DNO voltage limits and solar PV generation

I agree with Mike in the principle but...

One solution might  be a local voltage reducer  in the building ( a low voltage high current winding to oppose, or buck, the incoming supply, auto-transformer style)  so the 250V DNO side is then transformed down to more like 230-235 V in the building, better for the inverters, and better for things like the life of  light fittings too.

Harry hasn't said whether it's a G83 or G59 (or indeed G98 or G99) connection but it's worth remembering that from the DNO's point of view a private transformer would mean the OV/UV settings are no longer standard, which is By Agreement only so no longer G83/G98 and if they don't agree with you that you can use standard 230V settings after a 250/230V transformer (or similar) a separate relay would likely would be required, commissioning and all. This is because the connection agreement, strictly speaking, is concerned with the voltage at the point of connection (the cutout) you would need to adjust the voltage settings by the transformer ratio so the DNO sees the same +/-% on at the POC*. This is all do-able (I've done similar with the DNO's permission) but may or may not be a cost-effective solution.


Also if you are going to the expense of a G99 relay and commissioning you could, if you're satisfied yourself that there won't be other local problems from voltage rise, fit the G99 relay at the origin (with contactor at the inverter(s) and manually adjust the inverter settings to a wider range (as it's no longer the G59 interface protection).


Are there any discretionary loads the PV could be controlling? Perhaps an immersion tank? Obviously this reduces export too so only worthwhile if it's actually doing something useful; then again if it is a useful load there's also a benefit in the difference between import and export rates p/kWh.


Might be worth considering whether adjusting the power factor setting will help (within the limits of the connection agreement). From memory can't remember whether G83/G98 give you that option though.


I would check the calcs for the private cable with an eye to an upgrade since if the volt rises by 11V=4% I'd consider it rather undersized for the generator. But it might be that there's a high impedance joint somewhere that can be fixed, or perhaps more likely the voltage is swinging on the DNO's side because of generators their network wasn't designed for, and all that PV isn't diversifying... Don't forget that if the DNO does come to site measuring the voltage, finds it high, and then back within limits when the PV is turned off, the club might not be allowed to turn it back on again if it's found to be in breach of the connection agreement, even it was a G83 system.


*(Side track but this does mean that voltage optimisers or anything else with a non-fixed ration are a problem and generally require a separate relay upstream, which is specifically noted in the latest documents; in an hotel room so not got copies to hand)

I agree with Mike in the principle but...

One solution might  be a local voltage reducer  in the building ( a low voltage high current winding to oppose, or buck, the incoming supply, auto-transformer style)  so the 250V DNO side is then transformed down to more like 230-235 V in the building, better for the inverters, and better for things like the life of  light fittings too.

Harry hasn't said whether it's a G83 or G59 (or indeed G98 or G99) connection but it's worth remembering that from the DNO's point of view a private transformer would mean the OV/UV settings are no longer standard, which is By Agreement only so no longer G83/G98 and if they don't agree with you that you can use standard 230V settings after a 250/230V transformer (or similar) a separate relay would likely would be required, commissioning and all. This is because the connection agreement, strictly speaking, is concerned with the voltage at the point of connection (the cutout) you would need to adjust the voltage settings by the transformer ratio so the DNO sees the same +/-% on at the POC*. This is all do-able (I've done similar with the DNO's permission) but may or may not be a cost-effective solution.


Also if you are going to the expense of a G99 relay and commissioning you could, if you're satisfied yourself that there won't be other local problems from voltage rise, fit the G99 relay at the origin (with contactor at the inverter(s) and manually adjust the inverter settings to a wider range (as it's no longer the G59 interface protection).


Are there any discretionary loads the PV could be controlling? Perhaps an immersion tank? Obviously this reduces export too so only worthwhile if it's actually doing something useful; then again if it is a useful load there's also a benefit in the difference between import and export rates p/kWh.


Might be worth considering whether adjusting the power factor setting will help (within the limits of the connection agreement). From memory can't remember whether G83/G98 give you that option though.


I would check the calcs for the private cable with an eye to an upgrade since if the volt rises by 11V=4% I'd consider it rather undersized for the generator. But it might be that there's a high impedance joint somewhere that can be fixed, or perhaps more likely the voltage is swinging on the DNO's side because of generators their network wasn't designed for, and all that PV isn't diversifying... Don't forget that if the DNO does come to site measuring the voltage, finds it high, and then back within limits when the PV is turned off, the club might not be allowed to turn it back on again if it's found to be in breach of the connection agreement, even it was a G83 system.


*(Side track but this does mean that voltage optimisers or anything else with a non-fixed ration are a problem and generally require a separate relay upstream, which is specifically noted in the latest documents; in an hotel room so not got copies to hand)