10 Wp solar panel, two 3400 mAh Li-CoO2 18650 batteries in parallel, permanent small ~50 mW load. A shunt regulator limits battery voltage to 4.1 V. An externally powered ESP32 measures sol and bat powers for ThingSpeak.
Indoor temperature, atmospheric pressure and relative humidity (in D1 building of Wroclaw University of Technology) measured remotely by energy-harvester-supplied sensor system (arduino/BME280/nRF24L01+/ESP2866).