8.7

Although remarkable amount of sunshine hit the earth daily, the rays do not strike anyone site on the planet for 24 hours a day, 365 days a year. Furthermore, some parts of the planet received too low an intensity of light to be practical for solar collecting. the difference is right Ia of the geographical location and because of local factors such as cloud cover, aerosols, smog, haze. One way to tap into the suns energy is to use a photovoltaic cell, a device that converts light energy directly to electric energy, sometimes called a solar cell. Takes only a few PV cells to produce enough electricity to power your calculator or digital watch. If more power is required, PV cells can be combined into modules or arrays to make up solar panels. Many people today power their homes and businesses for solar PV systems. When light shines onto a TV cello, and may pass right through the self, be reflected, or be absorbed. If absorbed, the energy may cause an excitation of the electrons in the atoms of the cells. Photovoltaic cells are made from a class of materials called semiconductors, materials of a limited capacity of conducting an electric current, most semiconductors are made from Crystaline form of silicon. And and type semiconductor is 80 layer with an abundance of electrons. It the P type semiconductor is the layer with a defect of electrons. The element silicon was one of the first semiconducting materials developed for it using computers and PV cells. In actuality, Pure silicon semiconductors do not allow an electric current to flow unless they are doped. Doping as a process of intentionally adding small amounts of other elements. These dopants are chosen for their ability to facilitate the transfer of electrons. Silicon is for electrons in its outer energy level, gallium has three and arsenic as five. Ass both types of doping increase electric conductivity of silicon because electrons can now move from an electronic Rich to an electron deficient environment. A photovoltaic cell typically includes multiple layers of doped n- and p-type. The electric circuit. For a PV cell to convert as much sunlight as possible into electricity, the semiconductors must be constructed in such a way to make the best use of the photons energy. The first challenges that all the silicon is the second most abundant elements in the Earth’s crust, it is most frequently found combined with oxygen silicon dioxide.  The second challenge is that the direct conversion of sunlight into electricity is not very efficient. A photovoltaic salad could, transform up to 31% of the radiant Energy to which it is sensitive into electricity. Typically a commercial solar so now has an efficiency of only 15%, but even this is significant increase over the first solar cells built in the 1950s. One approach to increasing commercial visibility is to replace crystalline silicon with the noncrystalline form of the element. Other researchers are developing multi layered solar cells. By alternating thin layers of tea type and type doped silicon, each electron has only a short distance to travel to reach the next p-n junction. Maximum theoretically predicted efficiencies could improve to 50% for two conjunctions, 56 for three conjunctions and to 72% for 36 conjunctions. Multilayer technology, compared with single cell technology, uses smaller quantities of silicon, and the process can become highly automated. Thin-film solar cells are made from amorphous silicon or non-silicon materials. These thin films use layers of semiconductor materials only a few micrometers thick. Solar modular units used plastic lenses or mirrors to concentrate sunlight onto very small but a highly efficient PV materials. Because of the diffuse nature of sunlight, photovoltaic Technology is well suited to distributed generation. Because PV installations are relatively maintenance free, they are particularly attractive for electric generation in remote regions. Electricity generated by photovoltaic cells during the day must be stored using batteries for use at night. In addition reviewing some of our dependence on fossil fuels, an economy based on solar electricity would reduce the environmental damage of extracting and transporting these fuels. However for the long term, we can turn too many renewable energy sources. 

