You can use this setup to measure a DC between 0 – 25V (ie Solar Battery Voltage) and send the Data via WiFi to your MQTT Server. This is V1 where you have to power the Wemos with 5V via USB. In V2 you will be able to use the power from the current you are measuring (coming soon).
You can find the code for Arduino IDE here.
And the .stl for the Case here. The case-design uses a M3 10mm screw to fix the lid to the base. The Wemos can be clipped in the case an de Sensor is held in position by the lid. There is enough space for cooling.