# Objective

The experimental objective of this lab is to evaluate different sources of renewable energy and use the results of that evaluation to design a vehicle that is powered by a renewable energy source or a capacitor that is charged by a renewable energy source. The design will be entered in a competition that is judged by a ratio that uses distance traveled, travel time, and cost. The highest ratio wins.

# Overview

From sails to power boats, windmills to pump water, or water-driven wheels to power machinery that mills grains, humans have been using renewable energy sources for millennia. A significant amount of our energy production comes from non-renewable resources, such as oil, natural gas, and coal. The detrimental effects on public health and the environment from burning fossil fuels have prompted greater interest and investment in renewable energy sources, including solar, wind, and hydroelectric power though hydroelectric power is not considered in this lab. Scientists and engineers must address concerns about the inability of some renewable sources, notably solar power and wind power, to generate power consistently so there is equal interest in developing energy storage devices that can operate at grid-scale or hold sufficient energy to power entire communities for an extended time after being charged by a renewable energy source.

## Types of Renewable Energy

Renewable energy is a type of energy that can be harnessed from naturally replenished resources. Some examples of this are sunlight, wind, and water. There are many benefits to using renewable energy. They are clean energy sources, and they come from abundant sources that do not become depleted. If these renewable resources can be harnessed effectively, they can solve the problems with using non-renewable energy sources (NextEra Energy Resources, 2012). In the last few years, renewable energy has been the fastest-growing energy source globally (International Energy Agency, 2021). In this lab, solar and wind energy will be used.

### Solar Power

Sunlight, like any other type of electromagnetic radiation, contains energy. Typically, when sunlight hits an object, the energy that it contains is converted into heat. Certain materials can absorb and convert that energy into an electrical current. In this form, sunlight can be used as a power source or stored for later use.

Solar panels are devices that generate electrical current from sunlight. The panels contain a crystalline material that absorbs and converts the sunlight into electricity. The crystalline material has a repeating structure formed by a network of covalent bonds where electrons are shared by atoms within the crystal. Traditional solar cells are made from crystalline silicon.

To produce a current, there must be a difference in the concentration of electrons between one area and another to cause their flow. In a silicon solar cell, a concentration difference is created using two types of silicon, p-type and n-type. The p-type silicon is created by adding atoms, such as boron, that have one fewer electron in their valence energy level than silicon has. As a result, a vacancy of electrons, or a hole, forms. The n-type silicon is created by adding atoms that have one more electron in their valence energy level than silicon has so that there is an excess of electrons that can move around the crystal structure and create an electrical current. In a solar cell, p-type and n-type silicon are sandwiched together to create a p-n junction, as shown in Figure 1 (Locke, 2008). The p-type area is positively charged, and the n-type area is negatively charged.

When sunlight hits the silicon on the solar panel, the photons from the sunlight energize the electrons in the material. The electrons within the crystal move to a higher energy level, creating holes. If the p-type and n-type silicon are connected with a wire, the electrons will flow from the n-type layer to the p-type layer, and electrical current is generated.

Figure 1: A Silicon Solar Panel Showing the Electron Flow

Other materials have been used in the production of solar panels. Panels made from copper indium gallium (di)selenide (CIGS) have a smaller crystalline structure and are less expensive than silicon. CIGS panels are relatively flexible and can easily be shaped into flexible films. The use of CIGS to make solar panels is referred to as thin-film solar technology because of its flexible nature. CIGS panels are not as good at converting absorbed light into electrical current compared to silicon, but for mass production purposes, CIGS solar panels are the more cost effective approach to produce solar panels for frequent use (Locke, 2008). In the last decade, perovskite materials have also received attention for thin film technologies because of their competitive efficiency (Dey et al., 2021).

### Wind Energy

Wind turbines are used to capture the wind’s energy and convert it into electrical energy. The blades on wind turbines are slanted so that as the wind passes over the blades, it creates an uneven pressure on each side, causing them to rotate. The spinning blades drive a low speed shaft connected to a gearbox. The gearbox converts the low speed rotation to a high speed rotation through a high speed shaft. The high speed shaft is connected to a brake and then into an electrical generator where mechanical energy is converted to electrical energy (Layton, 2011).

