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

Agreed it add up. "Small" is relative though. From memory an ordinary tariff meter can have a self consumption of up to 2.5W - so say 160kWh over 10 years (a few £10s perhaps) - which we seem to tolerate. Probably dwarfed by all the appliances left on standby.

I cant see " 10's of watts consumed over 10's years  lifetime being a  credible  answer ?

Maybe not 10s of Watts - even if it did use the constantly energised contactor approach, a typical 100A DP contactor (e.g. https://docs.rs-online.com/4fde/A700000008377683.pdf) takes only something in the region of a couple of Watts to hold closed. You could probably engineer that down a bit if needed. Plus a bit for some control electronics no doubt, which will add a bit more, but all the same still comparable with a smart meter I would have thought.

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 ?

Not necessarily - some relays are latching - only needing power to move the contacts and need no power at all once the contacts have reached their intended position - likewise for motorized circuit breakers, so only a small backup power source would be needed to open the contacts after a grid fail. DNOs actually use batteries in some of their substations to power motors and circuit breakers when the normal power source fails - so there is a good precedent for that sort of thing.

Is this grid tie hidden costs ?.

I'm not sure that anyone's hiding anything - I think most engineers will understand that all control system will inevitably consume some power. While it's relatively small (you'd only be using G99 if you've got the potential to export > 16A/phase) it's just not headline news. Rather like the couple of hundred watts of electricity your gas boiler takes when burning gas.

And what goes to waste ( eg back to grid)

Hardly waste - in the grand scheme of things it's displacing the same amount of fossil fuelled generation whether it's consumed on site or somewhere down the street (which is why the original FT tariff pays out primarily on energy generated rather than energy exported). As ever you won't get the retail price for exporting, but most suppliers are currently offering in the region of 15p/kWh at the moment (SEG tariff), but agreed that by and large self-consumption is more efficient.

   - Andy.

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

Agreed it add up. "Small" is relative though. From memory an ordinary tariff meter can have a self consumption of up to 2.5W - so say 160kWh over 10 years (a few £10s perhaps) - which we seem to tolerate. Probably dwarfed by all the appliances left on standby.

I cant see " 10's of watts consumed over 10's years  lifetime being a  credible  answer ?

Maybe not 10s of Watts - even if it did use the constantly energised contactor approach, a typical 100A DP contactor (e.g. https://docs.rs-online.com/4fde/A700000008377683.pdf) takes only something in the region of a couple of Watts to hold closed. You could probably engineer that down a bit if needed. Plus a bit for some control electronics no doubt, which will add a bit more, but all the same still comparable with a smart meter I would have thought.

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 ?

Not necessarily - some relays are latching - only needing power to move the contacts and need no power at all once the contacts have reached their intended position - likewise for motorized circuit breakers, so only a small backup power source would be needed to open the contacts after a grid fail. DNOs actually use batteries in some of their substations to power motors and circuit breakers when the normal power source fails - so there is a good precedent for that sort of thing.

Is this grid tie hidden costs ?.

I'm not sure that anyone's hiding anything - I think most engineers will understand that all control system will inevitably consume some power. While it's relatively small (you'd only be using G99 if you've got the potential to export > 16A/phase) it's just not headline news. Rather like the couple of hundred watts of electricity your gas boiler takes when burning gas.

And what goes to waste ( eg back to grid)

Hardly waste - in the grand scheme of things it's displacing the same amount of fossil fuelled generation whether it's consumed on site or somewhere down the street (which is why the original FT tariff pays out primarily on energy generated rather than energy exported). As ever you won't get the retail price for exporting, but most suppliers are currently offering in the region of 15p/kWh at the moment (SEG tariff), but agreed that by and large self-consumption is more efficient.

   - Andy.

ok .  Thanks Andy  accept power consumption is small   ( Hard to see when an electromagnet is hold large contacts together against a quite forceful spring  but hey guess tech has moved on . .  Clarify when you said latching I guess you mean mechanically latching  Had some experience of those  dodgy things Give nerves if for fail safe.  

I asked for DNO regen payback   Just 4p / kwhr. ??    

Anyone know of a reliable website where I can calculate energy off solar panels .  To get some idea . I just still dont trust the solar industry constant jargon or just talk down to you . 

Still contemplating off grid.   No hidden things  Less to go bump in the night. . 

The only reliable answers I get are here !!  

thanks again  Ms O