Grade: 9-12 Version 1 June 2016 Solar for Aquaponics Extension Design and size an off-grid, ground-mounted solar PV system to sustainably power an aquaponics system www.seiinc.org
Table of Contents Curriculum Introduction... 3 Curriculum Key... 4 Setting the Stage... 4 ActivitIes... 4 Assignments... 4 Handouts... 4 Extensions... 4 Academic Content Standards... 5 Materials List... 11 Tips for the Instructor... 15 Assessment... 16 Background for Lessons... 17 Solar for Aquaponics Pre & Post Test... 19 Solar for Aquaponics Pre & Post Test: Teacher KEY... 22 Lesson 1: Energy & Climate Systems... 25 Key Words... 25 Preparation... 26 Setting the Stage: Energy Sources... 27 Optional Activity: Energy Sources Pros & Cons... 30 Setting the Stage: Generating Electricity... 30 Activity 1: Building a Generator... 31 Discussion: Turbine Generators... 33 Setting the Stage: Carbon Cycle... 34 Optional Activity: Carbon Movement Through Reservoirs... 37 Optional Activity: Carbon s Journey... 38 Assessment... 38 Demonstration: The Greenhouse Effect... 38 Discussion... 40 Setting the Stage: The Greenhouse Effect... 41 Discussion... 42 Activity 2: Strength of the Evidence... 43 Optional Activity: Climate Science Research Project... 44 Assessment... 44 Handout: Energy Sources Pros and Cons... 45 Handout: Poster Presentation Guide... 47 Handout: Building a Generator... 48 Handout: Carbon Movement Through Reservoirs... 50 Handout: Carbon s Journey... 51 Handout: Carbon s Journey: Teacher Key... 54 Handout: Greenhouse Effect Experiment... 55 Handout: Strength of the Evidence... 57 Handout: Strength of the Evidence Data Organizer... 62 Lesson 2: Solar Science... 64 Key Words... 64 Preparation... 65 Activity 1: Energy and Solar... 65 1
Discussion... 66 Setting the Stage: Energy, Power, and Solar... 66 Activity 2: Understanding Current... 68 Setting the Stage: Solar Electric Systems... 69 Activity 3: Solar Cell Demonstration... 70 Discussion... 72 Assessment... 72 Extensions... 72 Setting the Stage: The Benefits of Solar... 73 Discussion... 75 Setting the Stage: Solar Industry... 75 Assignment... 79 Assessment... 79 Handout: Computer Energy and Power Use... 80 Handout: Solar Research Project... 81... 82 Key Words... 82 Preparation... 83 Setting the Stage: Solar Design... 83 Activity 1: Solar System Components... 84 Setting the Stage: Sizing A System... 86 Discussion... 89 Setting the Stage: Solar System With Battery Backup Design... 89 Activity 2: Solar System with Battery Backup Design... 90 Handout: Solar System Design Cards... 92 Handout: Sizing the Components of the Solar Electric System... 96 Handout: Solar System with Backup Battery Design: Teacher Key... 100 Lesson 4: Solar Site Assessment & Installation... 104 Key Words... 104 Preparation... 105 Activity 1: Maximizing Solar Power Production... 105 Discussion... 105 Setting the Stage: Solar System Site Choice... 106 Activity 2: Solar System Design... 107 Setting the Stage: Solar Installation Preparation... 108 Activity 3: Practicing with Power Tools... 111 The Solar Installation Project... 111 Activity 4: The Solar Installation... 111 Handout: Maximizing Solar Power Production... 113 Handout: Solar Site Assessment... 116 Solar Site Assessment: Teacher Key... 118 Handout: Using Power Tools... 120 2
Lesson 3 Overview Estimated Time Ø 1 lesson (60 minutes class time) Standards Covered NGSS: HS-LS2-7, HS-ESS3-4, HS-ETS1-2 CCSS Math: A-SSE-4 CCSS ELA Language: 1,6 CCSS WS 1,2 CTE Energy, Environment & Utilities: B1.0, B7.0 Engineering & Architecture: D2.0, D2.1 Objectives: Students will be able to: Correctly assemble the components of a solar power system Calculate the optimal size for a solar system based on electricity usage Prep Time 1-2 hours for reviewing the lesson, assembling materials, and arranging the solar install on campus Handouts 3.1 Solar System Design Cards 3.2 Solar System with Backup Battery Design Materials (for each student/group): Solar System Design Cards Pipe cleaners Internet Access Solar photovoltaic system sizing is based on the electricity usage of the aquaponics system. This lesson introduces students to the components of a solar electric system and instructs students on how to size a solar system to power the air and water pumps in the aquaponics system. They will base the system design on the pumps total electricity usage. KEY WORDS DC Disconnect: A safety feature that allows the DC current from the modules to be interrupted before it reaches the inverter Inverter: An electronic device that converts direct current (DC) from solar panels into alternating current (AC), the form of current used to power homes, buildings, and most appliances Insolation: Incident solar radiation the amount of solar power on a given area over time, measured in kilowatt-hours per square meter (kwh/m 2 ) Racking: The mounting system that attaches the solar array to the ground Charge Controller: A device that limits the rate at which electric current is added to or drawn from electric batteries Battery: A device in which chemical energy is converted into electricity and used as a source of power Pump: A mechanical device using suction or pressure to raise or move liquids, compress gases, or move air 82
