The Solar Bottle Lamp is a solar-powered light that reuses a waste plastic bottle by attaching a 3D-printed solar lamp in place of the old plastic cap. It also makes clever use of the light-refracting properties of water!

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I designed this lamp as a low-cost solution for lighting rural homes, replacing their harmful kerosene lamps and at the same time upcycling some of the millions of waste plastic bottles that are daily thrown into the garbage. These lamps are also great for decorating a garden, for camping or traveling, or for emergencies when the power is out.

A Liter of Light

My design was inspired by the Moser bottle daylight lamp invented by Brazilian mechanic Alfredo Moser. The concept is that clear plastic beverage bottles filled with water can be fixed into the roof of an unlit building to refract sunlight around a room, equivalent to a 40W–60W bulb. In 2011, Illac Diaz used Moser’s technology to start Liter of Light, a grassroots movement to provide solar lighting to communities around the world.

The Moser bottle is simple and inexpensive, but it only works during the daytime. So I designed a solar bottle cap that can provide light during the night.

How the Circuit Works

A

The solar lamp can be considered as a standalone solar photovoltaic (SPV) system and contains four basic components (Figure A):

 Solar panel — converts solar energy to electrical energy

 Controller — charges the battery (charger) and drives the load (driver)

 Battery — stores the electrical energy

 Load (LED) — provides the desired light output

The circuit, shown in Figure B on the following page, can be broadly divided into two parts. The charger circuit extracts power generated by the solar panel during the day and charges the battery. It’s based on a TP4056 single-cell Li-ion charger module. The LED driver circuit powers the LED, automatically switches it on at night, and controls the brightness.

B

During the day, the solar cell generates voltage and turns ON the transistor Q2, so it doesn’t have the current bias to the base of transistor Q1. Q1 is OFF so the LED will go out.

When there is no sunlight, there’s no solar current to base Q2 so it will not conduct, but at the same time, transistor Q1 will conduct. Now the battery’s current will flow to the LED through the resistors (R3 or R4).

The 3-pin button switch is used to connect either R3 or R4 in the LED circuit. When the pole is connected to R3, the brightness is Low (high resistance, low LED current) and when connected to R4, the brightness is High (low resistance, high LED current). You can learn more about the circuit in my video.

YouTube player

Bottled Sunshine

Enjoy your new Solar Bottle Lamp! You can make a few similar bottle lamps and place them around your garden or lawn.

Charge it

• USB charging — Before the first use, it is recommended to charge the battery. You can easily charge the lamp through a micro USB cable by connecting it to any USB power source like a phone charger. The red LED indicates that the battery is charging and the blue LED indicates charging is complete.

• Solar charging — You can also charge the battery by placing the bottle lamp in bright sunlight for at least a day (Figure S).

S

TEST IT

Press the button switch to set the desired brightness (Low/High) and test the lamp by covering the solar cell with your hand. The light should be turned on (Figure T)!

T

Place the bottle lamp in the bright sunlight, and the solar cell will charge the battery. When the sun goes down, the lamp will be automatically switched on (Figure U).

U

MODIFY IT

• Weatherproofing — You can apply epoxy spray paint at the joint of the 3D-printed enclosure to make it more water resistant. Apply conformal coating to the PCB to protect the board and its components from the environment and corrosion.

• Easier build — Use a PVC-wrapped battery with its own JST connector to avoid use of terminal plates.

• Light mods — Add some soap solution to the water to diffuse the light more, or add food coloring to make the light colored.

• Roof mount — To light a room or shed, you can follow Liter of Light’s instructions for mounting the lamp on the roof.

Project Steps

1. ASSEMBLE THE PCB

For assembling the PCB, you’ll need a decent soldering iron, solder, and nippers. It is good practice to solder the components according to their height, beginning with the shortest components: first solder the resistors, diode, and transistors, then the female JST connectors, the button switch, and finally the TP4056 module (Figure C). Trim the excess legs off the components using a nipper.

C

Note that the button switch is mounted on the bottom side of the PCB (Figure D).

D

2. 3D PRINT THE ENCLOSURE

The enclosure (Figures E and F) has 5 parts. The main body is designed to fit all the components including the battery. The top cover is designed to cover up the main body and accept the solar panel on top. The LED holder is used to hold the LED, and the diffuser is used to diffuse the LED light in all directions. The button cap is used to operate the pushbutton switch on the PCB from outside.

E
F

 

 

 

 

 

 

 

 

 

Download the STL files and print the parts in PLA, ABS, or PETG filament. You need support structure for printing the main body and top cover (Figure G).

G

Removing the support from the cap’s threaded area may require a screwdriver or other sharp object. After removing the support, smooth out the threads by twisting and untwisting the cap a few times on a soft drink bottle.

 

3. MOUNT THE SOLAR PANEL

The enclosure is designed to fit a typical 55mm or 60mm square solar panel. The panel I’ve used here is rated for 6V and 50mA. Insert the terminal wires from the solar panel into the slot in the top cover and solder them to a male JST connector’s wire leads. Or you can solder them directly to the PCB pads later (SOL+ and SOL–).

H

Mount the solar panel on the top cover by using epoxy glue (Figures H and I). Also seal the panel from inside using epoxy, so that water will not enter the enclosure.

I

4. INSTALL THE BATTERY TERMINALS

Solder a male JST connector to the battery terminals. I always prefer to use red wire for the positive terminal and black for the negative. The one with the spring contact is the negative terminal. Again, if you’re not using JSTs, you can solder these terminal wires directly to the PCB later (BAT+ and BAT– pads).

Then install the terminal plates into the battery slots as shown in Figure J.

J

 

5. MOUNT THE LED

For illumination I’ve used a big 8mm 0.5W “straw hat” LED. Solder another male JST connector (or hookup wires) to the LED’s terminals: red to positive and black to negative.

Mount the LED into the holder and then install it in the main enclosure, using the notch to align it. Now seal the LED from all sides. You can use hot glue (Figure K), but I recommend using epoxy glue instead.

K

Then install the diffuser (Figure L). You can apply epoxy glue to this joint as well.

L

6. INSTALL THE BUTTON CAP

Insert the switch button cap into its hole in the main body. You have to align the notches perfectly (Figure M).

M

7. INSTALL THE PCB

Align the PCB mounting holes with the mounting studs in the enclosure. Then secure it with two 8mm screws (Figure N).

N

8. CONNECT EXTERNAL COMPONENTS TO PCB

Now connect the LED, battery, and solar panel to their terminals on the PCB. You can connect these via JST connectors (Figure O) or directly solder to the soldering pads. If you prefer to solder directly, be sure the polarity is correct. To prevent mistakes, the polarity is marked on the PCB.

O

9. ASSEMBLE THE ENCLOSURE

P

Close the top cover by aligning the mounting studs. For a better joint, I’ve designed this as a snap-fit arrangement (Figure P). Now use 20mm screws to tighten both the parts together (Figure Q). You may apply epoxy glue at the joints to make it weatherproof.

Q

10. PREPARE THE BOTTLE

The solar lamp is compatible with any soft drink bottle cap. Take an empty soft drink bottle and clean it thoroughly. Fill the bottle with water and add a few drops of chlorine bleach to prevent algae formation and keep the water clear.

Close the bottle with the Solar Bottle Lamp (Figure R) and your lamp is ready to use!

R

 

Conclusion

For more part numbers and sources, go here.