not working might be subjective - say its a 150l rated heat pump now it is trying to heat up double the volume of water its rated for - will it warm water yes but how warm is another story -
Total or just the geysers?
average around 17-22kwh a day
5-10Kwh to the Geysers if PV is crap we make due with 1 , if great both to high temp (and on medium days maybe both but lower temps etc) strategy helps lower the grid usage where posible.
Flat roof , 1 is vertical the other is...
on eskom you cant break even - they dont credit you on the account as a rand value its credits that can only be used for power and if im not mistaken you can only use it the the same time frame you sell
sell in day can only be used in day so its not like it helps you save at night