Sunday, March 11, 2018

ESP8266 powered by a solar panel and a 18650 battery

On my setup described in here I've added this solar panel from Banggood. If in the past the maximum of battery operated was around 48 days on one charge, now with the help from solar panel I am expecting to run 24/7 without the need to recharge the battery myself.

The panel has dimensions 165x135x2mm and is made from monocrystalline silicon and is rated to 6W and 580 mA.
Exposing it to full sun will produce 6.54 volts and after the diode (I've used a 1N4007) will have 6.00 V.

To connect the solar panel to charger board I've cut a USB to micro-USB cable and I've soldered the part with the micro-USB to the solar panel. The micro-USB cable now can be plugged directly into the charger in its micro-USB connector.

The entire setup is now made from:

Wemos ESP8266  - 1pcs
Wemos Lithium charger board - 1pcs - this is an old version or Wemos Lithium charger board - 1pcs - the new version
BMP180 temperature and pressure sensor - 1pcs.
Battery 18650 -1pcs
Battery holder - 1pcs

The code is the same as in the original post in here.

This is the picture with the module and the LED being GREEN ( battery is fully charged )
Green LED - fully charged

And the entire module with solar panel attached to the window.

The entire module with solar power.

Just after I've added the solar panel the voltage of the battery has start to increase.

Just connected the solar panel to the charger

Now after few days you can see that what is consumed during the night and during the day when there is not enough sun will be recovered in few hour of sun. The panel is mounted to a window where is having sunlight for three four hours in the afternoon.

In the next picture you can see four peaks (one every day), where the charger actually stopped the charging of battery. The charger is cutting the power to the battery at 4.26 - 4.27 V. You can see that by looking to the LED on the charger board that will light green. In the led is red it means that the charger is charging the battery. If there is not enough sun the led will be off which is good because will not drain the battery.
4 days run on solar panel

Now it will run forever and I don't need to load the battery every 48 days.

This is the current voltage on my setup in real time:

After a two days without any sun ( two days of rain) you can see that there are no peeks of fully charged. You can see this in the picture bellow.

Two days without sun, so there are no peeks

It will be interesting to see if the battery will be fully charged again in the next days with sun.

As you can see in few hours with sun the battery is full again, recovering after a two cloudy days. The LED is green again now.

LED is green again, battery is fully charged
I've let the module to work exclusively on battery for 10 days. I've reconnected the solar panel and in two hours the battery was again fully charged.

Solar panel connected after 10 days on battery

(- I will continue to update this post - )


  1. The max charge of that cell is 4.2v - by overcharging it you risk a nice bonfire on your window.

  2. I don't think that is overcharging since the charger stops charging the battery when the LED is green. Voltage measured directly on battery indicates 4.20 V when the LED is green.

  3. hello,
    very nice post!
    I was looking for this exact setup... connecting 1 or 2 6V solar panels to a battery charger and being able to run a Wemos D1 mini weather station (rainmeter+DHT22).
    is your system still running OK? any problems with 18650 battery management?
    thanks in advance!

    1. I don't have any problems with it. Just make sure to put the wemos in deep-sleep since you don't need to be running all the time. Getting temperature every few minutes is perfect, even in the cloudy days.

    2. Also make sure that you seal tight all the assembly. The solar panel in direct sun is getting pretty hot so isolate it well. Maybe you can put it over an aluminium plate to dissipate the heat. you can add an extra temperature sensor like DS18B20 to monitor the temperature of you panel.

    3. And btw, the blog about Manaslu is awesome !!!

  4. Hi do i really need the diode?

    I have a similar Setup.

    This charging shield
    A 6V 1W solar panel (200ma)
    A 18650 battery

    When i connect the 18650 battery and nodemcu it works.
    when i connect the 18650 battery the solar panel to the shield and from there i take the 5V and GND output and connect it to VIN GND of the nodemcu it doesnt work.

    but with a powerbank it does...

    Do you this it could be the diode the problem ? thanks in advance!

  5. It amuses me that, on your main board, you only solder in the pins you need to use. I thought I was the only one!

    1. Yes :-) is much easy to remove the connector later and use the module for other projects.

  6. Hello, nice post ! Where put the diode ?

    1. between the + from the solar panel and the + on the entry of the charger module.

  7. I really like reading through a post that can make people think. Also, many thanks for permitting me to comment!