A basic electrical generator is made of permanent magnets on each side with a rectangular coil connected to a commutator, which is a rotary electrical switch (Figure 2). The two permanent magnets on each side create a magnetic field. As the rectangular coil spins mechanically, the magnetic field through the area of the coil changes, creating an alternating current through the coil. The commutator switches the polarity of the coil just as the polarity of the alternating current changes, creating a direct current. The current is then output from the wind turbine (Layton, 2011).

Figure 2: The Internal Structure of an Electrical Generator (Layton, 2011)

## Energy Storage

Capacitors have many uses in circuits and signal processing. A capacitor is an electrical device that is used to store charge temporarily. Some capacitors can be used in place of a battery, but they operate very differently from a battery. A capacitor is charged by a voltage source logarithmically, as shown in Figure 3. In this lab, a capacitor will be used as the power source for the renewable energy vehicle.

Figure 3: Capacitor Charging Curve

Because of their design, capacitors are sensitive to the polarity of the voltage applied to them. The capacitors used in this lab must be connected with the proper polarity. In the lab, the capacitor’s negative lead must be connected to the negative applied voltage (Figure 4). Failure to do this will cause the capacitor to fail.

Figure 4: Polarized Capacitor

The energy a capacitor holds is proportional to the square of the voltage across the capacitor (1).

(1)

In (1), E is the energy, C is the capacitance, and V is the voltage.

## Electrical Components

The design of a circuit determines its behavior. In this lab, one circuit design will increase the speed output of a motor and the other will increase the torque output of a motor. In electrical engineering, different electrical components are represented by different symbols. Figures 5 show the symbols for a battery, DC source, and capacitor. They are all forms of energy storage devices.

Figure 5: (l-r) Symbol for Capacitor, DC Source, Battery

Different arrangements of electrical components allow engineers to design different devices. Components, such as resistors, inductors, and capacitors, can be arranged in two different ways. In a series circuit, the element's components are connected end to end. The current in a series circuit remains the same in all the electrical elements (Figure 6).

Figure 6: A Series Circuit

In a series circuit, as shown in Figure 6, the sum of the voltages across each element is equal to the voltage of the power source (2). Note that there is a singular path for current to flow through.

(2)

In (2), Vout is the voltage output and VA, VB, and VC represent the voltage of the individual components.

In a parallel circuit, as shown in Figure 7, the circuit's components are connected at opposing ends. The current that is supplied by the voltage source equals the current that flows through elements D and E.

Figure 7: A Parallel Circuit

The voltage across the elements that are parallel is the same (3). In comparison to a series circuit, a parallel circuit has multiple paths for the current to flow.

(3)

In (3), Vout is the voltage output and VD and VE represent the voltage of the individual components.

A digital multimeter will be used in this lab to read the current and voltage across components in circuits. Please read the Digital Multimeters Guidelines before performing this lab in order to understand how to properly operate a digital multimeter. Digital multimeters can measure either voltage or current, indicated by the symbols shown in the circuit diagram (Figure 8).

Figure 8: (l-r) Symbols for a Voltmeter and Ammeter

Depending on whether voltage or current is being measured in a circuit, the multimeter will be arranged in the circuit in a different manner. To measure the voltage across an electrical component, the multimeter must be placed in the circuit in parallel (Figure 9).

Figure 9: Multimeter in Parallel

To measure the current across an electrical component, the multimeter must be placed in the circuit in series (Figure 10). As described in the Digital Multimeters Guidelines, ensure the leads are connected to the appropriate multimeter ports depending on which value is being measured.

Figure 10: Multimeter in Series

After measuring the voltage and current across a component in a circuit, the electrical power output of that component can be calculated using the Power Law (4).

(4)

In (4), P is the power (Watts), I is the current (Amperes), and V is the voltage (Volts).

The motor provided in the lab is a 9 DC motor that will operate with voltages no more than 9 V with reduced torque and speed (Figure 11). A motor with no load operates under the current of 9 mA, and a stalled motor operates under the current of over 350 mA. Increasing the voltage provided to the motor increases the speed. Increasing the current, increases the torque.

