Solar Voltage Rise, a spanner in the FIT works?

mp3guy · 31-03-2021 12:09pm

That was something I wondered. If the grid is providing 244V, and a "magic box" taps it down to 234V for me, my inverter sees that and exports all the up to 245V (on the house side of the magic box), does this rise in voltage then pass back through the box to mean I'm really feeding in at 255V?

Sounds like you're heavily biased against the proprietors of these items

I might ring them and run this by them to see what they say.

Do you think I have options if my inverter supports reactive power control?

air · 31-03-2021 12:59pm

I'm not biased against anyone that sells real products that serve a useful function in an honest and transparent manner.

I've encountered honest reps working for companies selling them before that were genuinely naive and or just lacking the technical understanding required to realise that they're BS.

At most they will have an autotransformer inside.
Reactive power control won't help your situation.

If you do a cursory internet search you'll find plenty of horror stories on the subject.
You're obviously disregarding my advice if you're going to ring them so best of luck with it.

mp3guy · 31-03-2021 1:04pm

air wrote: »

I'm not biased against anyone that sells real products that serve a useful function in an honest and transparent manner.

I've encountered honest reps working for companies selling them before that were genuinely naive and or just lacking the technical understanding required to realise that they're BS.

At most they will have an autotransformer inside.
Reactive power control won't help your situation.

If you do a cursory internet search you'll find plenty of horror stories on the subject.
You're obviously disregarding my advice if you're going to ring them so best of luck with it.

I try to avoid believing what strangers post on the internet. In particular this sub forum has had a sizeable amount of misinformation on it before so I'm inclined to take everything with a pinch of salt.

I would love concrete evidence from you (and conversely from companies selling these items). Haven't made any decisions yet, but don't get too uppity if I don't take air's unverifiable word as truth. Any links to those horror stories? Anyone I can contact with first hand experience? Datasheets? Did a quick search myself and couldn't find anything.

air · 31-03-2021 1:06pm

mp3guy wrote: »

does this rise in voltage then pass back through the box to mean I'm really feeding in at 255V?

Yes, of course, this is exactly what I said in my previous post.
If you put a transformer between your inverter and the grid, you stand to export to such an extent that you will cause the local grid voltage to exceed that which is allowed.
You could find yourself liable for the consequences of this if it happens as a result of you installing uncertified equipment.

air · 31-03-2021 1:08pm

mp3guy wrote: »

I try to avoid believing what strangers post on the internet. In particular this sub forum has had a sizeable amount of misinformation on it before so I'm inclined to take everything with a pinch of salt.

I would love concrete evidence from you (and conversely from companies selling these items). Haven't made any decisions yet, but don't get too uppity if I don't take air's unverifiable word as truth. Any links to those horror stories? Anyone I can contact with first hand experience? Datasheets? Did a quick search myself and couldn't find anything.

Well why are you asking questions if you're not interested in taking anyone's word for it.
You obviously know noting about the subject, I know plenty and have invested enough time to explain the issues around them to you.
If you want to disregard my advice, that's well and good and your own prerogative, but you can do your own leg work.
What possible motivation could I have for talking down a particular product?
Good luck.

mp3guy · 31-03-2021 1:11pm

air wrote: »

Yes, of course, this is exactly what I said in my previous post.
If you put a transformer between your inverter and the grid, you stand to export to such an extent that you will cause the local grid voltage to exceed that which is allowed.
You could find yourself liable for the consequences of this if it happens as a result of you installing uncertified equipment.

Hence why I'll ask them if this happens. If they say yes, then it's obviously a non-starter. If they claim this doesn't happen, well then either they're lying, don't know or are doing something different to your assumption.

air wrote: »

Well why are you asking questions if you're not interested in taking anyone's word for it.
You obviously know noting about the subject, I know plenty and have invested enough time to explain the issues around them to you.
If you want to disregard my advice, that's well and good and your own prerogative, but you can do your own leg work.
Good luck.

You're right, I don't want people's word. I want concrete verifiable facts. Too much to ask for obviously. Anyone can say "I know plenty".

air · 31-03-2021 1:17pm

What facts do you want?
These boxes do nothing useful, it's hard to prove a negative.

Generally if they have anything inside, it's a small autotransformer that reduced the grid voltage slightly as it enters the house.
This will have the opposite effect on export obviously.

What mechanism do you postulate they employ that will manage to limit your voltage to?
How about you provide some facts yourself, post up a link or datasheet to a specific unit and I'll happily review it.

air · 31-03-2021 1:20pm

mp3guy wrote: »

Hence why I'll ask them if this happens. If they say yes, then it's obviously a non-starter. If they claim this doesn't happen, well then either they're lying, don't know or are doing something different to your assumption.

Assuming this unspecified unit is the typical type with an autotransformer, the only way it won't create a (medium term) voltage rise issue is if it has on load tapping, which I doubt it will as they're generally made as simply and cheaply as possible.

If it does have it, then it won't exacerbate the voltage rise issue but neither will it leave you any better off than where you started.

