Tiny Solar Energy Module (TSEM)

A 1 square inch PCB module with 2 tiny solar cells, a highly efficient Li-Ion charger and with 3.3V and 1.8V output

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This is a 1x1 inch PCB module with two tiny solar cells, a highly efficient Li-Ion battery charger and with two regulated outputs (3.3V and 1.8V). It harvests enough power from INDOOR light to power a simple BLE or LoRa sensor. The board has castellated vias so it can be surface mount soldered onto a mother PCB as well as soldered onto 0.1" headers to be used in a bread board. After the power harvesting challenge (semi finals) I have designed two TSEM derivatives and started selling on Tindie. and The last one stores it's energy in supercacitors!

Ideal for indoor applications

The AEM10941 harvesting IC is very suitable for indoor applications because it has an ultra low power startup. The boost converter starts at a very low 380 mV input voltage and 3 uW input power. The IC gets most power out of the solar cells by doing MPPT maximum power point tracking every 5 seconds. In addition the mono crystaline solar cells have a very wide spectral range resulting in 22% efficiency. This makes TSEM very suitable for indoor applications.

How much energy does is harvest indoors? 

Indoor light is about 1/100th of outdoor light or 10W/m2. At that power solar cell open voltage is 0.458V and I estimate Vmp at 0.36V per cell. Since we have two in series the booster will work at 0.72V input voltage. At that voltage boost efficiency is about 75% . LiPo charge efficiency is about 95%. Battery current is 5.72 times smaller than the solar current because the voltage increases from 0.72 V to 4.12 Volt. Finally I assume that indoor light is available for 10 hours a day. 44mA * 1/100th * 75% * 95% * 0.72V/4.12V * 10 hrs =  0.55 mAh is harvested every day. So an application must have an average current less than 0.55mAh/24h = 23uA, that's enough for a simple Bluetooth Low Energy beacon or a very simple LoRa application. However if the device is in full sun for only one hour a day it harvests ~10x more: 7 mAh. 

If you need to harvest more then you may connect an external solar panel to the castellated via's. Below is a comparison between the on-board solar cells and external solar cells with respect to cost, dimensions, and the energy harvested per day. 

Solar panelHarvested energy per day, indoors (mAh)Application average current (uA)
2x $1.02 On-board 0.5V/44mA 22x7mm Ixys KXOB22-12X1L0.5523
1x $1.06 External 1V/100mA 30x25mm1.145
1x $1.31 External 2V/100mA 79x28mm2.9120
1x $1.18 External 4V/100mA 70x70mm6.7279

The harvested energy can be stored in this 110mAh 3*20*25mm LiPo battery. This battery fits very nice below the module. 


  • PCB 2 layers 25.4 x 25.4 x 0.6 mm  (1 x 1 inch)
  • 2 onboard solar cells in series, 0.5V/44mA each, 22 x 7 x 1.8 mm each
  • harvesting IC input voltage 50mV to 5V. Input current max 110mA. MPPT every 5 secs, MPPT set to 70% (adjustable).
  • Battery: connect an external 3.7V Li-Po battery
  • 3.3V/80mA and 1.8V/20mA regulated outputs. These are enabled when battery voltage is between 3.60V and 4.12V (max charge voltage) 
  • voltage divider to monitor battery voltage using the host MCU
  • 3.3V status output pin that warns the host MCU if battery voltage drops below 3.60V


SRC - solar panel positive terminal, input to the harvesting IC, connect only when you use external solar panel in stead of onboard solar cells

GND - solar panel negative terminal, connect only when you use external solar panel in stead of onboard solar cells

BUCK - can be used to pull SELMPP1 and SELMPP0 high, 2.2V 

STATUS  - open drain output with 1M pull up, when battery voltage falls below 3.6V it goes low 600ms before the 3.3V output is disabled. Can be used to warn the host MCU to gracefully terminate writing to eeprom/flash and prepare for power outage. Voltage level 0/3.3V.

BAT_MEAS - analog output, provides a divided battery voltage for the host MCU with ratio 10/(4.7+10) =0.68*Vbat

GND - 

BAT+ - connects to Li-Po positive terminal

GND - connects to Li-Po negative terminal

3.3V - power supply output, provides 3.3V to your application circuit

GND - ground connection for the 3.3V output

1.8V - power supply output, provides 1.8V to your application circuit...

