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DESIGN OF ENERGY EFFICIENT LOW POWER PV REFRIGERATION SYSTEM Amanullah Fatehmulla1 A S Al Shammari2 A M Al Dhafiri1 A A Al Bassam1 1Department of Physics and Astronomy College of Science King Saud University P O Box 2455 Riyadh 11451 Saudi Arabia 2Department of Physics College of Science University of Hail P O Box 2440 Hail Kingdom of Saudi Arabia Abstract Stand alone PV systems have shown to be reliable and cost effective for cooling Energy Efficient Low power PV refrigeration I INTRODUCTION The sun is the source of nearly all our energy with the exception of radioactive sources and the tides and will continue to be the most important nuclear fusion and fission reactors to be used 1 The growing demand for energy throughout the world has caused great importance to attach to the exploration of new sources of energy 2 The scientific basis for the utilization of solar energy by man was acquired some years ago but until recently it was not considered technologically feasible to make use of it on a large scale Already small scale applications are at work and steadily gaining new markets 2 Compared to the known and estimated reserves of fossil fuels and uranium the energy potentially available from renewable sources is enormous Solar energy is the only source from which we can use more energy without contributing thermal energy input to the atmosphere The Solar Energy falling just on the land surface of the earth each year equals about four times the total estimated fossil fuel resources and about four thousand times humanity s current global energy consumption 3 Approaches can be devised to decrease energy consumption targeting directly reduction of carbon footprint One of the ideas is to make use of renewable energy wherever Greening 4 10 can be done In this paper an application of solar energy for refrigerating through our selected design has been presented and discussed It goes with the concept of converting solar energy into electrical energy which in turn changes into mechanical energy that helps the circulation of air or chilled brine cooled by vapor compression refrigerators in most instances The process of storing the electrical energy which comes from the solar cells and to use it as a secondary source during night or in cloudy days has been explained II MATERIAL TOOLS AND METHODS Of all the possible applications of solar energy its use for cooling seems the most fitting This is one of the few uses in which the supply of energy and the demand for it are closely matched In the distillation of water for drinking and the pumping of water for irrigation the greatest need also occurs during periods of greatest insulation but with cooling requirements the matching extends in many situations even to the variation within the day To achieve this the following tools have been considered in our design and fabrication for low power PV refrigeration system A Solar panels B Controller C Battery D D C powered refrigerator A Solar Panels Solar panels from Solarex Corporation USA are the main source of electrical energy for our cooling system which converts solar energy into electrical energy Each panel consists of 36 single crystalline silicon solar cells with an output of 6 volts To obtain 12 V the two panels are connected 978 1 4577 0069 9 11 26 00 2011 IEEE in series The area of each panel comprises 1 2m X 0 3m 0 36m2 In order to characterize the chosen solar panels in the present work the polarity I V characteristics and the details of curve and fill factor including energy conversion efficiency of the same have been carried out B Controller The system of control and charge regulation is from ATERSA LEO series LEO 1 made in Spain It uses the micro controller in the management of a photovoltaic system There is a possibility to change the regulation voltages available in a 12 24 V version with best resolution of 1 and two types of batteries can be selected C Battery In our system arrangement the battery works as a secondary source during night or in cloudy days In our design a lead acid battery liquid electrolyte has been used which is configured for 12 volts and 75 Ampere hours It is made by the Japanese company of Yokohama D D C Powered refrigerator Power chill iceless cooler 37 9 liters from Coleman USA has been integrated in our system design which works with 12 DC TABLE I MEASUREDVOCANDISCFORFOUR DIFFERENT GROUPS OF SOLAR PANELS III RESULTS AND DISCUSSION Electrical characteristics for solar panels Each panel output is around 6 volts Table1 In the present low power PV refrigeration system development 12 volts are needed So the two panels modules B1 and B2 which show a good value of Voc and Isc are connected in series to double the value of the voltage Fig 1 5 Figure 1 B1 B2 modules connected in series Current Voltage characteristics Current voltage characteristics or I V curve describes the solar arrays electrical terminal characteristics completely To get this curve the solar arrays are connected in the circuit as shown in Fig 2 By choosing a proper load 6 resistance R from zero to high value the I V curve is obtained Setting R 0 Isc is obtained and with a high value of R Voc is noted for the arrays i e when Isc 0 In between several values of voltage and the corresponding values of current are obtained to draw the I V curve Curve and Fill Factor From the I V curve the fill factor for these arrays has been calculated Fill factor is used to describe the squareness or sharpness of the I V curve 7 Using the optimized values from I V curve in Fig 3 and equation 1 the fill factor is found to be 0 61 scoc mpmp IV IV FF 1 Figure 2 Electrical Circuit to get I V curve Energy conversion efficiency The efficiency of solar arrays shows that the utilization of solar energy to convert it into electrical energy It is defined as the ratio between the power output Pout and the power input Pin From I V curve Vmp Imp are noted and then Pmp VmpxImp Pout can be obtained using equation 2 As the area of the solar arrays is 0 72 m2 the Pout is calculated to be 67 40 watts m2 By using solar meter the light intensity measured is Pin 700 watts m2 at 14 00 Hours or 2 00 P M Hence the efficiency of solar arrays is found to be 9 63 012345678910111213 0 0 0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0 5 5 6 0 6 5 7 0 7 5 8 0 8 5 9 0 Im 5 54 Vm 8 76 Voc 11 8 Isc 6 7 Pm Vm Im Output current amp Output Voltage volts Figure 3 I V curve for modules B1 B2 connected in series 2 mwatts arraysofArea P P mp out This means that 9 63 of solar energy is converted to electrical energy by using the said solar arrays Charging and discharging for the Battery The batteries are required for any photovoltaic system to store the electrical output from the solar system to use it as a secondary source during night or cloudy days In our system a 12 V battery has been used The details of the same were described in the experimental part Charging and discharging process has been carried out for this battery to determine how long time will the battery with this capacity can serve Fig 4 shows the charging phase of the battery in terms of voltage as a function of time It is evident from the figure that the voltage increases with time almost linearly up to 5 hours of charging Thereafter it voltage stabilizes The charging process was allowed till it is almost stabilized constant Fig 5 shows the discharge curve for the battery The voltage of the battery is decreased as time passes Thereafter 18 hours it drops and it needs charging Hence battery can not run the pump and it starts discharging completely after continuous running of 18 hours So this kind of battery with this capacity can serve for 18 hours Charging and discharging of the battery through the controller helps to measure the charge intensity battery voltage and the consumption of the D C refrigeration system 012345678910 11 7 11 8 11 9 12 0 12 1 12 2 12 3 Voltage volts Time hours Figure 4 Variation of Battery voltage with time charging Voltage and Specific Gravity of the electrolyte in Battery Fig 6 shows the variation of specific gravity with the voltage of the battery The specific gravity increases with the increase of the battery voltage and when it decreases the specific gravity starts decreasing This change in specific gravity with the voltage is due to charge intensity in the battery which is proportional to the voltage of battery 000204060810121416182022 8 5 9 0 9 5 10 0 10 5 11 0 11 5 12 0 Voltage volts Time hours Figure 5 Variation of battery voltage with time discharging 11 611 711 811 912 012 112 212 312 412 512 612 7 1190 1195 1200 1205 1210 1215 1220 1225 1230 1235 1240 1245 1250 1255 1260 1265 1270 1275 1280 Specific Gravity Voltage volts Figure 6 Variation of specific gravity with the voltage of the battery Solar Refrigeration Typical requirements from the background against which the practicability of solar cooling has to be judged are briefly reviewed now In refrigeration many food stuffs including fruits vegetables meat fish and dairy products can be maintained in a fresh state for periods of the order of weeks at a temperature of 0 to 3 C For long term storage deep freezing at 18 to 25 C is necessary Factors demonstrating the connections for all components of the refrigeration system variation of refrigeration current consumption and refrigeration temperature versus time have been considered Performance In the present study the performance of a refrigerator powered by solar energy 12V DC has been carried out This refrigerator is connected in place of load resistor as shown in Fig 2 Table II shows the details of the variation of voltage consumption current specific gravity of the electrolyte and systematic decrease in the refrigeration temperature over a period of 6 hours It is clear from the table that the cooling effect has been achieved by 2 hours time Cost comparison between electrical solar energy used to run a low power refrigeration system Refrigerator consumption current 4 1 Amps Refrigerator voltage 12 volts Power needed to run our refrigeration system 49 2 watts 0 0492 kW Calculation of the cost of solar energy needed to run our refrigeration system 18 hours daily Two panels are enough to run our refrigeration system which cost about US 300 00 cost of PV system Table II PERFORMANCE OF REFRIGERATOR Time hr Volt V I A Sp Gravity Refrig Temp C 11 00 12 14 4 1190 32 11 3012 073 566118529 12 00 12 06 3 565 1180 26 12 30 12 04 3 562 1180 24 13 0012 43 543117522 13 30 12 02 3 556 1174 20 14 0012 023 553117517 14 30 12 01 3 555 1185 15 15 00 12 3 531 1175 10 15 3011 993 54811749 16 00 11 98 3 541 1175 8 16 30 11 97 3 529 1165 7 17 00 11 96 3 533 1165 6 Calculation of the cost of electrical energy needed to run our refrigeration system for 18 hours daily The energy needed daily 0 0492 kW 18 hours 0 8856 kWh day Note 5 6 hours day excluded in charging process The average cost of electrical energy 10 cents kWh So the daily energy cost 0 8856 kWh day 10 cents kWh 8 856 cents day The energy cost per year 8 856 cents day 365 days year 3 232 44 cents year The energy cost in US 32 32 year In view of the above calculations and the initial cost of our PV system including the initial electrical installation cost to run the low power refrigeration system a plot showing the comparison of the energy cost incurred with PV and conventional systems and years of operation has been drawn Fig 7 051015 0 100 200 300 400 500 600 700 800 Payback period Cost in US Years of operation Solar Energy Cost Electrical Energy Cost Figure7 Cost comparison between the PV and Conventional energy in operating a low power refrigeration system From Fig 7 it is clear that the PV and electrical energy costs intersect at 7th year of operation which is the payback period Since the maintenance cost is low or approximately nil it appears that the PV energy becomes almost free after 7 years and it demonstrates the economic effectiveness Therefore electrical energy will cost more than solar energy especially for large scale application the cost will increase rapidly In addition to that the solar energy is clean and safe Our experience of the design and development of PV low power refrigeration system with relatively low cost suggests that this small scale technology can contribute to solving problems of cooling like small area refrigeration including the transportable and small cold storage container with integrated PV energy supply systems These systems can be erected on or around a vehicle to obtain the cooling needs while on drives including picnics or especially in remote desert areas Also it supports our experience that by the use of renewable energies in windy and sunny areas a simple cheap and reliable irrigation pumping or cooling refrigerating systems can be applied avoiding the disadvantages of the already existed diesel powered systems 8 9 However photovoltaic powered refrigeration systems have reached a technical maturity and are characterized of a high reliability Further they offer the advantages of reduced operation and maintenance cost IV CONCLUSION A systematic review and importance of solar energy has been presented The functioning of solar cells and their parameters has been elucidated The significance of solar cell arrays their advantages and assemblies have been described Finally a successful attempt has been made with the development of a solar refrigeration system using the solar energy The results of I V characteristics for the solar panels used are promising Test results of charging and discharging processes for the battery including