Why is inverter cut off voltage so high?

[Marco]

The power companies in my country are getting desperate to deal with excessive rooftop solar and unwanted currents on the distribution grid.

Why didn't government mandate the cut off voltages for inverters be substantially lower than the max voltage power companies have to maintain? The power companies have to maintain <253 same as the inverters.

If the inverters had to cut off at say 243V they could just change the tap on a local transformer as a way to regulate rooftop solar. It would not be popular, but at least they'd have it in their toolbox.

[Siwastaja]

Because on grid-level, maintaining balance of production and consumption is not based on voltage, as the grid is very low-impedance.

High voltage is a last mile problem, absolutely nothing to do with nation-wide balance of production and consumption. So if inverters started to cut off at lower voltage, many inverters would cut off when there is still demand for the generated power in the grid. The only reason for voltage limit is to avoid causing damage by overvoltage, which again would be a localized problem.

[tszaboo]

Please don't believe the bullshit that those companies are feeding you.
Repeat after me: There is no such thing as too much solar generation.
If there would be, then the voltage increases, and the inverters shut off. As you already seen it, every inverter sold in the EU, by law, cannot output voltages that are higher than the maximum specifications for the grid. You cannot overload the grid with too much solar. What you can do is, hurt their bottom line. This costs them money. And that's why they started this nonsense explanation that there is too much solar. They lie to you for money, it's that simple.
And now politicians and the ACM and the people without solar started believing them and mobbing us with extra costs. Oh and the lobbying. They had zero issues fixing the price for 1 EUR/KWh, when diesel generators were cheaper than buying electricity from them, and now their profits are bad.

[Marco]

High voltage is a last mile problem, absolutely nothing to do with nation-wide balance of production and consumption. So if inverters started to cut off at lower voltage, many inverters would cut off when there is still demand for the generated power in the grid. The only reason for voltage limit is to avoid causing damage by overvoltage, which again would be a localized problem.

They now have zero control over currents from inverters except letting voltage rise above 253V, which they are not allowed to do intentionally ... but I have my doubts, they almost certainly do it on the sly with regulators looking the other way if they don't abuse it too much.

I don't like these unspoken rules, better just handle it in the open. Which they could, if inverters had 5% headroom instead of the full 10% the powercompanies have.

[Marco]

If there would be, then the voltage increases, and the inverters shut off.

As far as I know they have service level agreements which disallow voltage to go over 10% too, regardless of small generators ... so they would be breaking their contract if they do this structurally.

What caused me to question this is the plan in Zeeland to pay people with rooftop solar to turn it off. As I said, desperate.

[tszaboo]

If there would be, then the voltage increases, and the inverters shut off.

As far as I know they have service level agreements which disallow voltage to go over 10% too, regardless of small generators ... so they would be breaking their contract if they do this structurally.

What caused me to question this is the plan in Zeeland to pay people with rooftop solar to turn it off. As I said, desperate.

The same 10% as inverters. There is nothing magical here, a power plant cannot output more, an inverter cannot output more.

What breaks my mind is this:
We have net metering. It's a subsidy. It's the elected government making a decision that they are going to support the people with solar panels to advance green transition. Subsidies by definition mean that whoever is using it, it's going to be cheaper, and for other people it's going to be more expensive.
So with this declared, unelected electricity companies, all of them at the same time decide that they are going to charge people with solar panels money. Because it makes electricity more expensive for everyone else, and it's unfair. Guess what, that's the whole point of a subsidy.
So an elected government made a decision, that a unelected cartel of energy companies unmade. All of them at the same time. And the orders for solar installations are down 95% since last year. And the electricity price came down by drumroll, 1.5 cents for everyone else. I guess they couldn't afford that 1.5 cents to save the environment. Meanwhile we have 13.5 cent tax on KWh, and VAT on top of that (because of course tax on tax).

[Marco]

A powerplant is under their control, when they want less current on a leg of the  high voltage distribution network they can modulate the power of two or more plants in different locations to do so.

Needing to break their service level agreements to control rooftop solar is a problem.

[tszaboo]

A powerplant is under their control, when they want less current on a leg of the  high voltage distribution network they can modulate the power of two or more plants in different locations to do so.

Needing to break their service level agreements to control rooftop solar is a problem.

Do you think that's happening?

[Marco]

Do you think that's happening?

They payment scheme in Zeeland shows they are both desperate to control rooftop solar and to avoid doing so through excessive voltage.

Basically most PV on sunny days is flowing to the Randstad industry, there is as of yet sufficient demand but the grid wasn't designed for current flowing that way. Long term we need more batteries and intermittent hydrogen generation, but for now they need to prevent overloading the grid.

[tszaboo]

Do you think that's happening?

They payment scheme in Zeeland shows they are both desperate to control rooftop solar and to avoid doing so through excessive voltage.

Basically most PV on sunny days is flowing to the Randstad industry, there is as of yet sufficient demand but the grid wasn't designed for current flowing that way. Long term we need more batteries and intermittent hydrogen generation, but for now they need to prevent overloading the grid.

Right, so how exactly this overload happens? Like which parameter is overloaded?
Because the cables are not zero impedance, and they are designed to operate with a high voltage transformer on one end, and load on the other. The transformer being the higher voltage. So the typical setpoint  (ratio) for this transformer is higher than nominal voltage. When houses start feeding back electricity, the voltage increases further. Finally the houses closer to the transformer will be able to generate electricity, the ones further away will shut down their inverters. So where is the overload? Do we get to see sparks?

I especially love when they talk about that the grid cannot handle more consumers because it's overloaded with solar. Producers. So somehow electricity flowing in one direction is overloading the wires that can't handle the other direction? Does this make any sense to you?

