Introduction to the School Power Naturally Solar Learning Lab

Introduction to the School Power Naturally Solar Learning Lab™

Lesson IV

A Lesson Related to the Virtual Array Tour Series

TEACHER INFORMATION

LEARNING OUTCOME

After honing their graph interpretation skills, students are able to access archived individual and aggregated school data to resolve questions researched through inquiry-based teaching and learning.

LESSON OVERVIEW

In this lesson, inquiry activities that hone skills such as graph interpretation are featured, as students investigate their school’s data and the archived, aggregate data from the 50 participating SPN schools.

GRADE-LEVEL APPROPRIATENESS

This Level II and III lesson is appropriate as an introduction to solar energy data interpretation for students in grades 5–12.

MATERIALS

A computer (preferably with MS Excel software available) capable of providing access to the Internet

Sufficient copies of Student Handouts One, Two, and Three

A globe of Earth (optional)

Protractors

SAFETY

No safety precautions are necessary.

ADDITIONAL SUPPORT FOR TEACHERS

There are 60 School Power Naturally (SPN) lessons available for downloading at www.SchoolPowerNaturally.org. Some of the lessons that would mesh well with this lesson and the solar array tour series are listed below, along with a brief description of content:

· SPN Lesson #3, To Go Solar or Not to Go Solar (Through role-play, students evaluate the feasibility of installing a PV system on the roof of a new school.)

www.SchoolPowerNaturally.org

· SPN Lesson #23, Photocells: The Photoelectric Effect (Students are introduced to the photoelectric effect [the basic physical phenomenon underlying the operation of photovoltaic cells] and the role of quanta of various frequencies of electromagnetic energy in producing it. The inadequacy of the wave theory of light in explaining

photovoltaic effects is explored, as are the ionization energies for elements in the third row of the periodic table.)

· SPN Lesson #26, Orienting a Photoelectric Cell (Students learn the optimum angle for orienting a solar collector relative to the rays of incoming sunlight. Equinoxes, solstices, and various locational ideas might need to be reviewed before students undertake their investigations using meters, light sources, and photovoltaic cells.)

· SPN Lesson #27, Allocating Energy from a Photovoltaic System (Students distinguish between power and the amounts of electric energy generated or used. The purpose of the lesson is twofold: Students inventory their use of electric energy for home appliances and compare this with the typical total of 6.5 kWh produced in New York State by a 2 kW photovoltaic system. Then students allocate the photovoltaic electric energy, as it is generated, to appliance use on an hourly basis.)

· SPN Lesson #32, The Sun, Earth’s External Heat Engine: Astronomy Model (Part 1) (Students become familiar with the variables that control Earth’s solar energy supply. After exploring the source and nature of solar energy, the genesis of radiation, and the structure of the Sun, gas spectra are observed and sample astronomical spectra analyzed. Mathematical models are developed and used to make calculations for the following astronomical variables that control solar energy availability on Earth:

o the yearly variations in Earth-to-Sun distance as the cause of seasons;

o the differences in Earth’s polar versus equatorial distance to the Sun as the cause of equatorial and polar climates.)

· SPN Lesson #33, The Sun, Earth’s External Heat Engine: Astronomy Model (Part 2) (Students work with the variables that control Earth’s solar energy supply.

o Previously, in Part 1, students developed mathematical models, making calculations having to do with two astronomical variables that help control heat energy on Earth. The importance of these variables in controlling heat gain by Earth is typically overestimated by students.

o In Part 2, a scale model of Earth’s orbit is mathematically modeled and evaluated, locations of Earth on that orbit are determined, and a model of Earth is used to study the effect of latitude on the availability of sunlight energy at Earth’s surface. Also, models of Earth are used to measure sunlight angles at solar noon and to compare length of daylight for various latitudes at the solstices and equinoxes.)

