INA219 is a popular IC to use with Arduino and Raspberry Pi to measure current, voltage and power. It uses I2C communication however, there are two known problems with these modules. 

These lack filtering, and exposes the IC to transients and noise, which often breaks it. Another issue is related to voltage measurement. To measure voltage accurately one needs ground reference from the power side. But, there is also I2C communication, which requires a ground reference from the Arduino or Raspberry side. These two references have a small difference, because of the voltage drop in wires. If two of these references are joined together, there will be a ground loop, which causes all sorts of issues. If they are not joined together at INA219, then the voltage reading will be inaccurate. For example, a high current on the power side results in voltage measurement to be lower than it actually is.

To solve the first issue, a proper RC filtering and TVS diodes are added around the current sense resistor. The second issue is solved by using a Ti's ISO1540 I2C isolator, which galvanically isolates I2C bus. Personally I meassure only current with a analog to analog isolator. Input Current output Voltage. In between is a analog to digital - opto isolator - digital to analog conversion. I think this is also as a tinker board available. ah, here it is, under 5 euro. https://www.ebay.de/itm/New-4-20mA-0-5V-Current-To-Voltage-Module-Board-Insulation-Signal-Converter/222513574113?hash=item33ced7b0e1:g:6usAAOSwtGlZG0Hi Now on the current side you can add a resisotor in Line to restrict the current to 4-20mA and and a filter, hook it up streight to the Solarvoltage. Adjust to your needs until you get the desired voltage range at the input of the Pi (MCP3008). In this case it doesnt matter how long your wires are.