0
\$\begingroup\$

I'm helping my son with his 7th grade science project. We've had a good deal of fun with our experiments with Solar Arrays and charging 12 volt UPS batteries! But, I am not sure how to interpret the data!

Our original hypothesis was that the length of the wire between the solar panel and the battery would affect the voltage charge the most. We do NOT think that was true!

We just need to get some good charts out of the data to show something that we learned!

enter image description here

\$\endgroup\$
11
  • \$\begingroup\$ Dude, just go away. We all get it, you're God's gift to us all. It's a kids science project, I just wanted some simple help. I guess I go back to digging dtiches tomorrow. \$\endgroup\$ Jan 7, 2020 at 1:25
  • 1
    \$\begingroup\$ What did you learn? What do you want to learn? \$\endgroup\$ Jan 7, 2020 at 1:27
  • \$\begingroup\$ Honestly? I didn't learn anything, it was a poorly constructed project and I'm to blame for that. I don't operate with the scientfic process everyday of the week. I work and try to feed my family. I thought it would be a fun project with my son and it was. He learned how to solder, he learned how a battery can charge and discharge with a simple light and a solar panel. But, now? Now I don't know what to do. So all of your super complex electrical mumbo jumbo doesn't help me. \$\endgroup\$ Jan 7, 2020 at 1:33
  • \$\begingroup\$ For useful values plot time difference in hours X axis on left side and max voltage at the end of day. as Y axis then use 1 for sunny and 0 for cloudy and plot that as well then you can see how much higher the battery voltage is on sunny days vs cloudy days. and we can only assume you had some overnight LED or load. We can't guess what wire you used. but if not warm, it shouldn't matter.Choose Scatter XY plot with dots only. \$\endgroup\$ Jan 7, 2020 at 2:15
  • 1
    \$\begingroup\$ @RussellMcMahon: There's at least one comment that has been deleted before the "Dude, just go away" comment. I expect the "go away" thing was in response to the earlier, deleted comment. \$\endgroup\$
    – JRE
    Jan 7, 2020 at 11:49

3 Answers 3

2
\$\begingroup\$

The 7 steps in conducting a scientific experiment are:-

1) Pose a Testable Question:

2) Conduct Background Research:

3) State your Hypothesis:

4) Design Experiment.

5) Perform the Experiment.

6) Collect Data.

7) Draw Conclusions.

Now you are at step 7, and you have a quandary. The data doesn't appear to support your hypothesis! But hold on a minute - exactly what were you expecting, and why?

Your research should have told you how and why wire length might affect the charge voltage, and how to design an experiment which would give meaningful results. So let's examine the experiment to determine what results you could expect from it. Then you can organize the data to see if it supports the theory.

The factors that might have affected the end of charge voltage are:

  1. Light intensity.

  2. Charging time.

  3. Wire length.

  4. battery voltage before charging.

Battery voltage increases roughly proportionally to the amount of charge put into it, and the solar panel is capable of putting out a current proportional to light intensity. But the resistance of the wire might restrict charging current to a lower value, which should result in lower battery voltage. Wire resistance is proportional to length. You are hoping the increased resistance of the longer wire will have a measurable effect.

So you could plot a graph with wire length on the X axis and battery voltage on the Y axis. But to get meaningful results you need to separate out the confounding factors of light intensity, charging time, and battery starting voltage.

For voltage you can subtract start voltage from end voltage and show the difference.

To remove charging time from the result, divide the voltage increase by time to get eg. volts per minute. To account for light intensity you could plot 3 curves, one for each intensity (mildly cloudy, clear sky, sunny).

If the graph shows a clear relationship between wire length and voltage increase for all three light intensities then the results support your theory. A stronger effect at higher light intensity might indicate that the panel is restricting current in lower light. If results appear to be 'random' then perhaps the wire has too little effect, or some measurements are not sufficiently precise (light intensity) or not a good proxy for charging current (battery voltage).

Ohm's Law says that Resistance = Voltage / Current. The higher the resistance the less current will flow in a circuit, so a longer wire should reduce current and increase the length of time needed to charge the battery. But the solar panel and battery also have resistance. If that is much higher than the wire resistance then wire length will have little effect.

If the experiment does not show a 'positive' result it doesn't prove that the wire length has no effect, but just that it is not significant in this case. This is good news, because it shows that the panel can be positioned a considerable distance away from the battery without adversely affecting charging time. Therefore if this is the result then the experiment was a success!

\$\endgroup\$
1
  • \$\begingroup\$ I love this answer! Thank you! I have been working on this for my son today, this should be fun. \$\endgroup\$ Jan 7, 2020 at 21:13
1
\$\begingroup\$

I think the most reasonable thing to do is to try and demonstrate from the data that things were all over the place and no correlations could be found and explain that it was likely because your controlled variables were not controlled enough (things like battery start voltage, and especially sky conditions). Battery voltage is not linear with charge and not easily predicted so you can't interpolate or extrapolate from different starting points, so if you don't start in the same spot every time you can't really use the data. And recorded sky conditions are pretty vague and the human eye is really terrible and distinguishing true brightness, and even if it was, the sky isn't going to stay constant anyways. The only real way around this would be to have multiple setups with identical panels and batteries (a tall order) running at the same time under the same sky, or obviously control your sky by having your own dark box and light source.

I would start by grouping data together where as many variables as possible are held "constant" to show that it's all over the place. Your conditions are already all over the place so there is probably going to be more than one way to do these groupings, and all are likely to be fairly unsatisfying given how many things are varying when they shouldn't be.

Definitely group similar sky conditions together for one of them. The random starting voltages and end times are going to throw a big wrench into things though no matter which way you slice the pie.

Experiments are tough. The real world is fuzzy, noisy, and not ideal compared to the perfectly, clean, ideal theory you are usually trying to match your experimental results up with. Things already vary on their own enough to mess up all your results without you making the process worse by not controlling things enough.

And outline how you would do the experiment again. For starters, definitely keep the starting voltages the same, solar panels and batteries the same if possible, and keep either the end time the same and measure the end voltage, or keep the end voltage the same and measure the time. And keep the sky conditions IDENTICAL. If you're wanting to find out the effect of wire resistance then you don't actually need all those different sky conditions; One sky condition is enough (or just multiple setups running under the same varying sky conditions, regardless of what they are). It just helps to have more, but for it to be useful you need a complete set of data for a single sky condition.

\$\endgroup\$
1
  • \$\begingroup\$ I like this answer too. I plan to show both of these to my son! \$\endgroup\$ Jan 7, 2020 at 21:14
0
\$\begingroup\$

What I would do is figure out the time it takes to charge up 1 volt. For instance, if it takes 5 minutes to charge a battery 1 volt with a wire length of 25, then it should take 10 minutes with a wire length of 50.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.