Solar-powered Pop-up Paper House

So... Hi! It's Alvin here with his first instructable : ) 
This instructable is on a small project on making a solar powered pop-up paper house. The paper house will convert the light it receives into energy for its interior lighting, lighting up the LEDs inside the house. At the end of this instructable, you will be able to make this very simple little paper toy perfect as a decoration just sitting in your room or as a gift sent to a friend in the form of a pop-up card.

So, here are this material used. By material, I am referring to the things that will go onto the paper house. 

• Pop-up paper house cut out from a 190gsm paper (you may download the pattern in the next step)
• 2 LED, flat and bright models preferred (I used 1 Red and 1 Blue LED)
• 14 pieces of 52mm x 6mm small solar cells 
• Some conductive ink
• Some instant glue
• Some copper tape
• Elmer's glue

As for the beloved tools... 

• Pen cutter
• Forceps
• Random metal rod

Theses are pretty much all the tools you need. Within all these tools, only the pen cutter is truly needed. You may forget the forceps if you think you have nice hands and you can throw away the random metal rod and replace it with a toothpick. 

So, to start with, let's prepare the paper cutout.

The first image is the very simple paper pattern needed in this project. I have the paper pattern prepared by pepakura designer 3, a very handy software for preparing paper pattern. Although it's not a free soft, they offer a free viewer that can display and print their special .pdo files.

For this paper house, you can just download the .jpg file and have the pattern printed onto a thick A4 sheet (around 190 gsm). There are two house in one sheet just in case anything bad happens when you cut out the pattern.

Pay closer attention to the second photo and you will see that one window was not cut out. That window was left there in order to make the inside of the house darker, creating a better contrast when the light is up. Instructions on how the holes on the two roofs are cut out will be found in step 4. 

A dummy house shows how the lower layer of the roof is connected to the house's wall, as well as how the house is flattened. The missing upper roof will be glued onto the trapezoidal flat region of the lower roof later on but, don't do that now as we will still need to do some circuit connection on the roofs first. 

After having an idea of how the house is to be folded, you can now use the pen cutter to create the fold lines along the dotted lines by carefully cutting just a very thin surface layer of the thick paper. This scribing action will aid forming the house's shape as you pops it up from a flat pattern. Note that if you wanna do a mountain fold, you scribe the upper surface of the paper. and if you wanna do a valley fold, you scribe the back side of the paper.  In this model, only two lines on the lower roof and one line at the door need to be scribed underneath. All other lines are scribed on its upper surface.

The solar panel is what powers the LED inside the house. With each solar cell giving out 0.55 volt max, 7 solar cells in series will give out 3.85 V max. Yet, since only the bottom sides of the first and last solar cell are connected in this connection method, only 6 out of 7 cells are used to power the LEDs. The first cell acts as a dummy cell that gives out no power. The maximum voltage is thus just 3.3 V. One addition more cell will make the LED brighter if you LED can take the extra current but I didn't do so because one extra cell will make a panel too large for this roof.

To connect the solar cells in series, I connect successively the bottom side of a cell to the top side of the other. Solar cells are not that good a conductor. To aid the current flow, bus bar, the more conductive white region on the solar cell, is printed onto the cells. That is why you can see that I am only applying the conductive ink onto the bus bar. After applying 2 dots of instant glue onto the cell edge and a dot of conductive ink onto the edge of the bus bar, I placed the second solar cell onto the first with a 1mm overlapping. Repeat this for 5 more times and you will get a panel consists of 7 cells. Note that the more you overlap, the less of the cell is exposed to sunlight and thus the less current you can get from the cell.

Before I put the panel onto my paper house, I measured its current under a light just to see if all connections are good. My panel gives 80 something mA when not shaded by my fingers but you can still see 57.6 mA when I took the photo with my other hand.

Don't worry too much if the current reads zero. It may only be caused by a bad connection or two. If this happens, identify the bad connection with an aid of a multimeter and use a hot air gun to soften that connection. Then, pull the connected cells apart and redo that connection. You may also simply do another panel from the beginning instead, if you prefer so.

