Thursday, March 22, 2012

Here Comes the Sun

The guts of the system (plus some load)
Solar panels, I’ve been told, now cost about half of what they did a year ago. And it’s true — for less than $200, you can build a charging station for your mobile gadgets from off the shelf parts. Just add one sunny window, or take it with you on camping trips to run lights and a radio.

I bought most of the pieces for my system at Amazon and a local auto parts store. Here’s a list of similar items (links go through my affiliate account, so I’ll get a few cents if you buy them through the links). Prices shown were current at the time I typed this in. More about these items below.

Stuff you need:
Left to right: solar panel +/-, battery +/-, load +/-
The heart of the system, obviously, is the charge controller. The controller that comes with the solar panel is a dirt-cheap single-chip design, and is good for 3A at 12V — sized perfectly for one 30W panel. I was expecting the controller to simply provide regulated voltage, and was planning to hack a UPS I had laying around. But when I looked at the instructions, I found that it has a built-in charger circuit, and you just have to attach a 12V battery using the furnished alligator clip leads. Sweet!

The solar panel itself is pretty basic. It has an aluminum frame and a power cable coming out the back. You should cover the leads and the panel itself until you have things hooked up — bare wires touching metal on a bright day can make an impressive spark! (How do I know this?) There are optimum positions for solar panels, but hanging it in a south-facing window (preferably not shaded) is sufficient. It will produce power from dawn to dusk.

Speaking of the battery, you want an appropriate size. Too big, and you spend a lot of money for no gain. Too small, and you’ll be out of juice too soon at night. Since the USB charger I have is rated for 1A, and most gadgets only take a couple hours to fully charge, anything between 8Ah and 12Ah should work very well. Unless you’re only using the system outdoors (like on a camping trip), or installing the battery in a ventilated basement, always use a sealed lead-acid (SLA) battery for this system. Car batteries vent hydrogen gas, which could cause havoc inside your house.

If you’re willing to hack your car charger, you can skip the auxiliary power outlet (also called a cigarette lighter socket). On the other hand, it does provide a clean way to disconnect the car charger if you need to break the system down (like if you’re moving it around). Car chargers are also fused, which provides some protection if you overload it or short it out.

Finally, the power delivery. I personally wouldn’t fool with a USB car charger that isn’t capable of delivering 1A or more — large tablets (like an iPad) won’t charge with anything less, and you want to have some juice left over for your other gadgets. A charger that provides one or two USB jacks and two or three cigarette lighter sockets is a good way to go: the lighter sockets provide a convenient way to plug in your cellphone car charger, and you could run a fan during the day while the solar panel is holding up the battery.

The nice thing about this setup is, the only tool you need is a small Phillips screwdriver. Attach the battery (using the clip leads, don’t forget that red is positive!), then the solar panel, then the auxiliary socket. Plug in the car charger, then plug in your gadgets.

Now this, of course, is just the gateway drug. Eventually, I hope to upsize the system to provide enough power to run the laptop and the network (DSL/router) gadgetry, along with a few emergency lights. I think 100W should be sufficient, but prices continue to come down… and the wife would be thrilled if it could run the TV and DVD player…


  1. Thanks for blogging about this. I was really interested when you mentioned it to know how it all went together.

  2. Now we're in trouble, both of us are interested.

  3. Andi, I was amazed how easily it went together. Almost all of it plugs together, just four screw terminals to deal with.

    Jim, that actually sounds good — no fighting over whether to do it!


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