RWEP_Final2_48_studentassignment aw
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Pico Power Generation for the Developing World Student Project Assignment
A remote mountain village has limited access to electrical power and, as a result, the village homes are lit with candles and kerosene lamps after dark. Narrow mountain paths limit access to neighboring villages and limits the supply of diesel for the village’s generators. Your task is to develop a small and sustainable source of electricity for the village using mechanical techniques. The goal is to create a power generation system that can power a lamp used for night-time reading for approximately 10 minutes. Further, it is assumed that the user of the system wants to concentrate on reading during this 10 minutes of use; it will be necessary to store energy for the task. To achieve this goal, you are stepped through several Units of instruction to gain an understanding of topics that form a part of the solution. Unit 1: Energy - The Big Picture 2 hours This Unit has two purposes, and two corresponding parts: 1. to benchmark your energy consumption for a common activity or over a period of time; and 2. to draw attention to the fact that converting energy from one form to another involves losses. Please complete a brief energy audit for the task or time period specified by your instructor. A worksheet is provided for this purpose . It is not important to be overly precise when completing this audit. If you use equipment that does not appear on the list, create a new line in the audit and fill in the information as best you can, perhaps by researching the equipment online, or using the information located on a tag on the device (often located close to the power cable). What is your total energy consumed (in kWh and Joules) for this audited task/time? How do you think this consumption compares to that of individuals in other parts of the world? In the second part of this Unit, determine the efficiency of the system shown in Fig. 1 by measuring the power output from the battery (via the current and voltage) and the power delivered to the loads. Plot the percentage efficiency of the inverter (100% (P out /Pin )) versus the load power. Can you characterize the efficiency of the inverter by this graph? Although the inverter is performing an electrical-to-electrical conversion, can you comment in general on the efficiency of conversion from one form of energy to another? For example, when charging a battery, do you think that all the electrical energy gets converted into chemical energy?
Pin = IDC VDC I DC Battery (Lead Acid) + V DC − Inverter Pout = IAC VAC I AC + V AC − Load
Figure 1: The system used for the second part of Unit 1. The inverter is powered by the chemical storage (the battery), and converts this electrical energy into a form that is usable by the load. By measuring the power input to the inverter and the power it is delivering to the load, you can determine the percentage efficiency of the inverter. Unit 2: Conversion Methods 1 hour In this unit you will experiment with one manner by which mechanical energy is converted into electrical energy. Specifically, you will examine generation of Alternating Current (AC) electricity using a bicycle and a dynamo (a simple AC generator) attached to its wheel. Attach the dynamo 1
to the rear wheel of a bicycle (turned upside-down). Attach a lamp and a speaker to the bicycle dynamo as shown in Fig. 2.
Dynamo 6V, 3W
Incandescent Lamp (6V)
Speaker or Headphones
Figure 2: Schematic representation of the test setup for Unit 2. When you vary the wheel speed (by cranking the pedal) the bulb’s light intensity will change. Because the generator is an AC device you may also see the light flicker. At the same time, the speaker (or headphones) will emit a sound corresponding to the AC signal. As you vary the cranking speed, how does the frequency of the sound change? Does the volume change? How does the light intensity change? If the light bulb in this circuit was replaced by a 60W household incandescent light, do you think it would light up? Conversely, if a bulb smaller than the one you are provided with was connected, would it light up? Unit 3: Rectification and Regulation 2 hours Most electricity is generated using Alternating Current (AC) methods. Many devices, however, require Direct Current (DC) to function. In this unit you will discover methods for converting AC into DC via rectification and filtration. Using the bicycle dynamo and various circuits provided by your instructor, you are asked to evaluate their operation according to the following criteria: output light flicker, output brightness, circuit complexity, circuit size, and circuit cost. Your lab instructor will provide you with a prototyping breadboard, diodes, capacitors, wire and LEDs (Light Emitting Diodes). The diodes act as one-way valves for electricity, while the capacitors act to store and filter out fluctuations in voltage levels. You’ll be able to evaluate the fluctuations by connecting an LED; the flickering of the light from the LED