[Marco]

In the extreme, sagging cables and boiling transformer oil. Traditional production was near consumption, not power from the whole country flowing to the Randstad.

Obviously they can just allow voltage to rise above 253V but I suspect they are contractually obligated not to do so. Hence the desperation.

[tszaboo]

In the extreme, sagging cables and boiling transformer oil. Traditional production was near consumption, not power from the whole country flowing to the Randstad.

Obviously they can just allow voltage to rise above 253V but I suspect they are contractually obligated not to do so. Hence the desperation.

But do you understand Kirchoff's current law?
There is no such thing as too much generation. And if the voltage is already high at the power plant, the inverters see even higher voltage when they generate. It's not the same everywhere it's a dynamic system with resistances in between.
And the only way to direct current from places is when there is a voltage difference. It follows the same laws as your regular circuit. How would you get sagging cable? That cable is designed to carry more current from the power plant to the consumer (by the high voltage transformer turns ratio and nominal voltage), and the consumers are limited by this impedance (and the firmware of the inverter) of how much electricity they can feed back.
The situation they are talking about is impossible.
What is possible is that they are obligated to buy electricity back when the price is negative. And that costs them money. And they lie to you.

[nctnico]

Please don't believe the bullshit that those companies are feeding you.
Repeat after me: There is no such thing as too much solar generation.

No, but there is something like a congested grid which can't bring amount of electricity generated to places where it is needed.

[tszaboo]

Please don't believe the bullshit that those companies are feeding you.
Repeat after me: There is no such thing as too much solar generation.

No, but there is something like a congested grid which can't bring amount of electricity generated to places where it is needed.

True, which is something that is under their control since the mainline is under variable voltage control.
So it's quite possible that a consumer is fed by a fossil power plant and inverters are shut down other parts of the country.
Yet this is not an overload.

[tszaboo]

Actually this is a software and organizational problem. DSOs if they would be a little smarter, they would sell the solar generation on the day ahead market, not the spot market. At least more of it. Then they would receive a few cents for the electricy instead of costing a few cents.  But instead they are making it the consumers trouble.

[nctnico]

Please don't believe the bullshit that those companies are feeding you.
Repeat after me: There is no such thing as too much solar generation.

No, but there is something like a congested grid which can't bring amount of electricity generated to places where it is needed.

True, which is something that is under their control since the mainline is under variable voltage control.
So it's quite possible that a consumer is fed by a fossil power plant and inverters are shut down other parts of the country.
Yet this is not an overload.

It is an overload. You have X transport capacity and Y to transport. If Y exceeds X, you need to limit Y. There is no argueing around that. You can't make a powerline transport twice its rating by making the voltage a few percent higher.

[tszaboo]

Please don't believe the bullshit that those companies are feeding you.
Repeat after me: There is no such thing as too much solar generation.

No, but there is something like a congested grid which can't bring amount of electricity generated to places where it is needed.

True, which is something that is under their control since the mainline is under variable voltage control.
So it's quite possible that a consumer is fed by a fossil power plant and inverters are shut down other parts of the country.
Yet this is not an overload.

It is an overload. You have X transport capacity and Y to transport. If Y exceeds X, you need to limit Y. There is no argueing around that. You can't make a powerline transport twice its rating by making the voltage a few percent higher.

Overload by too much consumption is possible and off topic. Overload because too much generation, is not possible, because the voltage increases and the inverters switch off. Voltage increases because the feed line has a resistance, and the feed line is designed to handle the voltage difference. QED.

It's the equivalent of saying: I've put too much current into a resistor, without increasing the voltage, and it overloaded.

[Siwastaja]

Oh, this was another nutjob word salad thread after all. Nice. We didn't have too many already.

[Marco]

How would you get sagging cable?

Transformer taps are not static. If voltage in Zeeland is 253V, they can change the tap to have it generate a higher voltage on the high voltage side to push current to the Randstad and lower the mains voltage in Zeeland. They can overpower the resistance of the wires. Obviously they won't do that to the point of failure, but not doing that means letting the voltage in Zeeland getting too high and breaking their contractual obligations.

[tszaboo]

How would you get sagging cable?

Transformer taps are not static. If voltage in Zeeland is 253V, they can change the tap to have it generate a higher voltage on the high voltage side to push current to the Randstad and lower the mains voltage in Zeeland. They can overpower the resistance of the wires. Obviously they won't do that to the point of failure, but not doing that means letting the voltage in Zeeland getting too high and breaking their contractual obligations.

Of course they are not going to overload the grid intentionally.
How does the voltage get too high? The inverters are limited to 253V, the transformer cannot be 253V because Ohm's law. If that's also 253V there is no current. It has to be lower.

[Marco]

How does the voltage get too high? The inverters are limited to 253V

That is already too high, they can't just run at the edge ... hence the desperation and trying to pay customers to take their PV offline.

[tszaboo]

How does the voltage get too high? The inverters are limited to 253V

That is already too high, they can't just run at the edge ... hence the desperation and trying to pay customers to take their PV offline.

Sure they can. It's within specifications for everything. So is reducing the output of the inverter.
What they dont like is paying negative prices.

[Marco]

If they were allowed to just turn off (most of) the inverters by running the mains voltage near 253, they could do that for free ... yet they are paying people to turn them off instead.

Why do you think they are doing that?

[tszaboo]

If they were allowed to just turn off (most of) the inverters by running the mains voltage near 253, they could do that for free ... yet they are paying people to turn them off instead.

Why do you think they are doing that?

Can you please post a reference for this?

[Marco]

https://tweakers.net/nieuws/225662/stedin-en-eneco-vragen-huishoudens-in-zeeland-om-zonnepanelen-uit-te-zetten.html