Figure 11: LEGO 9V Motor

# Design Considerations

• Which source yields the most voltage per unit cost?
• Which circuit configuration will provide the most voltage across the load? Parallel or series?
• Which aspects of the competition formula are most advantageous?

# Materials and Equipment

### Materials with Price List

Table 1: Materials and Costs
Material Unit Cost Per Unit
Horizon Wind-Turbine 1 $7.50 Solar Panel 1$10.00
1 F 2.7 V Capacitor 1 $3.00 Alligator Clip Set 1 pair$0.50
LEGO Kit (Limit One Per Design) 1 $0.00 LEGO to Alligator Clip Connector 1$0.10
Tape 1 foot \$0.10

### Equipment Used

• Horizon wind-turbine
• Sunforce 50013 1 W solar battery charger
• Heat lamp
• 3 V power supply
• Digital multimeter
• Music voltmeter
• 9 V DC motor
• A 1 F 2.7 V capacitor
• Three alligator clip sets
• Standard LEGO kit
• Lego to alligator clip connector
• Scissors
• Tape

# Procedure

The power storage device and power sources will be tested individually. The results of the tests will be used in determining the best power source for the sustainable energy vehicle.

## 1. Testing the Power Storage Device

During this part of the procedure, a capacitor will be charged and discharged with a music voltmeter. The current of the circuit with two capacitors, a music voltmeter, and a multimeter in series and in parallel will be measured.

### Charging a Capacitor

1. The circuit in Figure 12 will be created to charge a capacitor. Connect an alligator clip to each of the cables coming out of the 3 V power supply. Red is positive and black is negative.
Figure 12: Circuit to Charge a Capacitor
2. Connect one of the unconnected alligator clips to one of the leads of the ammeter (the multimeter set to measuring current).
3. Connect the rest of the unconnected cables (one from the ammeter and one alligator clip) in series to the leads of the capacitor with the polarity indicated.
4. Charge the capacitor until the current in the circuit is 0 A.
5. Discharge the charged capacitor by connecting it to the music voltmeter. The capacitor is discharging when the music voltmeter audibly plays a song.

### Capacitors in Series and Parallel

1. Charge two capacitors with the method used to charge one capacitor.
2. Wire the two capacitors, the music voltmeter, and the multimeter in series.
1. Refer to the schematic presented earlier to wire a circuit in series.
2. Remember to check for the proper polarity, otherwise the circuit will not run.
3. Record the current produced by the circuit in series.
4. Repeat steps 1-2, but wiring the circuit in parallel. Instead of recording the current, record the voltage produced by the circuit

## 2. Testing the Power Sources

One type of renewable power source will be assigned and analyzed as determined by the TA. Using the digital multimeter, both voltage and current must be measured and recorded, and power must be calculated.

### Wind Turbine

1. Connect the wind turbine to the music voltmeter using the alligator clips following the schematic presented earlier. Measure the voltage and current across the music voltmeter using the digital multimeter.
2. Adjust the position of the turbine blades near the fan to find the highest voltage and current that can be generated.
3. Calculate and record the power generated by the turbine and give the information to a TA.
Figure 13: Circuit to Measure Voltage of the Wind Turbine
Figure 14: Circuit to Measure Circuit of the Wind Turbine

### Solar Panel

1. Connect the solar panel to the music voltmeter using the alligator clips. Place the solar panel near the heat lamp and measure the voltage and current across the music voltmeter using the digital multimeter.
2. Adjust the position of the solar panel to find the highest voltage and current that can be generated.
3. Calculate and record the power generated by the solar panel and give the information to a TA.
Figure 15: Circuit to Measure Voltage of the Solar Panel
Figure 16: Circuit to Measure Current of the Solar Panel

### Data Analysis

1. The TA will display the power data from each renewable energy source on the board. Based on the power output of each renewable energy source and the analysis of the circuits in series and parallel, determine the best power source and circuit design to power a sustainable energy vehicle with two capacitors.

Caution! The heat lamps and solar panels may become extremely hot when used for a long duration of time. Do not touch them immediately after use and turn them off when not in use.

## Competition Rules

The competition rules must be followed at all times during the competition. Violation of any of these rules will result in the disqualification of the design.

