Why is inverter cut off voltage so high?

[tszaboo]

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

Op sommige momenten wordt daardoor meer energie opgewekt dan er gebruikt wordt, met als gevolg dat de druk op het elektriciteitsnetwerk toeneemt.

Translation:

At times, more energy is generated than is used, resulting in increased pressure on the electricity network.

Once again, how is this possible? Electricity is not a liquid or gas, it doesn't have pressure, and obeys Kirchoff law. It's not a bucket.

Your question was: why don't they do it if they can? Because they cannot. This is Eneco and Stedin, they are responsible for billing. They are also obliged to pay you if you generate electricity. The grid is operated by Enexis. They probably asked Enexis to increase the voltage, who has zero incentive to do so, because they are getting a flat fee for delivery.
No indication on what is overloaded. No blackouts or any failures in this record breaking summer.
Also, they are going to compensate 40c/KWh based on... not generated electricity? How does this actually work?

And here is an article talking about how all this amount of extra charge might be illegal:
https://tweakers.net/nieuws/225436/acm-gaat-extra-onderzoek-doen-naar-kosten-en-vergoedingen-van-zonnestroom.html

Let me ask you this. They point at solar panels as scapegoats, and started charging ~20-30 EUR for 2 million households with solar every month. That's ~600 MEUR a year. You see some inventive to lie about this?

[Simon]

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).

what the hell are you waffling on about? I don't know about your country but in mine you get paid 15p/kWh of export and they sell it for 30p/kWh, we have to pay for our own solar panels, I don't see the subsidee. The only clever thing I can do is use my battery, charge it at night for 7.5p/kWh and then I can use it during the day instead of paying 30p/kWh.

Inverters are current sources that follow the grid voltage, it's all really simle, it just works, no conspiracy to see here.

[nctnico]

In the Netherlands there is a lot of turmoil about solar panels at the moment. There are a few things at play:

1) The government promised that people would get the same price per kWh they provide to the grid as they would pay per kWh for as long as they use more than deliver to the grid. Call it a 'kWh per kWh subsidy'. The government and energy companies pay for this as a form of subsidies to motivate people to get solar panels.
1a) If people deliver more to the grid, the energy companies would pay a certain amount to the people for the energy. Typically this wasn't a large amount.
1b) This arrangement would originally end by 2025. Then it got changed to a gradual changeover period between 2025 and 2031 (IIRC). However the latest plan from the new parliament is to stop this kWh for kWh subsidy per 2027.
1c) The number of solar panels on homes is far greater than projected; the amount of energy produced is 3 times higher than expected / planned for. The 'kWh for kWh subsidy' should have been stopped in 2021 but this date got shoved around several times.

2) Energy companies have found a loop-hole where they can charge people for supplying the grid with energy. A feed-in tariff. At the same time the electricity prices have been lowered. So people get less from the 'kWh for kWh subsidy' and must pay to feed into the grid. The effect is that solar panels have a much longer ROI than they used to have and what people planned for.
2a) Once the 'kWh for kWh subsidy' stops, the feed-in tariffs are supposed to dissapear.
2b) For example: I pay 21ct per kWh but I get 12ct per kWh I deliver to the grid (if I would supply more to the grid than I consume). However, I have to pay a 240 euro/year feed-in tariff based on the amount of electricity I supply to the grid. Even my relatively cheap DIY solar system went from a ROI of 2 years to 5 years. And the 5 years number is low due to the massive payback I got in 2022 which paid for 1/3rd of the install. People who paid full price for a similar installation I have, are looking at an ROI of 10 years instead of 5 years.

3) The Dutch electricity grid is seriously congested in many places. At the level that new homes and companies can't get grid connections due to shortage and at other places renewable energy can't be fed into the grid. Some companies are actually running on diesel generators in order to have electricity. This is all because the government body which gouverns investments in the electricity grid choose to ignore specialists telling them in 2008 the electricity grid would become seriously congested in 15 years. So nothing happened to expand the grid for 15 years while the need for expansion was obvious all this time.
3a) This grid congestion leads to all kinds of creative solutions in order to keep the grid manageable. Appearantly in some regions people are asked to turn their solar panels off and being compensated for not supplying energy. It is like paying a wedding band NOT to play but here we are.

However, none of this has to do with inverter cut-off voltages.

[tszaboo]

what the hell are you waffling on about? I don't know about your country but in mine

You have different rules.
We have net metering, it's the law. Yet they made some illegal changes, every single electricity provider at the same time to charge people with solar panels. Some per KWh you feed back, some a flat fee per month.
Also, sale price of excess electricity went from ~25 cent/kwh to 3 cent in 3 years.

