Solar options for home in 2022.

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563 posts

Ultimate Geek

#3215801 8-Apr-2024 17:33

@EgorNZ 245.8V is quite high (~7% higher than 230 nominal) and could well be what is causing your inverter to clip. According to the interwebs the volt-watt clipping for inverters in NZ should start at 244V. Does the timing of AC voltage dip just after 1pm correspond to the local maximum of the AC power? What's the AC voltage at the start of the day (say before 9 am) before you get significant generation?

EgorNZ

50 posts

Geek

#3215806 8-Apr-2024 17:40

neb: Related question that came up a few days ago, our HWC cycles on and off at random, at least as determined by the thermostat, including in the middle of the night when we're running off battery. So I thought of using a Shelly relay to turn off the power to it from midnight to maybe 8am so it'll either run from free 9pm-midnight power or solar during the day, but not unnecessarily heat the water from batteries at 3am. (Insert 3-page discussion of it being a heavily insulated cylinder that doesn't lose much heat, we won't run out of hot water, and a future enhancement is to match excess solar consumption to having the HWC running, the current step is just to reduce battery drain overnight). Can anyone see any problems with this? To wire a Shelly into the HWC power do you need an electrician or is it OK as a DIY?

Same thing here, so I'd be interested in an answer to that too. Looks like a Shelly Plus 1PM (rated at 16A) should be up to the task?

HarmLessSolutions

969 posts

Ultimate Geek

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#3215808 8-Apr-2024 17:45

wongtop:

@EgorNZ 245.8V is quite high (~7% higher than 230 nominal) and could well be what is causing your inverter to clip. According to the interwebs the volt-watt clipping for inverters in NZ should start at 244V and by 246V cause the inverter output to drop to 20%. Does the timing of AC voltage dip just after 1pm correspond to the local maximum of the AC power? What's the AC voltage at the start of the day (say before 9 am) before you get significant generation?

According to our installer an odd situation exists so far as nominal grid voltages are concerned. NZ is still operating with a 240V grid for the most part and our rural supply definitely indicates this is the case though our installer did do a firmware upgrade on Fronius Australia's suggestion as we were experiencing inverter outages due to grid (low) voltage fluctuations. Apparently Australia reduced their nominal grid voltage a few years back (to 230V) to better buffer against with the amount of PV input they have there but even though NZ and AU are supposed to share grid specifications it seems the memo got lost before reaching NZ so we've stuck with 240V.

Also based on our inverter issues it is more likely that grid voltage issues would result in (brief) inverter outages than what EgorNZ is seeing here.

https://www.harmlesssolutions.co.nz/

EgorNZ

50 posts

Geek

#3215824 8-Apr-2024 17:59

wongtop:

@EgorNZ 245.8V is quite high (~7% higher than 230 nominal) and could well be what is causing your inverter to clip. According to the interwebs the volt-watt clipping for inverters in NZ should start at 244V. Does the timing of AC voltage dip just after 1pm correspond to the local maximum of the AC power? What's the AC voltage at the start of the day (say before 9 am) before you get significant generation?

Hmm, that could explain it then. The AC L1 line on that chart starts at ~239V when power is first produced at 07:50 and again ~239V at 19:15 when power falls to zero. But in the middle around 13:00 the voltage peaks at 246.22V.

At 13:20 there is a slight dip in AC voltage back to 245.53V which corresponds with a spike in output to 5.18kW:

That's not the max output for the day though, which is 6.04kW at 10:45, when AC voltage is 244.45V. That's 15 minutes before the clipping starts.

EgorNZ

50 posts

Geek

#3215826 8-Apr-2024 18:06

HarmLessSolutions:

According to our installer an odd situation exists so far as nominal grid voltages are concerned. NZ is still operating with a 240V grid for the most part and our rural supply definitely indicates this is the case though our installer did do a firmware upgrade on Fronius Australia's suggestion as we were experiencing inverter outages due to grid (low) voltage fluctuations. Apparently Australia reduced their nominal grid voltage a few years back (to 230V) to better buffer against with the amount of PV input they have there but even though NZ and AU are supposed to share grid specifications it seems the memo got lost before reaching NZ so we've stuck with 240V.

Also based on our inverter issues it is more likely that grid voltage issues would result in (brief) inverter outages than what EgorNZ is seeing here.

I think the "Voltage AC L1" metric from the Fronius is the output from the inverter, not the grid supply? There's also a metric for "Voltage AC L1 feed-in-point" from the Primary Meter, which I assumed to be the grid supply, this reads solidly in the range of 239V-242V all day.

eonsim

398 posts

Ultimate Geek

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#3215881 8-Apr-2024 18:52

EgorNZ:

@wongtop Here's the chart again with the voltage and current. The AC voltage looks flat throughout. The MPP1 current is clipping at 22.00A, which matches the rating on the inverter, the DC voltage doesn't dip though. Meanwhile, MPP2 has high voltage and low current?

Looking at that data either your second String MPP2 is suffering significant shadowing or there is something significantly wrong with it.

