The idea of free energy is an appealing one.  It's even more appealing when you can tap into that free energy using a few cheap parts that are easily obtained and assembled.  So, here's an easy electronics project to build a simple solar-powered battery charger using only a couple parts and no tools.  This charger can be built in a few minutes using about five dollars in parts but can provide years and years of free energy.  Plus there is always a little satisfaction in knowing you built it yourself, no matter how simple the project is.

Before we start I'll say that I am in no way an electronics expert.  Heck, I'm not any sort of expert, so don't expect me to reveal the Holy Grail or anything special here.  What I can say is that I have built a couple of these solar battery chargers and tested them out and they work great.  No amount of knowledge or degrees on the wall can deny the fact that I'm getting free power using five bucks worth of parts, and you can too.

There are only a few parts for this solar charger and they are easy to get.  The most difficult thing to find (for a good price) will probably be the solar panel itself.  You do not need a large panel, and little “experiment” or hobby solar panels can usually be found at the local Radio Shack or electronics store.  In this example we will be charging two AAA batteries, and we will be doing it with a small one volt solar panel.  The local solar panels were rather expensive, so instead of buying them I found a couple little one volt panels on eBay for about $1.25 each.  You can use a larger panel, and it would charge the batteries quicker, but this is about charging batteries on a budget so we're keeping it cheap.
The only other thing we need are a battery pack and a diode to control the flow of electricity.  A two battery holder can be found at Radio Shack for less than 2 bucks and they sell two packs of diodes for about $1.50.  I went with a 5.1 volt diode since this is more voltage than the batteries and the price was right.  I am pretty sure the voltage rating of the diode won't matter so long as it is more than the combined voltage of the batteries you intend to charge.
Not including sales tax, the total investment in this project was $4.75 and I have an extra diode to build a similar project in the future.  Here is a picture of the parts needed for this solar charger.

The first thing to do is make a loop on each end of the diode leads to make it easier to connect to our circuit.  You can connect the diode in many different ways (pc board, solder, connecting screws, etc) but I found making loops on the end of the diode to be quick and simple.  Once the diode is ready, strip some insulation from the ends of the battery pack wires and then connect the positive (red) wire to one end of the diode.  Make sure to connect to the end nearest the black stripe on the diode.  If you connect to the other end, the solar recharger will not work properly and will drain the batteries instead.

In order to understand why it's important to hook the positive wire to the correct end of the diode, I should probably explain what a diode is and how it works.  A diode is a small electrical component that acts as a one-way gate for the flow of electricity.  It allows an electrical charge to flow in one direction, but not the other.  So by connecting the end nearest the dark band of the diode with the positive wire of the battery pack, we allow electricity to flow from the solar panel into the batteries, but not from the batteries into the solar panel.  Since we are using a one volt panel to charge two batteries totaling much more than one volt, we need the diode in place to make sure the batteries are charged instead of just draining their power.
It's also important to note that even if your solar panel outputs more voltage than the batteries you are charging, it is still a good idea to put a diode in place.  The solar panel won't always output the rated voltage (especially at night) and it's always easier to protect against battery discharge than to find out you have no electricity when you need it.

The next step is to connect the other end of the diode to the positive (+) terminal on the back of the solar panel.  This is easily done if you made a loop in the diode lead as in the picture below.

Now we connect the negative (black) wire from the battery pack to the negative (-) terminal on the back of the solar panel.  This completes the electrical circuit.

I used a piece of electrical tape to keep the battery pack in place and provide a stable little base for the solar panel.  This keeps tension off the wires (preventing them from coming undone) and also provides a nice stand to prop up the solar panel in the sun.

At this point you can put your newly constructed battery charger in the sun and start enjoying the benefits of free energy (provided you have some batteries to charge).  Since we are only using a one volt solar panel, it will take a while to recharge two 1.5 volt batteries, but they will get a full charge in time.  The diode makes sure the batteries only receive power and don't give any away, so slowly but surely our little solar panel will store up free energy from the sun.

I hope you enjoyed this little tutorial on building a solar powered battery recharger and get a chance to harness this free energy source soon.