Introduction: DIY Portable Solar Powerbank (w/ 110v Outlets & USB Ports)

This week we are building SlimPanel, an intelligent all-in-one solution for portable solar energy production. SlimPanel has all the needed components inside a portable 1 inch enclosure. Basically it's a huge but portable powerbank that can power 220v/110v appliances and USB devices. It uses an Arduino for its brains and can be upgraded to work with the Intel Edison IoT.


My reason for building this project is to develop and deliver a cheaper alternative for non-renewable energy. Yes the technology has been invented but the incorporation to fit everything you need inside the Solar Panel's enclosure is far from conventional. Rich or poor, people need electricity. The project aims to deliver electricity to areas that have no access to electricity. Other than that, the project can be of use to the consumer level. People can use it as a source of electricity wherever they choose to go. In my opinion, this is an important tool for survival.


This is our investigatory project for our physics class in High School. I'm planning to enter this for this year's Google Science fair and for Intel's science contest. The project is still in the making and I'm build several prototypes to reach perfection.


Here's teaser of my upcoming video tutorial:

It can power a 32" LCD TV and a Laptop too!


The project is still in the making. I'll be updating this guide frequently until I stop and decide to build the SlimPanel v2.0. Your opinion is what matters most to me, it helps a lot on building my version 2.0.


Step 1: Google Science Fair 2015 and Intel 2015 (Research Paper)

I'm joining this in several science fair contests. Hope I win same as last year.


Cool new high production video coming soon!

Step 2: Glossary - Words to Understand

Charge Controller -

Voltage Divider -

Battery Balancing -

Inverter -

Regulator -

Lithium Batteries -

Step 3: Layout of the Electronics - How It Works

Here's a block diagram of the project. I apologize for the poor quality, I've used MS Paint to make the diagram. Anyway, I wrote a layman's description below on how the system works. I wont use too much technical terms so that everyone would understand.

How It Works:

1st.) The solar panel converts sunlight to electricity during day.

2nd.) The power output of the solar panel goes through a junction going to a voltage divider. The voltage divider makes the output voltage below 5 volts making it readable to the Arduino MCU's analog pin. This voltage divider keeps track of the solar panel's output voltage.

3rd.) After passing through the junction of the voltage divider, the power output of the solar panel enters the charge controller section of the circuit.

4th.) The MCU runs an Algorithm to control the charging cycle of the charge controller.

5th.) After the solar panel's power output has passed through the charge controller (with the MCU's permission), it will then go through a junction to another voltage divider. The second voltage divider (this one) is used for getting the battery's voltage (used for power status).

6th.) After going passing through the voltage divider's junction, the panel's output now gets to charge the Li-ion battery pack.

7th.) The charging wont stop until the MCU has detected that the battery is full.

8th.) In addition, there's another line (parallel to the charger's charging line) that goes to the MOSFET load switcher. The load switcher is in charge of turning the appliances on and off automatically. It works very similar to relays. Again, the MCU has control to the load switcher. You can modify the program in step # 31 to add some cool new features to the SlimPanel.

9th.) The load switcher follows the written program. The default program will only supply electricity to the USB charger and Power Inverter if the battery has enough power (16v low cut-off). You can customize the MCU's program to add a menu selection.

10th.) The USB Charger regulates the output power of the battery and lowers it to 5V (2A). The output then goes to the modified USB HUB. The hub extends the number of ports.

11th.) The inverter converts the Regulated 12v to AC (220v), the power used for wall appliances.

12th.) While all of these are happening simultaneously, there are other modules that are also operating. Ones like the tact buttons (for control), LCD screen (for displaying the battery status and power modes, Bluetooth module (for smartphone control and telemetry) and WiFi module (Intel IoT).

Step 4: Gather the Parts & Materials

Here are the parts you'll need:

General Components:

- 12v to 220v Inverter

- 2A USB Charger

- 20W Solar Panel

- Arduino Uno

- LCD Screen

- USB Hub

- 18650 li-ion Battery

Discrete Components:

- ATmega328 IC (Included with Arduino)

- 28 Pin IC Socket (for Atmega328)

- 16mHz Crystal Oscillator

- 22pF Ceramic Capacitor



- 2N3904 NPN Transistor

- SPDT Switch


- AC Sockets

- Epoxy

- Super Glue

- Glue Sticks

- Silicone Sealant

Step 5: Might As Well Buy an Intel Edison (IoT)

The original plan was to build the project having the Edison as the MCU. I failed to do so since I'm lacking the compact breakout board for the Edison. I'm still planing to pursuit to use my original on the Version 2.0 of SlimPanel.

