In this instructable I will show how I built a 90Wp (watt peak) 'portable' solar panel. It weighs 14kg, It has a deployed size of around 900mmx900mm (3'x3') and folds in half for transport. It has ports to power or charge USB devices, 12V car cigarette lighter devices and 12V lead batteries. Devices can also be wired straight to the panel. It has epoxy encapsulated cells, meaning that the vulnerable part (the cells) are completely protected from the surroundings and any water. It costs around €200 to make.
You might ask, why? I got stuck with a batch of solar cells. I didn't really have anything I could do with them, so I tried to create something with it. The Portable solar panel I created has more power than most comparable panels and is cheaper to make. It may be a bit heavier and bulky, but I works and serves me great.
Step 1: Gathering Materials and Tools
Before you can start, you will need some materials. You don't need a 1 on 1 match, it all really depends on what you can get. This instructable describes how to make a panel in general. You can also make a panel completely different to mine, making it smaller or larger.
Materials I used:
- Extra clear tempered glass panels, 4mm thick 440mm by 825mm;
- Clear UV resistant epoxy resin, 1.6kg was just enough ;
- Clear silicone caulk;
- Wood (44mmx33mm and 27mmx18mm);
- Tape (I used kapton tape, not the tape shown in the picture);
- Monocrystaline 125mmx125mm 2.5Wp solar cells (36x (initially 40));
- Tabbing wire;
- Bus wire;
- Flux pen;
- Solar charge controller;
- 5V DC-DC converters;
- USB ports;
- a variable DC-DC converter (used for 12V);
- 12V car connector block;
- Wood primer;
- White paint;
- Aluminium corner strip;
Tools I used:
- A radial saw;
- A table saw;
- A router with rounding bit;
- Soldering Iron;
- Caulk gun;
Step 2: Making the Frame
For this step you will be using different electric saws, If you do not know what you are doing, find someone who does know. Especially the table saw is extra dangerous since the guard needs to be removed. I am in no way responsible for anything you do to basically anything.
Use common sense.
The frame is made from 69x33mm timber. I used 44mmx33mm timber and 27mmx18mm, but I had too little height and added a band around the frame to add height. Two equal square frames need to be cut that slightly (10-15mm) overlap the glass. Then the guard is removed from a table saw and the saw is lowered to the amount the glass panes overlap plus some extra. Very Super Extra carefully cut out a band of wood from inside of the frame in every piece (on the 33mm side). Then adjust the saw so it will leave 15mm on the 69mm side and cut the band loose. The hole this leaves will be used to seat the glass in. Test the fit before assembling the frame. Stack both frames on top of each other to see how symmetric they are. This is important when the hinges are fitted.
Cut out a 30cm long piece around 3cm deep in one of the sides. Be very careful with this, the piece needs to be placed on the opposite frame. This will become the space for the handle and electronics.
Pre-drill, countersink and screw the frame together. Then test the fit of the frame again. If it is satisfactory disassemble the frame and use construction glue on all the edges. Screw the frame together again and let the glue dry. At this point, also place the piece of wood cut for the handle on the opposite frame in such a way that it will fit when the frames are closed.
When the frame is dry, use a plain router to make a nice round edge on all the outside. This is more for aesthetic purposes than functional ones. When all is done, fit the hinges on the frame on the side of the handle.
Step 3: Painting the Frame
Painting the frame will protect the wood from water. First use a primer. I was impatient, so I used spray primer. If you want better results, use normal wood paint primer.
I used the paint I could find, so I picked white. In retrospect, I would probably have stained the wood to keep it more natural, but I like it enough and I am not changing it now. Use several coats of paint and sand between layers to get a nice finish.
Step 4: Assembling the Solar Cells
The cells only produce 0.5V each, so the cells need to be wired in series. If you have as many cells as you are going to need (like I had) you will need to be extra careful when handling the cells. The package says that the cells are as fragile as egg shells and when handling these cells, you will discover that this is actually an understatement. They are extremely brittle and flex only a little. Because I wanted to handle the cells as little as possible, I soldered the directly on the glass panel. This way I don't need to move them to the glass when I am done. A drawback of this is that the glass is a giant heatsink, so the cells do receive some more stress from temperature differences.
