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Lets say I have a solar panel that gives off 5 volts at 30mA. if I were to put a ten ohm resistor in series with it would There be basically no effect because a 10ohm resistor woulkd limit it to half an amp, which is way more. Or does the solar panel act like ~ 167 ohm resistor, and adding a ten ohm resistor will limit it to 28mA?

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The problem is that there isn't a simple linear relationship between the output voltage and current of the solar cell. Ideally, each solar cell would come with a full set of specs, including a graph describing exactly how much voltage you get at different loads.

5V @ 30mA is just one point on this graph. Many suppliers also list how much voltage you will get at open circuit, and how much current you get at short circuit.

For example, this cell is rated at rated at 6.7V and 30mA, and gives 8V open-circuit, and 44mA short-circuit. So we have:

8V @ 0mA (open circuit)
6.7V @ 30mA (nominal)
0V @ 44mA (short circuit)

If you plot this on a piece of paper, you'll notice that these three points do not fall on a straight line. But if needed, you could interpolate between them to get a decent estimate of how it will behave at intermediate values.

Solarbotics actually did a really nice job, and kindly generated a set of comparison charts, indicating how the current and voltage change with load for all their solar cells.

anybody? For some weird reason it said god hart posted last, but there are no posts on this forum...