Step 6: Measure the Components

Grab your note pad and vernier caliper then write down the measurements.You'll be needing them later.

Step 7: Mark the Cutouts

Plan and layout the placement of parts then draw the acquired measurements to the solar panel's aluminum frame. Don't use ballpens or markers they will smuge, use pencil instead.

Step 8: Grind Some Metal!

You are probably wondering how were you suppose to cut the aluminum frame. The answer: you could use your electric drill and jigsaw. First, drill a hole for the buttons and a hole at the center of the rectangular markings. Next, useyour jigsaw to finish off the remaining metal from the rectangular markings. If you have access to a jigsaw, you can use a hacksaw or you can use a rotary tool.

Step 9: Smoothen the Edges

Use your metal file to smoothen the sharp edges. Do it slowly and patiently, there's no going back once you have filed too much metal.

Step 10: Hack the USB Hub

In this step, you'll be needing a USB hub. As much as possible, buy the cheapest one. Quality doesn't matter that much since we will be removing most of the components inside.


I used a USB hub to expand the number of USB ports of my USB car charger. You will need to hack your USB port to remove all the vampire components. The USB hub consumes electricity to power the IC that expands the ports, we wont be needing that since we are only tapping in the hub's power line. Once you are done desoldering the components, solder two hookup wires to the DC power jack.

Step 11: Hack & Acquire the USB Charger's Internals

Find a 12 USB charger with a 2.1 ampere output. Some mobile devices like the latest apple products only charge at 2.1A, they won't work with chargers rated below 2.1 amperes.


Find a way to dismantle the USB charger. You can open most of the cheap chargers by using a screw driver to push apart the plastic division. The expensive ones usually comes off by unscrewing the tip of the 12v plug's fuse area.

Step 12: Connect the Hub to the 12v USB Charger

Now, solder the wires of your hacked USB hub to your USB charger's USB port (note: I removed the female plug from the charger). Next, solder two hookup wires to the charger's 12v input.

Step 13: Mount the Hub to the Panel

Hot glue the USB hub together with the 12v charger's circuitry on the solar panel.

Step 14: Mount the AC Sockets

These AC sockets were supposed to be snap-ons although the double wall aluminum frame was too thick. The latches didn't work so I hot glued them too. For the wiring of the outlet, both of them are soldered in parallel.

Step 15: Disassemble the Inverter

I you happen to have a 12v inverter lying around, you can use it for the project. If you don't, you could buy one from eBay or Amazon. They don't cost that much, if you buy the right ones. Their price range lies around $5-$25. As much as possible, buy the 75W version, anything higher than that will consume too much electricity and will drain the battery faster.


When you happen to find or buy one, check it if it works and find if it's fit for your appliance's voltage. Next, dismantle the inverter to get the circuit inside. Be sure to exercise caution, some inverters contain charged capacitors that could cause electric shocks. You can dismantle the inverter by unscrewing the fuse head found at the tip of the 12v plug of your inverter.

Step 16: Connect the Sockets to the Inverter

The wires that you've soldered to the AC sockets can now be soldered to the AC output of the 12v inverter.

Step 17: Mount the LCD

I bought this cheap 8x1 character SPI LCD from e-Gizmo for P90 ($2.00). It was perfect since the LCD was able to fit within the solar panel's frame. You can mount it by simply using hot glue, same to the tact buttons.

Step 18: Mount the Buttons

Step 19: Do Some Outdoor Testing (Getting the Voltage)

Aside from using my solar panel's datasheet as reference, I thought it would be wise to do some testing to see if the values of the datasheet were accurate. It turns out that the solar panel's max (no load) voltage was 3v higher than the one specified in the datasheet. Acquiring the max voltage is very important, it dictates how the number of battery-cells your solar panel can charge. You will also need the max voltage later for constructing the voltage divider of the charge controller circuit later on.

Step 20: Build a Dual 12v Regulator

I plan to use 5 Li-ion cells connected in series. When connected in series, the batteries will yield a max voltage of 21v. The inverter and USB charger will only operate at voltages ranging from 11-14v. In order for us to use the appliances safely, we would have to regulate the supply that goes to the charger and inverter. In this project, I used and designed a linear regulator since I was not able to get hold of a Switching Regulator/ Buck Converter. This is a huge step down for me, although I'm still planning to replace this Linear regulator with a much more efficient switching regulator, if ever I get hold of one.


If ever you chose to build the linear regulator, you can download the zip file below. The zip file contains everything you need: the schematic diagram, the Printable PCB Layout (PDF) and the raw fritzing file.

Step 21: Assemble the Dual Regulator

In assembling the linear regulator, bend the transistor and regulator's pins facing forward. When you solder the tansistors and regulators, the metal (heatsink) portion must be facing upwards. Be sure to use a mylar insulator and plastic washer for the 7805 regulators and the TIP35C transistors. If you don't have one with you, you can simply cover the 7805 with a thick peice of masking tape (no need for the TIP35C transistors). Now screw both transistors to the heatsink, leaving the regulators unscrewed. The transistors do not need insulation since the metal plates are both connected to a common rail, the regulators on the other hand are connected to the opposite voltage of the rail so they need to be isolated from the heatsink. The regulators do not need to be screwed to the heatsink since they don't dissipate too much heat.

Step 22: A Better Alternative for the Regulator

If you are patient enough to wait for the shipping, I would suggest buying a buck converter. Buck converters are much more efficient than linear regulators.

Step 23: Connect the Regulator to the Other Components

Connect the output of the regulator to the inverter and to the 12v USB charger. Leave the input hanging. For now, I'm using epoxy to mount the heatsink. A smart suggestion would be to screw the heatsink directly to the Aluminum frame of the panel.

Step 24: Build the Charge Controller Circuit

This is the heart of the project. The charge controller controls everything. It regulates the voltage and current coming from your solar panels which is placed between a solar panel and a battery. It is used to maintain the proper charging voltage on the batteries. As the input voltage from the solar panel rises, the charge controller regulates the charge to the batteries preventing any over charging.


What's The Advantage of Building One Instead of Buying One?

Pre-made charge controllers are meant to work directly out of the box. Yes, a pre-manufactured controller is easier to use but it has its limitations and that would be the lack if customizability. The answer to that is to build a DIY Charge Controller, having an Arduino as its brain. We all know what Arduino's could do, pretty much anything I guess. If ever you'd want to set a different voltage cut-off, you can just program it with your laptop. If you would like to add other functions, you could program the it do do what you want as well.


I've acquired the circuit's design from my good friend, Debashish (Deba168). He has designed three outstanding solar charge controllers, here in instructables and I highly recommend his projects.


This guide won't explain the detailed process of building a charge controller since it is to broad to teach, instead you can visit these well documented instructables of Debashish (Deba168) on building one from scratch:




BTW, In this project, I used the charge controller design from the fist link.

Step 25: Add a Balancing Charger Circuit (Soon to Upgrade)

Recently, I got help from Adam Munich in designing a better charger (his design) for the SlimPanel project. The balancing charger is designed to charge Lithium batteries, Li-ion to be specific. It's designed to keep track of each Li-ion cell's voltage. I was not able to implement the balancing charger to my current version of SlimPanel since I was not able to get hold of the shipment in time. I'm planning to add it to my 2nd version of the project. Since lithium batteries are very sensitive to draining, a lithium balancing charger is recommended to prevent explosions. The balancing charger circuit makes sure that each lithium cell receives an equal charge distribution.

Step 26: Alternatives for the Controller

There's a wide variety to chose from. If you don't have enough experience to build an Arduino version, you can always choose to buy a ready made controller.

Here's a link to Amazon's top selling controllers: Solar Charge Controllers

Step 27: Assemble Li-ion the Battery Pack

Recently I found a store that sells lithium 18650 Lithium-Ion batteries for $2 each. Lithium batteries are the most efficient so far. They charge faster, have a higher current discharge rate, has great size to capacity ratio and is relatively cheap. Each cell rated at 3.7v (2000mAh). I soldered four of them in series to build a 14.8v (2000mAh) battery pack. Be sure to solder them fast, otherwise things could go wrong once you heat them up too long.