• The renewable energy vehicle must carry its power storage device (e.g. capacitor)
• The capacitors can only be charged for one minute using the provided power sources
• Each design will only be allowed one trial
• Do not touch the leads of the charged capacitor, this will discharge the capacitor
• Do not connect the power storage device until immediately before the trial is run
• The trial will end once the vehicle stops moving for a maximum of 5 min
• The design with the highest competition ratio (CR) wins (5)

(5)

In (5), distance, time, and cost are measured in feet, seconds, and US dollars respectively.

### 3. Sustainable Energy Vehicle Competition

1. Assess the materials provided and consider the data from testing the power storage device and testing the power sources. Keep in mind the variables of the competition ratio while choosing materials for the vehicle design. Make preliminary sketches during this process.
2. A minimum of 2 capacitors must be used in the design. The vehicle must carry the power storage device during the trial. While modifying the design, keep in mind the space needed to fit the power storage device (capacitor) and its wires. Prepare a cost list of the materials used in the design and specify the total price. A TA must approve the sketches and the cost list.
3. A TA will provide the materials needed for the design. If the design is modified during the construction, note the changes and explain the reasons for them. If the modifications require more materials to be used, update the cost list and have a TA approve it.
4. With the chosen power source, charge the two capacitors for 1 min each.
5. Construct the vehicle based on the sketched design.
6. Before entering the competition, make sure the motors turn in the desired direction of travel.
7. Run the trial.
8. Give the total cost of the design to a TA. The TA will provide the resulting competition ratio.

# Assignment

## Team Lab Report

Follow the lab report guidelines laid out in the EG1004 Writing Style Guide in the Technical Writing section of the manual. The following points should be addressed in the appropriate section of the lab report.

• Describe the rules, ratio, and design strategy of the competition in the introduction. What consequences did the rules and ratio have for any design decisions?
• Explain how solar panels and wind turbines work
• Discuss capacitors
• Discuss the advantages and disadvantages of the solar panel and wind turbine
• Describe the renewable energy vehicle design and explain the choices made in the design
• Discuss the power sources and their power output. How did the voltage measurements of the power sources impact the design?
• Discuss minimal design. Were all the materials purchased used? Describe the importance of minimal design and explain how it was employed in the design. Did the design minimize cost?
• Describe how the design succeeded or failed. What choices would improve the design’s standing in the competition?
• Discuss how the competition ratio can be increased, and how the design compared to the other designs
• Specify the power source chosen for the design
• Include the spreadsheet with every design's results. Describe the results and talk about other designs in the class

Remember: Lab notes must be taken. Experimental details are easily forgotten unless written down. EG1004 Lab Notes paper can be downloaded and printed from the EG1004 Website. Use the lab notes to write the Procedure section of the lab report. At the end of each lab, a TA will scan the lab notes and upload them to the Lab Documents section of the EG1004 Website. One point of extra credit is awarded if the lab notes are attached at the end of the lab report. Keeping careful notes is an essential component of all scientific practice.

## Team PowerPoint Presentation

Follow the presentation guidelines laid out in the EG1004 Lab Presentation Format in the Technical Presentations section of the manual. When preparing the presentation, consider the following points.

• Since one term in the competition ratio is cost, present the cost of the vehicle. Use the page How to Show Cost Data in Presentations for instructions on how to do this
• How would the renewable energy vehicle be improved?

# References

Layton, J.. "How Wind Power Works." How stuff works. Discovery, 2011. Retrieved 24 July 2012. <http://science.howstuffworks.com/environmental/green-science/wind-power.htm>.

Locke, S.. "How Does Solar Power Work." Scientific American. Scientific American, 2008. Retrieved 24 July 2012. <http://www.scientificamerican.com/article.cfm?id=how-does-solar-power-work>.

NextEra Energy Resources, LLC. "Benefits of Renewable Energy." NextEra Energy Resources. NextEra Energy Resources, 2012. Retrieved 24 July 2012. <http://www.nexteraenergyresources.com/content/environment/benefits.shtml>.

Reg Tyler, . "Types of Fuel Cells." Energy efficiency and renewable energy. U.S. Department of Energy, 2011. Retrieved 24 July 2012. <http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcells/fc_types.html>.