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Environmental Technology (ET) refers to the knowledge and skills that are necessary to manage, work with, and control hazardous materials and pollutants. These skills, based on applied science principles, and designed to reduce human health and ecological risks while being fully in compliance with governmental regulations. The general public has shown interested and political influence in the last 3 decades in areas relating to public health and the environment. Greater public involvement led the government to enact more laws related to protection of public health and the preservation of the environment. This change in the direction of public policy has resulted in the 1990s being heralded as the "decade of the environment".
Firstly, recycling is the process of wasted materials into new products to prevent waste of potentially useful materials, reduces the consumption of fresh raw materials, energy usage, air pollution (from incineration) and water pollution (from landfilling) by reducing the need for "conventional" waste disposal, and lower the greenhouse gas emissions as compared to virgin production. Next, renewable energy is that energy which is generated by biofuel, biomass, geothermal, hydroelectricity, solar energy, tidal power, wave power and wind power which come from renewable natural resources.
Secondly, water purification is the process of removing unwanted chemicals, biological contaminants, suspended solids and gases from contaminated water by methods used such as filtration, sedimentation, distillation, slow sand filters or biologically active carbon, flocculation, chlorination and the use of electromagnetic radiation such as ultraviolet light. Then, air purification is the keeping of air freshness and it can be done by green plants because all plants have the ability of convert Carbon Dioxide into Oxygen.
Thirdly, sewage treatment is the process of removing contamination from wastewaterand household sewage, both runoff (effluents) and domestic. Its objective is to produce an environmentally safe fluid waste stream (or treated effluent) for drinking water purpose as Singapore and a solid waste (or treated sludge) that suitable for disposal or reuse as farm fertilizer. After that, environmental remediation deals with the removal of pollutants or contaminants from environmental media like soil, groundwater, sediment, or surface water for the general protection of human health, the environment or from brownfield site for redevelopment purpose by excavation or dredging, SEAR (surfactant enhanced aquifer remediation), pump and treat, solidification and stabilization, in situ oxidation, soil vapor extraction, phytoremediation, dual-phase extraction, mycoremediation and mycofiltration
1.2 Objectives of the Study
One of the objectives is to make better understanding for the people on solar cells. This is to create more awareness among the people of Malaysia on the importance of solar technology.
Another purpose is to introduce information for example history on how solar technology is used in the past and in the present.
Next, it is to introduce the current development of solar cell technology to the people.
Besides that, our aim is to show how beneficial the solar cell technology towards us Malaysians for current and future use.
2.0 Literature Review:
2.1 History of Solar Technology:
In the 2nd century B.C a Greek scientist, Archimedes used light reflection phenomenon using a bronze shield to focus sunlight and producing heat/fire to wooden ships of the Roman Empire which were blockade Syracuse. (Although this is some type of myth, Greek navy had done an experiment to set fire in the wooden boat at a distance 50m and it was success in the year 1973.
In 1839, the discovery of the effects of photovoltaic cell, an experiment was conducted by a French scientist, Edmond Becquerel on a two electrodes that immersed in electricity-conducting solution, the results shows the generation of electricity increased when exposed to the sunlight and in 1876 a new discovery had been done about selenium that can create an electric energy when it is exposed to the sunlight by Richard Evans Day and William Grylls Adams.
Gerald Pearson, Calvin Fuller and Daryl Chapin had also developed the silicon photovoltaic cell in Bell Labs in United States and this is the starting point of the existence of Photovoltaic Technology in 1954. The 1st solar cell was capable to sustain sufficient amount of sun's energy and convert it into electricity that can run any electrical equipment. Bells Laboratory create a solar cell with efficiency 4% and later reached 11%. Later in 1982, the U.S. Department of Energy, along with an industry consortium, begins operating Solar One, a 10-megawatt central-receiver demonstration project. The project established the feasibility of power-tower systems, a solar-thermal electric or concentrating solar power technology. In 1988, the final year of operation, the system could be dispatched 96% of the time.