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MIT License.txt

Basically you can do whatever you want with the TSEM files. Waesome

plain - 1.04 kB - 09/15/2018 at 15:27



Eagle library with the TSEM R1 and R2 footprint

lbr - 23.04 kB - 07/18/2018 at 18:12



Eagle schematic design R2

sch - 177.41 kB - 07/17/2018 at 19:28



Eagle PCB layout design R2

brd - 76.62 kB - 07/17/2018 at 19:28



Gerber files as ordered from Elecrow

x-zip-compressed - 42.52 kB - 07/17/2018 at 19:28


View all 10 files

  • 2 × IXYS KXOB22-12X1 solar cell 0.5V/44mA solar cell
  • 1 × AEM10941 Highly-Efficient, Regulated Dual-Output, Ambient Energy Manager

View all 17 project logs

Enjoy this project?



hatonthecat wrote 02/17/2021 at 16:48 point

"Finally I assume that indoor light is available for 10 hours a day. 44mA * 1/100th * 75% * 95% * 0.72V/4.12V * 10 hrs =  0.55 mAh is harvested every day. So an application must have an average current less than 0.55mAh/24h = 23uA, that's enough for a simple Bluetooth Low Energy beacon or a very simple LoRa application. "

I am interested in testing that limit. The IxSolar series is sold as large as 4"x8" on Digikey:

If I used monocrystalline, SM262K10L 5.71W 1.02A 5.58V 1.09A 8.661"" L x 4.961""

I am assuming I could get about 832uA continuously from that. 

Edit: I understand 5.58V is too much for the input voltage- which is why I am looking into a lower voltage in parallel:

Other panels that appear to be efficient include: at 200 Lux: Power: 0.289mW  3.70 x 2.87 (in)

Operating Voltage: 1.6V

Current: 0.181mA

Average Voc: 2.4V 94.0 x 73.0 (mm) / 3.70 x 2.87 (in)

They also have a design tool, which lets me select number of cells, length and voltages:

I'm not sure which ones are more efficient for indoors, including Amorton AM1816CA, and not focusing on cost at the moment. E-peas mentions up to 7 solar cells in one of their kits, but I would like to know if AEM10941 has any limitations to maximum size of panels- I am looking into designing a microcontroller with integrated solar power manager - Sparkfun offers it as an option: requiring 10W panels. 

I am not sure if theirs is designed for indoor lighting since I don't know if requires a minimum amount of light to "cold-start" their power manager. Therefore, with an AEM10941, it could jump start trickle charging at a very slow rate, but fast enough to power the Apollo3 microcontroller (this is best in class, excluding the 3uA/mhz Apollo4, set to be released later this year. 

Theoretically, I could design four 4x8" panels that would fit around a 17" laptop keyboard with an Ambiq Apollo3 microcontroller that runs continuously, and not on sleep on "less than 1mA": and produce 3.3mA.

"operates less than 5mW at full operation)" (Features Tab)

Powering the an e-ink or reflective monitor might be more difficult but it is bistable and only uses power on refresh. Therefore if it uses less than 2mA the board could be powered entirely from a ceiling light.  This is a 4.4" that uses 5mW if backlight off. I would like to try it with 2.7" but I think more panels could power a larger screen.

  Are you sure? yes | no

Jasper Sikken wrote 02/17/2021 at 19:34 point

You seem to understand my calculations to estimate the amount of daily harvested energy. The AEM10941 input voltage range is max 5V. You need to make sure that the open circuit voltage does not exceed 5V. That often means you need to select 4V or less NOMINAL voltage. Either you put 1 or more 4V solar panels in parallel or put a few lower voltage cells in series. Note that a partial shade on a series string causes the whole string to malfunction. Also note that AEM10941 efficiency drops with solar panel voltage below 1V. So a tradeoff is to select about 2.0V nominal voltage and if you want mor epower you add more in parallel

  Are you sure? yes | no

hatonthecat wrote 02/17/2021 at 21:20 point

Thank you, I plan to try my kit soon. I ordered a dev-basic with BQ25570 but will order the AEM10941 after I gain more practice:

  Are you sure? yes | no

Kosma wrote 03/18/2020 at 20:10 point

Is possible add raspberry pi zero, and configuring for working only when have power?

For example, more power, wifi + email server working 1h per day but offgrid.

read and put e-mail and turn off.

  Are you sure? yes | no

warhawk-avg wrote 08/30/2018 at 09:27 point

Very Very cool...Love the energy harvesting chips...
Such a cool design!
Maybe even a slim cellphone battery mount for the back

  Are you sure? yes | no

Jasper Sikken wrote 08/16/2018 at 17:54 point

I am working on two designs using the AEM10941 without the onboard solar cells. One charges the a Li-Ion battery and the other charges a pair of super capacitors.

I have ordered the PCB from Elecrow and soon I will test them

  Are you sure? yes | no

x893 wrote 08/12/2018 at 21:20 point

This solar panel - perfect for small devices. I use with LTC3105 (one voltage)

Low current but charge small supercap.

  Are you sure? yes | no

Jasper Sikken wrote 08/12/2018 at 22:04 point

now THAT is a tiny booster circuit 

  Are you sure? yes | no

x893 wrote 08/12/2018 at 22:37 point

I see AEM10941 datasheet. Looks interesting. Can't find samples but possible buy some chips.

Thanks for information !

  Are you sure? yes | no

Jasper Sikken wrote 08/06/2018 at 18:51 point

I consider selling TSEM for USD24.90 on Tindie. Would you buy it? Why would you buy this module and not another tiny board like this one?

Would you prefer a AEM10941 breakout board without the to onboard solar cells?