8.6

Since hydrogen is a gas, It requires a different system for storage and transfer from that used for gasoline. As a gas, hydrogen also takes up a bottle of space. Although the refueling process does require a different system than a gasoline pump used for gasoline powered vehicle, The process is similar in that there isa nozzle and you squeeze a trigger to start the flow of hydrogen. Instead of compressing H2 into metal cylinders, in which the past have been a heavy and somewhat unwieldy, Chemical engineers are investigating other method for storing and transporting H2 that could reduce space and the need for high pressure gas compression. Metal hydride storage systems are ideally suited for P EM fuel cells that require high purity hydrogen. Because metal hydrides are selective and absorb only hydrogen and not longer gas molecules such as a, CO2, or 02, They react simultaneously as a storage material and a way of filtering out other gases. The second challenge is the projected demand for a dream as if you’ll. Over 93% of all Adams are hydrogen atoms. Although hydrogen is not nearly this abundant on earth, still there is an immense supply of the element. Fossil fuels, including natural gas and coal, as hydrocarbons, Or one possible source of hydrogen. As you can see in the equations 8.18, 8.19 and 8.20. The most convenient method of decomposing water into hydrogen and oxygen is by electrolysis, the process of passing a direct current electricity of sufficient voltage through water to decompose it into H2 and O2 (fig. 8.15). This process takes place in a electrolytic cell, a type of electrochemical cell in which electrical energy is converted into chemical energy. An electrolytic sal is the opposite of a Galvin excel, where chemical energy is converted to electric energy. When the water is electrolyzed in an electrolytic so, the volume of hydrogen generated is twice that of oxygen as shown in equation 8.20. Water electrolysis requires it out have the energy input. More of H2 then using methane to produce hydrogen and produces no CO2. Instead of burning fossil fuel to generate the enormous amount of heat needed to split water, another option is to use a sustainable source of energy, the radiant energy of the Sun. The the loss of electrons, as you’ve learned, corresponds to the oxidation, and in this case the oxygen in water can be oxidized  to 02. 

8.4

As concerns grow about the cost and availability of gasoline and about Clunes that gasoline powered vehicles in minute, more car owners are considered hybrid electric vehicles. These vehicles are propelled by a combination of a conventional gasoline engine and electric motor and buy batteries. Delivering about 50 miles to the gallon. The previous brands about half the gas land the cements about half of the carbon dioxide of a conventional car. The electric motor draws power from the batteries to start the car moving and to power it at low speeds. Using a process called regenerative breaking, the energy of the cars motion is transferred to the alternator, Which in turn charges the batteries during deceleration and breaking. Given that each gallon of gasoline burn releases about 18 pounds of CO2 into the atmosphere, the average vehicle and it’s from 6 to 9 tons of CO2 each year. Automobile manufacturers now provide more than one option for fuel efficient, low emission vehicles, allowing customers to choose the option that best meets their transportation needs. One such option is a plug-in hybrid electric vehicle. These vehicles use rechargeable batteries for short daily commutes to run an electric motor and switched to a combustion engine to travel longer distances. Electric energy provided by The battery decreases the direct emissions out the tailpipe. The cost to manufacture plug-in hybrid was estimated at about 18,000 more than that of an equivalent gasoline powered vehicle. The larger lithium-ion batteries were one factor in driving up the price tag. 

8.3

Developing technologies also rely heavily on batteries. Off grid skills solar energy installations also require the use of batteries to deliver Power at night. There is also an environmental price tag, that is, external cost that is borne by all. Part of the stands from the ingredients found in just about anybody, one or more medals. The refining process also requires Energy and produces delusions. Environmental price tag also includes The disposal of dead batteries. Even rechargeable batteries eventually have to be replaced because at some point the voltage just below usable levels. Of the chemicals can still be hazardous. During Throwing batteries that contain mercury, lead, or cadmium lead to many  the trash, ultimately into the landfill, Is a poorly planned scenario. And easy way to reduce the number of batteries that wind up in the trash is to switch the using rechargeable winds. Investing in a battery charger should easily pay for itself if used properly. Other metals commonly used in batteries, including cadmium. The lead acid battery represents one success story. There is a president and good reason for recycling metals. Chemicals and petroleum industries already have set protocols in place for recycling platinum catalyst. All the rechargeable batteries can be recycled, such as not yet the norm of single batteries. Having less mass is an advantage when it comes to building portable batteries. And being smaller is also an advantage in that lithium ions are small enough to fit within certain types of electrical materials. Furthermore lithium deposits 10 to be found in remote locations, such as one shown in figure a 8.8. 

