I would like to draw attention to the fact that according to some sources the carbon footprint of the current Internet is in the same ballpark or even higher than that of the airline industry. 
For this reason I would find it useful to put in place some mechanism for rewarding SAFE nodes powered by renewable electricity over those powered by CO2 emitting electricity.
IDEA A) Perhaps the network could reward node runners that use renewable electricity by sending more data to store on the green nodes than the “gray” nodes and thus reward green farmers more by building up the utilization rate faster.
IDEA B) Perhaps it could be feasible also to set a green premium where writing data to the network would cost a little more if the user has selected to store the shards only (or preferedly) on green nodes and to run the apps on green nodes. For those paying this green premium a certificate (probably just in the form of a “hosted green”-graphic) would be awarded to be used on the websites / apps to help in marketing to environmentally conscientious consumers.
Any other ideas would be much appreciated.
Whatever approach is possibly taken to make the SAFE Network greener and less carbon emitting the obvious problem is:
“How to determine reliably and unobtrusively if a node (not run in a data center where a 3rd party database knows that the hosting provider is committed to green electricity) actually uses electricity from renewable sources?”
If relying only on statement made by node owner, this would obviously open up the possibility to cheat in order to gain something.
Maybe it would be feasible for the electricity companies to build a system where the sources of electricity for some individual / organization could be queried or a digital certificate issued, but I do not know the SAFE Network so well enough to evaluate how something like this would effect the right to privacy of the farmers.
https://www.thegreenwebfoundation.org/ allows one to check the green electricity status of web hosts and Currently also offers a browser add-on that draws little dotted green line under links to sites that are recorded in the database as using green electricity. Selecting which link to visit or not to visit based on if they are hosted green does not sound applicable, but at least consumers could send messages to websites that they like to make the switch to green.