Solar Shrub

I'm a solar energy advocate, tinkerer, and enthusiast, but let's face it; solar panels are ugly!

Flat, rectangular panels can only be arranged in so many ways and always look industrial, boring, and out of place. So I decided to build a functional, but more aesthetically pleasing version of a USB solar charger.

I call my creation the "Solar Shrub". It's designed to resemble a round-leafed plant in a flower pot, but unlike a real plant, this one can charge my iPod, iPhone, and any other USB chargeable device!

I used eight 1.5 Volt round solar cells (leaves) attached to shrink-wrapped wires and clothes hangers (stems) to create an array capable of producing 5 Volts at about 300mA. I wired two sets of four cells in series (to get the voltage) and then wired the two arrays together in parallel (to get the current). I stabilized the power by building a 5 Volt Regulator circuit, then added an on/off switch, power LED, and female USB connector.

Now you can build one too! Just follow these instructions, then put it in sunlight, flip the toggle switch, and plug in your favorite USB device!

Materials for Power Circuit:

1 - 7805 Voltage Regulator (Radio Shack #276-1770)
1 - Heat sink for the 7805 (Radio Shack #276-1368)
1 - Hea sink mounting hardware(Radio Shack #276-1373)
1 - Red LED(Radio Shack #276-041)
1 - SPST mini toggle switch(Radio Shack #275-0324)
1 - 22uf capacitor(Radio Shack #272-1026)
1 - .01uf capacitor(Radio Shack #272-1065)
1 - 220 ohm resistor(Radio Shack #271-1313)
1 - 4.7k ohm resistor(Radio Shack #271-1124)
1 - 3.3k ohm resistor(Radio Shack #271-1122)
1 - USB extension cable (Male to Female)
1 - Blocking Diode (1N4001)(Radio Shack #276-1101)
1 - Round Proto Board (Radio Shack #276-004)

Materials for Leaves and Stems:

8 - Round solar cells (hacked from solar garden lights) (Lowe's #379421)
8 - Wire clothes hangers
1 - Roll each of red and black 22 AWG wire (Radio Shack #278-1224)
2 - Pkgs of assorted shrink wrap (Radio Shack #278-1610)
10 - Small wire ties
1 -  Can green spray paint

Misc Materials:

1 - 6" Clay Plastic Self-Watering flower pot (Lowe's #285869)
2 - Metal angle brackets
1 - CD
2 - Plastic standoffs(Radio Shack #276-1381)

Tools:

Soldering Iron
Solder
Wire strippers
Side cutters
Dremel

Most USB devices will charge with 5 Volts and ground delivered on the red and black wires of the USB connector. As I learned from Adafruit's wonderful video at (http://www.adafruit.com/blog/2010/08/03/the-mysteries-of-apple-device-charging-video/), Apple devices won't. You have to trick them by providing specific voltages on the other two wires. In this case, I'm sending approximately 2 Volts on the green and yellow data wires.

I used a round proto board to go with the round theme of the project, but you can just as easily use a square, boring board. I also decided to use jumper wires for the switch and LED so I could easily disconnect them from the circuit board after they were mounted to the flower pot. (What a strange sounding sentence.) You could just as easily hard-wire them to the board.

The circuit is a simple one based on the 7805 5 Volt Regulator with supporting components and a voltage divider to supply the 2 Volts mentioned above.

Assembly:

1. Solder the red wire (this will eventually connect to the positive terminal of the cell array) to the circuit board and to one side of a double-pin plug (for the power switch).
2. Solder in another double-pin plug for the LED and attach it to the open pin of the first plug.
3. Solder in the 220 ohm resistor, which connects the LED plug to ground.
4. Solder in the two capacitors. C1 is polarized so be sure to configure it correctly.
5. Solder in the voltage regulator.
6. Solder in the two resistors, which make up the voltage divider circuit.
7. Cut the USB cable about 6-8 inches from the female end and strip away the insulation and shielding
8. Attach the four wires of the USB cable to the circuit board.
9. Attach the black (GND) wire and create a "ground bus" across the back of the circuit board to link all components.
10. Solder jumper wires w/ female connectors to the switch and LED. Remember to slide some shrink wrap onto the wires before soldering. I've found it's really hard to get it on there afterward!
11. Test the circuit. I like to test things as I go along instead of waiting until the thing is all together. So I attached a 9 Volt battery to the red and black wires and tested the circuit with my iPod. Success!!!

The base of the Solar Shrub is, of course, a flower pot. I drilled holes for the switch and LED and cut out a slot for the female USB connector. In order to attach the USB connector to the base, I built a mount using a couple of angle brackets, some double-sided tape, and a tie wrap.  I added 2 holes to the base to accommodate the nuts and bolts that hold the connector into place.

I wanted the electronics to be somewhat protected from the elements so I decided to use a CD as kind of a false floor. I mounted the circuit board (upside down) to the bottom of the CD using plastic standoffs. The red and black wire that connect the circuit board to the solar array pass through the center hole of the CD. I also added felt strips around the base to support the CD.

I drilled two more holes in the CD so I could later mount the leaves and stems to the top of it.

The next step is to extract the solar cells from the garden lights. I found that most solar garden lights at my local retailers had square cells. I had to look around quite a bit to find round ones. I bought these at Lowes for around $3.25 each.

They were pretty easy to disassemble:

1. Remove the battery
2. Take out three screws
3. Cut a few wires
4. Pry the cells loose from underneath.

I did this 8 times, of course.

I tested each cell under load to make sure it provided approximately 1.5 Volts.

I cut various lengths of red and black wire between 6" and 10" and soldered them onto the 8 cells. Then, I slid 3.0mm shrink wrap over the wires and pushed in a length of clothes hanger wire to reinforce the stems. Once I had all 8 stems together, I spray painted them a nice shade of green (being careful to avoid the tops of the cells).

The self-watering flower pot came with a plastic insert that has holes which are spaced out perfectly for the Solar Shrub. So I bent the end of each stem, about an inch from the bottom, to 90 degrees and pushed them through the holes. Then I tie wrapped the hanger ends together to separate and stabilize them.

After I had all of the stems mounted, I wired the cells together in a series-parallel circuit as shown in the schematic. Then, I added a blocking diode to the positive (red) lead. This prevents reverse current through the cells when there is no sun light.

The last steps are to connect the output wires from the solar array to the red and black power leads on the circuit board, mount the plastic insert to the top of the CD (using 6/32 screws and nuts) and then take the Solar Shrub outside for a test.

The stems are rigid enough (thanks to the 22 AWG wire and the clothes hangers) that you can bend them into any arrangement you like. You can also tilt the cells in any direction you wish; toward the sun for example.

As you can see from the final photo below, IT WORKS!!! I'm now able to charge my iPod, iPhone, and other USB powered devices while enjoying the sunshine!