First cut tab wires (the thin metal strips) to the length of 1 top cell and 1 bottom cell (around 2 cells lengths minus 1cm). In case of 36 cells with 2 tab lines, you will need 60 long tab wires (5/6x36x2). You will also need 12 short (1 cell plus 4cm) tab wires (1/6x36x2).
Use flux on the tabbing lines (the thick white lines) on top of the cells and use a very hot soldering iron to solder the tabbing wires on top of the cells. I found that a hotter soldering iron worked better, even though you want to have as little heat as possible in the cells. A hotter iron transfers its heat faster and will make you be able to solder faster. Start on one edge, place your soldering iron on the tab until you see the tin melt and move the iron over the length of the tab. You should always have a small pool of molten tin in front of the iron. This molten tin will move over the tab like wave. Doing it right the first time is easiest. Fixing it later takes a lot of time.
30 of the cells should receive long wires. 6 of them should get the short ones. The cells with the short wires will be at the end of each row.
When all cells have tabbing wires on the front, tape the cells on the glass. At this point, I taped them directly to the glass, but I advice you to use tape to make a small spacer between the glass and cells. Else the air will not escape when encapsulating. The tabbing wires should go from the front of each cell to the back of the next cell.
Flux the metal parts of the back of the cell and pre-tin the 8 metal tabs with a tiny bit of normal soldering tin. This step shouldn't be necessary, but I found the normal connection to be too unreliable. Then solder the tabs to the pre-tinned spots on the back of the cell.
Use bus wires (the thick metal strips) to connect each row of cells to each other in series. Make sure the end of the bus wire is long enough to stick out of the encapsulation. Tap everything that can pull on the cells down. Bend the positive and negative bus wires up so there is something to solder to when the panel is encapsulated.
Step 5: Placing the Glass
Lay the frame as flat as possible. If the frame has a kink in it at this point, this will be glued in place.
Apply a generous amount of silicone caulk around the entire edge. If you use too little the epoxy will drain past the glass. Place the glass in the middle of the frame and push all the edges to make a good seal. Apply extra silicone where there might be too little.
use water with dishwash liquid and your finger (and a lot of paper) to smooth the silicone joint. Not only does this make the silicone joint look nicer, it will also make the joint seal better. Be SUPER careful here not to get the cells wet. I got a few drops of water on the cells, it took me an hour with a hair-dryer to get the water out of the cells again.
Let the silicone dry before proceeding to the next step.
Step 6: Encapsulating the Cells
For this step, use plenty of plastic and paper. If epoxy does leak, it is very important that it doesn't get on something you like. It will never leave again.
Before casting, make sure that the bus wires will stick out of the encapsulation. You do not want to dig these out when they are cast in.
To cast you will need a layer thick enough to cover your cells. In my case the panels are 44cmx82.5cm (converted to cm for calculation reasons). We are assuming here that epoxy weighs 1kg per liter. the best amount I can get is 1.6kg. This gives me a layer about 2.5mm. This was enough to encapsulate a panel.
Carefully pour the 2 components of the epoxy together in the proportion stated on the bottle and stir for a few minutes (but not too aggressive, bubbles are our enemy). Then pour with a little stream from high on one corner or edge of the panel and let the epoxy slowly creep to one side. When the epoxy has stopped flowing, or it has reached the other side. Tilt the panel a few times from side to side to spread out the epoxy.
You will have a tiny gap between the glass and cells. I didn't. I have air gaps in the encapsulation. While this is not harmful, it does look sloppy. You pour from the side to give the air time to escape, and the tiny gap created by the tape spacer helps with this.
Lay the panel perfectly flat and cover the epoxy (but do not touch it). Let the panel dry for at least a day.
Step 7: Adding Electronics
With the frame assembled and the glass encapsulated, the panel can be fitted with all electronics. I myself right now do not have a lead battery, so I will wire everything to the same port. When a battery is used, I will reconnect all wires the way the schematic is right here.
There are a few parts on the panel. The 5V converters allow usb devices such as smartphones and Arduinos to be powered and charged from the panel. The 12V connectors can be used to power everything that would be powered from a car's cigarette lighter (such as my LiPo charger)
Find a nice spot for the charge controller and mount it. I had no wood to mount it on, so I used a few brackets and a spare piece of wood to create space.
