batch file with:
"C:\Program Files\Planetside Software\Terragen 2 Deep Edition (Beta)\tgdcli.exe" -p %1 -hide -exit -r -o %2.bmp
shutdown -s
change the path to the tgdcli depending on version/where installed. other options -r for restart, -l for log off, etc. This might not work depending on version of windows you run.
to run the batch file, it would look like this.
path/to/batch.bat "path/to/project.tgd" outputname
so, if in the batch folder already (my terragen stuff folder) command for me would look like:
shutdownbatch.bat "projects/scene.tgd" myrender
when done, my computer shuts down. when i bring it back up, i navigate to the output which renders to the folder.