#### Wolfman29

##### Well-known member

- Joined
- Jan 14, 2011

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So I have been fiddling around with this solar cell, trying to make a decent (within 10-20% error, just for qualitative uses) LPM.

After a bunch of trial and error, I got some semblance of results...!

So first things first: I have this crappy solar panel from a long time ago, measuring in at something like 70cm^2.

Using that, I took out my solar panel outside (with a DMM attached) at highest light and measured the output current and voltage. Now, it's "common knowledge" that the sun outputs roughly 1000W/m^2 of land at highest light. So, using that and the voltage/amperage measurements, I worked out my solar-panel's efficiency to be roughly 7.8%: That is, if it was one square meter in size, it would be putting out roughly 78W of energy (at 70cm^2, it should be outputting 7W of energy, but it was only outputting slightly more than half a watt).

So that was the first step.

The next step was finding some curves that will show me how a typical solar panel reacts to different wavelengths of light. Here is what I used: What type of light cause a solar cell to work?

I tried both curves, and it seems like the second one is more accurate for my solar panel. I will get to that later.

So, I unfocused my lasers wide enough so that they covered the most area of the solar panel without losing too much energy by not hitting the panel and measured output *current*, because solar panels are current sources, not voltage sources.

My results for my three lasers were as follows:

200mW 532nm Rayfoss laser: 6mA

381m*A* LOC: 9mA

~900mA 445: 15mA

Now, there is a clear difference here, if only qualitative: the higher the power the laser, the more amperage it is producing. But how do we make this into a quantitative device?

Here's what I figured out: that second graph? It shows how much amps per watt an ideal solar panel would produce for each wavelength.

So, I did some estimating and got something like this:

660nm: .46A/W

445nm: .2A/W

532nm: .35A/W

Now, I tried it first with the first graph, but my results were so far off, and there was no reason the other one couldn't be more accurate for my panel, so I am trusting the other one is more accurate.

Anyway, what I did next was take into account the calculated efficiency of my solar panel.

I divided the found amperages by the efficiency percent to get "ideal" currents produced by panel.

So, here are those results:

Rayfoss 200mW 532: 77mA or so.

LOC: 115mA or so.

445: Roughly 192mA.

The next step was using these currents and the ratios found in the graphs for each wavelength to determine the wattage of my lasers. I divided this current by the decimal given in the graph, and the result would be the power in watts.

So, here are the final results!

Rayfoss 200mW 532: 219mW!

LOC (set at 380mA): 250mW!

445 (set at 900mA): 961mW!

How damn accurate do those seem?

It may just be a coincidence, but that is just far too unlikely... anyone else agree? Have I just stumbled upon a fantasticly cheap way to semi-quantitatively measure lasers?!

:drool: