This activity is part of our Engineering in the Classroom tool for educators! Click to learn more about the Next Generation Science Standards (NGSS) for engineering, make connections to NASA and discover more standards-aligned activities.

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### Overview

The process of switching to cleaner forms of energy is a complex issue. Think Green allows students to break the issue down into more manageable pieces and to explore solar energy. Students will model solar energy inputs at different locations, analyze the cost-effectiveness of installing solar panels, and determine the appropriate locations for solar panels.

In this lesson, students will:

• Access data and import it into a digital spreadsheet
• Model solar energy received at multiple latitudes under various conditions
• Compare cost-effectiveness of solar panel installations of various sizes
• Identify appropriate uses and locations for a solar collector
• Explain how using solar energy can benefit society

### Management

• Students can work individually or in small groups. While students will all use the same location for the initial data series, there will be variations in the locations selected for their alternate locations in Step 5.
• To answer the discussion prompts, students will need to be in small groups.
• Assessment questions should be inserted in the spreadsheet or written down.
• Extension activities can be done individually or in groups, depending on the needs of the students and/or class.

### Background

Solar energy is radiant energy that is produced by the sun. Every day, the sun radiates an enormous amount of energy. How much solar energy a place on Earth receives depends on several conditions. Most important, it depends on latitude (as it relates to the season of the year, the angle of the sun, and the number of daylight hours), but also the clearness or cloudiness of the sky.

In this activity, NASA satellite data for energy from the sun and cloud cover is analyzed. Different areas receive renewable solar energy in differing amounts.

A solar collector is one way to collect heat from the sun. A closed car on a sunny day is like a solar collector. As sunlight passes through the car’s glass window, it is absorbed by the seat covers, walls and floor of the car. The light that is absorbed changes into heat. The car’s glass windows let light in, but don’t let all the heat out. This is also why greenhouses work so well and stay warm year-round.

#### Vocabulary:

• Latitude: a measure that identifies the north-south location of a point on the Earth. It is the angle between the line connecting a point on the Earth and the Earth’s center, and the equatorial plane of the Earth. There are three ways to express latitude. The most familiar shows 0-90 degrees north latitude and 0-90 degrees south latitude. In the computer era, this became -90 to +90, where -45 is equivalent to 45 degrees south latitude. The third method is less familiar and is called the colatitude. Colatitude is 0 degrees at the north pole, 90 degrees at the equator, and 180 degrees at the south pole. So, 45 degrees south latitude is equivalent to a colatitude of 135 degrees.
• Longitude: a measure that identifies the east-west location of a point on the Earth. It is the angular distance along a line of latitude from the Greenwich Meridian (located outside of London) – a reference longitude set at 0 degrees. There are three equivalent ways to express longitude, and scientists tend to use them interchangeably. The most familiar for longitude is 0-180 degrees east longitude and 0-180 degrees west longitude. It can also be expressed as 0-360 degrees east longitude, or just 0-360 degrees longitude. In that case, 270 degrees east longitude is equivalent to 90 degrees west longitude. The third system arose in the computer era when carrying both a number (0-180) and a character (east or west) was inconvenient. The new convention of -180 to +180 was then developed. In this case, -90 is equivalent to 90 degrees west longitude.
• Pollution: a term referring to increased concentrations of undesired matter (solids, liquids or gases) in Earth’s water, atmosphere or land. It can be natural or man-made.
• Renewable energy: energy that can be replenished in a short period of time, such as energy from solar, wind, water or geothermal sources. Typically, there is little concern that these sources of energy will become scarce or used up, unlike fossil fuels. Fossil fuels include coal, oil and gas.
• Solar collector: a device that captures the sun’s energy and focuses it in a small area as a more usable or storable form. These devices can be simple, such as a greenhouse, or complex like solar panels or solar concentrators.
• Solar radiation: the electromagnetic radiation or energy emitted by the sun. The energy coming from the sun peaks in visible wavelengths, but also includes ultraviolet and infrared wavelengths.

### Procedures

1. Gather data on solar energy in your area.

• Find the latitude and longitude of your school by entering its address into the USGS' EarthExplorer. The latitude and longitude of the address entered will be displayed in the search results.

