In the days when solar panels were not cheap, many people (even large energy companies) used solar trackers to ensure that their panels were always pointing to the sun to ensure that they could get as much energy as possible. However, as the price of solar panels has plummeted, it is no longer economical to install complex machines to track the sun. But all solar power plants are still tracking something else, called the maximum power point (MPP), which ensures that even fixed panels can optimize power generation.
Although the small MPP tracker (MPPT) can be used for solar charging controller, and the price is in the range of $200, which is very suitable for small off grid settings, [ascas] aka [techbuilder] decided to launch a lower price open source version, because most of the costs of these devices are in research and development, not the actual components themselves. For this reason, his method for MPPT is basically the same as that of any commercial unit, which is called Synchronous Buck conversion. This uses a specially configured switching mode power supply (SMPS) to very quickly match the power output of the switchboard to the optimal power point under any given conditions. It can even work on many different battery configurations and chemical compositions, all of which can be configured in software.
It is incredibly extensive construction, deep into electrical theory and design options. A noteworthy design option is to use esp32 instead of Arduino, because higher resolution can be obtained during analog-to-digital conversion. There is even a long speech on the design of inductor core. Of course, all the contents of this project are open source. We have seen esp32 used with MPPT before. Although it is not so exquisite, it is still very interesting.