[coppercone2]

I can tell you one thing about US power companies, its serious nepotism. Meaning its in your interest to question them because its all in the family. Its literary run by like male heirs lol

if you work there they seriously expect your kids to work there too   

[Simon]

what the hell are you waffling on about? I don't know about your country but in mine

You have different rules.
We have net metering, it's the law. Yet they made some illegal changes, every single electricity provider at the same time to charge people with solar panels. Some per KWh you feed back, some a flat fee per month.
Also, sale price of excess electricity went from ~25 cent/kwh to 3 cent in 3 years.

Oh no, nearly the same rules. When we started you got 60p/kWh for everything you generated even if you used it, that was over subscribed and it then came down to 1.6p/kWh for new installs. I got in at my last house with 4p/kWh. They paid for what we exported at 6p/kWh so you got a 4p bonus for using your own and 10p for net export.

That is all over now and it is net metering of export at around 15p/kWh, my supplier gives me 16.5p as I also buy from them.

[tszaboo]

what the hell are you waffling on about? I don't know about your country but in mine

You have different rules.
We have net metering, it's the law. Yet they made some illegal changes, every single electricity provider at the same time to charge people with solar panels. Some per KWh you feed back, some a flat fee per month.
Also, sale price of excess electricity went from ~25 cent/kwh to 3 cent in 3 years.

Oh no, nearly the same rules. When we started you got 60p/kWh for everything you generated even if you used it, that was over subscribed and it then came down to 1.6p/kWh for new installs. I got in at my last house with 4p/kWh. They paid for what we exported at 6p/kWh so you got a 4p bonus for using your own and 10p for net export.

That is all over now and it is net metering of export at around 15p/kWh, my supplier gives me 16.5p as I also buy from them.

Not nearly. I also get charged for export now. You heard that right.
And that's not the point. The point is they are legally required to do net metering.
And now solar panels are apparently responsible for everything. Lack of capacity on the supply (!), high prices, probably also world hunger and WW2.

[Simon]

lots of governments made mistakes. In the UK they offered 60p when the buying cost to the consumer was 15p or less and this was for what you generated. Naturally anyone with money to invest jumped on it and in later years it became evident that they had not budgeted for the amount of people that would take it up. So they cut that bit to 1.6p and introduced the export tariff along side it and now it is export only.

The reason there are all of these devices that for example dump electricity into heating water to stop you from exporting was for these wealthy people who not withanding getting 4x the actual value of the electricity sought to make sure that none of it was exported. Where they could heat water at 1/4 the price with gas they instead heated the water with electricity they were paid for, meanwhile the grid was being run by gas fired power stations.

So companies like myenergy who claim to make green energy products are just a bunch of liars fueled by the money of the middle class that even when paid 4x what something is worth still won't supply it.

[Marco]

However, none of this has to do with inverter cut-off voltages.

It is the method of last resort to turn off otherwise uncontrolled small generators when there is too much power for consumption&transport.

If the cut off voltages were lower it could have been used as a more routine way to add control, now if they want automated control it will become a very expensive retrofit.

[tszaboo]

lots of governments made mistakes.

Very true. I heard stories of Spanish people running diesel generators in their basement overnight because it was worth it.
Or the other end, Hungary introduced an extra tax on solar panels because they have to be disposed at some point.

There are two things I'm a bit upset about. One is the lying about the technology, that is apparently so abundant and believable, that even engineers repeat these.
In 2017 in Belgium I was working at a company that was monitoring solar panel installations, and trading green certificates. We were actively monitoring the "too much production" issue and conceded that abut 5% of our customers were effected, about 50 EUR/year loss of their production.  We also worked on the mathematics and physics behind the grid. The idea behind it was that we could (with external communication) force inverters to generate some (the correct amount ) reactive power into the grid, that provides a very cheap way to compensate the reactive currents of large industrial installations.
We were also running some projects that would time the usage to the generation, with estimated 3% capacity savings nation wide. Doesn't sound like much, but that's a cost of a power plant right there.
Anyway, that's when an university professor showed the mathematics, on how "too much solar" is impossible. It's more complicated, but the basics are really just Ohm's law, with more current there is more voltage.
Anyway, fast forward some time, Belgian government cuts incentive for solar power and re-introduces it for coal power. Their policies (and the bad management of that company) ultimately put us out of business. So I have an axe to grind about bad policies and lying about solar.

