Grades 9-12 - EnergyWhiz
Contents
1. SunSmart Schools IV Teacher Page We ve Got the Power Student Objective The student e will be able to explain the relationship between irradiance and the amount of power DC output of the photovoltaic array e given a graph of a photovoltaic system s power output will be able to Key Words amperage current direct current DC irradiance kilowatts per hour kWh photovoltaic array deduce what the weather was for the aes given day vo ae N given the weather outside and the watts kilowatts time will be able to approximate the power output of the array Materials Time e computer or handheld device with 1 class period internet access computer with internet access capable of projecting for the class alternately graphs could be reproduced on overhead transparencies web based weather application with current and historical past month weather data Background Information Local weather has a dramatic effect on the electrical output from a photovoltaic array The most obvious factor is cloud cover but temperature also affects the output from the array higher temperatures decrease the electrical output slightly this will be covered in the later lesson Changes in Latitude Additionally in areas without adequate rainfall the photovoltaic output can be adversely affected by an accumulation of dust and bird droppings and of course snow cover will block sunlight from reaching the surface of the sol2. ar cells Luckily in Florida we don t usually have to worry about either of these two conditions Irradiance is the measure of the intensity of sunlight and is expressed as watts per square meter W m Ona sunny clear sky day at solar noon at sea level the typical irradiance level is 1 000 W m This value of irradiance is used as the standard test condition STC for Florida Solar Energy Center We ve Got the Power Page 1 photovoltaic testing and design calculations and is the basis of the manufacturers stated output for cells and panels On a clear cloudless day irradiance will peak at solar noon a graph of irradiance over time will produce a bell shaped curve Large banks of clouds thunderstorms and weather fronts are all readily apparent on a graph of irradiance and since photovoltaic output is directly related to irradiance these weather events can be seen on a graph of the output On consistently overcast days the curve will have the same width but will be much lower and on partly cloudy days with patch of clouds intermingled with bright sun the curve will tend to be spiky showing that the system produces more energy during sunny periods and less energy during cloudy periods Procedure prior to class Note Students should have completed the lesson Solar Powered System 1 from Understanding Solar Energy prior to beginning this activity 1 Familiarize yourself with the Sun Town static graphs on the Energy Wh
3. cription This is a shortcut that you can use when making calculations it is the system s nameplate rating provided by the manufacturer This value was obtained by testing and measuring the panel s output at Standard Test Conditions 1000 Wm Using this value you can take the nameplate rating of any array and figure its projected output during all irradiance conditions 5 How much electricity will your system produce when the irradiance level is at STC 1000 Wm Find the system size in your school description Record it here System size m This value is how much electricity your system is expected to be producing when the irradiance is 1000 Wm To check your projection of output check your graphs from question 2 for the times when the irradiance was 1000Wm Is your projection correct Describe any difference What might account for this difference Florida Solar Energy Center We ve Got the Power Page 7 6 What would your system produce when the irradiance is 750Wm Show your calculations below ahs Calculate the output from a different array in a different location Lake Sybelia Elementary in Maitland has a photovoltaic array with a nameplate rating of 2 0 kW How much electricity would you expect to be produced when the irradiance is 800 Wm Florida Solar Energy Center We ve Got the Power Page 8
4. her Channel provides local weather conditions and historical data Florida Solar Energy Center We ve Got the Power Page 4 SunSmart Schools IV Key Word Definitions We ve Got the Power amperage measure of the number of electrons flowing through a wire current current the movement of electrons direct current electricity DC an electric current flowing in one direction only This type of electricity is typically used in battery operated devices automobiles and boats irradiance measure of the amount of sunlight at a particular time and place kilowatt 1000 watts kilowatts per hour kWh the standard unit used to describe electricity usage over time photovoltaic array complete unit of solar modules power common term used to refer to output in watts voltage measure of the force of electricity in a circuit The volt is not a unit of flow it is analogous to pressure of water in a hose watts the standard unit used to measure electricity specifically the rate at which electrical energy is dissipated Watts are calculated by multiplying amperage and voltage Florida Solar Energy Center We ve Got the Power Page 5 SunSmart Schools IV Laboratory Manual We ve Got the Power 1 Irradiation is the scientific term for the amount of sunshine that strikes an object How does the amount of irradiation affect the amount of electricity that your school s photovoltaic system produces Write a hypothesis below