Then in 1986, World largest solar thermal facility was been commissioned in Kramer Junction on California. The solar energy was being concentrated onto a system of pipes circulating a heat transfer fluid using row of mirror at the solar field. A steam is produced by the heat transfer fluid used to powered a conventional turbine to produce an electric energy and, U.S. Department of Energy's Solar Energy Research Institute had been redesignated as the National Renewable Energy Laboratory by President George Bush in 1991.
A solar cell that was made from gallium indium phosphide and gallium arsenide had become the first solar cell that success to exceed 30% conversion efficiency and it was developed by The National Renewable Energy Laboratory in 1994. Then later in 1999, a photovoltaic solar cell that is able to convert 32.3 % of sunlight which hits the solar panel to electricity was developed by Spectrolab, Inc. and the National Renewable Energy Laboratory. The reason of this higher achievement is because they combine three layers of photovoltaic materials into a single solar cell. By combining the materials, it is able to receive sunlight concentrated much efficiently and can reach 50 times normal. To use such cells in practical applications, the cell is mounted in a device that uses lenses or mirrors to concentrate sunlight onto the cell. Such "concentrator" systems are mounted on tracking systems that keep them pointed toward the sun.
2.1.1 Facts of Solar cell:
In the early 1950s , R.S Ohl discovered that sunlight striking a wafer of silicon will produce a large number of free electrons. In 1994, G.L Pearson, C.S Fuller, and D.M Chapin created an array of several strips of silicon, placed them in sunlight, captured the free electrons converting them into electric current. It could only convert 6% of sunlight into useful energy.
Semiconductor materials such as silicon, gallium arsenide, cadmium telluride or copper indium diselenide are used in these solar cells. A solar cell or photovoltaic cell converts sunlight to electricity through photovoltaic effect. Photovoltaic is the area of technology and research related to the use of solar cells as solar energy. Cell assemblies are used to make solar modules or photovoltaic arrays. Photovoltaic cells generate energy useful where electric from the power grid is unavailable such as the use in satellites. The layer facing the sun's light is negatively doped with phosphorus. The layer below it is positively doped with boron. At the boundary layer, an electrical field is produced that leads to the separation of the charges (electrons and holes) released by the sunlight. In order to be able to take power from the solar cell, metallic contacts need to be fitted on the front and back of the cell. Screen printing is normally used for this purpose. On the behind of the solar cell it is possible to apply a contact layer over the whole surface using aluminium or silver paste.
A fine metal grid is used on the side facing the sun to keep the shaded area as small as possible. The front contacts are often applied using a screen printing process where silver paste is applied through a screen onto the silicon wafer.
Losses happen at the solar cell because of recombination, reflection and shading caused by the front contacts.
Silicon is not present in pure form, but in chemical compounds, with oxygen on the form of quartz or sand. The unwanted oxygen first has to be separated out of the silicon dioxide. To do this, the silicon is heated together with coke, carbon powder, charcoal in an electrical arc furnace to a temperature of 1800C to 1900 Celsius.
Monocrystalline silicon cells
Polysilicon is melted in a quartz crucible at around 1410 Celsius. A seed crystal with a defined orientation is dipped into the silicon melt and slowly drawn upwards out of t6he melt. In this process, the crystal grows into a cylindrical mono-crystal up to 30cm in diameter and several meters in length. The cylindrical mono-crystals are cut to produce semi-round or square bars, which are then cut with wire saws into wafers with a thickness at about 0.3mm. During the cutting and sawing of the mono-crystals and wafers, a large amount of silicon is lost as sawdust and needs to be re-melted, as well as the conical ends of the rods. The wafers are chemically wet cleaned in etching and rinsing baths to remove sawing residues and marks. The efficient rate of this cell is 14-18%.
Polycrystalline silicon cells
The silicon raw material is melted in a quartz crucible and moulded into a cuboid shape. The reason of this directed solidification is to make big numbers of the biggest possible homogenous silicon crystals, with grain size from a few millimeters to a few centimeters. The grain boundaries make up crystal defects with an increased recombination risk and have a negative effect on the efficiency of polycrystalline solar cells, which is lower than mono-crystalline cells. Using this method, large silicon blocks are made. The efficiency of this cell is 13 to 17%.