Again, if you had even a vague idea of what it was you were hoping to achieve it would be helpful.
There is no magic bullet that will allow you to push more energy onto a wire without raising it's voltage - physics 101.

mp3guy · 31-03-2021 1:31pm

air wrote: »

What facts do you want?
These boxes do nothing useful, it's hard to prove a negative.

First hand account/measurements would be ideal. e.g. "I bought one and here's a photo of the voltmeter proving it does X and doesn't do Y". Or, checkout this other forum where someone bought one and things went belly up.

air wrote: »

What mechanism do you postulate they employ that will manage to limit your voltage to?
How about you provide some facts yourself, post up a link or datasheet to a specific unit and I'll happily review it.

I postulate nothing, not my area of expertise, hence asking for information, not unverifiable opinions and assumptions.

air wrote: »

Again, if you had even a vague idea of what it was you were hoping to achieve it would be helpful.
There is no magic bullet that will allow you to push more energy onto a wire without raising it's voltage - physics 101.

I don't want to push more energy onto a wire? I want to prevent my inverter from shutting down. I don't care about pushing power out, just want to stop it cycling. Do you think Fronius's reactive power control solution is also bogus then? https://youtu.be/X8tsQhp7hM0?t=1592. It's based on reactive power control but you said that doesn't help, seems to be in contradiction.

air · 31-03-2021 1:46pm

I haven't given you any opinions whatsoever, I've explained what i expect is inside and how it works and what the issues it cause are.

I've only just clicked the link you provided and it all but confirms what I've been saying.
It says (3 Tappings of 4%, 6%, 9%) which all but guarantees that it's an auto transformer and will behave exactly as I have described.

How about you ask the supplier to confirm that it is in fact an auto transformer, then go an educate yourself on what an auto transformer is and how it operates and decide whether it will help you or not.

I haven't looked into the Fronius solution you'll need to investigate the specifics of EN50438 for voltage lag and lead to see if it will help here, I'm fairly sure it won't but I don't have a copy of the full standard.
That video is referencing a New Zealand grid standard by the looks of it.

air · 31-03-2021 1:49pm

mp3guy wrote: »

I don't want to push more energy onto a wire? I want to prevent my inverter from shutting down. I don't care about pushing power out, just want to stop it cycling.

The OP was interested in having his PV operate at full capacity.

If you only want to limit export such that your inverter doesn't shut down due to over voltage then you could create a relatively simple voltage sensing circuit that would in turn modulate the DC input to the inverter proportionate to the grid voltage.
I've seen this done before for different reasons and it would likely work on any inverter and not create any risks of non conformance on the AC side.

mp3guy · 31-03-2021 1:55pm

air wrote: »

I've only just clicked the link you provided and it all but confirms what I've been saying.
It says (3 Tappings of 4%, 6%, 9%) which all but guarantees that it's an auto transformer and will behave exactly as I have described.

That's just the Optivolt one, what about the Energyace one? That specifies "Choice of 4 voltage reduction settings (-10v, -15v, -20v, -25v)" which implies it works differently, i.e. it doesn't just tap down by a percentage, it's an absolute reduction. Same tech?

air wrote: »

How about you ask the supplier to confirm that it is in fact an auto transformer, then go an educate yourself on what an auto transformer is and how it operates and decide whether it will help you or not.

That's the plan.

air wrote: »

I haven't looked into the Fronius solution you'll need to investigate the specifics of EN50438 for voltage lag and lead to see if it will help here, I'm fairly sure it won't but I don't have a copy of the full standard.
That video is referencing a New Zealand grid standard by the looks of it.

Yes I'm trying to find out if there's anything said about it in the standard.

air wrote: »

If you only want to limit export such that your inverter doesn't shut down due to over voltage then you could create a relatively simple voltage sensing circuit that would in turn modulate the DC input to the inverter proportionate to the grid voltage.
I've seen this done before for different reasons and it would likely work on any inverter and not create any risks of non conformance on the AC side.

Now this sounds pretty cool, who did it? How? Links?

air · 31-03-2021 2:04pm

mp3guy wrote: »

That's just the Optivolt one, what about the Energyace one? That specifies "Choice of 4 voltage reduction settings (-10v, -15v, -20v, -25v)" which implies it works differently, i.e. it doesn't just tap down by a percentage, it's an absolute reduction. Same tech?

Sounds like just marketing spin to be honest, they've just converted the percentages to voltages I'd say.
But the bigger point is that, either way, it's of zero use to you whatsoever - I'm not sure why you're still entertaining them at this point as you seem to understand the operation now.

mp3guy wrote: »

Now this sounds pretty cool, who did it? How? Links?

It was some Australian guru with an off grid setup, there was no further details than what I described but it would be fairly simple to replicate with an arduino or similar. I haven't time to go searching for it.

Read the AC voltage X times per second and modulate the gate of a high voltage MOSFET on the DC input to the inverter accordingly.

If you have a look at OpenEnergyMonitor architecture and their PV diverters, a simpler version of the hardware used there could be modified to achieve it.

If I recall correctly he hadn't even added a capacitor on the input, just chopped the PV input and that was it.

mp3guy · 31-03-2021 2:10pm

air wrote: »

It was some Australian guru with an off grid setup, there was no further details than what I described but it would be fairly simple to replicate with an arduino or similar. I haven't time to go searching for it.