PREPARATION Ø Review the background material, the PowerPoint presentation, and the Lesson. Ø Print the following handouts found at the end of the lesson: Handout 3.1 Solar System Components 1 set per group Handout 3.2 Sizing a Solar System 1per student Ø Gather pipe cleaners of two different colors for the solar system components activity and either cut the Solar System Components cards for each group or provide them with a pair of scissors Ø Internet access is recommended for some steps of the handouts, but it is not required. Ø Assemble materials for the ground mounted solar installation (see Materials Matrix in the Intro). Ø Arrange the solar installation on campus. For assistance, please contact SEI at sei@seiinc.org. SETTING THE STAGE: SOLAR DESIGN Ø Solar power systems are comprised of many components beyond the photovoltaic cells and panels themselves. There are a number of steps required before power produced by solar systems can be used on site (in the case of an off-grid system) or flow into the grid. Mechanical Mounting Structure µ Recall, solar modules are a collection of solar cells wired together to form an array. Ø These solar modules are directly connected to a racking structure, which secures the system to a roof, the ground, or a shade structure. A weather station is often mounted near the panels to 42 42 Image Source: http://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/ 83
monitor wind speed, direction, and temperature. It collects data and sends it back to a monitoring system. Electrical Structure (DC side) Ø Photovoltaic cells produce electricity in direct current (DC). Ø The DC current then runs through a DC disconnect, an important safety feature that disconnects the output of the modules from the rest of the system. This is needed for system maintenance or troubleshooting. Ø From the DC disconnect, the DC current runs through a charge controller, which limits the rate at which electric current is added to or drawn from electric batteries. The batteries store the electricity that does not need to be used at that moment. Ø A solar system that uses batteries requires a charge controller. They are important to ensure a long life of the batteries. The charge controller is a voltage and/or current regulator to keep batteries from overcharging, which can reduce performance and lifespan. Ø In charge controllers, charge current passes through a semiconductor (a transistor), which acts like a valve to control the current. It is called a semiconductor because it passes current in only one direction. Electrical Structure (AC side) Ø The batteries are constantly supplying a DC current, which then runs through a system inverter to convert direct current (DC) from battery banks and solar panels into alternating current (AC). AC is what we use in our outlets and can travel long distances better than DC. The air and water pumps in the aquaponics system are mechanical device using suction or pressure to move air and water and they require AC power. Ø The electricity coming from the system inverter is then used to power the pumps in the aquaponics system. There is typically an air pump and water pump in an aquaponics system to keep the water aerated and cycling through. ACTIVITY 1: SOLAR SYSTEM COMPONENTS Ø In this exercise students will design an off-grid, ground mounted photovoltaic system with a system inverter, charge controller, and batteries to power the air and water pumps in the aquaponics system. A solar array contains many components. Students will work in groups of approximately four students to design a solar PV system with all the components using the solar system components cards from their handout. The answer key showing the correct layout for the system is at the end of this section. Ø Groups will need space on a large table or the floor to layout their systems. Ø We suggest giving this activity to students before describing the components and design of a solar photovoltaic system, allowing them to apply critical thinking skills to hypothesize about the function of system components and how they are arranged to produce and store useable AC electricity. Then allow them to modify their design once the functions of the components, provided in Setting the Stage, are described. 84