Wiring and Diodes
The first thing to do is to wire the panel. Use at least 0,75mm^2 wires if you have 5A like I do. Measure the bus tabs and solder wires long enough to reach the charge controller. On the side with no charge controller, use pieces of flexible wire to bridge the folding part. At this stage also solder in the diodes. These diodes will bypass the electricity if one panel is not producing, but the other is. This way you could also charge stuff with only one side of the panel in the sun. Tape all wires down with tape.
Because I don't have a battery, I have to make my own 12V. I used a DC-DC converter I had from the turret to create the 12V from the 20V that comes from the panel. It provides 6A max, and it is actually set for 13.5V, so the max power capable of coming from the 12V connectors is 80W. This is enough for my 50W LiPo charger and maybe even a small 12V fridge.
I got a 12V splitter for use in a car to get my 3 connectors. I simply cut of the connector and wired it to the DC-DC converter.
There are 2 (initially 3) 5V DC-DC converters on the panel. These are wired to usb ports soldered on a piece of experimental circuit board in such a way that there is 1 converter for every 2 usb ports. The DC-DC converters are 5V 3A and can convert from up to 22V, just enough for the raw panel voltage. Be very aware that this stuff falls under Chinese quality control. The stickers were the wrong way around half of the time. Look at the color of the wire to determine what is the input and output.
Step 8: Handle of Holding
I wanted to have a handle to easily move the panel. This handle needs to fit between the 2 pieces of wood when the panel opens, so I used a nylon band I had laying around.
Cut a piece of nylon the length you want to have the handle + 12cm. Fold over both edges 5 cm and use a soldering iron to melt 4 holes through each side. These holes need to be large enough to fit the screws.
Then use screws the thickness of the wood underneath and fender washers to screw the handle to the frame. Carefully increase the weight on the handle to make sure it is strong enough to hold the panel. Then shake the panel a few times with something soft under the panel to make sure it is strong enough.
Step 9: Finishing Touches
Home stretch, it is time for finishing touches.
First the edge the solar panel will stand on needs to be reinforced. When it is deployed in grass, no pressure will be on the frame, but when it is deployed on concrete or tiles, the edge might damage. To prevent this, an aluminium strip is added to the bottom. Holes are drilled through the aluminium and small screws are used to secure it in place.
Catchbolts will hold the panel shut when in transport. The hooks are attached to one side of the frame, the bolts are mounted to the other side. Test fit the bolts first to see if they provide enough pressure to hold the frame shut. I had to cut a piece of the hooks to make them fit better.
The legs at the back are used to adjust the inclination of the panel. The legs are made from spare pieces of wood. 4mm holes need to be drilled through the frame and M4 bolts are sunk in the frame. The legs are secured with M4 selflocking nuts. The legs are just short enough to fit in the frame. This way they can stand the frame up almost straight.
Step 10: Profit?
Now lug the panel to where you need it, fold it open, aim and use the sun to power whatever you need. I mostly use it to power my charging equipment for my model flying, but I have also had people asking me if they could borrow it for camps, to power the fridge and charge the cellphones.
The €200,- might be quite spendy if you compare it to a stationary panel (where €200 can but you a 240Wp panel), but for a portable 90Wp panel, €200 is incredibly cheap (for instance, 60Wp portable will cost over €300,-)
Step 11: Future Improvements
The panel is far from perfect, It has some issues that I would not dare to keep from you. Hopefully someone can learn from my mistakes.
- There are bubbles in the encapsulation. Encapsulation is a permanent process, once it starts, you can't stop it. When casting I immediately realized that the bubbles would not be escaping. I tried my best to keep them as small as possible, but there are quite a few prominent bubbles visible. If I ever were to make another panel in the future, I would increase the space between the cells and the glass, at least while casting, so all the bubbles can escape.
- 'Portable'. The keyword for this panel. It is quite weatherproof, The cells are so watertight that you can basically throw the panel in the water, take it out and produce power and it is rugged enough to be moved. Why the quotation marks you might ask? It is very heavy. 14kg heavy. Manageable, but heavy. Over half of this comes from the glass, the rest comes from the epoxy, frame and miscellaneous junk.
- The glass right now is unprotected. I planned on making covers for the glass, that could be shut when the panel is travelling, but I never had the materials handy to do so. For now this will be fine, but when the panel starts to travel more often, I might revisit this one and add the covers.