@ Tony Reeves 1

I sit corrected. Having googled and read a bit I have found that your are right about the local area transformer working both ways. Even so, there are limits to how much PV power can be fed into the system, and the limits can be significant... I found the following IEA report helpful:

http://www.hme.ca/gridconnect/IEA_PVPS_Task_5-10_Impacts_of_PV_Power_Penetration.pdf