Advantages of Li-ion:

As seen on the graph above, Lithium-ion batteries have a sudden discharge characteristic. Unlike Lead Acid Batteries, they would still maintain the same voltage until the battery runs low.

Step 28: Hot Surface Battery Hazard (Fix)

Lithium Batteries are sensitive to heat, being exposed to extreme heat could cause explosions. The solar panel, when exposed under sunlight, could heat-up up to +100° C. My solution for this was too add a huge 12v snail fan to cool the the surface where the batteries are mounted on. The fan is connected directly to the solar panel. The fan will turn whenever the solar panel produces electricity from sunlight. There no need for temperature sensors, I'm against overkilling prototypes.

Step 29: Hook Them Up Together

Now that you have all the parts mounted within the solar panel's frame, you can now connect everything together. Just follow the block diagram.

Step 30: Construct the Back Panel

Cut a piece of foam board then use it to cover the rear area of the panel. You can either screw it or hot glue it to the solar panel's frame.

Step 31: Program It

Download the codes below.

Step 32: Demo - Video

SlimPanel - Powering a 32" LCD TV and a Laptop:

Project Teaser:

Step 33: Coming Next - SlimPanel (v2.0)


terrefirma made it!(author)2016-10-06

I'm wondering how and what you are doing related to this project. I'm amazed but not surprised that the public has not demanded more of this technology. Apparently the lobbyists and PR folks at the utilities are earning their pay...

matuzapata made it!(author)2016-09-17

hi, how long the battery charge?
greate job!

abhishek7xavier made it!(author)2015-03-07

Hmm,it's not a good thing to put all your electronics and specially battery all behind your solar panel. Significantly, it's gonna be a high temperature there that will decrease the performance and will dramatically shorten your component age!!

ASCAS made it!(author)2015-03-07

I'm currently evaluating the project by using an infrared thermometer. So far the snail fan (on step # 28 ) is doing a great job cooling the batteries. I also suspended the batteries with a thin block MDF wood to prevent the batteries from absorbing heat of the solar panel. Right now, I'm designing a labyrinth for the air's pathway so that the whole panels gets cooled down evenly.

kahrloz made it!(author)2016-08-21

I was thinking the same thing, you need to put something to separate the batteries form the panel, to decrease temperature and also so the fan blows under and on top of the batteries

Luis+Doporto made it!(author)2016-08-19

Great instruction but I still need to learn more to start to follow your direction. Thanks for sharing it!

greener1122 made it!(author)2015-09-10

Ah, if only you COULD do what you're doing and it be practical for powering most electronic appliances since it's so compact. But, yes, it worries me that the lithium ion batteries are within the panel itself and could overheat. Also, even though they're lithium, they still have limited capacity compared to standalone deep cycle marines which I use in my one panel system that has 2KW (2000 watts) of paractical AC output. You can see at power from sun dot com. Another configuration of this idea you can see at plugged power dot com. I was skeptical at first but they've done the due diligence and there's no need for ANY batteries--you just plug into a wall outlet and it puts power into the grid to offset your usage. (But no good for off grid).

TomO14 made it!(author)2016-05-15

you need to be extremely careful about connecting any power charge to the grid . . . when linesmen are working, they shut down power from the power station, not the "downstream" line. . . thus, a linesman could be working on a line he expects to be dead and is really live due to your generating device attached to the grid. People with house generators, windmills, etc. have a system built in to disconnect from the grid to prevent this type of problem

PortablePower made it!(author)2016-03-21

When will there be the Instructables to slim panel v2.0

M+FaiqK made it!(author)2016-02-26

Where have you learned electronics and programming?

M+FaiqK made it!(author)2016-02-26

Where have you learned electronics and programming?

Dr.Bill made it!(author)2015-12-06

lasersaber on UTube

Science+Tower made it!(author)2015-12-06

Can you show us how to build a 220v inverter too?

ReneeA11 made it!(author)2015-11-13

love this, would really love it safer ,more powerful, cooler components and a all inclusive purchase list or possible buy it now button.

