If you are upgrading from a pre v0.4 release you need to first run pip3 uninstall sol as the package name has changed!
To install SOL you need to have an account to access our SOL PIP repository. You can check with your browser if you can login to: https://dav.neclab.eu/sol4ve/
If that works, you only need to execute the following command:
pip3 install nec_sol[torch,onnx] --extra-index-url=https://dav.neclab.eu/sol4ve/
This will automatically install all dependencies. I.e. if you do not need PyTorch support, just remove torch from the [...].
If you get an error like SSLError(SSLError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:852)'),) you need to add --trusted-host dav.neclab.eu to the installation command.