Harnessing the sun’s energy is a clean, effective way to produce heat energy. Demonstrating that in the classroom, however, takes some careful planning and ingenuity. In the past I’ve described how to use pizza box solar ovens to demonstrate the greenhouse effect. In this post, I show how to challenge your students to get creative and produce their own solar water heater.
The objective for the students is to take what they learned in the previous lesson, with the pizza box solar ovens, and apply it to making a solar water heater. I generally give the students a week to complete the construction phase (with parameters). As with the solar ovens, you will need a clear, sunny day, an area outside that will not be disturbed, and lots of opportunities to take temperature readings throughout the school day in order to complete the lab.
We attempted this lab on Wednesday of this week. The day started sunny; however, by lunch it was cloudy and extremely windy. Solar water heaters that did not have enough mass to them blew over. Water from beakers was spilled and thermometers thrown out. We have decided to try again, like good scientists, next week when conditions are better. Actually, this was a great opportunity to express to the students that these things happen in professional laboratories as well. We decided that even if science is unpredictable, we love it!
The parameters I give the students are that the solar water heater may not be any larger than a two-foot cube and it must have a place to insert a beaker of 50 mL of water and a thermometer. I could give students a detailed set of instructions on how to build the solar water heater that I want them to build, but I like the fact that they have to use the engineering design process in this assignment.
On lab day, we set up the solar water heaters and take an initial reading of the water and then leave the site. We return about three hours later, take a second reading, and make modifications (if desired). At the end of the school day, we take our last reading and chart our results. The next day we really consider the information we were able to collect and decide as a class what designs worked for converting the sun’s radiant energy into heat energy and what didn’t work so “hot.”
There are numerous directions you can use with this lab. I hope you give it a try. The students really gain a great deal from the experience, and it reinforces what they've learned about the greenhouse effect and energy conversion.