partial research on solar technology (solar power charger)

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partial research on solar technology (solar power charger)

  1. 1. UNIVERSITY OF ST. LA SALLE Aside from being portable, a Solar-powered Phone Charger is as efficient as the Wall Phone Charger A research requirement for English 2 Kirby Cabrillos, John Vingem Geaga, Reg Vincent Natividad, Ryan Ceazar Santua 10/7/2013
  2. 2. Contents 1) Abstract ........................................................................................................................ 3 2) Chapter I ...................................................................................................................... 5 3) Introduction ................................................................................................................. 5 a) Background of the Problem .................................................................................... 5 b) Problem Statement .................................................................................................. 6 c) Hypothesis of the Study .......................................................................................... 6 d) Significance of the Study ........................................................................................ 7 e) Research Objectives ................................................................................................ 8 f) Scope and Limitations of the Study ........................................................................ 8 g) Definition of Terms............................................................................................... 10 4) Chapter II .................................................................................................................. 11 5) Review of Related Literature ................................................................................... 11 a) The Conversion of energy from light into electricity ........................................... 11 b) Potential of Solar Energy ...................................................................................... 12 c) Computing for Efficiency ..................................................................................... 13 d) Analysis of the Related Literature and Related Studies........................................ 14 6) CHAPTER III ........................................................................................................... 15 7) Methodology .............................................................................................................. 15 a) Kind of Research................................................................................................... 15 b) Research Design.................................................................................................... 16 c) Efficiency Test ...................................................................................................... 16 d) Experimental setup................................................................................................ 16 e) Measurement of the output currents and voltages for both chargers and tabulation of results ................................................................................................................ 17 1|Page
  3. 3. f) Computation for the efficiency ............................................................................. 17 g) Calculation for the charging time ......................................................................... 18 h) Method of Analysis ............................................................................................... 18 8) Chapter IV ................................................................................................................. 19 9) Research Findings ..................................................................................................... 19 a) Efficiency test ....................................................................................................... 19 b) Calculation for the time required for a 1220 mAh battery to completely charge . 22 10) Chapter V .................................................................................................................. 23 11) Summary, Conclusions, Discussion and Recommendations ................................. 23 a) Summary ............................................................................................................... 23 b) Purpose of the Study ............................................................................................. 23 c) Restatement of Research Question ....................................................................... 23 d) Research Methodology ......................................................................................... 24 e) Results ................................................................................................................... 24 f) Conclusions ........................................................................................................... 24 g) Discussions ........................................................................................................... 25 h) Recommendations ................................................................................................. 25 12) Bibliography .............................................................................................................. 27 a) Books .................................................................................................................... 27 b) Published Thesis ................................................................................................... 27 c) Electronic Sources ................................................................................................ 28 2|Page
