Introduction
Below are instructions to assemble a seven-panel solar array capable of producing ~3.5v @ 400ma. It is designed to be a lightweight, durable structure to house a WSPR radio transmitter and GPS package.
Design objectives are:
- Lightweight
- Weather resistant
- Capable of high-altitude flight
- Integrated electronics package located on the panel
- Capable of producing 3.5v @ 400ma using lightweight polycrystalline silicon solar cells
The size of the array is 10cm x 12.2cm. It holds seven 19mm x 52mm polycrystalline silicon solar cells wired in series. Each cell is rated at 0.5v @400ma, producing a total of 3.5v @ 400ma. In the center is space to hold the electronics package and antenna connections.
Bill of Materials
The parts used to build the array are listed below with links to suppliers and the cost in US dollars as of September 2022.
| Description | Qty. | Link | Estimated Cost (US$) |
| Fiberglass tape good from -100 to 500 C | 2” | https://www.mcmaster.com/7574A11/ | $14.36 |
| 0.5V 400mA Solar Panel | 7+ | Amazon.com: AOSHIKE 100pcs 0.5V 400mA Micro Mini Solar Cell for Solar Panels 52mmx 19mm/2‘’x0.75” Polycrystalline Silicon Photovoltaic Solar Cells | $15.99 |
| Loctite Power Grab All Purpose Glue | .5oz | Amazon.com: Loctite 2029846 6OZ SQZ TB PG Adhesive, Single,White | $5.48 |
| Hefty Soak Proof Plates – 8.875″ | 1 | Hefty Everyday Soak Proof Disposable Plates – 45ct: Target | $1.99 |
| 30 AWG Wire Wrapping Wire | ~60cm | Treedix 5pcs 164ft Copper Hookup Wire Kit Wrapping 30AWG Cable Jumper Wire Solid Core Tinned Copper Wrapping Wire 5 Color | $13.99 |
| Solder Paste — OR — | .25oz | Chip Quick T3 Solder Paste No Clean Lead-Free in 5cc Syringe – Micro Center | $16.99 |
| Solder, 21 ga | 1 | MG Chemicals – 4901-227G Sn99 No Clean Lead-Free Solder, 0.032″ Diameter, 1/2 lb. Spool | $27.50 |
| Flux Pen | 1 | MG Chemicals 836-P No Clean Flux Pen, 10ml | $7.99 |
Tools
Recommended tools include:
- Solder gun or station (40w)
- Medium, flat tip (~3 – 4mm)
- Tip cleaner
- Heat resistant work surface
- Needle nose plyers
- Wire cutters
- Wire stripper
- Hobby (X-ACTO) knife with new blade
- T-Pin (or large sewing needle)
- Metal ruler (6” minimum; 12” recommended)
- Toothpick to apply glue
- Clear tape or spray tack to attach template to plate
- Optional – Scissors
- Optional – Magnifier light
- Optional – Soldering helping hands
Build Overview
Experienced builders or those don’t like to read lots of detailed instructions can refer to this summary. Here we cover the major build steps in sequence. You can apply your personal building techniques and use the detail steps for reference.
It is recommended to review the Build Details before starting.
1. Cut Out Frame
Use the pattern to cut out the frame with the hobby knife from the middle of a 8.825” foam plate. The area under to solar panels are removed to provide space for the wiring.
Use the T-pin to mark the corners of each solar panel and the four harness holes at the corners.
2. Wire and Glue Panels
Starting with panel one, solder the negative (top) lead with 10cm of wire. This is the negative lead connecting to the electronics package. Thread the wire through the frame to protect the solar panel.
Wire and attach panels using the following process:
- Solder the negative (top) wire to the solar panel
- Glue the panel to the frame using the corner holes for reference
- Cut the positive (bottom) wire to length
- Solder the positive wire to the panel
3. Check Voltage
Check and clean all solder joints.
Place the array in bright light and measure the voltage across the power leads. It should read between 3.0 – 3.5v indoors and 3.5+ in bright sunlight.
4. Attach Harness Support
Cut four 8mm x 17mm strips of fiberglass tape. Place on strip over each corner and folder under, covering the top and bottom of the corner and harness hole. Use the T-pin to open the harness hole covered by the tape.
5. Attach Tracker and Balloon Harness
Review the final assembly. Examine panels for cracks. Attach the electronics package and balloon harness.
Build Detail
1. Cut Out Frame
Print the template below. The right side is a high-contrast template used to make the frame. Cut out the right-side template about ¼” outside the rectangle.
Place the template on the inside center of an 8.825” foam plate. Center the template so the curve of the plate is equal in all four corners.
Put tape around the entire edge of the template. Before cutting the template out it may help to cut around the template, eliminating the curve of the plate.