Ø Give each student group one set of all eight cards in the Solar System Design Cards Handout and pipe cleaners of two different colors. Have students arrange the cards to mimic the way they think a system is structured. Explain that the two different colors of pipe cleaners represent the two different types of current that will flow through their wires: DC and AC. Instruct students to connect the different electrical components of the system with the pipe cleaner wires depending on the type of current at each stage. Optional: Provide Internet access to allow members of the group to quickly research the function of different components if they get stuck on a system design question. Optional: Ask students questions to help them arrange the components. Which components have they seen before? Based on the name of the components, what do students think the components do? (Think about the word inverter. What would this component be inverting? Think about the charge controller. What would it be controlling charge to?) Ø Once student groups have had the opportunity to layout their systems, have half of the groups travel around the room at a time for short peer presentations and observations on designs and why they arranged components as they did. Ø When student presentations are complete, fill in knowledge of system design and component function as needed. Ø The correct layout of a system will look similar to this: 43 43 SEI image created by SEI employee Liz Fitzpatrick 85
SETTING THE STAGE: SIZING A SYSTEM Derate Factors Ø A derate factor is a metric used to account for inefficiencies and power losses that occur between the electricity production at a solar panel and the delivery of electricity to what it is powering. The Solar System with Backup Battery Design Handout includes calculations around the derate factors covered below. Insolation Production tolerance: Panel performance is assessed using standard tests in a laboratory, but actual performance of panels once installed in the real world will differ; this derate factor accounts for the expected variation. Higher temperature: Panels are less efficient at producing electricity when the temperature is higher; this derate factor accounts for the temperature variation expected at the location of the system. Dirt and dust: The collection of dirt and dust on the modules reduces the amount of light that reaches the PV cells; this derate factor accounts for the loss of performance of the panel due to soiling. Module mismatch: All panels are slightly different, and since the panels are strung together sometimes power is lost as it moves through the array; this derate factor accounts for a minimal, but expected, amount of mismatching. Line loss: As the current moves through the wire, there are losses (in the form of heat) due to the resistance of the wire and other electrical connections in the system. This derate factor accounts for these energy losses. Ø The amount of energy a solar system can generate depends on the amount of sunlight the region receives. The amount of solar energy reaching your school is affected by the season, the time of day, the climate, and air pollution. µ Insolation, incident solar radiation, is the amount of solar radiation striking a given area over time, measured in kilowatt-hours per square meter (kwh/m 2 ). The map below shows insolation in different parts of the United States. You can see that insolation in the southwest is higher than in the northeast. 86
Solar for Aquaponics 44 Insolation can be used to determine the peak sun hours per day (PSH/D). A peak sun hour is the average number of hours per day of full sun at a given location. One peak sun hour is equivalent to 1,000 Watts of solar power striking one square meter of surface area for one hour. Areas with higher insolation have higher peak sun hours per day. 45 Ø The graph below shows solar radiation, measured in Watts per square meter, at different times of day. Solar arrays produce the most power when the sun is highest in the sky. 44 45 Solar radiation peaks around noon so maximum power production occurs at this time. The next graph shows the amount of solar radiation received over the course of a day. Source: http://www.nrel.gov/gis/solar.html Source: http://www.nrel.gov/gis/solar.html 87
(W/m 2 ) 46 Solar power production occurs during a time when power demand is higher and electricity is valuable. This means the energy generated by a solar system is worth more than electricity produced at other times of day. Peak demand happens later in the day than peak solar production. Solar power in combination with other forms of renewable energy can be used to reduce peak demand. For example, wind power produces more energy at night when the wind blows stronger. The graph below shows the power demand at different times of the day. 47 46 Source: http://www.ars.usda.gov/main/docs.htm?docid=15616 47 Source: http://www.eia.gov/todayinenergy/detail.cfm?id=830 88