  4. 4. Abstract Aside from being portable, a Solar-powered Phone Charger is as efficient as the Wall Phone Charger Kirby Cabrillos, John Vingem Geaga, Reg Vincent Natividad, Ryan Ceazar Santua October, 2013 As world‟s resources are diminishing, government agencies and non-government organizations are pushing a greener solution through the use of renewable energy sources. It was forecasted by some scientists such as Thomas Alva Edison that Solar Energy will be the future energy source. However, it is still being studied on how to improve the technologies used for utilizing solar energy. The solar panel for example, laboratories throughout the world are chasing to develop the most efficient solar panel. At present, the German-French research team holds the record for creating the 44.7 % efficient solar panel. This means that their solar panel made of nitrogen and boron can convert the 44.7 % of sunlight it receives into energy. The portable solar phone charger is one of the devices that use light to charge a phone. It is really portable that people on the road or on a camping can carry it into their pocket and charge their phone where ever they want. However, it all boils down on how fast the solar charger could transmit its charge and how efficient the charger is. A solar charger can charge a phone anywhere but it should also be considered if it is as efficient 3|Page
  5. 5. as a wall charger. With this problem, an experiment was conducted to check if a solar charger is as efficient as the wall charger. Efficiency test was conducted with the solar charger and the wall charger. With the result obtained from the experiment, the solar charger that has 69.33 % efficiency is close to the wall charger that has 71.85 % efficiency. The result indicates a positive response and researchers conclude that solar charger is indeed efficient as the wall charger. Also, the time for a 1220 mAh battery to be fully charged using both chargers was calculated. The result indicates that it takes 2 hours and 40 minutes to charge the battery much longer compared with the 2 hour time recorded for the wall charger. The experiment shows that the world is now a bit closer to the perfection of solar technology. Further studies on solar technology would help for the study on renewable energy. 4|Page
  6. 6. Chapter I Introduction This chapter presents the background of the problem, problem statement, and hypothesis, significance of the study, and the scope and limitations of the study. Background of the Problem Mobile phones are currently the most popular form of wireless communication in almost all the countries throughout the world. According to the estimation of the International Telecommunication Union, there are over 6.8 billion cellphone users around the world and the number is growing fast as technology gets better and cost of production lowers. However, the average lifetime of a cellphone battery according to G. Chiang and S. Bajaj (2011) is only around 8-12 hours with moderate usage. This becomes very inconvenient for people especially on the road or occupied with work. People must bring a wall phone charger and look for a power source in order to charge. Meanwhile, the portable solar-powered phone charger is a device that uses light rays of a minimum amount as the energy source to charge a phone. Cellphones are then charged without plugging into a power source. One of the advantages of using a solar-powered phone charger is its portability. The size and weight of the charger make it fit into anyone‟s pocket. However, the 5|Page
  7. 7. worthiness of a solar charger boils down to how quickly it transmits a charge, and how much power it gives off to the phone or how efficient the solar charger is. The Webster‟s dictionary defines efficiency as the quality or degree of being efficient. Technically, efficiency refers to as the ratio of useful energy delivered by a dynamic system to the energy supplied to it. Efficiency is simply derived by the total output over the total input. Problem Statement This research deals with the examination of the efficiencies of both solar-powered phone charger and the wall phone charger. Specifically, the study should able to answer the question if a portable solar-powered phone charger is as efficient as the wall phone charger. Hypothesis of the Study Solar-powered phone charger is as efficient as the wall phone charger. With a very little marginal difference of about ±5%, the study will prove the researcher‟s hypothesis that a solar charger is as efficient as a wall phone charger. 6|Page
  8. 8. Significance of the Study “I‟d put my money on the sun and solar energy. What a source of power! I hope we don‟t have to wait until oil and coal run out before we tackle that” (Thomas Alva Edison, 1931). The oil embargo of the 1970s prompted a national surge of interest in solar energy. A solar water heater was installed in the White House, and photovoltaic panels first came into play, notably in California. While previously solar power as a direct source of electricity had been limited to esoteric functions, such as in spacecraft, companies began to form with the idea of using solar as a regular source of power for ordinary homes (E. Goffman, 2008). Theoretically, solar might seem an ideal energy source, as it is free and virtually limitless. According to Greenpeace, The solar radiation reaching the earth„s surface in one year provides more than 10,000 times the world„s yearly energy needs. Furthermore, harnessing just one-quarter of the solar energy that falls on the world's paved areas could meet all current global energy needs comfortably (Flavin). A recent study conducted by the United States National Renewable Energy Laboratory (NREL) shows that the annual average solar energy power in the Philippines is around 4.5 to 5.5 kWh per square meter per day and the Asia has the minimum solar energy technical potential of 0.18 terawatts and a maximum of 6.56 terawatts annually. Results are much higher compared to Europe which has only 0.24 of maximum energy potential. The North Africa has the highest potential of 17.55 terawatts and followed by the Sub-Sarahan Africa with 15.12 terawatts. 7|Page