Alternatively, you can use USGS LandLook to search for your school using the magnifying glass search icon in the upper left. The latitude and longitude will be displayed in the lower left of the map.

You can also try right-clicking a location on Google Maps and select “What’s here” to display the latitude and longitude of that spot. Or in Bing Maps, right-click a location to open a menu that shows its latitude and longitude.

Here is an example for the location of the Jet Propulsion Laboratory in Pasadena, California:
latitude: 34.199635
longitude: -118.174654

• Round your numbers to two decimal places. A negative longitude indicates the location is west of the 0 degree longitude line. For instance, in the example above, you can use -118.17 or 118.17 W.
• In the example above, the latitude reads 34.20 N and the longitude 118.17 W.
2. Go to the My NASA Data Earth System Data Explorer.

• Click Data Set, choose Atmosphere, expand All Data.
• Under Longwave and Shortwave Radiation at Earth's Surface select Monthly Flow of Energy into Surface by Shortwave Radiation.
• Select Time from the options below Line Plots on the left of the screen.
• Enter the latitude and longitude near the compass rose icon.

• Enter the latitude in both boxes above and below the icon.
• Enter the longitude in both boxes to the left and right of the icon.
• Select a 12-month time span from the Start date/time and End date/time dropdown menus (e.g., January 2018 to December 2018).
• Click Update Plot in the upper left of the screen.
• Displayed is the graphed data for the monthly average amount of solar energy from the Sun (all sky conditions, i.e. clear and cloudy days) for the latitude and longitude entered.
• To get the data in numerical form so it can be used in a spreadsheet, click Show Values or Save As… at the top of the page.

• Show Values: After clicking OK in the Show Values options screen, a window will appear with data that can be copied and pasted into a spreadsheet. In the monthly rows at the bottom, the number to the right of the colon shows the energy received at the surface in Watts/m^2.
• Save As…: In the new window that opens after clicking Save As…, select CSV (comma separated value) on the Select a Data Format dropdown, and click Save. A window will open with the data in a format that can be copied and pasted into a spreadsheet. In the spreadsheet, the data in the monthly rows at the bottom can be separated into columns, separated by commas, with the column furthest to the right showing energy received in Watts/m^2.
3. Transfer this information into a Microsoft Excel or other spreadsheet program (Microsoft Excel is the most common spreadsheet program, so instructions will refer to Microsoft Excel functionality)

• Open a blank worksheet.
• Copy the incoming solar energy information into a spreadsheet in a manner that resembles the table below.

The data for this exercise is the numerical value that follows the colon in each month line (e.g., 337.100). It can be typed directly into the table, or the "Text to Columns" function can be used to separate the data for easy copying.

 School Location B Location C July August September October November December January February March April May June
• Create your graph. Highlight the data in column A and B, and select a line graph from the Insert or Chart menu (depending on which version of software you are using).
4. To get a better idea of the availability of solar energy around the world, choose two other locations: one location in higher latitudes and one in lower latitudes. Repeat the process from the above steps to collect your data, and enter it into your spreadsheet and chart. You can add the next column of data to your chart by selecting the chart and then clicking and dragging the small square anchor in the upper right corner of cell B1 to cell C1. You can also add the data to the chart by right-clicking the chart and choosing Select Data from the menu. In the Data Source menu, add a new series and select the Name cell, Y values, and X-axis labels.
5. Now that students have looked at solar energy from different locations, it should be clear to them that latitude and time of year play big parts in determining how much solar energy is received at a given location. Have students collect data on how many kilowatt hours per square meter per day (kWh/m2/d) are received at your school.

• Visit the NASA POWER Data Access Viewer.
• Select Renewable Energy from the User Community dropdown menu.
• Select Climatology as the temporal average.
• Enter the latitude and longitude of the school site.
• Select CSV as the output file format.
• In the parameters section, search for and select the Insolation Over A Consecutive Month Period parameter from the Energy-Storage System Sizing submenu.
• Click Submit.
• Click the CSV button to open or save the output data as a comma-separated values file.

