PV Gap

Mabel Said:

Why doesn't my Solar Cell from my Calculator work?

We Answered:

It is really easy to burn out LEDs by letting too much current through, I have definitely blown out a few without even noticing. You need to have a current limiting resistor in the circuit if you use the battery, without the battery I doubt there is enough current to turn the LED on. So if you have another LED, I would recommend testing with that.

Second possibility I could see is the polarity of the LED, it will only work with currrent in the right direction. Look it up and check that.

Assuming the solar cell can produce enough current and voltage (LED needs about 1.3 V and 15 mA), there really aren't any other possibilities beyond those. It is a simple circuit so only so many things can go wrong.

Ralph Said:

how resistant are solar cells to rain, test of time? how reliable is it to buy one according to this?

We Answered:

NanoSolar sells their product with a 20 year warranty. But of course you can't buy them because Germany has contracted to buy all they make.

You do need to have a warranty that covers the product payback period, and you can generally find that, but not much better.

Most installations have better than 90% of panels still working 5 years beyond warranty expiry, but a small number have had complete destruction as a result of hail high wind, or oddly enough, sun. (overheating damage).

I would say you need insurance against all perils.

Nathaniel Said:

Finding the amps of a solar cell on a multimeter?

We Answered:

Solar panels run a typical 12 watts per square foot, which equates to about 1 watt for 12 square inches. Your 5x5 panel, it typical of the average, will run about 2 watts, exactly as you say yours is rated. Ohms law says that at the voltage you specify, you will get the equivalent current you specify. That is how they rate solar cells. The problem is in HOW you measured the cell. You short circuited the cell by simply connecting your current meter across the terminals. BAD, bad, bad. Solar cells behave unpredictably when shorted and can actually damage themselves. You may have permanently damaged your cells if you tried to simply measure current with your meter. The only way to accurately measure is under load, which means a resistor, and then you measure the voltage drop across the resistor and then calculate the current. An alternative is to connect your current meter in series with a resistor. I have several solar battery chargers used for charging NiMH cells. Each has 4 cells in series to get to 2 volts, and a 3.3 ohm resistor in series to limit the maximum current if you put in a dead cell. Without the resistor, the cells would effectively be short circuited by the dead battery. Your meter when set on a current scale is simply a low value calibrated resistor, typically 1/10th of an ohm or less and a millivolt meter reading the voltage drop. The voltage drop is proportional to the current so they can print an ampere scale on the meter face instead of the actual millivolts the meter is actually measuring. Never, EVER, short solar cells. Always use a load or a load limiter in any circuit with a solar cell. The ratings sound about right for the surface area of each cell, but what you measured may be the remains of what is left after you damaged them by shorting them You can TRY using a 1000 ohm resistor as a load and see what kind of voltage drop you get. When soldering, use the lowest heat you can for the shortest amount of time you can to get a solid joint. The cell is brittle and too much heat for too long will crack the substrate.