PV Gap

Linda Said:

Why, when you first connect a solar cell to a watt meter it first spikes and then continuously falls?

We Answered:

Solar cells operate under the so-called photo-electric effect. Here the momenta of photons strike bound electrons of photo electric material and that causes those electrons to become free electrons. Free electrons are the ones that create the current in your wattmeter.

Before you hook up the wattmeter, the solar panel is an open circuit; so those free electrons build up in the panels. When you hook on the meter, that closes the circuit and a current of free electrons starts to flow. Because of the buildup of free electrons while the circuit was open, the initial current surge is higher than the steady-state flow.

Once the excess electrons are siphoned off through the wattmeter, the remaining free electrons reach a steady state level because the sunlight is creating as many free electrons as the wattmeter is siphoning off.

Dwayne Said:

How would I go about Charging a 9 Volt Battery with 2 Solar Cell Modules without over charging?

We Answered:

This depends on the chemistry of the battery - there are rechargeable NiMH (Nickel-metal hydride), NiCD (nickel cadmium), and Alkaline batteries. The charging circuitry would depend on the battery's chemistry. Some companies make integrated circuit chips that control battery charging - however there are some challenges. You'll need to add additional components, and make sure you can get the controller chip in a form that can fit on a breadboard. You can find charging circuit controllers on DigiKey. Here is the URL:

http://search.digikey.com/scripts/DkSear…

Good luck!

Esther Said:

What is the maximum temperature a Radio Shack solar cell can withstand?

We Answered:

That is a fascinating idea. I did a little bit of research and it could actually come in quite handy to use a toaster oven as a soldering iron. It's very tedious to solder a lot of components. I found this url which you may have already seen:

http://www.seattlerobotics.org/encoder/2…

which discusses how to use the oven as a soldering iron. It has some recommendations on temperature. Your best bet would be to take the part numbers of the radio shack parts and google them and then look at the specs on them to see how much heat they can withstand. I did that and found this page however, it didn't provide all the details:

http://rsk.imageg.net/graphics/uc/rsk/Su…

You might need a solder that melts at a low temperature. That might be your best bet and then buy some spare solar cells and give it a try. What I would do first is heat the oven up and then try melting a small piece of solder first, or as that one link suggested, getting some of the liquid solder type stuff. If it doesn't damage the components, that might be a neat way to run through soldering multiple items fast.

Can you calibrate your temperature? That might be a good thing to do as well.