2021
August 05: ESP and solar panel Part 2; the results2020
December 26: ESP and solar panel Part 1; the setup August 22: ESP-8266 power issue with ME6206 regulator2019
October 18: How to use alarm syscall in Ruby2018
December 20: Decode Oregon Scientific sensors with RaspberryPi and Arduino2016
October 19: How I recovered a dead hard drive with a freezer September 28: Drawing a ground plane in Kicad June 27: Quick Ruby On Rail memo2015
December 18: Signal handling and Ruby December 14: EventMachine is good but... September 18: My custom ortholinear keyboard February 08: Quick Sinatra boilerplate2014
September 16: Wifi access point on a Raspberry Pi March 24: Linphone and G729 on Opensuse2013
November 11: Ext4 rescue tips November 05: Why this blog is'nt running Wordpress ?ESP and solar panel Part 2; the results
- August 05, 2021
In the previous episode, we saw the setup to measure solar panel production with an ESP. Today we are going to see the results with the two different controlers.
CN3791
The CN3791 needs a bit of tuning to setup the Maximum Power Point the controler will use. It can be adjusted with a variable resistor. I found the best value to be 5.2V for my 6V solar panel.
The result is quite clean. The controller keep the panel voltage around 5.2V to get the maximum power. Once the panel hits the shades (just before 10am on the graphs), the power drop a lot but still produces a few mW at 5.2V.
The production peaks at 1.2W, which is way less than the expected 4W of the solar panel's datasheet.
TP4056
With the TP4056, it's a bit more messy. There is no MPP tracking (and no tuning). It draws as much as it can pulling the voltage down to around 4V, with an average at 4.6V. As a result the energy produced is a bit more chaotic but it's still working.
The production peak is around the same.
Conclusion
The TP4056 seems to be a little bit less efficient but the results are quite similar in both full sun and shades. A better setup would be required to measure the impact on the battery charges, as the voltage required to charge it will depend of its charge level (ie, 4V will not be enough is the battery is nearly full).
One thing to note though is the impact of the panel's temperature. As soon as the panel reached around 40°C, the harvested power dropped by half. With the temperature returning below 35°C, the prodution went back to normal. To note, the temperature sensor at the back of the panel it not in proper contact with it. Some thermal grease would be needed. The real temperature of the panel might be much higher.
But the main take away is: To get good solar power, you need good sun.