corresponds to the fluctuations in voltage and current. Test each circuit at three different speeds (slow, medium and fast) and evaluate the operation according to the criteria specified, above. WARNING: capacitors with large values are polarized, as indicated by the markings on their package. Be sure that you connect the terminals correctly and do not exceed the device’s rated voltage. Failure to do so can result in a fire or an explosion. Electrical loads typically require a particular voltage to operate correctly. For the specific circuit indicated by your instructor, connect a voltmeter to the output and crank the pedal for five minutes while maintaining an output voltage between 6 and 8 volts. How hard is it to mechanically regulate the output voltage? Devices exist to perform this regulation electronically. Connect one such device, a 7805 (5V) regulator as in the circuit provided by your instructor. Crank the bicycle wheel and measure the output voltage again. How constant is it? Unit 4: Storage and Release of Energy 2 hours The problem at-hand requires a system that can store enough energy to complete a particular objective at a later time, a requirement typical of power systems. For instance, the size of a hydroelectric dam directly correlates to the amount of energy it can store. The dam designers need to carefully determine how much energy it needs to provide, and then size it accordingly. To do this, it is important for the load on the system to be characterized. This is a complicated process since, in this case, the load depends on time-of-day, the temperature, and many other factors. 2
Fortunately, our task is not so complicated: we need to store enough energy to power a particular load (a resistor and LED) for a minimum of 10 minutes. There are many manners by which this energy could be stored, but we have chosen a relatively robust method for you: super capacitors (also known as ultra capacitors and by various trade names). These devices are similar to batteries in that, once charged, they will deliver electrical energy to a load. The difference lies in how they store the energy: a battery uses chemical storage, and a capacitor uses an electric field. The “super” capacitor is simply a capacitor that is manufactured in a way that allows it to store more energy than a normal capacitor. WARNING: capacitors with large values are dangerous devices. ALWAYS ASSUME THEY ARE CHARGED and handle carefully. Capacitors can become charged by the potentials in the air surrounding them! Even though the voltage may sound small, the amount of energy stored is large enough to kill! Please review the data sheets for the super capacitors provided in your laboratory. Heed the warnings, above. Your lab instructor will step you through safe-handling procedures. From the equation, CV 2 (1) E= 2 where E is the energy (in Joules), V is the load’s required operating voltage, and C is the capacitance, determine the capacitance required to power the load for a duration of 10 minutes. Assume that the load requires 5V and draws a current of 10 mA. Design a super capacitor network that provides the required capacitance (or slightly more). Is it desirable to drastically exceed the capacitance? Why or why not? This circuit will be used during the “charge” and “discharge” phases of operation: 1. During charging (using the final, regulated circuit developed in the last Unit), what is the calculated voltage across each of the super capacitors? Is this voltage less than the rated voltage of the super capacitor? If not, redesign your circuit such that is. 2. During discharge, what is the voltage provided by your super capacitor circuit? Is this voltage compatible with the load? Have your instructor verify your circuit design prior to constructing it. Charge your instructor-approved super capacitor network using the system developed in the last Unit (with no other load connected). How long does it take to charge the super capacitor network to 5V? Disconnect the super capacitors from the charging unit and connect to the load (the LED and resistor). How long does it take for the charge on the super capacitor to drop enough that the current through the LED is only 8mA? Describe how the LED intensity changes with respect to time. With recharged capacitors, connect to two loads (LEDs and resistors) in parallel. How long does it take until there is only 8mA flowing into one of the LEDs? Comment on what you have observed. Unit 5: Generate and Compete! 6 hours Consider the role of the user of the overall system (consisting of the charger, the storage element, and the load). This will affect many details of the system design that you may not have considered. Package the system such that the overall design is weather-proof, portable, and convenient to use. Comment on the effectiveness of your design. Is the system cost related to its capacity (in terms of energy)? What is the maximum time you can turn on the light? How much time does it take to charge the system to achieve this? Are the project objectives met? Lastly, compare and discuss the amount of energy stored and utilized in this application with the amount audited in Unit 1. 3