  Are you sure? yes | no

Kris Winer wrote 08/07/2018 at 15:53 point

The nice thing about a board with just the boost converter is that you can tailor the selection of solar cell(s) to match the application. I like the 50 mm Panasonic Amorton AM-5412CAR a-Si cells since they are still small but provide 7 mA per hour in full Sun, meaning about 40 mAH per day on average, enough to power a 2 mA device. But the point is that many user don't want to pay in board size and price for solar cells that might not fit their application.

  Are you sure? yes | no

Jasper Sikken wrote 08/07/2018 at 20:21 point

Hi Kris, I think you're right. The board that I will be selling won't have the solar cells and will be much smaller than this one. 

  Are you sure? yes | no

Jasper Sikken wrote 08/12/2018 at 06:09 point

I have designed a new PCB and ordered from Elecrow.

  Are you sure? yes | no

fabian wrote 08/04/2018 at 17:52 point

please make a experiment. put this outside on one year and tell me. it working 24h or not.

nothing more

meybe send data to server or other way check device is working or not.

  Are you sure? yes | no

Jasper Sikken wrote 08/04/2018 at 18:24 point

What do you think that could fail? Solar cells, capacitors, the AEM10941 IC, resistors, or the the external battery?

Uninterrupted functioning could we be checked by monitoring the 3.3V and 1.8V outputs using another device that logs any voltage dips. In my opinion it may be hard to make such device thats works for a year and does not falsely trigger. 

  Are you sure? yes | no

Jan wrote 08/05/2018 at 07:12 point

That fabian has zero projects, criticizes many decisions of makers with zero positive feedback and just asks for changes or "do this or that (please)". Wouldn't even pay attention to this troll... 

  Are you sure? yes | no

fabian wrote 08/05/2018 at 15:04 point

my english is not good. Solar  is a capricious device.

Rather you would underestimate the size of the panel, but until you do it you will not know. Therefore, do an experiment and you will know if it suits you. Can it work completly offgrid. It is important that it is useful and not just a gadget for nothing. test it. I foud interesting art. meybe help You

  Are you sure? yes | no

Jasper Sikken wrote 07/17/2018 at 20:13 point

In PCB revision 2 I added 1.8V regulated output to the TSEM. 

  Are you sure? yes | no

Robert Poser wrote 07/08/2018 at 19:03 point

Nice! There are two more solar cells from Ixys with same form factor but higher open circuit voltage available. Have you considered rather using one of them since the booster efficiency would be better there ?

  Are you sure? yes | no


[this comment has been deleted]

Robert Poser wrote 07/08/2018 at 19:58 point

A link is here.

The active cell area decreases a bit with more single cells. Maybe KXOB22-04X3F-ND with 1.8V open circuit voltage is worth trying..?

  Are you sure? yes | no

Jasper Sikken wrote 07/08/2018 at 19:49 point

Great idea, I thought they were not available, but I see them at digikey and I ordered a couple of the 1.5V/15mA cells (KXOB22-04X3F). Now effiecincy goes from about 85% (1V) to 95% (3V). 

  Are you sure? yes | no

Jasper Sikken wrote 07/10/2018 at 15:45 point

In my design I have 2*0.5V*44.6mA=44.6mW solar cells. To get 10% more booster efficiency I could change to 2*1.5V*13.38mA=40.14mW which is 10% less power. So that doesnt make sense. Then I choose for the more economic 0.5V solar cells.

  Are you sure? yes | no

Mark Jeronimus wrote 06/29/2018 at 12:43 point

I can't find this chip in shops (Farnell etc). Where did you find it?

  Are you sure? yes | no

Jasper Sikken wrote 06/29/2018 at 20:32 point

I got a few samples from e-peas. I will ask when chips become available at the large distributors.

  Are you sure? yes | no

Jasper Sikken wrote 06/30/2018 at 14:02 point

I dont think they will be available at the large distributors soon. E-pease carefully selected a few distributors. See here.

  Are you sure? yes | no

Jasper Sikken wrote 06/28/2018 at 10:44 point

@Alexandre LE GALL I learned from e-peas that most of their customers chose for standard configurations that don't require extra pins. I wanted to keep it simple and chose for lipo only (no super capacitor) and use only 3.3V output because that is standard for most MCUs.

  Are you sure? yes | no

Alexandre LE GALL wrote 06/28/2018 at 10:17 point

The AEM10941 is very interesting compared to the BQ25504 (the energy harvest chip I use in my project) : There are two integrated regulator and a balance feature for dual-cell supercapacitor !

I think you would make an external connection for the cvercharge, overdischarge, charge ready, and the balance pins.

  Are you sure? yes | no

Jasper Sikken wrote 06/25/2018 at 15:24 point

Sorry initially I wrote the incorrect part number. Glad you found it

  Are you sure? yes | no

Stephen Edwards wrote 06/21/2018 at 08:41 point

cant find this chip. Is the code correct?

  Are you sure? yes | no

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