)." Wind turbines can be damaged in thunderstorms because of their tall and thin shape. This is the way most wind turbines are damaged (Perry).

 

The history of nuclear energy starts in 1939 when the first successful experiment with nuclear fission was conducted in Berlin by German physicist Otto Hahn, Lise Meitner, and Fritz Strassman. Later, during the Second World War, many nations were trying to develop nuclear energy with the focus on nuclear reactors. "The first self-sustaining nuclear chain reaction was obtained by Enrico Fermi in 1943, and reactors based on his research were used to produce the plutonium necessary for two of the nuclear weapons (Norwich)." The first time electricity was produced by a nuclear reactor was on December 20, 1951 "at the EBR-I experimental fast breeder station near Arco, Idaho, which initially produced about 100 kW. … The world's first nuclear power plant that generated electricity for commercial use was officially connected to the Soviet power grid at Obninsk, USSR (Norwich)." The second reactor was in Calder Hall in Sellafield, England and the first one in the United States was the Shippingport Reactor in Pennsylvania. In 1955 the first Geneva Conference met to explore nuclear technology. In 1957 EURATOM was launched alongside the now European Union. The International Atomic Energy Agency was also established that same year. In 1960, Pittsburgh became the first nuclear powered city. The capability of nuclear plants quickly rose from less than one gigawatt in 1960 to 100 gigawatts in the late 1970s, and 300 gigawatts in the late 1980s. Ever since the 1980s, the capacity has risen more slowly. It reached 366 gigawatts in 2005 due to the Chinese expansion of nuclear power. In the Western world a popular movement against nuclear power gained strength. It was based on the fear of a nuclear accident and latent radiation. These fears took shape in 1979 at Three Mile Island and the 1986 Chernobyl accident. These stopped many countries from building nuclear power plants. However many countries are still continuing to work on nuclear power plants (Norwich).

 

The basis of nuclear power starts with nuclear fission. Uranium is the natural choice for nuclear power plants. Uranium-235 is the isotope usually used, but it only makes up 0.7 percent of the naturally found uranium. U-235 decays naturally by alpha radiation. "It throws off an alpha particle, or two neutrons and two protons bound together (Brian-1)." U-235 is one of the materials that can undergo induced fission which is when a free neutron goes into a U-235 nucleus; the nucleus absorbs the neutron, and then becomes unstable and splits immediately. It splits into two lighter atoms. Gamma radiation is released when an atom is split. The resulting two atoms will release beta radiation and gamma radiation. The only problem is that for this to work, the sample of uranium needs to be enriched "so that it contains 2 to 3 percent more U-235 (Brian-1)."#p#分页标题#e#

 

In the nuclear plant the first step to turning nuclear fission into electricity is to "control the energy given off by the enriched uranium and allow it to heat water into steam (Brian-3)." The enriched uranium is usually formed into inch long pellets with about the same diameter as a dime. They are then arranged into long rods and then the rods are collected together into bundles. These bundles are then submerged in water inside a pressure container. The water acts as a coolant because the uranium would usually overheat and melt. To prevent the overheating, control rods are used. They are made from a material that absorbs neutrons. They are then inserted into the bundles and can be lowered or raised controlling the rate of the nuclear reaction. To produce more heat the control rods are raised and to produce less heat the control rods are lowered. To shut down the reactor, the control rods are completely lowered down. The uranium bundle produces extreme amounts of heat. This heat heats the water and turns it into steam. The steam then drives the turbine which then spins the generator to produce power. There are some nuclear power plants where the steam from the reactor heats another loop of water to steam which drives the turbine. This is more advantageous as the radioactive water and steam never touch the turbine. There are also some nuclear reactors that use gas or liquid metal as the coolant. This allows it to be operated at higher temperatures (Brian-3).

 

The outside of the nuclear power plant is as important as the inside. It does not look much different from a coal plant, "except for the source of heat used to create steam (Brian-4)." Extra precautions are required in this case. There are three layers to the nuclear power plant. The first one is a concrete liner that houses the reactor's pressure container. It also acts as a radiation shield. It is within the second layer, which is a steel containment vessel. This contains the reactor core and the equipment the workers use to refuel and maintain the reactor. The second layer serves as a barrier to prevent any leaking of radioactive gases or fluids from the nuclear power plant. The last layer is an outer concrete building. This protects the steel containment vessel. It is strong enough to survive the damage caused by "earthquakes or a crashing jet airliner (Brian-4)." It is necessary to prevent any escape of radiation and radioactive steam in case there is an accident.

 

Nuclear energy has advantages, but has some of the biggest disadvantages for any alternative energy source. One big advantage is that is creates massive amounts of energy from small amounts of fuel. It also costs about the same as coal, so it is not that expensive to make. It does not produce any greenhouse gases and only produces small amounts of waste (Darvill-N). It is also reliable because it is not affected by strikes and shortages around the world. The biggest disadvantage to nuclear energy is nuclear meltdowns and disasters. This occurs when is a shortage of coolant in the nuclear reactor. There is also the danger of radiation exposure during the mining and extracting of uranium. The rubble and debris left behind can cause cancer and mutations. It could also be the cover for the development of nuclear weapons (Pilgrim). Another big disadvantage is that the nuclear waste left is very dangerous. "It must be sealed up and buried for many thousands of years to allow the radioactivity to die away. For all that time it must be kept safe from earthquakes, flooding, terrorists and everything else (Darvill-N)." One last disadvantage is that nuclear energy is not renewable. Once all the uranium has been used up, that is the end.#p#分页标题#e#

 

In today's society many people want alternative means of energy. Three main ones are solar power, wind energy, and nuclear energy. Solar power is the ultimate renewable energy source as it comes from the sun. Wind energy is one of the fastest growing alternative energy sources in the world. Nuclear energy is very powerful, but also very dangerous. All of these have advantages and disadvantages to using them. These three alternative energy sources are some of the few that are gaining grounds in the world as a new energy source.