[Simon]

You are talking about the smart grid. Having made an utter mess of "smart" meters governments have still not learnt and are letting private businesses battle it out to see who wins rather than just set up a committee and get a technical standard hammered out so that companies large and small can offer their products and ideas and things move faster without a single company monopoly.

I have in fact wondered about setting inverters to output slightly more than a power factor of 1 to help balance the grid. Obviously this cannot be the sole solution or we are back to having much more current flow on the grid than the wiring can take but distributed generators that supply a power factor over unity would be manageable locally and lots of local systems being better balanced would make a big difference to the main grid backbone.

[johansen]

You are talking about the smart grid. Having made an utter mess of "smart" meters governments have still not learnt and are letting private businesses battle it out to see who wins rather than just set up a committee and get a technical standard hammered out so that companies large and small can offer their products and ideas and things move faster without a single company monopoly.

I have in fact wondered about setting inverters to output slightly more than a power factor of 1 to help balance the grid. Obviously this cannot be the sole solution or we are back to having much more current flow on the grid than the wiring can take but distributed generators that supply a power factor over unity would be manageable locally and lots of local systems being better balanced would make a big difference to the main grid backbone.

programming in a fixed power factor of 1.05 or 1.1 only offsets the amount of capacitors needed to compensate, it doesn't do anything else. 

where i live, 100KVA capacitors can occasionally be seen on power poles, to cancel out the inductance of the powerline, or reduce the amps a little due to say, 0.9 powerfactor of homes these days (probably used to be worse) . 100 kva is only 10 amps at 12700 volts or 22uf (granted actual values are different as there are three capacitors at 7200v line to ground. those capacitors last decades, and have very, very low losses.
 
my guess is, a solar farm at 100% amperer output delivering 1.5 power factor (ltes say the solar energy input is at 70% and the current is at 100% so that's 70% reactive power plus 70% real power means 100% amps output..

lets say you run the solar farm at 100% current all the time regardless of solar incident energy. What is the cost to the inverter's life? lets assume power flow stays positive at all times (it would be 2% negative, at night to offset losses of reactive power production.) -the solar operator is going to want to get paid for the 2% reduced production caused by the increased losses in the inverters.

my guess is, its not worth it.

now, if the utility has control over the inverter's power factor.. it will help with short term voltage control (due to the inductance of the transmission line and the varying load in the nearby location).. but it will not control the power or the frequency, as the solar farms are always delivering 100% of what they can, unless they are contractually or actively limited by the grid operator "somehow".

in otherwords, the dynamic power factor control may be able to be used to increase the life of tap changers... but that's about it.

that.. "somehow" is the problem and the solution. everyone wants to make the most amount of money possible, but the grid demand is fixed, unless dynamic price lowering can increase consumption.

[johansen]

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.

this can work for controlling micro grids, when the frequency is fixed by a central fixed battery inverter, and when you can tolerate a much wider swing in voltage.

the power grid isn't controlled by voltage its controlled by very complicated agreements between power producers as to who is going to generate x amount based on y price. and they all mutually work to keep the frequency constant, although there could be bad behavior by certain producers intentionally to destabilize the grid but i think they would quickly lose money trying that.

there is no massive battery to keep the frequency fixed, so if power in>power out, frequency rises. voltage doesn't always rise or fall. voltage can fall and current increases while the frequency increases and total power increases.

in america, perhaps not now but 10 years ago, half of the power grid's load was induction motors over 100 hp. as more and more loads switch to VFD driven machines, the load will stay constant regardless of the grid voltage, or frequency (within 10% limits)

a direct online induction motor: when the voltage rises, current goes down.. power factor goes up, which means the generators don't need as much excitation to produce the same power. its a closely regulated dynamic problem that is not intrinsically stable. when the frequency rises, the load increases. significantly. as in 1% increase in frequency is a 3% increase in load for most large pumps. the effect of that is a significant stabilizer.

a 230v motor may draw 12.5 amps full load at 87% power factor at 93% efficiency. when the voltage drops to 208, that motor will draw 15 amps at around 83% power factor and 89% efficiency.

as much less of the power grid is resistive loads, which decrease in current as voltage goes down, and much more of the grid is fixed power loads due to all the electronic drives.. the grid is going to become less and less stable.

[Marco]

Rooftop solar for the moment isn't controlled at all, except for by voltage ... and adding any other sort of control is expensive.

