I had yesterday a call with @Andreas about some strategies to get a solar powered gateway working.
You can move a node in a convenient way to a power saving device: Just switch off power for hungry components and send the MCU to sleep. This is difficult to do for a geteway because a gateway has to listen all the time supposed it does not know whe new packages arrive from the nodes.
So we discussed yesterday if it is possible that an IRQ can wake up a sleeping MCU and it seems to be possible see:
There is very high “listening current” for the RFM described so we have to tweak things here also but it seems a good starting point.