Depends on the size of the generator, of course. For domestic systems it's normally the voltage at the generating station being driven too high, I believe. Which needs adjustment of transformer settings and perhaps reinforcement of the cables to reduce voltage drop. For large direct grid-connected systems there's a map showing points where there's available spare capacity on the network and solar farms etc are generally built near them. Otherwise again, lots of new cable needs to be laid.

Posted By: owlmanAs I understand it, it's also the number of other users in the immediate area who use up the power before it gets to the first substation.

Well, the number of other consumers only matters in so far as they affect the voltage and whether it breaches limits. Or less likely, the current rating of the local system.

Posted By: Peter_in_HungaryI am thinking of the low voltage local network where several domestic PV systems are feeding in at a level that exceeds the local demand which will cause a voltage rise (yes?)

Yes.

What needs to change on the grid so that this over voltage is not a problem? Can (will) the excess power be absorbed by the grid through the low to medium voltage transformer and from there all the way back to the power station that reduces output to compensate.

Each local transformer is set so it delivers a legal voltage range under normal conditions. If they build another house or two and add them to the circuit they may need to increase the transformer setting to deliver slightly more voltage so it stays in the legal range at the houses. PV complicates things, because it pushes the voltage up and tests the other, high end of the range. So if there's a lot of PV they may need to turn the transformer down. But then it gets dark at night etc etc. There's only so much they can do. So they may need to split a circuit and put a new transformer in, and/or beef up the circuits so there is less loss in them. Ultimately, depending on how much generation is connected and the topology of the local grid, other parts upstream of the local bits may need upgrading as well. But it's all real work involving people in fluorescent jackets, not pushing buttons in offices. And yes, ultimately it results in one or more power stations reducing their output a bit.

Posted By: Peter_in_HungaryOtherwise how is it managed?

First off, if everyone plays by the rules and submits a G98 notification/G99 application, the DNO will know exactly how of each type of generation there is on any particular section. They can then increase transformer size if needed or retap existing transformers to keep voltages within statutory limits- 230vac +10%/-6%. AFAIK theres a range of supply logging goes on in sub stations and the DNO can see if voltages are fluctuating in unexpected ways, so if a whole street installs PV without notifying the DNO, the DNO will know they've done it as the local substation voltage will rise every time the sun shines.
I read somewhere of somone saying their DNO retapped their local transformer seasonally to lower the local voltage in the summer when there was a load of PV pushing it up.

Posted By: philedgeI read somewhere of somone saying their DNO retapped their local transformer seasonally to lower the local voltage in the summer when there was a load of PV pushing it up.

I don't quite understand that. PV doesn't push the voltage up at night, so at night conditions are the same as if there was no PV. Perhaps there was a large electric space heating demand that needed the voltage to be pushed up in winter?

FWIW, More than you, or I, ever wanted to know about transformer taps https://electrical-engineering-portal.com/transformer-voltage-regulation

And for no particular reason, similar for forecasting https://otexts.com/fpp2/

Posted By: philedge

Posted By: djhI don't quite understand that. PV doesn't push the voltage up at night, so at night conditions are the same as if there was no PV.

I think the idea is that by dropping the voltage the daytime PV doesnt push the voltage over 253v and at night they would run a slightly lower voltage than optimum.

Yes, but then there'd be no need to adjust it upwards in winter?

If you have a smart meter, it can report voltage and current readings to the DNO, if they request. That can give them a heads up if the voltages down your street are pushing too high on sunny days, or too low when everyone is using their electric heaters and EV chargers. So, they could make better decisions whether to approve any more PV on the same feeder/phase as your house.


For example, with no loads, our smart meter reports 229.7V, but when I turned on some heaters, the current went up by 19.4A and the voltage reduced by 5.8V. So the apparent impedance of our supply is 5.8/19.4 = 0.3 Ω .

If I applied to add say 15kW of PV, my voltage would go up to 250V which would be within limits, so the DNO could approve it. It would be my problem if the extra impedance across my home installation pushed up the voltage to trip my inverter.

By repeating this at different times when my neighbours are using more/less power, the DNO can work out how much of the supply impedance is on wires that I share with neighbours, and whether my PV would mess up the voltages at their supplies. They could consider if my export is at the same time as the neighbours, and whether they might want to reserve capacity to increase the substation voltage in future once we all get EV chargers.

(Edit to add: exporting lots of power will pull down the voltage of the Neutral conductor, as well as increasing the voltage of the phase conductor. There are various permutations of how closely Neutral is coupled to Earth. IDK if the 253V legal voltage limit is measured relative to Earth or to Neutral, that could affect the answer a bit. I note the meter doesn't have an earth connection.)