  9. 9. Studying about solar technology would be very essential for the world‟s nonrenewable energy resources are already diminishing. The future of this technology relies on such studies that involve reviewing the present solar technologies. Examining if a single solar charger could charge a cellphone efficiently as the wall phone charger, would determine on which areas on solar technology have to improve. Research Objectives This study aims to examine the efficiencies of a solar charger and a wall phone charger and be able to analyze the results and conclude that a solar charger is as efficient as a wall charger. Scope and Limitations of the Study This study mainly focuses on examining the efficiencies of both solar charger and a wall charger to conclude that the solar charger is as efficient as wall phone charger. This study also involves the computation for the complete charging time of a 1220 mAh Li-ion battery using both of the chargers. The results may not be applied to all solar devices since the study only covers a single solar charger and wall phone charger for testing. This study would have been more comprehensive, meaningful, and far-reaching if it covered more solar devices which should have provided the much detailed basis for 8|Page
  10. 10. comparison. This, however, would mean more time, money and resources which researchers didn‟t have. 9|Page
  11. 11. Definition of Terms Amperes –unit of current, milli-Amperes –Amperes over 1x10^-3 Complete charging time- the time required for a battery to be fully charged Current –rate of flow of electric charge, can be calculated by voltage divided by the resistance. Efficiency- The quality or degree of being efficient. In this research, it is referred to as the relationship of voltage and current by output power. It is given as the output power divided by the input power. Kilowatt hour (kWh) - a unit of work or energy equal to that expended by one kilowatt in one hour. mAh- milli Amperes-hour. Battery rating. Photovoltaic (PV) cells – semiconductor material such as silicon that generates voltage when light strikes at it. Power- needed to turn on a mechanical or electrical device. Power (solar input) - product of voltage and current coming in of the circuit. Power (solar output) - product of voltage and current coming out of the solar cell. Voltage- Electric potential or potential difference expressed in volts. 10 | P a g e
  12. 12. Chapter II Review of Related Literature This chapter presents a synthesis of facts that supports the following topics: The conversion of energy from light into electricity; the solar energy potential; mathematical approach in determining efficiency; and calculating the time for a battery to be completely charged. The Conversion of energy from light into electricity sunlight solar panel charger circuitry battery Figure 2.1: The Conversion of light energy to electrical energy flowchart. Just as Law of Conservation of Energy states that “Energy cannot be created nor destroyed but can only be transformed from one form to another”. This is where the idea of solar energy came from, to transform the sun‟s raging light into lifelong, unharmful, 11 | P a g e
  13. 13. and sustainable energy source for the human beings. An online journal, HowStuffWorks explained the process on how sunlight is converted into electrical energy. Light basically from the sun is absorbed by the Photovoltaic (PV) cells (made of semiconductor material like silicon) or commonly known as solar cells, and directly converts into electricity. When light strikes the semiconductor material, a certain amount is absorbed which means energy from the source is transferred into the material and magnetic field causes electrons to flow in a certain direction that now produces the current. The power generated by the PV cells flow through a circuit design to charge the battery. Potential of Solar Energy A famous online magazine Live Science (2012) stated that the sun is the power of the future in the 21st century. In the past, harnessing solar energy was an expensive option for many to invest in and bank on solar energy for the provision of their energy needs. However, advancements in technology made solar energy available with much lower cost and improved efficiency. Now with further study and understanding, solar energy can become the main source of energy for all. Think Solar Energy, an online database stated that the solar energy is the future source of our energy source and continuous improvement is a must. The market share of solar energy is still low. Current electricity generation from PVs is only of the order of 2.6GW compared to 36.3GW for all renewable energies, hydroelectric power excluded. Developed countries are steadily increasing their investments in solar power plants, and IEA projections for 2030 give an enhancement of 12 | P a g e