8.2

Most everyone is inserted contact. Into a flashlight, calculator, or digital camera. One end of these batteries is marked with a +; The author with an A -. These markings point to the fact that electron transfer at work. Klein sounds each produce 1.5 votes, but larger ones can sustain a current through the external circuit for long time. The current, or rate of electron flow, is measured in amps or likely in milliamps for smaller cells. The voltage of the battery is primarily determined by its chemical composition.  The alkaline cell is based on chemical reactions involving zinc and manganese. Oh alkaline batteries, from the tiny triple size to the large cells, produces the same voltage, 1.5 voltz. However, the voltage is a function of chemicals involved. Only a few volts are possible with a single galvanic cell. Long-lasting cells may find their way into your body. For example, the widespread use of cardiac pacemakers is largely due to the improvements made in the electrochemical cells rather than in the pacemakers themselves. Cars indeed has changed our world! We take the lead acid battery for granted. It powers an electric motor that replaced the hand crank that people once used to start cars. overall a Chemical equation sums up two half reactions. Because lead acid battery have the advantage of being rechargeable and low cost, may be used together with wind electric generators. In an automobile, the weight of the lead acid battery is a disadvantage. Another disadvantage  is the chemical components in the battery. If battery are to be used sustainably, we must meet these challenges. 

8 + 8.1

We rely on a flow of electrons or better known as electricity. To heat or cool our living or workspaces, to provide light to read by, and to power our TV sets. We have also created a convenient size portable sources of electricity, better known as batteries. They power our cell phones, MP3 players, laptops, and even our heating aids and motorized wheelchairs. There are practical limits to the long-term availability of both fossil fuels and metals used to power batteries. fissionable isotopes are difficult if you’ll to obtain. The combustion of fossil fuels also release sulfur dioxide and nitrogen oxide, leading to diseases in the air Quality and increases to health cost. Batteries are a big and growing business worldwide due to consumer demand for products that require them. Although we commonly use the word battery, a standard flashlight battery is correctly called a galvanic cell. This is a type of electrochemical cell that converts energy released in a spontaneous chemical reaction into the electrical energy. All galvanic cells produce useful energy through the transfer of electrons from one substance to another. One is for oxidation, a process in which a chemical species loses electrons. The other is for reduction, a process in which a chemical species gains electrons. We referred to these two parts is half reactions. the half reaction is a type of chemical equation that shows the electrons either lost or gained by reactants. Half reactions are a bit different from chemical reactions that we used earlier in this text. The movement of electrons through it and external circuit produces electricity, the flow of electrons from one region to another that is driven by difference in potential energy. Electrochemical reaction provides the energy needed to drive a core this razor, a power tool comment or countless other battery operated devices. Electrolytes, electrical conductors with in a cell that serve as sites for chemical reactions, facilitate this electron transfer. At the anode, Oxidation takes place and is the source of electrons in the current flow. At the cathode, Reduction takes place. Once electrical circuit is completed, then a voltage can be measured across the cell, the difference in electro chemical potential between the two electrodes. The chemical reaction that takes place in it and Ni– CD cell is more complicated than represented in the equations. Batteries come in many shapes and sizes, each one unique rematch tutus. Most electrochemical cells converted to chemical energy into electric energy with efficiency of about 90%. Compare this with the much lower efficiency of 30 to 40% that characterize coal fired power plants that generate electricity. 

7.10

Regardless of whether a country contains many nuclear power electric generators only a few, the Associated risks and benefits must be weighed by all involved. Risk in the voluntary such as those associated with windsurfing or bungee jumping. We have no control over the increased risk of radiation exposure at cruising altitude. Greenhouse gas generations release a total of 2,000,000,000 tons yearly. Over 100,000 workers have been killed in American coal mines since 1900. In a year, a 1000-MW coal fired power plant Burns over 10,000 tons of cool and could easily release 300 tons of SO2 and release 100 times of NOX daily. Nuclear power plants produce no common downside, although CO2 emissions are associated with the mining, milling, enriching, and transporting of uranium and handling of spent reactor fuel.  As you know it earlier in this chapter, nuclear energy carries tremendous emotional overtones. The possibility of a major disaster, Looms large in human consciousness. The risks associated with energy produced by nuclear plants clearly are different from those associated with other types of power generations. 

