Not sure about G99, but my older (and simpler) G83 PV inverter certainly does clunk as it connects/disconnects - so mechanical contactor seems a good guess. To connect not only does the mains have to be present, but the PV side providing power as well - so I suspect most of the power needed comes from the local generator. Whole site G99 systems might be different though.

A while ago I did worry the night-time consumption during the hours of darkness (one of those simple clip on energy monitors suggested it was in the 10s of Watts) - but later measurements with proper Watt Hour meters confirmed the manufacturer's figures were about right (I don't recall the exact numbers off hand, but I'm pretty sure it wasn't more than 1W).

All in all it's probably very small amounts - like tariff meters.

    - Andy.

hey hello   hmm very small   amounts ??   Don't understand how very small amounts if the coil of a contactor is maintained energised for 10 years Adds up ? 

Do I understand  The normal fail safe state of a contactor is de-energised  And if safety critical  perhaps two in series .  So to maintain physical contact grid to generator they must therefore be energised : All day all night 24/7 Until such time as grid fail is detected ? 

I cant see " 10's of watts consumed over 10's years  lifetime being a  credible  answer ?  Is this grid tie hidden costs ?.

I cant see the normal state of contactors being de-energised: Otherwise they would need to be energised  and remain so for duration of grid fail . Where woud lthe power come from for that ?  If motorised contactors cant see the difference ? 

Effort again to understand evidence of where solar energy ( JOules)  falling on panels is actually usefully consumed  by eg household appliances. And what goes to waste ( eg back to grid)  Appears London is offering 4p/Kwhr for regen  They just don't want it .

ciao Ms Otis 

hey hello   hmm very small   amounts ??   Don't understand how very small amounts if the coil of a contactor is maintained energised for 10 years Adds up ? 

Do I understand  The normal fail safe state of a contactor is de-energised  And if safety critical  perhaps two in series .  So to maintain physical contact grid to generator they must therefore be energised : All day all night 24/7 Until such time as grid fail is detected ? 

I cant see " 10's of watts consumed over 10's years  lifetime being a  credible  answer ?  Is this grid tie hidden costs ?.

I cant see the normal state of contactors being de-energised: Otherwise they would need to be energised  and remain so for duration of grid fail . Where woud lthe power come from for that ?  If motorised contactors cant see the difference ? 

Effort again to understand evidence of where solar energy ( JOules)  falling on panels is actually usefully consumed  by eg household appliances. And what goes to waste ( eg back to grid)  Appears London is offering 4p/Kwhr for regen  They just don't want it .

ciao Ms Otis