Given that commercially available panels are approximately 15-20% efficient, they will not generate the total amount of solar energy received per day at a given location. Have students calculate how many kWh/m2/d could be generated using a 15% or 20% efficient solar panel.

You may elect to have students calculate values for both 15% and 20% efficiency. They should enter this data into a spreadsheet in a column marked kWh/m2/d from January through December. Remember these values are per day and need to be converted for monthly totals.

6. Use your school's utility bill to compare how many kWh per month your school uses to how many kWh/m2/d can be generated by solar panels. You may need to collect multiple utility bills to complete this comparison. Enter the kWh per month used by the school in the spreadsheet in a column marked kWh from January through December. Students should then calculate how many square meters of panels would be required to generate all the electricity needed to power the school per month.
7. Contact local solar installation companies to find out the costs of solar panel installations of different sizes. Given different size installations and the amount of power they would generate, have students determine what the ideal solar installation size would be for the school. The ideal size is reached when the cost of solar panel installation offsets the cost of the electricity that would otherwise need to be purchased over the course of their estimated lifetime. (Most panel manufacturers offer a 25-year warranty.)

### Discussion

After completing step 8 above, students in small groups will answer the following questions and be prepared to answer them in a class.

• Do you think it would be cost-efficient to build or buy a solar panel installation? Why or why not?
• Explain why knowing the average amount of cloud cover in a given area would be important when deciding whether or not to use solar energy as a power source.
• What is the relationship between the seasons (winter, spring, summer and fall, or wet/dry, depending on location) and the amount of solar energy that a particular place receives?
• Using the Global: Climate Zones, Observed Climate Data, 1976-2000 map, explain how latitude affects climate zones (a free EarthData login will need to be created to access the high-resolution maps).
• What would the lines on the solar energy chart look like for a location in the southern hemisphere? Why?

### Assessment

If you/your students are familiar with formulas, use them in Excel to answer the following questions. Otherwise, use paper and pencil or calculators.

1. What is the average monthly solar energy your area receives in a year with no clouds?
2. What is the average monthly solar energy your area receives in a year with clouds?
3. What is the average difference in solar energy received in a year with clear skies compared to cloudy skies?
4. What is the average difference in solar energy received in a year between your three locations, for both clear skies and cloudy skies?
5. How many square meters of solar panels at 20% efficiency would your school need to power all energy needs per month, and per year, for the school?
6. How many square meters of solar panels would need to be installed to make an installation of solar panels a cost effective measure?

### Extensions

1. How much pollution (emission of greenhouse gasses) does your home or school create? Use the utility bill for your home or school and the Environmental Protection Agency (EPA) Emission Calculator.
2. Many locations allow energy users to indicate if they want the power they purchase to come from sources such as natural gas or renewables. Use your home or school utility bill to investigate the cost differences between natural gas and renewable energy, such as wind power. In some locations, the utility bill may contain the natural gas surcharge and the wind power surcharge. If it does not appear on your bill, use the Green Power Partnership website to estimate the premium for green sources of electricity, such as solar or wind power, for a location in your state.
• Is the natural gas surcharge constant or does it fluctuate? (This may require comparing several utility bills for different seasons.)
• What is the surcharge for green power resources such as solar or wind power?
• Find out if purchasing solar or wind power will eliminate the natural gas surcharge on your utility bill.
• Would you save by going green and purchasing solar or wind power over natural gas? If so, estimate how much you would save.

3. Discuss possible locations on campus for solar panel installation. Using a free lux meter app for Android or iOS, measure incoming light at those locations during different times of the day and different times of year on clear days to select an optimal location for potential solar panel installation. In a fashion similar to how students graphed incoming solar energy at different latitudes, they can graph lux readings at different locations on campus. Converting lux to watts per meter squared is a complex calculation that involves knowing color, temperature and wavelength, but there is a simplified approximation for sunlight -- multiply your lux measurement by 0.0079 to determine watts per meter squared. This can help students compare locations.

Lesson plan contributed by Cindy Henry, Oklahoma City, Oklahoma with updates and modifications in 2015.