Ribbon pulled silicon cells
To discourage high material losses and encourage material usage, various ribbon-pulling ways have been created. The silicon ribbons have already possess the thickness of future wafers, so the flat surfaces are cut into pieces with lasers.
They have been developed to comply with requirements and the manufacturing costs of solar cells. Alternative production ways such as vapour deposition, electroplating, and use of Ultrasonic Nozzles are good because they decrease high temperature processing significantly. The most lucrative second generation materials are cadmium telluride, copper indium gallium selenide, amorphous silicon and micromorphous silicon. These materials are put in a thin film to a supporting substrate like glass or ceramics to decreasing material mass and costs.
In the early 1990s there has been increased development for producing solar cells. In these photoactive semiconductors are used as thin layers to a low priced substrate. The ways used consists of vapour deposition, sputter processes (cathode sputtering) and electrolytic baths with many layers. The thickness range of that certain layer is big and differs from a few nanometers to tens of micrometers. Various photovoltaic materials are deposited with different deposition ways with a diversity of substrates. Thin Film Solar cells are often classified based on the photovoltaic material used. Even though the efficiency is low, the energy collection can under certain conditions be quite considerable. The usage of diffuse and dim light is better in thin film cells and there is a more preferred temperature coefficient. Thin film cells have less sensitivity to shading.
During the early 1990s research labs have been for many years able to create a very efficient crystalline silicon cells with efficiency of up to 25 percent. The electrical losses are reduced. The source material used here is a truly pure polycrystalline silicon rod with a mono-crystalline silicon seed at its end. This material is really expensive. Third generation technology was created to overcome poor electrical performance of second generation technology at the same time producing at low manufacturing costs. Research right now is aiming conversion efficiencies of 30 to 60% while maintaining low cost materials and low manufacturing methods. They can exceed the theoretical solar conversion efficiency limit for one energy threshold material, that was counted in 1961 by Shockley and Queisser as 31% under 1 sun illumination and 40.8% under maximum concentration of sunlight. Technologies includes: Silicon nanostructures, Up/Down converters, Hot-carrier cells, Thermoelectric cells.
2.2The current use of Solar cells:
2.2.1 Architecture and urban planning:
This type of technologies has influenced the buildings designing since the beginning of the architectural history. The methods of this technology were firstly employed by the Greeks and the Chinese who used this technology for many things such as warming up their houses in the cold seasons. The common concept (definition) of Solar is mostly related to Sun. one of the classic examples of this solar technology design is the Socrates Megaron house, the newest solar design nowadays are using computer modeling.
2.2.2 Solar thermal energy:
It's a very useful way converting the solar energy to get a thermal energy instead of it. The Solar Thermal Energy low temperature collectors are mostly a flat plates generally used to heat swimming pools. The medium temperature collectors are also flat plates but are often used for heating the water and used also for the residential and the commercial purposes. The high temperature collectors are often used for collecting or creating the electricity, this type of Solar cells coverts.
This type of power is a conversion of sunlight into electricity. Either by using photo voltaic or indirectly by using concentrated solar power.CSP systems use mirrors or lenses and tracking systems to focus a large area of sun light into a small beam. Photovoltaic converts light into an electric current by using the Photoelectric effect.
2.2.3 Solar Chemical:
This type of Solar Applications uses the solar energy to perform the chemical reactions. The chemical processes offset energy that would otherwise come from a fossile fuel source and it can also convert the energy of the solar into a storable and transportable fuel. Solar induced chemical reaction can be divided into two categories thermo chemical or photochemical. It is also possible to produce a variety of fuels by the artificial photosynthesis.
The solar has also many other application which being currently used in various things in our life such as the of the solar for saving or storing energy. The solar is still considered as a major way to have the energy for our daily life.