Digimeat made it!(author)2015-03-10

This an awesome project, BUT I feel that I must point out that you should add a thermal sensor in v2.0 or to this one. You risk fire because you basically have li-ion batteries in a solar oven. Just have the Arduino or Edison cut off the power if the batteries get into the dangerous temps.

ReneeA11 made it!(author)2015-11-13

good idea,cheap safety too

Bullfrogerwytsch. made it!(author)2015-04-11

The cells you have there, Don't have over discharge protection for each individual cell, The fact the cells aren't balance charged can lead to killing the batteries cell by cell, There are protection circuits you can purchase for each cell, which would ensure no single cell could be over discharged, Vastly improving the lifetime of your battery pack. Also, It is likely at the price you are paying for those cells, that they do not really have the capacity they are said to have, to test them you need to give them a constant load (while protected by an over discharge protection circuit.) and time how long they can maintain output under that constant load.

Also, Charging Lithium ion batteries is best done in a few stages (constant voltage and constant current) to prolong lifetime and get the best capacity out of them.

With Intense loads like a television or laptop running off this small battery pack, The risk of over discharging seems pretty high to me, Not to mention i don't think it would last long enough to be very useful for such intense loads.

I would think a few 6 battery series packs could be put in parallel, having each individual cell balanced.

(i understand you probably know most of these things, I just thought i may as well say it anyway just for other people to read as well)

ReneeA11 made it!(author)2015-11-13

your right, all this trouble and so few batteries. also the ballancer

thetoolman made it!(author)2015-07-05

Wow this is awesome. I want to make one but don't have the in depth electrical knowledge you do. I can handle the mechanical parts OK. Could I get acceptable results by using just the panel, inverter, battery pack and 5v usb charger? I'm sure it runs more efficient but do I need all the Ardunio stuff.

ReneeA11 made it!(author)2015-11-13

same here ,did you ever get an answer?

prabha.vj.376 made it!(author)2015-09-17

You are the master of royal queen ,man.

vespas made it!(author)2015-03-13

You need to add a battery balancer/protection. Cells in series will soon discharge to different voltages (the pack will become unbalanced). This can be EXTREMELY DANGEROUS as over- or under- voltage cells can catch fire (which, being a metal chemical fire, requires a special type of extinguisher to put out) or explode!!! Of course, once a cell catches fire, the one next to it will soon do the same, until the whole pack goes. A li-ion protection pcb will connect to the intermediate points in the pack (the connections you have soldered between cells) and 'cap' over charging of each cell. It will also protect from short circuits and some offer temperature protection as well. Look on ebay for a '6S' protection pcb (Since you are using 6 cells in series). The cheap cells you are using are especially dangerous (there is a reason branded cells cost $10 each!), just google for 18650 explosion to see what I mean. As it is, your construction is an accident waiting to happen, the pack WILL become unbalanced!!!

billbillt made it!(author)2015-07-25

Here comes the CyberNannies again!!!....

ASCAS made it!(author)2015-03-13

I'm guessing you didn't read the whole guide before commenting. I've already explained what you have said in Step #25.

vespas made it!(author)2015-03-13

It's just that the picture of the 6 li-ions soldered in series freaked me out... I think you should emphasise the need for the balancer more, at the moment it sounds like it's a 'nice to have' feature to be added in the future, while in reality it's an essential safety feature!

billbillt made it!(author)2015-07-25

Wonderful tour-de-force!.... Genius!!...

samshim99 made it!(author)2015-04-22

Awesome project! Probably one that I won't be building anytime soon though. lol. Question though. Could you add ground to the AC sockets? Maybe a 2 awg wire attached to a tent stake? Maybe one of these?

MauroS2 made it!(author)2015-04-12

my doubt is how with a 20W panel can you provide power to a computer and a television, by my count a panel would need more power, at least 150 w to be able to have the television and the PC connected at most during +/- 3 hours. or not?

MauroS2 made it!(author)2015-04-12

how many hours can you have the computer and the TV connected, only with the energy from the panel?

