Electro Danno: Do-It-Yourself Solar Panel

Since the fall semester has ended, I have met up with one of my good engineering friends and designed and built an ~18 watt solar panel. The project took around 40-50 hours total and was a complete success!

The finished panel looks great (see picture on the right). Of course, like most do-it-yourself (DIY) projects, we (mostly me) ran into some problems. The day the bus wire was to be installed I accidentally broke 5 solar cells! Breaking the solar cells would have been no big deal, however, the cells were already joined to the base of the pegboard. In order to remove the broken solar cell, a de-soldering was necessary, but also careful removal of the silicon, not to break any other nearby cells. Then, after preparing a new solar cell, the cell had to be soldered together with the other solar cells, along with placing another blob of silicon to bond the cell and pegboard. About an hour was taken because of the breakage. Although, it did bring up some laughs.

Other problems included were accidentally cracking the plexiglass from drilling a hole for the screw to go in, as well as placing a solar "chain" (six solar cells soldered together in series) backwards. The latter error caused a lot of troubleshooting and confusion. We noticed this problem when we tested our connections with a multimeter and found that the voltage was around 13 volts instead of the theoretical ~18 volts. After finding the backward chain, my friend and I thought it would be easiest to run a bus wire in between the adjacent chains to be correctly wired—because the chain was placed backwards, it was being connected in parallel instead of the being connected in series. You can see the bus wire towards the bottom of the panel.

Having a 12 volt sealed lead-acid hobby battery, diode , and DC to AC (Direct Current to Alternating Current) inverter on hand, we built a small electrical power system. The intent of the solar panel is to charge the 12 volt battery thereby storing energy for later use. The diode is used to "block" the electricity going into the solar panel from the battery, otherwise the battery would discharge into the panel during the night or low light levels. The DC to AC inverter is necessary to power AC loads such as lamps or computers.

This panel is perfect for small loads such as charging your cell phone, camera, mp3 player, or anything that requires 5 volts, as well as LED (light-emitting diode) lighting. I have used this same setup for lighting my room with LEDs. It did not output the same amount of luminosity as a compact fluorescent or incandescent, but was satisfyingly enough.

Unfortunately, the panel is not powerful enough to provide enough power for ideal loads, such as your computer. Here is an example with this particular panel:

My ASUS EP121 tablet PC requires 120 volt AC at 1.5 amps. A watt is volts * amps. Therefore, 120 * 1.5 = 180 watts. Let's say I've used it long enough that it requires 3 hours of charging. If the watts and time are multiplied, a watt-hour is obtained. So, 180 watts * 3 hours = 540 Wh, or 0.540 kWh. This is how much energy is required.

Now, a short lesson on electro-chemistry. Because my tablet requires AC for charging, power from the battery will go from the battery through the inverter and to my computer's battery. Through this process the 12 volt DC power from the battery gets converted to 120 volt AC power. Carefully considering the converting process, for every 1 AC amp, 10 DC amps are required. Why? For the battery: 12 volts * 10 amps = 120 watts. For the inverter: 120 volts * 1 amp = 120 watts. This process is very important because of the battery's ability to provide the required amps necessary in the conversion. If the battery cannot supply 10 amps, then the inverter cannot supply 1 amp of AC.

Since 180 watts are required to charge my tablet, an approximately 15 DC amps from the battery are required to provide the 1.5 AC amps. The battery would also be required to provide that amperage for the 3 hours.

Because the battery is small (about 5 or 7 amp-hours) the capacity of the battery cannot provide the total needed amps. Therefore, the computer cannot be charged with this particular system—it needs a larger battery bank.

Here is a website that gives a lot of information about lead acid batteries and will also give you a better understanding of how batteries work: http://www.vonwentzel.net/Battery/00.Glossary/

As mentioned, a large enough battery bank would provide the needed power; then again, the small panel would take days to charge the batteries to max.

All in all, this project was extremely fun, informative, and educational. I would love to build another sometime again. If you're interested in building your own, here are a few links to get you started: