RenderPal provides a way to globally define Environment Variables. It is done throught the RenderPal.env file.
For more details, see the end of the RenderPal documentation: RenderPal environment variables file
For example if you did not instal the package locally on each render nodes, you need to specify the Maya Module Path in this file.
Notice that the RenderPal.env file is not a script file. So the variable expansion will not work and you should replace all variables (found between % or !) by their real value.