A remote mountain village has limited access to electrical power and, as a result, the village homes are lit with candles and kerosene lamps after dark. Narrow mountain paths limit access to neighboring villages and limits the supply of diesel for the village’s generators. Your task is to develop a small and sustainable source of electricity for the village using mechanical techniques. The goal is to create a power generation system that can power a lamp used for night-time reading for approximately 10 minutes. Further, it is assumed that the user of the system wants to concentrate on reading during this 10 minutes of use; it will be necessary to store energy for the task. To achieve this goal, you are stepped through several Units of instruction to gain an understanding of topics that form a part of the solution. Unit 1: Energy - The Big Picture 2 hours This Unit has two purposes, and two corresponding parts: 1. to benchmark your energy consumption for a common activity or over a period of time; and 2. to draw attention to the fact that converting energy from one form to another involves losses. Please complete a brief energy audit for the task or time period specified by your instructor. A worksheet is provided for this purpose . It is not important to be overly precise when completing this audit. If you use equipment that does not appear on the list, create a new line in the audit and fill in the information as best you can, perhaps by researching the equipment online, or using the information located on a tag on the device (often located close to the power cable). What is your total energy consumed (in kWh and Joules) for this audited task/time? How do you think this consumption compares to that of individuals in other parts of the world? In the second part of this Unit, determine the efficiency of the system shown in Fig. 1 by measuring the power output from the battery (via the current and voltage) and the power delivered to the loads. Plot the percentage efficiency of the inverter (100% (P out /Pin )) versus the load power. Can you characterize the efficiency of the inverter by this graph? Although the inverter is performing an electrical-to-electrical conversion, can you comment in general on the efficiency of conversion from one form of energy to another? For example, when charging a battery, do you think that all the electrical energy gets converted into chemical energy?
Pin = IDC VDC I DC Battery (Lead Acid) + V DC − Inverter Pout = IAC VAC I AC + V AC − Load
Figure 1: The system used for the second part of Unit 1. The inverter is powered by the chemical storage (the battery), and converts this electrical energy into a form that is usable by the load. By measuring the power input to the inverter and the power it is delivering to the load, you can determine the percentage efficiency of the inverter. Unit 2: Conversion Methods 1 hour In this unit you will experiment with one manner by which mechanical energy is converted into electrical energy. Specifically, you will examine generation of Alternating Current (AC) electricity using a bicycle and a dynamo (a simple AC generator) attached to its wheel. Attach the dynamo 1
to the rear wheel of a bicycle (turned upside-down). Attach a lamp and a speaker to the bicycle dynamo as shown in Fig. 2.
Dynamo 6V, 3W
Incandescent Lamp (6V)
Speaker or Headphones
Figure 2: Schematic representation of the test setup for Unit 2. When you vary the wheel speed (by cranking the pedal) the bulb’s light intensity will change. Because the generator is an AC device you may also see the light flicker. At the same time, the speaker (or headphones) will emit a sound corresponding to the AC signal. As you vary the cranking speed, how does the frequency of the sound change? Does the volume change? How does the light intensity change? If the light bulb in this circuit was replaced by a 60W household incandescent light, do you think it would light up? Conversely, if a bulb smaller than the one you are provided with was connected, would it light up? Unit 3: Rectification and Regulation 2 hours Most electricity is generated using Alternating Current (AC) methods. Many devices, however, require Direct Current (DC) to function. In this unit you will discover methods for converting AC into DC via rectification and filtration. Using the bicycle dynamo and various circuits provided by your instructor, you are asked to evaluate their operation according to the following criteria: output light flicker, output brightness, circuit complexity, circuit size, and circuit cost. Your lab instructor will provide you with a prototyping breadboard, diodes, capacitors, wire and LEDs (Light Emitting Diodes). The diodes act as one-way valves for electricity, while the capacitors act to store and filter out fluctuations in voltage levels. You’ll be able to evaluate the fluctuations by connecting an LED; the flickering of the light from the LED corresponds to the fluctuations in voltage and current. Test each circuit at three