After downloading the .pdf pattern, you will find that the hole in the first image cannot be found in the pattern. That is because I am not sure of what kind of LEDs you are using. So, the first step here is to cut out the holes according to the LEDs of your choice. The edge of the first rectangular hole, around 2mm x 3mm,  shall be around 5 mm from from the center fold line. The second hole shall be cut according to the separation between the two legs of an LED.

Now let's cut out the holes on the upper layer of the roof. The holes near the center fold line shall best be aligned with those on the inner layer for ease of connection. Those holes shall drift away from the center fold line for just a bit due to the paper thickness. Then, use the solar panel prepared in the last step to measure the separation between the two holes on the upper layer of the roof. Holes shall be directly under the first and last solar cell. In the photo attached, you can see that there is a shaded region between the 2 holes on one side of the upper roof. That shaded region corresponds to the second hole of the lower layer. You can then cut out a strip of copper tape of around 2-3 mm wide and connect the holes at the sides and at the shaded regions as shown in the photo. This can then be glued onto the lower roof with some random glue. Instant glue will do this just as well but emer's glue will certainly do a better job. 

To connect the LEDs to the solar panel, I first apply some Elmer's onto the upper roof followed by some conductive ink into the hole near the edge. I've done a bad example by applying conductive ink at two holes at the same time since it sticks much better when it is wet. It would be ideal to apply conductive ink just before a connection is made.

Then, position the bottom side of the last solar cell of the solar panel to the conductive ink. Note not to let the ink contact with the back side of other solar cells or you will short the solar cells in contact. Remember to flip over the assembly to ensure good positioning. Additional conductive ink might also be added to make a better connection.

When both panels are connected, I flipped the assembly over and dipped the legs of the 2 LEDs into the pool of conductive ink located at the two holes on the lower roof. The conductive ink in the two holes near the center line goes directly to the bottom of the first cell in the solar panel. It is very important have the LEDs connected in the right polarity. A wrong polarity will just give you a dead LED. If you don't know it already, the bottom side of a solar cell is actually the positive side. If you are sticking the solar panel onto the roof in the same direction as I did, the positive side should be the lower end of the panel.

With the LEDs in places,  a complete circuit is formed. I held it under a light to confirm a working assembly before I glued it onto the rest of the house. This step also completes the assemble of this paper house : )

You are basically done with this paper house in last step. This step is a summary of some optional further steps to take:

• Additional solar cell

Since one cell is a dummy, the voltage supply is not really enough to power up up a blue LED fully when resistant of conductive ink is taken into concern. Since the LED I used can sustain quite a high current, the house will be much brighter if I can add another solar cell and boost voltage up a bit.

• Drifted LED position

The two LED hit each other when the house is flattened. This not just hinder the house from flattening, but stresses the fragile solar panel. If a flatter bright LED could be sourced and the two LEDs are offset from the middle line a bit, the house will lie flatter. This will also light up the house better.

• Encapsulation 

To prevent the fragile solar panel from damage, silicones or 2-part epoxies are nice candidate for encapsulating the solar panel. You may dome the solar panel if you have no intention to flatten the house again. Alternatively, ironing an EVA sheet under a PET sheet will also be a nice encapsulation method that offers some protection to the solar panel. The house may still pops up if you did this carefully.

• Making a pop-up version

This paper pattern was originally designed to be a pop-up house. Although, this version cannot completely flattened due to the LED thickness and the fragile solar panel, sticking a folded card with the fold line aligned to that of the house's floor will make it a semi-pop-up house. The house will lie as flat as the flat LED you can get.


That's it. Hope you enjoy this paper house and my first instructable : )

So, this is a P.S. section in response to a comment asking about how to make the house a pop-up house. 

Basically, all you need is a thick backing paper of around 20cm x 10cm, with a fold line at the middle and little mark right at the center. Then, apply Elmer's glue to the back of the triangle (marked with a blue dot) and align the edge of that triangle to the center point of the backing as shown in the photo. Then, apply glue to the top triangle and close the backing. Before the glue dries completely, try to open the the backing paper to see if the house opens well. You may need to adjust so a bit due to paper's thickness.

You will still need to put the upper roof and the solar panel on before you can get a good looking pop-up house but as mentioned earlier, the thickness of solar panel and the LED makes this a very poor pop-up house. I suggest you to go for either a pop-up house (with no LED and something else replacing the solar panel) or just solar-powered paper house.

Enjoy : )