Read the AC voltage X times per second and modulate the gate of a high voltage MOSFET on the DC input to the inverter accordingly.

If you have a look at OpenEnergyMonitor architecture and their PV diverters, a simpler version of the hardware used there could be modified to achieve it.

If I recall correctly he hadn't even added a capacitor on the input, just chopped the PV input and that was it.

Sounds pretty cool but a little out of my own comfort zone.

I think I found at least a copy of EN 50438:2013 here https://shop.gwl.eu/docs/web/2018/EN_50438_2013-BS.pdf and it seems to state in section 4.5 that "In order to avoid disconnection due to the over-voltage protection the micro-generating plant is allowed to reduce active power output as a function of this rising voltage. If this function is activated, the micro-generating plant may reduce active power according to a logic chosen by the manufacturer. Nevertheless, this logic shall not result in steps of output power. " so it sounds like it's allowed.

air · 31-03-2021 2:28pm

Sounds good and good work on finding a copy of the standard for free.

It's a sensible solution for sure at a grid level but again not much use to the OP.

Also I just watched a minute or two of that video but he mentions that the volt watt limiting is only active when the inverter is at full power, which likely means it will be of little or no benefit to you either.

It wouldn't take much for Fronius to allow full output shaping in response to grid voltage and it would make their products a lot more useful for people off grid also.

Given your automation experience etc I expect you could construct a DIY power limiter very easily, you'd just need to be mindful of the hazards of the DC voltages at play.

mp3guy · 12-05-2021 2:20pm

I finally had the ESB out. They stuck a voltage monitor on at my meter for about 10 days. The engineer shared the data with me, it was well below 250V the entire time, usually around 244V.

He did some live measurements at various sockets for me too (with two different meters) and was getting 244-246V while the two inverters/Zappi would read from 248V-250V. So it appears that they read high, quite high, 4V high! The engineer suggested maybe upping their internal limits to see if that stops them cycling, and maybe getting my own multimeter to read voltage at sockets in the house to be sure. But as far as they're concerned, it's not a problem.

He did say the solution would be to move the transformer further away from me, which would involve doing work on my neighbour's land. So I've a few options.

air · 12-05-2021 3:19pm

It's still on the high side for sure though.
Are your inverters close to you main board? If they were a long way away, there might be scope to upgrade the supply cable perhaps although really clutching at straws.
You don't have much leeway between your average grid voltage and the upper limits.

KCross · 12-05-2021 4:13pm

mp3guy wrote: »

I finally had the ESB out. They stuck a voltage monitor on at my meter for about 10 days. The engineer shared the data with me, it was well below 250V the entire time, usually around 244V.

He did some live measurements at various sockets for me too (with two different meters) and was getting 244-246V while the two inverters/Zappi would read from 248V-250V. So it appears that they read high, quite high, 4V high! The engineer suggested maybe upping their internal limits to see if that stops them cycling, and maybe getting my own multimeter to read voltage at sockets in the house to be sure. But as far as they're concerned, it's not a problem.

He did say the solution would be to move the transformer further away from me, which would involve doing work on my neighbour's land. So I've a few options.

You'd need a friendly local ESB engineer to get that work sanctioned.

As you said, technically there isnt a problem on their end.... they are within spec so are very unlikely to go moving transformers to satisfy your requirements, but you can but ask!

What you really need are a few new neighbours drawing off the same transformer!

mp3guy · 12-05-2021 4:22pm

KCross wrote: »

You'd need a friendly local ESB engineer to get that work sanctioned.

As you said, technically there isnt a problem on their end.... they are within spec so are very unlikely to go moving transformers to satisfy your requirements, but you can but ask!

What you really need are a few new neighbours drawing off the same transformer!

Actually he was very friendly, gave me his boss's office number and his own mobile number, said to let him know if I wanted to go any further with it.

Scoobydoobydoo101 · 17-04-2023 9:18am

@mp3guy What was the end outcome here? Who did you contact to monitor the voltage?

It sounds like I have a similar issue. On days where I am feeding into the grid the voltage is up around 252v and the inverter is faulting out.

Can/will this do damage to the inverter long term?

graememk · 17-04-2023 10:04am

https://www.boards.ie/discussion/comment/120486675#Comment_120486675

Won't do any harm to the inverter it's well within it's own limits.

Villain · 09-06-2023 1:52pm

Interesting thread and I had read it before I got solar, which was installed 2.5 months ago. I did get the very odd Grid over voltage alarm when system was generating at max and I plugged car in.

However my neighbour got solar installed this week and ever since during the day when we are both exporting I keep hitting grid over voltage alarm. Highest I've seen is 255v on Grid side. Rang ESB and they said they will look at installing Voltage monitoring but I told them its clear as day the issue is voltage is high now we are both exporting. 4 houses on transformer and we are last two about 200m from transformer. The ESB are going to see a LOT more of this!

ELM327 · 12-06-2023 7:55am

Yes I get this too sometimes during the day, lots of PV exporters around me which ups the grid voltage. I got around this by upping the parameters to G99 standard.