[nctnico]

There are two things I'm a bit upset about. One is the lying about the technology, that is apparently so abundant and believable, that even engineers repeat these.
In 2017 in Belgium I was working at a company that was monitoring solar panel installations, and trading green certificates. We were actively monitoring the "too much production" issue and conceded that abut 5% of our customers were effected, about 50 EUR/year loss of their production.  We also worked on the mathematics and physics behind the grid. The idea behind it was that we could (with external communication) force inverters to generate some (the correct amount ) reactive power into the grid, that provides a very cheap way to compensate the reactive currents of large industrial installations.
We were also running some projects that would time the usage to the generation, with estimated 3% capacity savings nation wide. Doesn't sound like much, but that's a cost of a power plant right there.

I'm missing one important element in this story: does the grid have the capacity to transport the electricity where it needs to go? If you look closely at your electricity bill, you'll see a significant amount of money goes into transport costs already; for a household the transport costs can be 50%. IOW: it makes no sense to transport electricity far away if that means the transport costs are going to dominate the price per kWh.

[Simon]

correct, micro generation is actually quite good. If you distribute generation to match consumption there is little transport, but this is hard work which is why there will always be a grid but with plenty of distributed generation the effective capacity of the current infrastructure is extended.

[Zero999]

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.

Because they would get a huge number of returns, as it's very common for the mains to be a higher voltage than 243V. Where I work, the mains voltage regularly exceeds 253V, so this would be unacceptable.

[Simon]

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.

Because they would get a huge number of returns, as it's very common for the mains to be a higher voltage than 243V. Where I work, the mains voltage regularly exceeds 253V, so this would be unacceptable.

It's what some dick head at myenergy did with the zappi, in the end mine was replaced. The fuckheads based everything on 230V totally ignoring that much of the country is still on 240V substations. Why on earth we would turn everything down I don't know, I prefer my extra 5%, it means 5% less current required so less than 95% of the usual power transfer losses. My old house was easily at 254V overnight. where I am now is a fairly stable 230V

[tszaboo]

There are two things I'm a bit upset about. One is the lying about the technology, that is apparently so abundant and believable, that even engineers repeat these.
In 2017 in Belgium I was working at a company that was monitoring solar panel installations, and trading green certificates. We were actively monitoring the "too much production" issue and conceded that abut 5% of our customers were effected, about 50 EUR/year loss of their production.  We also worked on the mathematics and physics behind the grid. The idea behind it was that we could (with external communication) force inverters to generate some (the correct amount ) reactive power into the grid, that provides a very cheap way to compensate the reactive currents of large industrial installations.
We were also running some projects that would time the usage to the generation, with estimated 3% capacity savings nation wide. Doesn't sound like much, but that's a cost of a power plant right there.

I'm missing one important element in this story: does the grid have the capacity to transport the electricity where it needs to go? If you look closely at your electricity bill, you'll see a significant amount of money goes into transport costs already; for a household the transport costs can be 50%. IOW: it makes no sense to transport electricity far away if that means the transport costs are going to dominate the price per kWh.

If it doestn't the voltage goes up and the generation stops.
But you have to look at the two issues separately. The grid needs improvement anyway, because our load went up because of electric cars. Having more generation capacity is never bad. Worst case is that you cannot utilize the capacity and inverters are switched off because of that.
When I look at the electricity bill, I think it's 3 cent/KWh is the grid, 13.5 cent taxes, and 9 cent is the electricity price.
What you are talking about is the fixed costs: leasing you the smart meter (quite a scam), operating the network, making sure they walk away with 1.2 billion EUR profit for 2022 (Enexis) and then complain that they have to spend money on the network. I genuinely don't know why the DSOs are a for profit organization.

[Zero999]

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.

Because they would get a huge number of returns, as it's very common for the mains to be a higher voltage than 243V. Where I work, the mains voltage regularly exceeds 253V, so this would be unacceptable.

It's what some dick head at myenergy did with the zappi, in the end mine was replaced. The fuckheads based everything on 230V totally ignoring that much of the country is still on 240V substations. Why on earth we would turn everything down I don't know, I prefer my extra 5%, it means 5% less current required so less than 95% of the usual power transfer losses. My old house was easily at 254V overnight. where I am now is a fairly stable 230V

It depends, sometimes a slightly higher voltage is better, sometimes not i.e. when it's powering a linear regulator, which is the case for most LED lamps.

[Siwastaja]

Rooftop solar for the moment isn't controlled at all, except for by voltage

It is also controlled by frequency.

... and adding any other sort of control is expensive.