  14. 14. solar electricity generation up to 13.6GW (80% of which will be from photovoltaic cells, and the rest (2.4GW) from solar thermal plants). However, this amount will not exceed 6% of the total electricity production from non-hydro renewable energies. It is worth noting that passive solar technologies for water heating, not included in these statistics, represent a fairly large amount of power. IEA estimates a power production of 5.3GW in 2002 and an increase up to 46GW by 2030. Computing for Efficiency Power as defined by the Webster‟s dictionary is the time rate at which work is done or energy emitted or transferred. In science, power can be calculated in various ways. Power can be calculated in terms of resistance and current, it is the square of the current multiplied by the resistance (P = I2R). Power can also be calculated in terms of current and voltage, it is simply the product of the current and the voltage (P = IV). In all sciences, efficiency is defined as output over input. The efficiency of an engine for example is the ratio of the output work or energy to the input work or energy. By this, efficiency could be plotted in an equation as: or . Each battery has a rating. This rating refers for how much a particular battery can hold charges. An iPhone 3gs battery for example has 1220 mAh. Computing the time to completely charge a battery is given by the formula, hours = . Continuous current refers to as the current running in a single direction of the battery. A recent study about the power generated from the transformer-rectifier circuit was published by an online journal, righto.com (2012). Based on their study, the average power output of the transformer-rectifier circuit is around 6.5 Watts. 13 | P a g e
  15. 15. Analysis of the Related Literature and Related Studies The related literature and related studies cited contains information relevant to the experiment. Scientific ideas and results are presented in order to provide mathematical approach for determining the efficiency of any device. After a thorough review of the related literature and studies, it was found out that there are several studies about the energy efficiency of different types of cellphone chargers. They were however focused on the energy loses when the cellphone is not connected in the charger but the charger is still connected in the power source. 14 | P a g e
  16. 16. CHAPTER III Methodology This chapter presents the kind of research and research design used for the study as well as the procedures of the experiment. The procedure used in this study was based on the study conducted by Porter, et al (2008) regarding the Energy Efficiency Battery Charger System Test Procedure that was commissioned by the Pacific Gas and Electric, California Energy Commission-Public Interest Energy Research Program, and Southern California Edison. Kind of Research The kind of research used in determining whether a portable solar-powered phone charger is as efficient as a wall phone charger was experimental research. Experimental research is a design in which “an investigator manipulates and controls one or more independent variable or more variables for variation concomitant to the manipulation of the independent variables” (Kerlinger, 1986). Experimental research has been considered by Travers (1978) as the most prestigious method of advancing scientific knowledge. V. Ardales (1992) stated that the “ideal true experiment” study is the best done in a laboratory setting where the researchers have full control in manipulating study variables and ruling out confounding ones. 15 | P a g e
  17. 17. In this research, the independent variable was the input power of both solar charger and wall phone charger. And the dependent variable was the efficiencies of the solar charger and the wall phone charger. While the extraneous variables were the time which the experiment was conducted, the type of the weather on the date of testing, the type of solar panel used, and also the number of trials conducted. Research Design The research was divided into two parts, the efficiency test and the calculation for the time in which batteries will be completely charged. In efficiency test, currents and voltages were measured for the output side of the chargers. The test for solar charger was conducted in four trials with an interval of one hour starting at 11 o‟clock in the morning. The test for the wall charger was also conducted at the same time. The test was replicated four times to determine its average power. The calculation for the time in which the battery will be completely charged was done after completing the efficiency test. With the given formula, hours = , the time can now be drawn by the quotient of the battery rating over the continuous current. Efficiency Test Experimental setup The solar charger used in the experiment was ROHS P2600TM.While the wall phone charger used was an original box type iPhone adapter charger. The same multi16 | P a g e
  18. 18. tester was used for each of the chargers. The experiment was conducted outdoor with an approximate air temperature of 29 degree Celsius. The experiment started at exactly 11 am. Measurement of the output currents and voltages for both chargers and tabulation of results Being the independent variable, the input current for the solar charger was set at 1000 milli-Amperes and the input voltage at 6 Volts since it was found on the product specification. Meanwhile, for the wall charger, the power was at 6.5 Watts. The next step was finding the output power for both chargers. Using a multitester, the current and the voltage were measured in the output terminals of the portable solar-powered phone charger; its product was then recorded under the output power of the solar charger. The same procedure was done for the wall charger and the result however, was recorded under the output power of the wall charger. Computation for the efficiency A simple calculation was conducted to determine the efficiency of both chargers. For the portable solar-powered phone charger, the recorded average output power was divided by the input power. To get its percentage, the quotient was multiplied by 100. This was labeled as efficiency percentage of a solar charger. The same procedure was followed in computing the efficiency of the wall charger. The result was labeled as efficiency percentage of a wall phone charger. 17 | P a g e
