Solar power Anti Islanding The cost ??

Hello all   G99  etc consumer advice  What are the standby running costs to monitor grid fail and and eventual inverter physical separation ?  Anyone know ? 

Q: How is physical separation achieved for islanding protection when grid is detected as down ?  There is much tech mumbo jumbo " phase detection " zero crossover " but no genuine answer as to what the standby costs of running all this this actually is 

Appears ( however fail is detected ) final physical separation is achieved by a plain old electro mechanical contactor ?  It is simply de-energised  Contacts separate and we are done ? 

Could it be that these power  devices are maintained energised all year 24/7 consuming power until here is an issue ? 

If so can the solar grid tie industry tell us what power is consumed in this effort and where does it come from ? 

ciao Ms Otis 

  • 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.

  • Physical disconnection is required.

    Contactors can be used, and often are for relatively simple installations or inside equipment. But other options exist, such as motorised circuit breakers, which can be U/V trip and hence very similar to a contactor, or shunt trip where backed up by a battery (often but not always using a protection relay also providing fault protection for the circuit).

    As Mike says overall power consumption is negligible compared with the power being controlled (but it might need considering, for example, in the design of the enclosure).

  • 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 

  • 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. 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.

  • Hi

    Generally speaking I use the Ziehl UFR1001E Anti Islanding relay, The full load current under 5 simultaneous faults (impossible) is 130mA

    The plausible full load is 30mA

    Obviously  if you are using this device you will have Coils to consider, Assuming a full standard Domestic supply that might be 60mA 

    Plus a 24v psu

    If you said 100mA maybe £50/year by the time you factor in all the gubbins. 

    I suppose it could be measured with a clamp meter for an accurate base. 



    Edited for sloppy calc’s

  • 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 

  • thanks martyn   just run that calc for me again  amps x volts    Do we assume 240V coil feed ?   for 24/7  annual looks more like £40  or so .. 

    but hey its not huge... thanks again  Ms O 

  • Yes, My Bad. 

    The Full load for the Anti Islanding relay was at 24v DC - still need to calc for the 24v supply as well - which I missed, You are correct on the Isolating Contractors, they are usually 230/240v AC. 

    Relatively rare that particular install in domestic but the client demand was on grid with full capability of running off grid in either mains fail or by choice, we had a few critical load items from the UPS side of a Victron MultiPlus and an Auto Transfer Switch from grid to critical backup with a load manager in a grid off scenario. 

    On your other point re ‘Off Grid’ this really needs a sound business case where it is a choice vs a necessity. 

    It is very difficult to provide accurate data on solar production so most installers use standard data with adjustments for location etc. 

    If you use the Victron Eco system and install ESS the VRM Portal is second to none in reporting and is free. No guessing necessary once you have a bit of your own actual data. 

    Often what is missed is things like the cost per cycle on batteries.  

    I cannot remember what the Full cycle cost is but something is telling me it was around £0.30p /5kWh based on 25Years and average use. For the PylonTech 48v batteries. 

    This of course is going to be different for on and off grid uses

    I am working on a system at the moment with a friend, 16 x 370w panels across 3phase with either 5 or 10kW of Batteries.

    This is not an off grid installation as their demand  level still requires the grid as Batteries to mitigate that would be unrealistic in the UK for them. 

    The estimated payback time is circa 5 years which is monitored and reported on in real time with a BMS - Always nice to know when an investment has paid off in financial terms as well as Polar Bears! 



  • Hello Martyn 

    Sounds like your a very experienced solar installer Me just trying to understand what is offered in the jargon  before I leap. 

    Understand solar install is zero VAT as well as kit supply . ? Struggling to understand what is in scope of zero vat for an installer. My scheme ( sort of off grid generator)  cannot work  eg if I dont rewire the kitchen . Meaning floor has to come up and more.

    Plus a garden trench for an ac cable ? 

    Is it possible I could tap your advice on what is or is not in zero VAT scope for an installer if I give the list ...  ?    Happy to do this off line if you like . This is about money rather than technical . 

    On that issue I am stuck My kit supplier has given me an estimate but only based on a standard grid tie . The end. . 

    ciao Ms O  

  • Ha, not sure I’d say that, I’m better on the controls and automation side of things than panels on roofs etc! 

    Solar is simple when compared to the VAT side of things, seems impossible to keep up. 

    The way I understand it at the moment is Solar and battery installs are VAT free and in addition as of March 2024 the addition of Batteries to an existing system is also VAT Free.

    This would only include parts pf the installation strictly for the Solar installation. Rewiring if a kitchen on the face of it would not be VAT free, it may be 5% if you could demonstrate it is absolutely necessary for the energy savings part - A long shot I would guess.

    This is of course only tree for installed equipment by VAT registered Companies.

    As an individual you cannot purchase without VAT (Save for a reclaim on New self builds) 

    You could use smaller contractors who are not VAT registered to save there if that is a thing in your area. 

    Most Solar suppliers and installers I come across are ‘stuck’ in ‘normal’ installs mode and dont really want to get in to the more complex installations - No money there for them in comparison to the ‘easy’ stuff.

    Not quite out yet but you could also have a read of the draft PAS 63100, not too heavy going. 

    Here is a short blog I wrote a few years ago that may be of interest.