· SPN Lesson #34, Blocking the Sun: Earth’s External Heat Engine and the Earth System (This lesson is the conclusion of a three-lab sequence that investigates the factors controlling the amount of insolation reaching Earth. Students analyze displays of data and draw conclusions regarding energy from sunlight; determine how wavelengths are affected by the atmosphere; and contemplate t mechanisms at work in the absorbing, scattering, refracting, and reflecting of radiation. In addition, they chart the movement of frontal systems across New York State through the use of Internet sites and the SPN network of solar collector sites.)

TEACHING THE LESSON

This lesson features inquiry teaching and learning and extensively uses the online School Power Naturally database (SunViewer.net™), which presents and archives data from the solar array of your school and the arrays of the other participating schools in New York State. The lesson is intended to be used following a series of three lessons that explain and make use of the SunViewer™ software. The first of these, lesson I, features a virtual tour of the solar photovoltaic array, showing photos of and explaining the components and their operation. The solar array combined with the data-monitoring system, software, and Internet displays constitutes a Solar Learning Lab™.

Lesson II and lesson III explore the sections of the software that display live, real-time data. This platform serves as a segue into a variety of topics from closely related physical sciences to the history of the electric power grid. Lesson III features a discussion of the distinction between power and energy. The three lessons in the series provide a conceptual groundwork that makes this related fourth lesson much more valuable.

Lesson IV makes extensive use of SunViewer.net™, School Power Naturally’s Internet database. It contains data from the 50 schools participating in the School Power Naturally program. SunViewer.net™ also provides easy access to the database through a data portal. The portal is a powerful tool that allows the database to be easily queried over periods of days, months, or years. The data can then be downloaded or graphically displayed in the browser. Lesson IV presents the functionality and demonstrates applications of this tool.

HOW TO USE THE DATABASE

For lesson IV, use www.SchoolPowerNaturally.org to access the SPN home page. See figure 1.

Figure 1

After orienting the students to this page, click “On The School Roof” in the right-hand column. This will bring up figure 2, where an extensive exploration of single-site data will begin.

Single-Site Data

Figure 2

After going over the text with the students, click one of the “performance data” hyperlinks to bring up figure 3a.

Figure 3a

This query page, shown with “A. A. Kingston Middle School” selected, provides a flexible way to access and view the vast amount of performance data in the SPN database. Demonstrate for the students how to locate any of the 50 SPN schools by clicking on the arrow to the right of the school name box. To bring up figure 3b, click on this arrow and select “Dalton School.”

Figure 3b

The upper half of the query page is shown here with “Dalton School” selected.

Return to “A. A. Kingston Middle School” and click “Get Data,” bringing up figure 4.

(Note: Sometimes there is a delay while you wait for data; look at the lower left of the screen for progress messages. Time delays are more likely to occur when you begin seeking aggregate data later on in this lesson.)

Figure 4

Prompt the students, if necessary, to realize that figure 4 is an empty graph and that no power values are recorded for A. A. Kingston Middle School on January 1, 2003. (Note: This school’s PV system was not up and recording data at that time—hence the blank page.) Return to the query page and change the date in the pull-down box to May 12, 2005. Then click “Get Data,” bringing up figure 5a.

Figure 5a Figure 5b

Figure 5a shows a smooth power curve for a sunny day at A. A. Kingston Middle School. (Note: You might prefer to display your own school’s data for this and subsequent examples.) The smooth curve makes intuitive sense. On the x-axis, just past 7:30 a.m., you will see the point at which the system starts generating power. This beginning point corresponds to sunrise. Note that the power output rapidly increases until noon, when it begins decreasing. It continues to decrease until dusk, when it reaches zero again. Notice also that the maximum power is about 1.8 kW. These systems are rated at 2 kW and as expected on a day without clouds, the system is producing nearly 2 kW of power at noon.

To gain some perspective on expected values, go back to the query page. (Note: You will now begin using the various “radio buttons” shown.) Select the radio button “Irradiance.” Then click “Get Data” and you will see figure 5b, shown above on the right. Notice that at noon the irradiance peaks at about 1000 watts per square meter. On a clear day at noon, the irradiance is roughly 1000 watts per square meter. The solar industry uses 1000 watts per square meter as the standard for rating systems. This is referred to as the irradiance at standard test conditions (STC). The 2 kW rating of your solar array refers to its expected power output at STC.

Now find a cloudy day. Go back to the query page and set the date at May 31, 2005 (see figure 6).

Figure 6

In figure 6, select the “Energy by day” radio button. This will bring up figure 7.

Figure 7

The “energy by day” plot in figure 7 shows the total energy produced by the solar array for each day of the month. Note that the least energy produced was on May 14. The most energy produced was on May 12 (see the power curve plot for this in figure 5a).

Plot the power by selecting the “Power” radio button in the Daily Data section and clicking for May 14 and May 15 (see figures 8a and 8b, which provide plots of power output from both a very overcast day and a very cloudy day). Call attention to the values on the y-axis, and elicit that the scales are different. The plot on the left side has a very low power output, whereas the peak power on the right side is fairly high. Lead the students in a discussion about what they are seeing. Prompt them to suggest such factors as clouds, snow, time of year, bird waste, shade, and temperature. Note that these plots are from May, so they almost certainly do not indicate snow. While feces from large birds can impact array performance, the degradation in performance would be consistent only until the next rain and would not lead to jagged plots. Clouds instead are the culprit here. On the left side, it is likely that very overcast skies are indicated, and when this is the case, the system produces only a fraction of its maximum rated power. On the right side, the noon power production is near the system rating of 2 kW. As a result, the cloud cover is lighter; however, the jagged shape of the plot indicates fluctuations in output power caused by changes in the solar intensity incident on the solar modules. Check to be sure that the students realize that the values recorded for power are much less in 8a than in 8b (remember that we are working on graph interpretation skills).

Figure 8a Figure 8b

There are other things that can be verified with SunViewer.net™. Talk with the students about the solstices. What does the word solstice mean? If students are not sufficiently familiar with the astronomical mechanism governing the summer and winter solstices, get a globe out and demonstrate Earth’s axial tilt. A Web site that may be helpful is

http://cwx.prenhall.com/bookbind/pubbooks/lutgens3/medialib/earthsun/earthsun.html.

Invite the students to use SunViewer.net™ to explore the data and see if they can locate instances that confirm what they are expecting. In the example below, the students use the data-download capability of SunViewer.net to compare data from the summer and winter solstices.

Previously, graphical data was used to find a sunny day in May at the A. A. Kingston Middle School. Here a method is demonstrated that uses tabular data to find a sunny day. Bethlehem Central Middle School in Delmar, New York, is used. Set up the query page as shown in figure 9. The date is set at June 15, 2006. However, when requesting monthly data, the day does not matter; only the month and the year matter. In the Output Format section, select “Table.” In the Monthly Data section, select “Energy by day.”

Figure 9

Click “Get Data” in figure 9 to bring up the table shown in figure 10.

Figure 10

It is clear from this table that the most energy (9.7 kWh) is produced on June 13. Plot the power on that day, remembering to switch to “Graph” in the Output Format section. You may also want to look at the data on June 21, which is the actual solstice. On that day, slightly less energy is produced. The power plot has an odd shape, perhaps because the inverter was performing poorly due to thermal overload. So use the data from June 13, which is close to the solstice and produces a “cleaner” data set.

SunViewer.net™ allows you to download data into a spreadsheet. Doing so permits more sophisticated analysis and plotting, as this example demonstrates. Here it is assumed that you have MS Excel available on your computer. In the Output Format section of the query page, select the radio button “Raw Data File (CSV).” Make sure that the date is set for June 13 and that you have selected “Power” in the Daily Data section. Click “Get Data,” and a dialog box will pop up (see figure 11a). Click OK and the spreadsheet will automatically open and data will be placed into its cells (see figure 11b).