2.3Usage/Purpose of Solar Cell:
The modern solar cell is an electronic device, fabricated from semiconducting material. It converts a fraction of the energy contained in sunlight directly to electrical energy at a voltage and current level based on the factors such as the properties of the semiconductor, the solar cell design and construction technique, and the incident light.
Solar cell has been used in many applications by commercial companies, residents, and also military department such as power sources for homes and commercial buildings, landing obstruction lights for airport, water pumping for irrigation, perimeter alarm transmitters, electronic border fences, intrusion alarms for security, highway signs, portable backpack radios, remotely located, unmanned electronic surveillance systems, educational TV broadcasting, and etcetera.
Increasing oil prices, terrorist attacks on oil installations, high energy costs, adverse political environments, severe weather conditions, high capital investments, radiation from nuclear power station and global greenhouse effects have compelled energy planners to look for alternative sources to reduce reliance on fossil fuels and to switch to other clean forms of energy needed to protect Earth. With these reasons, all industrial and Western countries such as the United States, Germany, Japan, Brazil, Italy, Spain, and other European countries are turning to electrical power generation from solar cells.
2.3.1 The Cost:
Housing structure, protective cover, manufacturing tolerances, quality control inspections needed, panel size and type and number of solar cells installed on a given panel area determine the solar panel production cost. Preliminary solar panel cost estimates received from various panel suppliers and installers indicate that roughly 65% of the cost is for solar panels or modules, 15% of the cost is for the inverter and remaining 20% is for the labor required for panel installation. However, the overall solar power system cost for residential installations varies from 6 to 8 dollars per watt of the installed capacity. Based on this cost estimate, a 5 kW solar power system will cost currently anywhere from $30,000 to $40,000 before the rebates and tax incentives. According to panel suppliers, both the state and federal tax benefits come to about $10,000, which can have a pay-back time of 10 years for a family with a yearly electric bill of $2,000.
2.3.2 The Advantages:
There are many advantages worth considering when it comes to solar energy and everything that it offers.
Solar cells are not only environmental-friendly, but they offer clean, efficient, reliable, self-contained, reliable, quiet, maintenance-free, and year-round continuous and unlimited operation at moderate costs and uninterrupted sources of electrical energy. Furthermore, it's a long-term device as it can last longer up to 20-30 years. It also can be constructed to any size based on energy requirements. Solar energy is a completely renewable source of energy.
Moreover, very little maintenance is required to keep solar cells running. There are no moving parts as machines in a solar cell. Solar panels and solar lighting may seem quite expensive for the first purchase, but in the long run it is saving quite a great deal of money. After all, it does not cost anything to harness the power of the sun and thus make the most of the reality that solar power brings self-reliance. Besides, people have begun using it more and more not only for personal use, but for mainstream use as this energy helps people become self-reliant in a world where there is scarcity of electricity. Billions of dollars can be saved as people slowly get out of the huge energy crisis that they are facing today. Next, solar powered panels and products are typically extremely easy to install. Wires, cords and power sources are not needed at all. Tax breaks and incentives have offered for some area for installing solar panel systems, for example at California, offers such initiatives to their residents.
Solar power technology is improving consistently over time, as people begin to understand all of the benefits offered by this incredible technology.
2.3.3. The Disadvantages/Limitation:
The amount of sunlight being received by solar cell depends on the time of day, the season of the year, geographic location and climate conditions. Peak power levels are generated only under the summer sun and clear skies. Even if a tracking solar energy collection system is used, it's difficult to guarantee the uniform solar energy input .In addition, owners of commercial solar power systems must keep a reasonable number of spare parts for the system they own such as solar cell modules and shunt regulators.
Temperature affects the solar array performance. The solar array's design voltage of 15V will drop to 13V if the noontime temperature reaches 43oC.. The efficiency depends on the condition of the mirrors or lenses and the accuracy of the solar tracking apparatus.
The presence of moisture on the solar cell surface degrades the cell performance significantly due to losses by absorption and refraction, and causes the growth of organic substances. The ultraviolet rays of the sun darken the encapsulating material, leading to further reduction in the cell performance.
Sticky surfaces of modules collect dirt easier thus shading the panels.