MPP1 is 22A and 180V or ~4kW of generation

MPP2 is 3A and 400V or ~1.2kW of generation

MPP1 string has clipped as in it's generating more power than the MPP can use (see the flat A's line for it). While MPP2 has drastically declined from ~10AM where it was delivering ~8A or 3.2kW. If all your panels are facing in the same direction they should both be clipping or be at the highest point of there generation unless there is shadow on MPP2 or something else wrong.

Also the voltage tends to tell you how many panels you have in serial, with 400V that suggests either:

1) MPP2 has ~2x as many panels in serial as MPP1 (but is delivery a 1/4 of the energy)

2) MPP1 has two or more strings in parallel with would be doubling the Amps.

Either way unless there is shading or a issue I'd expect both MPPs to have a very flat AMP line at this time period.

@EgorNZ What panels do you have, and how many in total?

Jase2985

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#3215888 8-Apr-2024 19:14

neb: Related question that came up a few days ago, our HWC cycles on and off at random, at least as determined by the thermostat, including in the middle of the night when we're running off battery. So I thought of using a Shelly relay to turn off the power to it from midnight to maybe 8am so it'll either run from free 9pm-midnight power or solar during the day, but not unnecessarily heat the water from batteries at 3am. (Insert 3-page discussion of it being a heavily insulated cylinder that doesn't lose much heat, we won't run out of hot water, and a future enhancement is to match excess solar consumption to having the HWC running, the current step is just to reduce battery drain overnight). Can anyone see any problems with this? To wire a Shelly into the HWC power do you need an electrician or is it OK as a DIY?

i wouldnt use a shelly, from all accounts the run hot.

There are timers you can add to the switchboard which are made for this stuff or you can buy a bluetooth compatible one from kiwisparks

eonsim

398 posts

Ultimate Geek

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#3215960 8-Apr-2024 20:04

@EgorNZ I don't know exactly what panels you've got but lets say they are JAM72S10-420.

Nominal conditions:

max voltage is 39.6

Max Amps is 8A

Based on this MPP2 (400V, 8a max) is a string of 10 panels.
While MPP1 is 3 strings of 4-5 panels in parallel.

Assuming this is correctly balanced I'd guess a MPP2 is 9 panels and MPP1 3x5 panels.

So MPP2 should top out at 8A (which you briefly see around 10am. While MPP1 should top out at 24A (3x8) which would explain why you have a constant 22A which is probably the max for that MPP. But that suggests your MPP1 array is operating at least at 90% (22/24), and I'd expect if all the panels are facing the same direction with now shading that the MPP2 should be operating at a similar level (which it was at 10am). But during the middle of the day it appears your MPP2 is running at ~37% of capacity (3/8A), now if there was shading on one or more of the panels in that array it would make sense. Otherwise it maybe there is some sort of defect.

If there is no shading and as other speculate it's the line (AC) voltage being >245V I'd have personally thought that the reduction would be spread across both MPP if everything was working properly. I could be wrong on this so may want to talk to someone who knows more about it than I do.

In general for your setup:

Looking at your likely setup the Fronius is rated to 22A max for one MPP with voltages between 60-480V, which agrees with the clipping you see on MPP1. So if we calculate out the max likely generation you could be looking at the following:

22a*180V ~= 4kW for MPP1

8a * 400V = 3.2kW for MPP2

Max production is probably around 7.2kW, you may be able to get a bit more during peak summer 8kW if we assume the A's on the MPP2 can get to 9.8A in perfect conditions. With prefect conditions the current design should be able to generate ~8kW.

This will all change a little bit if you are using somewhat different panels than the ones I indicated at the top.

Note the design of the system looks okay as they have to keep within the voltage ratings for each MPP. With the voltage range of 60-480V the open circuit voltage for MPP1 is ~250V which fits nicely. While MPP2 at 9*50 = 450 is safely below the 480V max.

Ge0rge

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#3215963 8-Apr-2024 20:35

HarmLessSolutions:

According to our installer an odd situation exists so far as nominal grid voltages are concerned. NZ is still operating with a 240V grid for the most part and our rural supply definitely indicates this is the case though our installer did do a firmware upgrade on Fronius Australia's suggestion as we were experiencing inverter outages due to grid (low) voltage fluctuations. Apparently Australia reduced their nominal grid voltage a few years back (to 230V) to better buffer against with the amount of PV input they have there but even though NZ and AU are supposed to share grid specifications it seems the memo got lost before reaching NZ so we've stuck with 240V.

Also based on our inverter issues it is more likely that grid voltage issues would result in (brief) inverter outages than what EgorNZ is seeing here.

I'd argue that your installer doesn't quite understand our legislation. The NZ grid nominal voltage is 230V, as defined in the standards under Standard Low Voltage.

Separately, legislation allows for Standard Low Voltage to vary by no more than 6%, except for momentary fluctuations - so up to 243.8V. I struggle to see how your installer thinks we're a nominal 240V - otherwise we'd be allowed to go up to 254.4V.

