Hardware needed to log current values only to an SD card

I’ve just installed a geothermal system in my cabin and would like to log the energy it uses to an SD card that I can dump periodically on my computer for further analysis. What is the minimum hardware I need for that? emonTx? emonPi? If I wanted to monitor the outside temperature at the same time, should I go with a emonTx shield added to my Arduino or Rasberry Pi and add the temp sensor? I don’t really need the wireless network, etc.

If your comfortable with setting up the data logging etc on the raspberrpi and already have an arduino then yes the EmonTx Shield is probably the lowest cost solution to achieve what you want to achieve.

If you use the example arduino firmware here:

it prints the power values and voltage as space separated variables which you could then read and write to a file with a little python perhaps?

If you have an internet connection or home LAN then the larger emoncms raspberrypi SD card software stack might be of interest as you could then log and view the data on your network.