Solar Cell Battery

[lovesanimals]

I am making a solar cell battery for my science fair project. I saw an example of one on WorldWatts. I thought I could use it to do an experiment measuring how much salt it will take to produce the best reading since the materials just said "a couple tablespoons of salt added to tap water." I know that I need to make my experiment have a variable to measure and be able to graph. My question is about the procedures. If I do the experiment starting with distilled water and then add 1/2 teaspoon at a time, measure the reading on a microammeter, then keep going, will I have numbers higher than the microammeter will be able to read? I don't know how high the numbers can read on this digital one my dad bought? Also, does the angle of the sun matter?

[deleted-71588]

I'm a bit confused. Solar Cells are a technology where light (photons) causes a semiconductor like material to emit electrons. Batteries are a technology where a chemical reaction causes ions to accumulate at a cathode and an external circuit returns them to the annode. Table salt (NaCl) in water will disassociate and produce Na+ and Cl- ions raising the conductivity of the solution (salt water). I don't comprehend what a "Solar Cell Battery" is and how it relates to salt water.

With solar cells, the amount of current produced is a function of how many photos interact with the cell per second to free an electron. With batteries, the rate of the chemical reaction is mostly a function of the surface area of the annode and cathode although the temperature and strength of the electrolyte will have some effects.

Most digital meters have some level of protection against off scale situations; however, there are limits to this protection when there is a lot of power involved. If there is enough power involved to cause a problem for the meter, then there are significant safety issues with your experiment.

Please provide some additional information on your background research and what you are doing.

[deleted-71709]

I am also confused. I don't know what a "solar cell battery" is. Perhaps if you could provide us a link to the specific material you saw on WorldWatts, it would help us provide some guidance for you.

[deleted-71447]

I believe this is the experiment:
http://worldwatts.com/homemade_solar_ce ... _cell.html
As Craig mentioned, yes, the angle of the sun's rays relative to the copper plate will affect the rate of photons interacting with the copper plate and will affect the current.
It's a great experiment. Good luck!
Chris

[deleted-71588]

If you are dealing with Cu2O (cuprite or cuporous oxide) and Cu (copper) plates in a NaCl (table salt) solution, you have both a battery and a solar cell so I am no longer confused.

The battery portion is an oxidation reaction where Cu2O is being oxidized into CuO (cupric oxide). The rate of this oxidation is very slow at room temperature so the amount of current supplied will be small.

Cu20 is also a photosensitive semiconductor which will produce many times more current than the battery effect when in bright sunlight.

With extremely small amounts of NaCl in solution, the resistance of the water will be high enough that very little current will flow and the change in the current flow will change very little with small additions of salt until suddenly a significant change will occur and the current change will increase linearly with the addition of more NaCl until it reaches another point above which additional NaCl will have very little effect. Normally, this electrolyte behavior is not something that is investigated because it is extremely dificult to analyze the effects without dealing with parts per billion of various contaminants.

The surface area of the plates will have far more effect on the amount of current in your experiments.

the angle of the sun's rays relative to the copper plate will affect the rate of photons interacting with the copper plate

I'm less convinced than Chris. CuO2 produced via the annealing process described is going to be a very thin amorphous layer. I would expect that the more of the plate above the solution that is exposed to sunlight, the more current will be produced as long as there is enough solution contact between the plates and the incident angle probably won't have much effect. The surface area below the solution level is another story. Less area in solution will reduce the battery effect. Additionally, the solution surface will act as a partial mirror reflecting the sunlight (maybe onto the plate above the solution) and it will certainly change the incident angle below the surface because the speed of light in a salt solution is different than in air so there are boundary effects.

You need to construct a hypothesis and then figure out how to prove/disprove it with carefully controlled experimentation as there are a significant number of variables involved with this kind of an apparatus.

[lovesanimals]

Thank you for all the replies. Yes the link to the experiment was the one I was following. I didn't know if I could link that site in my question. Designing the experiment and making sure I know all the steps is the hardest part for me. Do I need any special formulas for measuring the copper plates? I was just going to have the salt as my variable, then the solar reading number as the other variable. My hypothesis is that the more salt added will make a greater electric current because salt water is a conductor of electricity. My question is: Will the concentration of salt in water effect how much energy a solar cell produces? Thank you for all of your help with this!!!!

[deleted-71588]

I gave you my best guess at what the salt (NaCl) concentration would do when all other things are held constant in a previous post.

With extremely small amounts of NaCl in solution, the resistance of the water will be high enough that very little current will flow and the change in the current flow will change very little with small additions of salt until suddenly a significant change will occur and the current change will increase linearly with the addition of more NaCl until it reaches another point above which additional NaCl will have very little effect. Normally, this electrolyte behavior is not something that is investigated because it is extremely dificult to analyze the effects without dealing with parts per billion of various contaminants.

At the very low concentration end, the purity of the water and any leftover salts, acids, or bases on your copper plates and the container holding them and any measuring or other apparatus like funnels, pour spouts, etc can significantly alter your results.

If you want to experiment with the conductivity of salt concentrations in water, I would suggest using a simpler setup that uses some smaller electrodes where you can control their surface area and separation distance better.

If you want to experiment with Cu2O solar cell power, I would try to come up with a hypothesis that did not involve salt water concentrations.

[lovesanimals]

Thank you for helping me again. Instead of measuring the salt levels, would the experiment be a better one for working with the temperature of the water and the readings from the solar battery. Cold water, warm water, boiling water? Wouldn't there be too many temperatures then?

[deleted-71727]

Lovesanimals,

As long as you keep everything else constant, you can certainly use cold warm and boiling (or close to it) water. You can even do other temps in between if you want. It is up to you to how far you want to take the project. I suggest only doing a few and if you see something interesting doing more. Sometimes you can't tell if something will be interesting until you try. If it isn't then try something else. Have fun with it! How do you think the different temperatures will affect things? If you can provide a good guess from your research then go for it!

Heidi