Supercapacitor is charged via Schottky diode, this current also disable step up booster,
In night or if it lose power booster is automatically started and very effectively discharge
supercapacitor and convert almost all stored energy because can work until 0.3V
PCB is now not optimizes to minimal dimensions, it can be much smaller
Operation TEST
Some assembled pictures:



Circuit is extremely simple to make it reliable.

What is the approximate cost for all of the parts?