The solar power box

I finally got around to completing a project I got started on months ago, and I’m pretty happy with the way it turned out.

I am a huge fan of alternative energy, especially solar and wind power. I think that in the future, these technologies will be affordable enough that everyone that has the spare roof space for panels or land to put up windmills will be able to get enough clean energy to power their every day lives. Given enough future improvements in battery technology, even cloudy and windless days here and there won’t be enough to cause much of a concern.

I wanted to be able to take a setup camping with me that could charge multiple cellphones in a reasonable amount of time, and have some spare capacity to be able to charge walkie-talkies, mobile ham gear, or even the batteries that we’re using in flashlights. For this task, I needed a bit more than the hand held portable solar chargers you see cheaply available on the market.

One day I walked into a West Marine store, and happened upon a set of 3 – 20W, weatherproofed, amorphous silicon solar panels (see here for a description of the different types of panels). These panels were on clearance and were being replaced with newer technology, but they were packaged very nicely with all sorts of different connectors as well as the ability to easily daisy chain the panels together by design.

You can see one of the panels below. I put an american quarter dollar on it to give some sense of scale. The panels are about 3ft (1m) long and about 1/3 as wide.


This single panel puts out 20 watts of power and enough voltage to charge a 12v lead acid battery of decent capacity. I decided that I wanted this setup to be portable so I opted out of a deep cycle marine battery for this application. Though consumer marine batteries have very good energy capacity (measured in amp hours), they are very bulky and heavy. I didn’t want this setup to be a large burden to lug around. The size of the panel makes it a bit cumbersome already, so adding 30 lbs of battery weight didn’t fit my idea of making this a portable setup.

Instead, I decided to purchase a couple sealed lead acid batteries like the ones that you can find in popular uninterruptible power supplies. The ones I purchased have a 7 amp hour capacity. I wired two of them together in parallel to offer 14 ah of capacity and a 12v output.

I had the batteries and the panel set up for a few months just sitting in the window with no case or anything enclosing any of it. It was just a hodge-podge of wires and looked like a science project. I knew I wanted something I could carry, so I tried attaching the panel and batteries to a cheap plastic rifle case with no luck. Since that failed, it was on to actually making a box out of wood. I enlisted the help of my father-in-law and my uncle and we came up with a pretty decent setup!


Here you can see the inside of the box with three 12v cigarette lighter style plugs. The first one on the left takes the input from the panel which they nicely supplied with a male plug end for just this use. The other two on the right are for whatever we want to plug into this thing. Currently the next time we go camping and deploy this box, I plan to bring a 120v inverter and a USB charging adaptor.

The large size of the box is so that the solar panel can sit on the top and carried along with the setup. Then when on-site, the panel can be detached and moved anywhere within about 8 ft of the box. You’ll note the batteries are wired up together with detachable cables and I’m using ground bars as bus bars for the positive and negative power feeds from the batteries. This makes everything on the inside a bit cleaner. The batteries can be detached by opening a latch and swinging that piece of wood out from above them.

In the picture below you can see the finished product charging an iPhone using the power of the sun!


Solar power appeals to me on multiple levels. This is not the first project that I’ve done using solar panels and lead acid batteries. In fact I completed a much larger one last year that I have a draft post just waiting to get finished here on wordpress. I guess I’ll have to try to get this up soon in between some of the other geek stuff!

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