Abstract

I describe how I used science and engineering practices to ask and answer a question about how a partial eclipse might be detected by the solar panels on my house. I share a simple investigation of how I used the amount of energy generated by the solar panels on my house as a way to understand the impact of the Moon blocking the Sun during a partial eclipse. I share the solar output graphs from the day before, the day of, and the day after the partial eclipse. These show the daily output patterns and how they changed as a result of the Moon covering part of the Sun during the day.

Investigation

On October 14, 2023, I was eager to watch the annular solar eclipse. In Tucson, Arizona, where I live, the path of the Moon did not block the entire Sun. Nevertheless, I was outside with my pinhole camera and eclipse glasses to observe the rare sight of the Sun appearing as a crescent in the sky. While observing a rare event is always exciting, the partial solar eclipse also provided me with the opportunity to use practices from science and engineering to answer a question I had about the eclipse.

As a teacher and curriculum developer, I design lessons to engage students in the science and engineering practices from the Next Generation Science Standards. Students ask questions, design investigations, analyze and interpret, engage in modeling, use mathematics and computational thinking, construct explanations, engage in argumentation, and communicate about science ideas to learn new science ideas. But sometimes students walk away from these lessons thinking that these practices are only useful in science class. They might not realize that these practices come in handy whenever one has a wonder or a curiosity to satisfy.

As I was using my pinhole camera and solar glasses to watch the Moon slowly move across a portion of the Sun, I realized that many people around me were going about their daily business without giving much thought to what was happening in the sky. Most people seemed to be unaware that a solar eclipse was happening because the sky did not appear to visibly darken. That got me wondering how much visible light was being blocked by the Moon during the partial solar eclipse and how one might be able to measure that without having access to fancy solarimeters. Then I realized that I had the perfect instrument on my rooftop – the solar panels on my house.

A few years ago, my family installed solar panels to generate electricity for our household use. The panels face south and collect the abundant sunshine we have in Tucson, turning it into electrical energy to power our household appliances. The solar panels require no maintenance, so there isn’t a need to give them much thought on a daily basis. They sit on the roof and do their thing, running the refrigerator, air conditioner, dishwasher, and washing machine during the daytime. The panels are hooked up to an app that I have on my phone so that I can check their performance occasionally, to make sure they are still operating as they should. I have noticed that on cloudy days the solar panels do not generate as much electricity as they do on sunny days because the clouds block some of the sunlight. I realized that this app might be able to show how the Moon’s shadow was also blocking light during the solar eclipse.

Figures 1 - 3 show what I found when I checked the app. On October 13, 2023 (Figure 1), a fully sunny day, the Sun rose at about 6:27 a.m. The solar panels began generating electricity at about that time. As the Sun rose higher in the sky, more solar energy began hitting the panels and the electrical output steadily increased each hour until about noon, when the Sun was at its zenith in the sky (Table 1). Then, during the afternoon, the angle of the Sun in the sky decreased to the west and less Sun energy hit the solar panels on the roof. The Sun set that day at 5:52 p.m. and the solar panels stopped generating electricity. A similar pattern was generated on October 15, 2023, the day after the solar eclipse (Figure 3).

However, on October 14, 2023, the day of the eclipse, the pattern was different (Figure 2). The graph started the same as October 13 and October 15, but then, around 8:00 a.m., there is a noticeable decrease in the amount of electricity generated by the solar panels. At 8:00 a.m. the electrical output was 0.578 kwh, down from 0.851 kwh the previous day (Table 1). At 9:00 a.m., the electricity generated by the solar panels was only 0.489 kwh (compared to 1.49 kwh) and at 10:00 a.m. it was only 1.2 kwh (compared to 1.86 kwh). Then at 11:00, the electrical output was back to normal at 2.03 kwh. There were no clouds in the sky that day to cover the Sun. The only thing partially blocking the Sun would have been the Moon! Indeed, the eclipse began that day at 8:10 a.m., reached its maximum at 9:31 a.m., and ended by 11:01. a.m. These times correlated with the decrease in electricity generated by my solar panels. While it may not have been noticeable to a person walking around outside that morning, the solar panels on my house experienced a decrease in solar input when the Moon moved between the Earth and the Sun, creating a shadow that blocked the amount of sunlight they received and decreasing the amount of electricity they could generate.

*Bolded text in table shows time of partial solar eclipse

I was excited that I could detect the effects of the eclipse with the solar power system on my house. My experience observing that other people were not noticing the eclipse prompted me to engage in the science and engineering practice of asking a question about a phenomenon that I observed. I then participated in several other science and engineering practices, including designing an investigation and collecting data from the app for my solar panels, interpreting the data, and constructing an explanation for the patterns I noticed in the data. The whole experience satisfied my curiosity and also prompted new questions that maybe I’ll answer another day, such as what would the solar panel output graph look like during a total eclipse? I’ll have to wait until Friday, November 20, 2207 to answer that question.