  19. 19. Calculation for the charging time The battery was connected in series with the multi-tester (ammeter function), 1kilo ohm resistor and the charger to identify what current was flowing through the circuit and the result was labeled as the continuous current. The continuous current divided the battery rating and the result was the time for the battery to be completely charged. Method of Analysis All gathered information was recorded and presented in both tabular and graphical form. The results from each test were then reviewed for any error in calculations. The efficiency percentage of the wall phone charger was multiplied by 0.05 (based from the 5% difference hypothesis of the researchers) to get the magnitude of the range. The success of the hypothesis as well as the study relies on this result. If the absolute value of their difference fits on the range, the study is therefore successful. 18 | P a g e
  20. 20. Chapter IV Research Findings This chapter presents the data gathered from the efficiency test and the calculation for the time required for a 1220 mAh Li-ion battery as well as the analysis of the results and the analysis and interpretation of data. The main purpose of this study was to determine the efficiency of both chargers and prove that solar charger is as efficient as the wall charger. A very simple experiment was conducted by the researchers. They used the battery of an iPhone 3gs with a rating of 1220 mAh as the unit for calculating the time required to charge completely. Efficiency test With the procedure to measure currents and voltages described in the third chapter of this study, following results were obtained. Solar charger Wall charger Trial 1 2 3 4 Ave. 1 2 3 4 Ave. Input (independent) Current (mA) Voltage (V) 1000 6 1000 6 1000 6 1000 6 1000 6 NA NA NA Output Current (mA) Voltage (V) 795 5.5 797 5.3 797 5.5 794 5.4 795.75 5.23 953 4.8 960 4.9 957 4.9 958 4.9 957 4.88 Table 4.1: Summary of measured currents and voltages (Note: the interval for each trial is in 1hour) 19 | P a g e
  21. 21. Table 4.1 shows the summary of the measured currents and voltages for both the solar charger and the wall charger. Since the input power for a wall charger was already given at 6.5 Watts, its current and voltage values were not needed anymore. The input current for the solar charger was 1 Ampere and its input voltage was 6 Volts. Calculating for the power and the efficiency of both devices, these data were gathered: Input Power (Pi=IiVi) Solar Charger Wall Phone Charger Output Power (Po=IoVo) % Efficiency (Po/Pi)x100 6 Watts 4.16 Watts 69.33 % 6.5 Watts 4.67 Watts 71.85 % Table 4.2: Calculated Input and Output power, and percentage Efficiency Table 4.2 shows the calculated input and output powers for both devices. The efficiency was also derived with the calculated output and input power. The average output power for the solar charger was 4.16 Watts while the output power of the wall charger was 4.67 Watts. The Output power of the wall charger was a bit higher compared to the solar charger. However, the input powers of both devices were not the same. Solar charger‟s input power was given by 6 Watts meanwhile the wall charger has 6.5 Watts. Calculating for their efficiency, the solar charger provided the value of 69.33 %. This means that the solar charger only uses 69 percent of its input 20 | P a g e
  22. 22. power. The percentage efficiency obtained from calculating from the wall charger‟s input current and voltage was 71.85 %. The efficiency of the wall charger is a bit higher compared to the solar charger. 0.8 0.7 Output power 0.6 0.5 0.4 0.3 0.2 0.1 0 0 0.2 0.4 0.6 0.8 1 1.2 Input power Figure 4.1 Efficiency of the solar charger (blue) and the wall charger (orange) Figure 4.1 shows the linear relationship between the output and the input power of a solar charger and wall charger. The 5 % difference can be calculated by taking the 5% of the wall charger efficiency or by simply multiplying 0.05 to the 71.85 % which would yield a difference of 3.59. Subtracting the difference from the wall charger‟s efficiency would give the minimum range of the 5% difference that is 68.26. Meanwhile, by adding the difference to the efficiency would give the maximum range of 75.44. Now that the range at which the researchers assumed to conclude that solar charger is as efficient as 21 | P a g e
  23. 23. the wall charger is 68.26 % to 75.44 %. Efficiencies that fall under this range are considered as efficient as the wall charger. Calculation for the time required for a 1220 mAh battery to completely charge Charger used Solar Charger Wall Charger Continuous current 458 mA 615 mA Battery rating 1220 mAh Complete Charging Time 2 hrs., 40 min 2 hrs. Table 4.3: Summary of calculated complete charging time The current flowing through the terminals of the battery and the solar charger was measured and the result was 458 mA. The result for calculating the time was 2.66 hours or 2 hours and 40 minutes. While the current flowing through the battery and the wall charger in series connection was recorded at 615 mA. There, the time required for the battery to completely charge using the wall charger is 1.98 hours or about 2 hours. Charging a battery using a solar charger takes longer than using a wall charger. 22 | P a g e
  24. 24. Chapter V Summary, Conclusions, Discussion and Recommendations This chapter presents the summary of the study. Included in this summary are a review of the purpose of the study, a restatement of the research question, the research methodology used, and a summary of the study results, conclusions and discussion. Recommendations for further research and possible studies conclude this chapter. Summary Purpose of the Study The main purpose of this study was to examine the efficiency of a solar-powered mobile phone charger and prove that it is as efficient as the wall phone charger. Restatement of Research Question The research questions for this study were: (1) what is the efficiency of a solarpowered mobile phone charger and a wall phone charger? (2) What is the time required to completely charge a 1220 mAh battery using both chargers , and (3) is solar-powered mobile phone charger efficient as the wall phone charger? 23 | P a g e