Compared to the expense of solar installation itself, not that much, but of course, what is "expensive" is subjective. But so far, there has been no need, and despite monthly nutjob panic threads on eevblog forum, nothing bad has happened even though some kind of disaster or collapse has been "just right around the corner" for years.

[nctnico]

... and adding any other sort of control is expensive.

Compared to the expense of solar installation itself, not that much, but of course, what is "expensive" is subjective.

It means adding a couple of hundred euro of installation costs (hardware, wiring, configuration). And operating & maintaining the control system at the energy grid's end isn't free either. So there are extra one-time costs and recurring costs and all eat into the ROI of the solar panels.

[Siwastaja]

It means adding a couple of hundred euro of installation costs (hardware, wiring, configuration). And operating & maintaining the control system at the energy grid's end isn't free either. So there are extra one-time costs and recurring costs and all eat into the ROI of the solar panels.

That's right; including the biggest cost item (at least here), namely sales, it's even more than just a couple of hundred. Our box for example could control solar inverters (just that currently we just monitor PV-only inverters, and control battery hybrid inverters), but it does cost something to install and operate. People are happily buying it, and paying us a smallish annual fee for the service, because it allows increase of solar self use by controlling their loads, too. It pays back for itself and shortens the ROI actually in most customer cases. In those where it does not, we don't recommend buying it.

So far we don't control anything based on grid operator input (control based on customer's own needs is still the primary way to operate as it produces direct cost savings to customer) but this would be under discussion sometime in the future. Though, then again, the priority order is obvious: if there are any loads to turn on, this is done before reducing PV production.

But sure, we already have some negative priced hours. For example, right now, -0.01€/kWh. Add transmission fee (e.g. 0.08€/kWh) and it makes a lot of sense to self-use that energy instead of turning the inverter off.

Luckily, or almost magically, Finnish governments have somehow forgot to ruin the PV market. No subsidies, no weird artificial pricing models.

[Someone]

... and adding any other sort of control is expensive.

Compared to the expense of solar installation itself, not that much, but of course, what is "expensive" is subjective.

It means adding a couple of hundred euro of installation costs (hardware, wiring, configuration). And operating & maintaining the control system at the energy grid's end isn't free either. So there are extra one-time costs and recurring costs and all eat into the ROI of the solar panels.

Complete bollocks, what is needed to be added to current residential inverters that would cost that much?
https://www.eevblog.com/forum/renewable-energy/stability-of-grids-with-a-high-percentage-of-asynchronous-sourcing/msg5580399/#msg5580399
Stability and control can be had for zero hardware cost, just some software and administrative changes. Only if the grid was 100% residential solar inverters (obviously impractical and never going to happen) would any overlaid control channel beyond frequency be needed, and thats only IF there was a desire to maintain long term frequency accuracy (which few grids around the world bother with).

Or is this going to become another of your throwaway inflammatory "points" which are entirely misleading without the corner case framing and unbelievable conditionals you do not include.

[Siwastaja]

... and adding any other sort of control is expensive.

Compared to the expense of solar installation itself, not that much, but of course, what is "expensive" is subjective.

It means adding a couple of hundred euro of installation costs (hardware, wiring, configuration). And operating & maintaining the control system at the energy grid's end isn't free either. So there are extra one-time costs and recurring costs and all eat into the ROI of the solar panels.

Complete bollocks, what is needed to be added to current residential inverters that would cost that much?
https://www.eevblog.com/forum/renewable-energy/stability-of-grids-with-a-high-percentage-of-asynchronous-sourcing/msg5580399/#msg5580399
Stability and control can be had for zero hardware cost, just some software and administrative changes. Only if the grid was 100% residential solar inverters (obviously impractical and never going to happen) would any overlaid control channel beyond frequency be needed, and thats only IF there was a desire to maintain long term frequency accuracy (which few grids around the world bother with).

Or is this going to become another of your throwaway inflammatory "points" which are entirely misleading without the corner case framing and unbelievable conditionals you do not include.

nctnico is building on the premise that somehow these control devices would need to be retrofitted on existing inverters. It's an interesting scenario to discuss, but let's indeed remember that there is no basis for the idea that any of this would be necessary. Even if there was some sort of magical point after which there is too much PV and it needs some new type of control, this additional control would then apply to new installs.

As for centralized remote control, many of the inverters actually installed here are already internet-connected, in the cloud services of the Chinese manufacturers. The WiFi connectivity stick costs some tens of euros extra. This is so that installers can remotely monitor the performance or fault codes of the inverter if the customer has any problems or calls back.