Teaching Tips

Teaching Tips: The Solar Collector Experiment

Synopsis:
In this module students use a simulation to design and construct a system that best collects and retains heat from a heat source. Students use a cup, water, rocks, black and white aluminum foil, and a heat lamp to create their solar collector.

Big Ideas:
a. Different materials have different specific heat values.
b. Materials gain/lose heat at different rates.
c. Temperature is the average kinetic energy of the particles in a system.
d. Heat is the total kinetic energy of all of the particles in a system.

Misconceptions Addressed:
a. Heat and temperature describe the same quantity.
b. Heat flows from objects with more heat to objects with less heat.
c. Color does not affect the rate of heat gain.

NSES Grade 5-8 Standards
a. Physical Science
i. Properties and changes of properties in matter
ii. Transfer of energy
b. Science and Technology
i. Abilities of technical design
ii. Populations, resources, and environments

The Experiment

The Solar Collector PSI Sim™ is a virtual representation of an experiment that is often done in the classroom. If you do this experiment, it may be a good idea to do the PSI Sim™ first, since there are aspects to the module that will help students do the real experiment more efficiently. For example, the methodology section contains a movie of a student doing the "real" experiment. Also, doing the simulation will help students understand the variables they can control and how the experiment will be undertaken. As with most PSI Sim™ modules, The Solar Collector is designed to help students understand the idea of manipulating variables. Therefore, stress these issues when asking students to reflect. For example, ask "What factors did you take into account when you designed your solar collector?" "What materials did you choose for your collector and why did you choose them?" How well did your solar collector convert light energy to heat energy?" and so on.

Calories

Most students associate calories with dieting, but few know that the calorie (the unit, that is) is defined as the heat required to raise the temperature of 1 gram of water by 1 degree Celsius from 14.5 degrees to 15.5 degrees Celsius (note that there is a slight variation in the heat required to raise temperature one degree depending on the temperature). It may be a good idea to talk about the idea that the calorie is a unit used to measure heat energy. Joules and BTUs (in the British Engineering System) are also used to measure heat energy.

Heat and Temperature

Students are often confused about the difference between heat and temperature, even after learning the definitions. One way to help them work out the difference is to focus on the difference between average and total. A good illustration to use is that of an iceburg. A large iceburg has a very low temperature (which measures average kinetic energy), but because of its great size (mass) can have a high amount of heat (a large number of molecules). It's temperature is low, but because of its great mass, its heat content may be high. The heat of an object depends on three qualities: (1) its temperature, (2) its mass, and (3) its composition.

Passive vs. Active Solar Collectors

The solar collector in this experiment has no moving parts, that is, it doesn't adjust to the direction of the light. We call this fixed type of solar collector a passive solar collector. A greenhouse is also a passive solar collector. Students may have seen pictures of the giant motorized solar collectors in New Mexico or elsewhere. These are active solar collectors because they move with the sun's rays. These are very effiecient at harnessing the sun's rays, but there is a tradeoff. It takes energy to move them. The idea of tradeoffs is a major theme in scientific inquiry. There are many types of solar collector. We are using a direct-gain collector in this experiment. Light (heat) travels directly into the collector in this type of system. Systems where the light warms air, which in turn warms the main collector (or thermal mass) is called an indirect-gain solar heater.