DISCUSSION Ø What are the pros of solar electricity? Solar power is renewable, so it won t run out. Unlike fossil fuels, solar power generation does not release greenhouse gases as a byproduct of producing electricity, so it doesn t contribute to climate change. Solar power is economically valuable because peak production overlaps with high electricity demand during the daytime. Ø What are the cons of solar electricity? Solar production is not ideal in all locations, because of insolation and the limitations of available space (physical space, but also taking into consideration space limited because of shading). It is an intermittent resource solar photovoltaic systems only produce electricity during the day, and produce less when environmental conditions impact direct radiation on the panels (for example, overcast skies, a cloud passing by on a sunny day, or the shorter winter days). Solar arrays must be cleaned to maintain maximum production. The systems have high initial costs. The production of PV equipment generates some emissions. Ø What are some things that might reduce the power output of a solar system? Derate factors (production tolerance and module mismatch, temperature, line losses), shading, dust on the modules, cloudy skies. SETTING THE STAGE: SOLAR SYSTEM WITH BATTERY BACKUP DESIGN Ø Solar panels, inverters, batteries, and charge controllers are all designed for different amounts of power, current, voltage. When selecting components for your solar system, it is important that each component has the features you need and is sized appropriately. Use the materials listed in the materials matrix and in Lesson 4 as a sample system design.inverterthe main function of the inverter is to change the frequency of the DC to AC at 60 cycles per second to mimic the electricity we use. Ø There are different types of inverters, but the one that we will use in this project are pure sine wave inverters. In order to convert DC to AC, inverters must take the constant DC voltage and change it to a sine wave curve that goes above and below 0 volts. When inverters first came out, the most common way to do this was to make the voltage go straight up and down, creating a blocky signal. This is called modified sine wave. More advanced modified sine waves make multiple steps, trying to come close to a pure sine wave. Batteries Ø A solar powered aquaponics system requires batteries in order to be able to power the air and water pumps at night when the panels are not producing energy. Batteries are essentially devices in which chemical energy is converted into electricity and used as a source of power. The batteries in this system will store the energy created by the solar panels and supply the air 89
and water pumps with constant energy. Typically, one designs batteries to have 2-3 backup days of energy storage. Ø The best batteries for solar applications are deep cycle AGM (absorbed glass mat) batteries. These batteries have a higher initial cost, but if you would rather pay extra up front and never have to maintain the batteries after installation, AGM is the way to go. AGM BATTERIES ARE ALSO SAFER BECAUSE THERE IS NO FREE ELECTROLYTE. AGM BATTERIES ELIMINATE THE SPILL HAZARD THAT EXISTS WITH LEAD-ACID BATTERIES. THE ELECTROLYTE (BATTERY ACID) CANNOT FLOW FREELY AND IS EVENLY DISTRIBUTED ACROSS THE ACTIVE PLATE SURFACES.ACTIVITY 2: SOLAR SYSTEM WITH BATTERY BACKUP DESIGN Ø Provide each student with a copy of the Solar System with Backup Battery Design Handout. Explain that students will use the handout to determine the size of the major components in the solar electric system needed to provide the electricity to power the air and water pumps in the aquaponics system. Ø Using the Solar System with Backup Battery Design Handout, walk students through the process of sizing the major components in a system. o Step 1: Calculate the power demand of the air and water pumps. The power required by the air and water pumps can be found on the manufacturer s information sheets for the pumps. Students may need to look for the pumps online to find additional details about how much power the pumps need. o Step 2: This amount of power is the minimum size of the inverter in the system. Research a pure sine wave inverter for this project. o Step 3: Calculate the daily energy use of the air and water pumps. o Step 4: Calculate the total annual Greenhouse Gas Emissions associated with energy use of the pumps in the aquaponics system. o Step 5: Take into account derate factors in order to calculate the amount of DC power the system needs to generate. o Step 6: Calculate the amount of batteries for the system with backup days of energy storage. o Step 7: Determine the solar radiation for their geographic location. One way to quantify solar radiation is peak sun hours per day. The average for California is 5 peak sun hours per day (PSH/D). For a more accurate figure, provide students with Internet access or use a projector to display the chart on the website below. http://www.bigfrogmountain.com/sunhoursperday.html o Step 8: Calculate the size of two solar panels for this array. o Step 9: Determine the charge controller size and type your system needs. 90
o Step 10: Students will sketch their system and label the solar panels, charge controller, batteries, and inverter. Be sure to tell them to label the size that they just calculated of each component on their diagram. 91