  25. 25. Research Methodology There were two experiments conducted for this research. First, the efficiency test which was testing the solar charger and recording the output current. Multiplying the output current and output voltage provided the output power. And the input power was given by the charger specifications. Dividing the output power over the input power provided the value for efficiency. Multiplying the quotient by 100 provided the percentage efficiency of the product. Using the same procedure above, the efficiency of the wall charger was measured. The ideal efficiency of the charger was 100 percent. An ideal charger refers to a charger which doesn‟t have power losses due to some factors like heat and power absorbed by each components of the charger. An ideal charger is not yet available today since all components of a charger is working, and work requires energy, the energy is then the reason why it is impossible for now to achieve a hundred percent efficiency for a device. Results The calculated efficiency of the solar-powered phone charger was about 69 percent and the wall charger efficiency was at 71.85 percent. The time required for a battery to fully charge a 1220 mAh using a solar charger is 2 hours and 40 minutes. Meanwhile for the wall charger, it takes about only 2 hours. Conclusions The findings of this research indicate a positive response that solar-powered charger is as efficient as a wall charger. The calculated efficiency of the solar charger 24 | P a g e
  26. 26. falls within the range which was assumed by the researchers to be ±5%. With 69 % of efficiency, solar charger is within the range of 68.26 % to 75.44 %. With this, the portable solar-powered phone charger is indeed as efficient as the wall phone charger. The power generated by solar charger is 4.16 Watts and it can completely charge a 1220 mAh battery for 2 hours and 40 minutes. While the use of the wall charger takes only 2hours to charge the same battery. With these conclusions, the researchers are now able to conclude for the problem of this study. Discussions These findings indicate the wall charger has a higher efficiency and it takes a shorter time to charge a battery. However, it still indicates a positive result. Not all energy are transferred but dissipated to other forms like heat. There may be several reasons why the efficiency is not that high aside from the power losses. The type of solar cells was not that really new and it may have also low efficiency (referring to the power absorbed from the sun). Recommendations After obtaining the results discussed above that answer to the problems presented in determining if the solar charger is as efficient as the wall charger, the researchers have arrived at the following recommendations to further improve the study: 1. The study has focused only on the efficiency of a single solar charger. In lined with this, researchers highly recommend using other varieties of solar chargers. 25 | P a g e
  27. 27. 2. If the future researchers may come into the probability of making efficient chargers, researchers recommend using highly efficient solar panels and design a stable circuit with lesser but effective components. 3. Moreover, future researchers are recommended to use varying amount of light to consider the effects of brightness in charging. 4. Lastly, for future studies, it is recommended to use brand new products and much newer materials. It is also recommended to focus more on the possibilities of utilizing the solar energy as future energy sources for any electrical devices. 26 | P a g e
  28. 28. Bibliography Books Ardales, V. B. (1992). Basic Concepts and Methods in Research, Cubao, Quezon City: Great books Trading. Asperilla, J. F. (1990). Dynamic Physics for Philippine High Schools,(3rd ed.). University of the Philippines: Phoenix Publishing House, Inc. Published Thesis Bhargava, A., Timilsina, G., Polialov, J. (2004), Study on Electrical Efficiency of Alberta’s Economic Sectors, Abstract. Bolla, R., Bruschi, R., D‟Agostino, L. (2011), An Energy-aware Survey on Mobile-phone Chargers, p. 8. Bonner, J. (2012), Portable Solar Panel Charging Station, p.31. Bosshard, P. (2006), An Assessment of Solar Energy Conservation Technologies and Research Opportunities, pp. 5-6. Cunningham, L. J., Roberts B.A., (2011), Renewable Energy and Energy Efficiency Incentives: A summary of Federal Programs, p.5. de Groot, H. (2008), Solar Energy- Power for a New Age: An Analysis of the Integration of Photovoltaic and Thermal Solar Systems in Buildings, p.4. de Regt, E., Diaz, J. D., Pai, S. (2011), Solar Cellphone Charger, Abstract. Foroudastan, S. D., Dees, O. (2006), Solar Power and Sustainability in Developing Countries, pp. 3-4. Geist, T. (2006), Designing Battery Charger Systems for Improved Energy Efficiency: A Technical Primer, p.4. 27 | P a g e
  29. 29. Green, M. A., Emery, K., Hishikawa, Y., Warta, W. (2011), Solar Cell Efficiency Tables, Abstract retrieved from Wiley Online Library. Ostendorp, P., Foster, S. Calwell, C. (2004), Cellular Phones, Advancements in Energy Efficiency and Opportunities for Energy Savings, Executive Summary. Electronic Sources Than, K. (2005), Power of the Future: 10 Ways to Run the 21st Century, http://www.livescience.com/11324-power-future-10-ways-run-21st-century.html Think Solar Energy (2004), Solar Energy, the Future Source of Energy, http://www.thinksolarenergy.net/114/solar-energy-the-future-source-of-energy/solarenergy-solar-system/ 28 | P a g e

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