7.9

High-level radioactive waste has high levels of radioactivity because of the long half lives of the radioisotopes involved. High-level radioactive waste comes in a variety of chemical forms including ones that are highly acidic or basic. Huge quantities of HLW also were created during the Cold War because reactor fuel was reprocessed to produce plutonium for nuclear warheads. In contrast, low-level radioactive waste contains smaller quantities of radioactive materials then high level radioactive waste. LLW includes a wide range of materials, including contaminated laboratory clothing, gloves, and cleaning tools from medical procedures using radioisotopes. LLW are significantly less then those from HLW. Nearly 90% of the volume of all nuclear waste is low-level. Spent nuclear fuel is the radioactive material remaining in the fuel rods after they have been used to generate power and nuclear reactor. These rods contain primarily u– 238 with about 1% of the U-235 that did not fission. Each nuclear reactor in the United States, approximately 30% of the fuel rods are placed annually on rotating schedule. the water serves both to cool the fuel it and to absorb Alpha and Beta radiation. They are expensive to operate, and some corrosion of the metal rods occur underwater. In the absence of reprocessing, two options exist for the storage of HLW: monitored storage on or near the surface and storage in geological repositories deep underground. HLW must remain isolated under the ground water for at least 10,000 years to allow the high levels of radioactivity to decrease significantly.

3 mile

The accident to unit 2 happened at 4 am on 28 March 1979 when the reactor was operating at 97% power. Three mile island was an accident that was a five on the 7 point international nuclear event scale. The accident started in the nonnuclear section which struck open to the primary system. As a result large amounts nuclear reactor coolant escaped. The mechanical failures were compounded by the initial failure of plant operators to recognize the situation as a loss-of-coolant accident due to inadequate training and human factors, such as human-computer interaction design oversights relating to ambiguous control room indicators in the power plant’s user interface. A hidden red indicator light manually over-rid the automatic cooling system of the reactor because there was too much coolant water present in the reactor. Three Mile Island nuclear power plant in USA a cooling malfunction caused part of the core to melt in the #2 reactor. The TMI-2 reactor was destroyed. Some radioactive gas was released a couple of days after the accident, but not enough to cause any dose above background levels to local residents. There were no injuries or adverse health effects from the Three Mile Island accident. 

7.5

Chernobyl still stands as the world’s worst nuclear power plant accident. During an electrical power safety test at the Chernobyl Unit 4 reactor, operators deliberately interrupted the flow of cooling water to the core. The temperature of the reactors rapidly rose. Also, the operators had left and insufficient number of control rods in the reactor and other control rods couldn’t be reinserted quickly enough. Therefore, the steam pressure was too low to provide coolant, due to both operator error and faulty reactor design. A chain of event happened soon after which quickly produced a disaster. An overwhelming power surge produced heat, rupturing the fuel elements and releasing hot reactor fuel particles. As a result, this made it explode on contact with the coolant water, and the reactor core was destroyed in seconds. The heat ignited the graphite used to slow the neutrons in the reactor. When water was sprayed on the burning graphite, the water and graphite reacted to produce hydrogen gas.  Several people working at the plant were killed outright, and another 31 firefighters died in the cleanup process from acute radiation sickness. An estimated 250 million people were exposed to level of radiation that ultimately may cause illness. Years later, the number had risen more than 5000. People would be more afraid of nuclear power plant accidents because it spreads around in our atmosphere and doesn’t go away for years and years. As a result, you can still died because the atmosphere is still full of toxic gases.