DNO voltage limits and solar PV generation

Well, the voltage rise on the consumer side of the meter is not the DNOs problem,  and presumably the inverters trip limit of 264V was designed to allow for some of that. (inverters sold in places like South America, where the wiring is thinner and the regulation more erratic are programmed with wider default limits)

There is a general problem that all the transmission and distribution in the UK is designed assuming the voltage slope is downhill from the power station as the source to the consumer as the load. Obviously reversing roles and that direction of slope has some serious implications, and there will be cases, designed for nearly 250V at the transformer and 20V or drop to the consumer, where reversing that slope takes things out of spec. Ideally the DNO would move a transformer tap, but that may not be so easy for them to do if then the folk at the other end of town drop out of permitted tolerance in the other direction.

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.



how big is the supply, and how much PV power are we talking?

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'd get back to the original installers (if still trading) and get them to tweak a control knob to bring the Voltage down before the high Voltage damages equipment.


This is at a local bowls' club. I imagine a bowls' club to have a few lights, a kettle and perhaps a radio in a damp wooden shed in a smooth field. Does this site actually benefit from a solar installation?


Z.

"get them to tweak a control knob to bring the Voltage down".

Don't follow. I thought the voltage rises to the level needed to export the power being generated.. No control knobs to tweak.

Regarding loads, you forgot the beer coolers!

"Harry hasn't said whether it's a G83 or G59".

Harry hasn't said because Harry doesn't know but it is whatever would have been a standard connection to a clubhouse 20 years ago.

There is an overhead line in the vicinity (3.3kV?) with a small pole mounted transformer on one of the nearest poles and a transition to HV cables on the other. Where these cables go isn't obvious, i.e. we haven't located a transformer, but the supply could be from either. If it is from the pole mounted Tx then it is probably only the club that it is supplying.

Advanced inverters are needed with lots of sophisticated capability.


It is a very technical and challenging subject.

https://www.youtube.com/watch?v=bzCoE2dzSlg


Z.

Although American this video shows the general set up for grid tie inverters.

https://www.youtube.com/watch?v=Yf6nPGPuKoU


Z.

The adjustment(s)  will not be a modification if the parameters have drifted out of spec. It will be more like a re-calibration.


Z.