Using the metal ruler and a sharp hobby knife carefully cut the outside of the template. Several light cuts are better than one or two heavy cuts. Heavy cuts cause the foam on the bottom to bunch up and result in rough edges.
After each side is cut, apply tape from the top to bottom, holding the template in place. This keeps the template in place while the remaining sides are cut.
2. Insert Panel Markers
Use the T-pin, to mark the corners of each solar panel and the four harness connections on the corners. These marks will be used later to position the panels in the correct location.
3. Remove Panel Cutouts
The foam under each panel is be removed to make it easier to solder the positive side of the panels and allow them to lay flat on the frame when glued.
Use the metal ruler and hobby knife to cut the inside of each panel marker. Try not to cut beyond the edges at the corners. This can weaken the frame and make it difficult to attach the panels.
The wide lines outlining the holes are where the solar panel will overlap the frame.
When completed the frame should look like this.
4. Remove Template
Remove the template by cutting the paper between the solar panels along the edge. Bend the paper over the edge and peel the tape off the bottom without damaging the frame.
5. Frame Layout
This picture shows the solar panel numbers and wire routes. Use this reference when wiring and gluing the solar panels. Symbols in the picture are:
Note the wires between panels 3 and 4 and between 6 and 7 cross from top to bottom half-way between the panels.
6. Cutting Wire to Size
Wires connecting the panels are bare. Only the leads to the package are insulated to identify their polarity.
Stripping 32 ga wire can result in broken wire. Use the correct size wire cutters or are very careful. It may be easier to strip longer lengths of wire, then cut to size.
| Number | Length | From | To |
| 1 | 10 cm | Panel 1 top | Negative lead |
| 2 | 3 cm | Panel 2 top | Panel 1 bottom |
| 3 | 6 cm | Panel 3 top | Panel 2 bottom |
| 4 | 8 cm | Panel 4 top | Panel 3 bottom |
| 5 | 6 cm | Panel 5 top | Panel 4 bottom |
| 6 | 6 cm | Panel 6 top | Panel 5 bottom |
| 7 | 8 cm | Panel 7 top | Panel 6 bottom |
| Pos | 12 cm | Panel 7 bottom | Positive lead |
Wire lengths listed are longer than needed for ease of handling.
7. Soldering Solar Panels
The most challenging part of the build is soldering the wires to the solar panels. The panels are very thin and fragile. They must be handled carefully. Lay out your workspace to ensure they are protected but can be easily picked up. Use extra foam to lay the panels on.
Plan on using about 10 – 12 panels on your first build. Broken panels can be used to practice soldering.
Use the wire lengths above and the layout information in 5. Frame Layout. Mark off each wire connection and panel when completed.
7.1 Apply Solder Paste
Start with the top/blue/negative side first.
Refer to 5. Frame Layout to determine which direction the wire should go. For negative (top) panels this generally does not matter, since this will be the first connection on the panel. On some panels one of the top solder pads may be longer or wider. Use the longer or wider side for the connection. In the Negative Side picture, the right solder pad is slightly longer than the left.
Apply solder paste using the needle tip. Start at the edge and work in for about 5mm. The paste should stay within the pad and be about 1.0 – 1.5mm thick.
7.2 Solder Top Connection
Carefully place the wire in the solder paste and do not move it. Use helping hands or other options to keep the wire in place. Keep the solar panel flat on a heat resistant surface when soldering to avoid the risk of breaking it.
Use a 3 – 4 mm flat solder tip. The larger size retains heat better when soldering. The process is fast using a light touch so heat retention makes a difference.
With a hot, clean solder tip lightly touch the wire and paste. Start at the center of the panel and move to the edge. This helps keep solder at the edge of the panel where it connects to the wire. The soldering process should take about ½ second.
Examine the connection under a magnifying glass. If touch ups are needed, avoid adding more paste and always keep the solder tip moving when in contact with the paste.
7.3 Mark Hole for Wire
Gently place the panel in its location on the frame. Use the corner holes as reference markers. Make sure the wire is orientated in the proper direction. Use the T-pin to make a hole for the wire to pass to the bottom. Except for panels 3, 4 and 7, the hole is about 2 mm away from the center edge of the panel.
Panel 3’s through hole is off center and should be in the middle, between panels 1 and 2. See Close-up of Panels 1,2 and 3. Panels 4 and 7 connections run the length of the panel and their hole is located between the panels they connect to.
7.4 Glue Panel to Frame
Place the solar panel on a flat surface, gray side facing up. Be careful not to press on the panel because the wire raises the center from the surface.
Using a toothpick or T-pin apply a thin layer of glue around the edge of the panel. Only apply glue 2mm from the edge. This is the width of the frame overlap under the panel. Very little glue is needed to hold the panel in place.