HarmLessSolutions

969 posts

Ultimate Geek

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#3215965 8-Apr-2024 20:48

Ge0rge:

HarmLessSolutions:

According to our installer an odd situation exists so far as nominal grid voltages are concerned. NZ is still operating with a 240V grid for the most part and our rural supply definitely indicates this is the case though our installer did do a firmware upgrade on Fronius Australia's suggestion as we were experiencing inverter outages due to grid (low) voltage fluctuations. Apparently Australia reduced their nominal grid voltage a few years back (to 230V) to better buffer against with the amount of PV input they have there but even though NZ and AU are supposed to share grid specifications it seems the memo got lost before reaching NZ so we've stuck with 240V.

Also based on our inverter issues it is more likely that grid voltage issues would result in (brief) inverter outages than what EgorNZ is seeing here.

I'd argue that your installer doesn't quite understand our legislation. The NZ grid nominal voltage is 230V, as defined in the standards under Standard Low Voltage.

Separately, legislation allows for Standard Low Voltage to vary by no more than 6%, except for momentary fluctuations - so up to 243.8V. I struggle to see how your installer thinks we're a nominal 240V - otherwise we'd be allowed to go up to 254.4V.

This would appear to confirm our installer's take on the situation.

"Since 2000, the nominal voltage in most areas of Australia has been 230 V,[2][3][4] except for Western Australia, which remains at 240 V, and Queensland, which transitioned to 230 V in 2020. The voltage in New Zealand, Fiji, Tonga and Papua New Guinea remains at a nominal 240 V, and in the Solomon Islands it is 220 V."

https://www.harmlesssolutions.co.nz/

Ge0rge

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#3215968 8-Apr-2024 20:59

A Wikipedia page with no reference to the claim that the NZ voltage is 240V, vs the govt.nz page detailing the Electrical Safety Regulations?

HarmLessSolutions

969 posts

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#3215971 8-Apr-2024 21:19

Ge0rge:

A Wikipedia page with no reference to the claim that the NZ voltage is 240V, vs the govt.nz page detailing the Electrical Safety Regulations?

The default grid voltage in our rural locality appears to be 240V +/- 2V with peak usage periods reducing that down to around 230V (+/- 2V). Perhaps an intentionally high 'normal' to provide a buffer in what is an area with some pretty tired infrastructure ?

Reality vs. regulations?

https://www.harmlesssolutions.co.nz/

EgorNZ

50 posts

Geek

#3215974 8-Apr-2024 21:38

eonsim:

@EgorNZ I don't know exactly what panels you've got but lets say they are JAM72S10-420.

Nominal conditions:

max voltage is 39.6

Max Amps is 8A

Based on this MPP2 (400V, 8a max) is a string of 10 panels.
While MPP1 is 3 strings of 4-5 panels in parallel.

Assuming this is correctly balanced I'd guess a MPP2 is 9 panels and MPP1 3x5 panels.

I have 24 panels, the model is JAM54S31-420 - these have a max voltage of 30.09V and max current of 10.57A at NOCT.

Thanks for the explanation, there's complexity here that I hadn't realised. What does "correctly balanced" mean in this context?

eonsim:

So MPP2 should top out at 8A (which you briefly see around 10am. While MPP1 should top out at 24A (3x8) which would explain why you have a constant 22A which is probably the max for that MPP. But that suggests your MPP1 array is operating at least at 90% (22/24), and I'd expect if all the panels are facing the same direction with now shading that the MPP2 should be operating at a similar level (which it was at 10am). But during the middle of the day it appears your MPP2 is running at ~37% of capacity (3/8A), now if there was shading on one or more of the panels in that array it would make sense. Otherwise it maybe there is some sort of defect.

If there is no shading and as other speculate it's the line (AC) voltage being >245V I'd have personally thought that the reduction would be spread across both MPP if everything was working properly. I could be wrong on this so may want to talk to someone who knows more about it than I do.

Yeah I'm doubtful that shading could cause this kind of differential between panels. There are trees around the house, but the angles are such that they only obstruct when the sun is low in the sky, i.e. early morning and evening. Not at 1pm in March.

Ge0rge

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#3215976 8-Apr-2024 21:50

HarmLessSolutions:
Ge0rge:

A Wikipedia page with no reference to the claim that the NZ voltage is 240V, vs the govt.nz page detailing the Electrical Safety Regulations?

The default grid voltage in our rural locality appears to be 240V +/- 2V with peak usage periods reducing that down to around 230V (+/- 2V). Perhaps an intentionally high 'normal' to provide a buffer in what is an area with some pretty tired infrastructure ?

Reality vs. regulations?

Oh definitely - being rural myself I tend to see on or over 240V more often than I see under, and when it does go under, it isn't by much - lowest today was at 0535 when it was 235.2V. Technically it's all still within the 230V +/- 6% though.

neb

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#3215977 8-Apr-2024 21:57

Ge0rge:
I struggle to see how your installer thinks we're a nominal 240V

This says nominal 240V.

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