Hey Jurgen, sorry for the delay. Did you get this working ?
I would recommend following the installation instructions provided on the OpenSprinkler Weather Service github page [HERE]. This does not use nvm as it is not necessary for this installation.
If you are experiencing problems the I would suggest: 1) ensuring OSPi is on the latest Stretch release of rasbian, 2) ensuring the OSPi is up-to-date sudo apt-get update and sudo apt-get upgrade; 3) removing anything in the weather directory and re-downloading from github; 4) then try the instructions again. I have certainly had versioning issues with node before.