For the final unit, we studied solar heating in general and solar hot water heaters in particular. Working individually, we started with a web quest researching solar hot water heaters. As a teacher, think about what question to ask so that the students aren’t landing on the same webpage and thus sharing the same info. Alternately, give them the search term and assign groups to report on the first page of results, second page of results, third page etc.
After fifteen minutes, we wrote our facts up on the white board.
Next we were put into pairs, and each pair decide how to sort the facts written (make their own categories) and then add two more each, and make a poster with this information. This makes students think about all the shared information, since students tend to want to interact only with the portion they are responsible for. We then shared out our new information.
Another group’s sort, with the new facts in green.
To see if different colors absorb solar radiation at different rates, we did an experiment. We were given mason jars painted with different colors: white, orange, and black. We filled the jars with equal amounts of water and took the starting temperature of the water. We then took our jars outside and placed them in the sun. We took the temperatures of each jar at even time intervals and recorded the results.
We then wrote up a lab report following this template:
1. Beginning ideas – What are my questions?
2. Tests and Experiments – What did I do?
3. Observations – What did I see, hear, smell, feel? How did I measure what I observed? Graphs and interpretation of graphs of any data collected.
4. Claims – What can I claim as a result of my observations?
5. Evidence – How do I know? Why am I making these claims?
6. Reflection – How have my beginning ideas changed?
7. Redesign or Extension – How can I use my new ideas to improve my design (engineering) or investigate something new?
We also had to graph the temperature vs. time data for each colored jar on the same axes, and use the graph to address the question, “Does the color of the jar make a difference in the heating of the water?” making sure to support all claims with evidence.
There are many possible extensions to this experiment, such as: type of heat transfer (radiation, conduction, convection), estimating temperature at certain time, Newton’s Law, graph analysis (curve fit, find the linear functions): will it eventually plateau and would they all be the same?
We did a graph analysis using TI-84 graphing calculators to graph and do a regressive analysis of the data. I want a class set of these calculators so badly!!
Finally, we were put in groups of four to build a solar water heater to increase the temperature of 1 gallon of water as much as possible in 45 minutes. We brainstormed in groups and came up with a design. We could bring anything we wanted from home, but we were limited to spending no more than $10 on the project. We would have ninety minutes to build the next day, and then after our lunch break we would test our designs!
The first group’s was a solar reflector-type, with a gallon can in the center for the water, insulated with bubble wrap.
Group two used a coiled black hose, and a gravity siphon to circulate the water.
The third group used reflectors focused on an aquarium which would function like a greenhouse.
Our group used a coiled black hose, with a pond pump to circulate the heating water. We also used solar reflectors. Unfortunately, it worked too well, and our rig melted in the concentrated sun!
So for our experiment we just used the solar collectors.
This was the culminating activity of the week. We discussed our results, and how each rig could be improved, as well as which type would be best suited for large-scale use. We even had a representative from Maker Ed who encouraged our work!