Jonathanrjpereira made it!(author)2015-04-04

Which Science Fair Contest are you joining this year?

sarahhanahghan made it!(author)2015-04-01

this will be great in the summer

Constructed made it!(author)2015-03-29

Wow. Greatest instructable I have seen in a while. How do you enter the Google science fair? I have a project I would like to enter as well.

Awesome Instructable!

Barbara+Pevafersa made it!(author)2015-03-18

Wow, great design and idea

Mr+AbAk made it!(author)2015-03-11

Superb Ible.....Thanks for Sharing....

Elac. made it!(author)2015-03-04

Neat idea.

I've used the space behind a solar panel to warm up/ pre-heat water.

How does the high temp in that space affect the components, especially the batteries and their charging circuit?

How long does it take the components to reach their maximum operating temps. in full sun on a warm day when being used?

ASCAS made it!(author)2015-03-05

I haven't tested the exact temperature after being exposed to sunlight but I will do it soon. For now, I used a low power 12v snail fan to cool things down. The temperature inside the panel is probably playing somewhere around 40-80 degrees Celsius. As far as I know, Li-ion batteries could withstand the given temp since RC cars heat up even more.

Elac. made it!(author)2015-03-07

Thanks for the info.

For longevity and safety the 18650s should be charged at temps not exceeding 45C, best below 30C.

And discharged at temps below 60C. Above 80C you risk breakdown (specifically the SEI layer) and thermal runaway.

Best case scenario for operating at temps above 60C will be reduced capacity and charge/discharge cycles.

Might want to look into upgrading that snail fan and leaving a space between the solar panel back and the batteries for airflow.

Maybe use the Arduino and a thermistor to monitor the batteries temp. and automatically stop the charge/discharge if temps. get to high.

ASCAS made it!(author)2015-03-07

Great idea! This will come in useful in my next attempt to build a 2nd version. Anyway, I have just updated the guide, you can check it out.

Elac. made it!(author)2015-03-10

Your guide is excellent, many great tips that go beyond the building process.

With your great attitude and ambition SlimPanel v2.0 will be tops.

Abitcrazy made it!(author)2015-03-08

You are a very smart kid, and that gives me hope for our future! This is way too complicated for an average person (or so it seems to me!!).

eysenbachja made it!(author)2015-03-08

This is so cool! I made a similar panel system but mine is only usb but is simpler. I hooked up the usb car charger directly to the solar panel leads and through usb charged a portable power pack. This way i can grab the power pack without having to bring the whole solar panel. Link:( I really like the outlet adition.

WildOne1985 made it!(author)2015-03-08

Tip: Don't solder the batteries. Just get a 18650 battery box from eBay (~$1,5). That way you save time, effort AND you can easily change the batteries if you want.

Amiel+Garcia made it!(author)2015-03-08

Nice Bro I've been waiting for this. Gonna build this too for my house!

shroudedglory made it!(author)2015-03-07

What is plugged into the USB port on the inverter?
One way to control the heat issue could be to to have the electronics in a compartment that folds out of the space in the back.

QAZW made it!(author)2015-03-07

Looks nice, well made. Instructable is also well made. I want to ask you can you give me link of the 18650 batteries you bought? I'm hoping that they are cheaper than to buy a laptop battery and disassemble it or to buy fake capacity batteries from ebay. Thanks..... ;))))

Bilow made it!(author)2015-03-05

Regarding the power supply, how can you draw 150W from a 20W solar panel ?
Nice project though.

Huntr98 made it!(author)2015-03-07

simple enough 220 volts 150 watts you divide 150 watts by 220 volts you get .6818 amp he has 2000 maH batteries or more simply 2 aH. Sooo 2aH divided by .6818 will give 2.9 hrs of usage if you use the entire 150 watts continously.

efahrenholz made it!(author)2015-03-06

He isn't drawing all the power from the panel. He does have lithium ion batteries which will supply the wattage. But they won't last long.

ASCAS made it!(author)2015-03-07

Yes. Although if you are just going to use the USB charger, you may be able to charge or power items 24/7.

ASCAS made it!(author)2015-03-05

It draws it from the battery reservoir, not directly from the panel.

About This Instructable




Bio: Hi I'm Angelo! I am a 18 y/o college sophomore taking my majors in BS-ECE at the DLSU. I use my course as ... More »
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