Thanks in advance for any advice to help with this situation.
My daughter is trying to create a school experiment to compare the electric output from solar panels Vs wind generated power. To do so, she wants to attach a solar panel to dc motor at various light conditions and determine the number of revolutions of the motor. She then wants to use the same size motor, attached to blades to catch the wind and determine how many revolutions occur where we live and the associated electricity generated from the wind.
The challenge she’s having is that the solar panels aren’t able to turn the motors. We have two 12 V / 125 ma solar panels.
I think there needs to be some matching of the panels to the motors, but don’t know how to do that. Is it that we need a 12 V motor?
I don’t think the motor is going to be a very accurate way to measure the output of the panel or the wind genny. A simpler way to do this is to use a simple resistive load, and measure how hot it makes a known quantity of water in a given time (measure the temperature rise). This will capture essentially 100% of the power from both the panel and the generator. The only critical piece of equipment is an accurate thermometer. Make sure the water container is well insulated. Also, make sure the resistor is waterproof.
Although this better than measuring motor revolutions, you’d still have the problem of matching the source (windmill or solar panels) to the load (resistor). The resistance value that extracts maximum power from the windmill is not likely to be the same value that’s optimal for the solar panels.
Maybe measure the open circuit voltage and short circuit current for each, and compute the source impedance and maximum available power?
In most cases, it is not practical to connect a load directly to a PV array (i.e. solar panel). This is for two reasons:
Over most of the PV array’s I-V curve, it behaves as a constant current source, not a constant voltage source. Most loads want to be powered from a constant voltage source.
Maximum power from a PV array occurs at only one point in the array’s I-V curve. Thus any arbitrary load will not extract maximum power from the PV array.
So when powering something from a PV array, you also need a charge controller and a battery. The charge controller will automatically adjust its input impedance to extract maximum power from the PV array, and the battery will produce a constant voltage for your load.
In your case, perhaps a fairer test would be to connect an adjustable resistor (potentiometer, rheostat, etc.) to each power source, and adjust the resistor for maximum power dissipation. Just make sure the adjustable resistor has a high enough power rating to safely dissipate its heat.
I have made many kid’s type motors out of sewing thimbles, wire and magnets. The problem is that they will draw lots of current and need to be push started. Even the professional kits they sell to demonstrate your concept need a push start under anything less than full sun.
There are tons of little motors around that take almost no current to operate. One example would be a motor from an electric tooth brush or similar small health care device like a nail sander. These small motors are used to running on perhaps 3V and 100ma or less. You can run such motors at 12 VDC without hurting anything. The trouble may be in measuring the RPM. You might have to slow the motor down by limiting it with a resistor. You might have to be innovative in marking the shaft so you can count revolutions. A light piece of paper glued on the shaft would work.
Have fun.
Precisely… that’s our fall back position. We can do some neat calculations with the approach we’re trying to set up, BUT, I really don’t have that much depth of understanding to get the apparatus to work properly.
Initially, we thought that it would be simple to have the solar panel power a small dc motor. Turns out that that’s not the case.
Going to keep fiddling with it. Thanks for your input and ideas.
This is where we are trying to head. Thanks! Step one, get the array of motors we bought to spin (varying ratings… low V and mI)… Step two, count revolutions using a piece of paper attached to the motor shaft with an easy to see indicator.
After we get past step one, I think using a rheostat to control RPM’s would be helpful.