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 

  • 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

  • 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 

  • 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.



  • Thanks Martyn  

    I replied to your blog website : List of things maybe you can point me to advice.  Ciao Ms o