Use the wire to lift the panel and prepare it to be placed on the frame. Slide the wire into the hole, then gently put the panel in place, using the reference holes for guidance. Do not press the panel in place – you will break it.
Verify the panel is aligned on the frame. If necessary, very gently nudge the panel. Once you are satisfied the panel is located where it should be, very gently press the top of the panel and bottom of the frame together with your fingers. Only press the edge of the panel where it overlaps the frame (~2mm).
If the panel cracks, remove it before the glue dries. Press up from the bottom center then move to the side. If the panel breaks into pieces, handle them carefully since the edges can be sharp. Slide the hobby knife along the top between the panel and the frame. Press up with the knife on the panel so you do not cut into the frame.
Soldered connections are shown for panels 1, 2 and 3. Note the offset hole placement for panel 3 on the right.
7.5 Route the Wire
Route the wire to the next panel using your fingers or needle nose plyers. Be careful not to put stress on the solder connection and risk breaking the panel. Refer to 5. Frame Layout for wire routing between panels.
Route the wire to the center of the bottom solder pad. Allow about 5mm of contact with the pad and cut the remainder of the wire.
Place the wire so it contacts the solder pad on its own.
7.6 Apply Solder Paste and Solder
Apply solder paste to the center bottom of the solar cell for the length the wire contacts the pad. Paste should be about 1 – 1.5mm thick.
With a hot, clean solder tip lightly touch the wire and paste. Start at end farthest from the wire and move toward it. This helps keep solder where it connects to the wire. Be careful not to touch the frame. The soldering process should take about ½ second.
Examine the connection under a magnifying glass. If touch ups are needed, avoid adding more paste and always keep the solder tip moving when in contact with the paste.
7.7 Solder Remaining Panels
Repeat steps 7.1 through 7.6 for each remaining panel. When routing wires on the bottom, be sure to flip the orientation of 5. Frame Layout because the frame will be upside down compared to the layout.
The bottom wire from panel 7 is the positive lead to the package. Route in along the bottom to a point close to the negative lead already in place.
Pictures of the completed top and bottom sides are below.
7.8 Add Harness Reinforcements
Cut four pieces of fiberglass tape approximately 8mm by 17mm. Place each piece in a corner next to the edge of the solar panel and covering the harness hole. Press the tape into place and fold underneath. Press both sides to seal the tape to the frame.
Repeat for the remaining corners.
Use a T-pin reopen the harness hole covered by the tape.
7.9 Clean and Test
Clean the solder joints with alcohol or solder cleaner. Very gently clean the connections with a cotton swap. Always support the other side of the connection when cleaning or testing.
Using a voltmeter put the array in bright light. The array should read 3.0v to 3.5v indoors and 3.5+v in bright sunlight.
Troubleshooting
Broken Panels
Removing broken panels is part of the process. Using care and a few general guidelines will help you to quickly replace broken panels. The most important thing to remember is to minimize damage to the frame when removing panels.
1. Unsolder the Connections
Follow the same process to connect the wires. Use a hot, clean solder tip to melt the solder and pry the wire free. Sometimes you can bend the wire to put a small amount of pressure on it so that it will move clear by itself once the paste is heated.
Be careful not to over-heat the wire or panel to avoid damage to the frame. The wire heats quickly and can melt the frame with 1 – 2 seconds of heat applied to it.
2. Remove Broken Panel
Use a new, sharp hobby knife to pry between the frame and the panel. Try to cut up into the panel to avoid damage to the foam frame. Breaking the panel can provide the opportunity to work from both directions. Remember the broken pieces may be sharp, so be careful.
3. Replace Panel
Using the steps above to solder the connections and glue the panel in place.
Depending on the location of the broken panel, you may be able place the solar panel on top of a thin coffee coaster or other heat resistant surface to solder the top connection. (I use old 4” tile squares.) Glue the panel in place and solder the bottom connection.
8.2 No Voltage
If after the standard checks on your voltmeter (e.g., correct DC voltage range set, good battery, leads not reversed, etc.) you still do not get a voltage reading in bright sunlight, then most likely there is a broken panel or a bad solder connection.
Examine the panels for cracks. It’s helpful to gently rub one side to the panel with a cotton swab dipped in alcohol. This highlights the cracks and you may see seepage on the other side.
If the panels are ok, then it may be a lose connection. The best way to proceed is start with panel 1. In bright sunlight, read the voltage between the negative lead and the top of panel 2. This is the voltage across panel 1. It should read ~.5v
If it does not, check the solder connections on the top and bottom of panel 1. Gently pull on the wires to see if one comes lose.
Continue checking from the negative connection to panels 3 through 7. Each panel should increase the voltage by ~.5v
Northern Illinois Bottlecap Balloon Brigade 