5. iz website These can be accessed by selecting the Sun Town school on the pull down menu 2 Familiarize yourself with the data being collected for your school s system or alternately if your school does not have a monitored photovoltaic array choose an available school from the list on the Energy Whiz website www energywhiz com for classroom use If possible use a school that is nearby or one that usually has the same general weather patterns as your school Navigate through the different screens so you will be able to guide your students in locating irradiance and DC output and also historical data irradiance and DC output for the last month 3 Locate a weather app that gives accurate current and historical weather data for your school or the school you have chosen Procedure during class 1 If necessary divide the students into groups according to how many computers are available to them 2 Lead the class in a discussion review of their findings from previous lesson on the different factors that can affect the output of photovoltaics making sure that weather is mentioned and discussed 3 Tell the students that they will be investigating how weather conditions affect the amount of electricity that the array at their school produces 4 Lead a discussion on the nature of sunlight during the day e Ask the class to describe how the brightness of sunlight changes throughout the day e Guide the students to talk abou
6. l in another part of Florida and predict what the weather at that school is based off the power output Have them check the weather service to see if they are correct 2 Have the students shade large areas of the array with sheets of cardboard or blankets to simulate heavy clouds Observe the output Have them cover areas with screen or gauze material to simulate hazy conditions Observe the output Internet Sites http rredc nrel gov solar old_data nsrdb National Solar Radiation Database contains 30 years 1961 1990 of solar radiation and supplementary meteorological data from 237 NWS sites plus a user manual to help in reading the tabular information http www ncdc noaa gov data access land based station data land based datasets solar r adiation National Oceanic and Atmospheric Administration s NOAA National Climatic Data Center is responsible for preserving monitoring assessing and providing public access to the Nation s treasure of climate and historical weather data and information Here you can find data on solar radiation and climate conditions in the United States http wrdc mgo nrel gov World Radiation Data Centre Worldwide solar radiation site http en openei org wiki Main_Page Open Energy Information OpenEI is a knowledge sharing online community dedicated to connecting people with the latest energy information and data Florida Solar Energy Center We ve Got the Power Page 3 http www weather com The Weat
7. t how the light from the Sun gets stronger and brighter from dawn to solar noon and then slowly gets weaker and dimmer until sundown 5 Draw the framework of a two axis graph on the board intensity of sunlight on the y and time on the x Don t worry about putting any numerical values on the y axis yet Ask Florida Solar Energy Center We ve Got the Power Page 2 students to draw on a sheet of paper what they think a graph of the intensity of sunlight would look like Students may work in groups or individually e After the majority of students have put something on their paper ask for a volunteer to share their idea on the board e Lead a discussion about this graph have students modify the graph to show their suggestions Guide them if necessary e When the students have closely approximated a bell shaped curve write the Energy Whiz website address on the board and have the students navigate there and select the irradiance graph for the Sun Town school e Have the students explain how this graph is similar and different from the graph that they created Ask the students to describe the weather for that day a Have the students switch to the graph showing irradiance on a day with an afternoon rainstorm They should be able to explain and point out sunrise sunset clouds and afternoon heavy clouds thunderstorm 6 Students should complete their Laboratory Manual pages Further Research l Have the students pick a schoo
8. that describes the mathematical relationship between the amount of solar irradiance and the electric output of your system 2 Gather the data to verify your hypothesis On the Energy Whiz website use irradiance and DC output graphs to support or disprove your hypothesis Use your own school s data if available Write your findings and conclusion below using graphs and or equations to support your conclusion Florida Solar Energy Center We ve Got the Power Page 6 To simplify discussions about the output of photovoltaic cells modules and arrays scientists decided on a set of conditions called Standard Test Condition STC that allow mathematical computations and comparisons to be made when input output and module size are variable The Standard Test Condition for irradiance is 1000 Wm Irradiance of this value occurs during solar noon on a clear sunny day in most parts of the world however here in Florida we often will have sunny days that measure higher 3 Look at the irradiance data you collected for question 2 Which dates and times had an irradiance level of 1000 Wm 4 Did the irradiance level on any of these days measure greater than 1000 Wm If so list which date s and time s went above standard test conditions Once you know the irradiance level and the size of a system you can predict how much electricity the system is producing You may have noticed a system size in kW listed in your school s des
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