different speeds (slow, medium and fast) and evaluate the operation according to the criteria specified, above. WARNING: capacitors with large values are polarized, as indicated by the markings on their package. Be sure that you connect the terminals correctly and do not exceed the device’s rated voltage. Failure to do so can result in a fire or an explosion. Electrical loads typically require a particular voltage to operate correctly. For the specific circuit indicated by your instructor, connect a voltmeter to the output and crank the pedal for five minutes while maintaining an output voltage between 6 and 8 volts. How hard is it to mechanically regulate the output voltage? Devices exist to perform this regulation electronically. Connect one such device, a 7805 (5V) regulator as in the circuit provided by your instructor. Crank the bicycle wheel and measure the output voltage again. How constant is it? Unit 4: Storage and Release of Energy 2 hours The problem at-hand requires a system that can store enough energy to complete a particular objective at a later time, a requirement typical of power systems. For instance, the size of a hydroelectric dam directly correlates to the amount of energy it can store. The dam designers need to carefully determine how much energy it needs to provide, and then size it accordingly. To do this, it is important for the load on the system to be characterized. This is a complicated process since, in this case, the load depends on time-of-day, the temperature, and many other factors. 2
Fortunately, our task is not so complicated: we need to store enough energy to power a particular load (a resistor and LED) for a minimum of 10 minutes. There are many manners by which this energy could be stored, but we have chosen a relatively robust method for you: super capacitors (also known as ultra capacitors and by various trade names). These devices are similar to batteries in that, once charged, they will deliver electrical energy to a load. The difference lies in how they store the energy: a battery uses chemical storage, and a capacitor uses an electric field. The “super” capacitor is simply a capacitor that is manufactured in a way that allows it to store more energy than a normal capacitor. WARNING: capacitors with large values are dangerous devices. ALWAYS ASSUME THEY ARE CHARGED and handle carefully. Capacitors can become charged by the potentials in the air surrounding them! Even though the voltage may sound small, the amount of energy stored is large enough to kill! Please review the data sheets for the super capacitors provided in your laboratory. Heed the warnings, above. Your lab instructor will step you through safe-handling procedures. From the equation, CV 2 (1) E= 2 where E is the energy (in Joules), V is the load’s required operating voltage, and C is the capacitance, determine the capacitance required to power the load for a duration of 10 minutes. Assume that the load requires 5V and draws a current of 10 mA. Design a super capacitor network that provides the required capacitance (or slightly more). Is it desirable to drastically exceed the capacitance? Why or why not? This circuit will be used during the “charge” and “discharge” phases of operation: 1. During charging (using the final, regulated circuit developed in the last Unit), what is the calculated voltage across each of the super capacitors? Is this voltage less than the rated voltage of the super capacitor? If not, redesign your circuit such that is. 2. During discharge, what is the voltage provided by your super capacitor circuit? Is this voltage compatible with the load? Have your instructor verify your circuit design prior to constructing it. Charge your instructor-approved super capacitor network using the system developed in the last Unit (with no other load connected). How long does it take to charge the super capacitor network to 5V? Disconnect the super capacitors from the charging unit and connect to the load (the LED and resistor). How long does it take for the charge on the super capacitor to drop enough that the current through the LED is only 8mA? Describe how the LED intensity changes with respect to time. With recharged capacitors, connect to two loads (LEDs and resistors) in parallel. How long does it take until there is only 8mA flowing into one of the LEDs? Comment on what you have observed. Unit 5: Generate and Compete! 6 hours Consider the role of the user of the overall system (consisting of the charger, the storage element, and the load). This will affect many details of the system design that you may not have considered. Package the system such that the overall design is weather-proof, portable, and convenient to use. Comment on the effectiveness of your design. Is the system cost related to its capacity (in terms of energy)? What is the maximum time you can turn on the light? How much time does it take to charge the system to achieve this? Are the project objectives met? Lastly, compare and discuss the amount of energy stored and utilized in this application with the amount audited in Unit 1. 3
