Thanks Rint and Kayleigh... I do have batteries for storage. but way too complicated to transport them to my son's flat on a daily basis.
They hold enough power for all our energy consumption during darker hours
there doesn't seem to be much info about net metering in spain. I did see this headline: ..."The Spanish government has proposed a Royal Decree with new self-consumption regulation which is expected to be approved in March or April. According to the new rules, power surpluses may be shared with other consumers or fed to the grid."........
this was in 2019 but I think it is only for people with energy production of 100kw +.
As far as I know, the occasional consumption I make of Endesa's electricity is nullified by the amount they take from me. But since they are taking VAST amounts of my energy, really I should also be able to transfer some of that energy to another consumer or two.