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Powercut, sun shining, PV not generating


vivienz

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We had a major power cut here yesterday evening. The DNO will be nack this morning to locate and fix the fault. We have battery backup that finally ran out this morning. The sun is shining so the PV should be kicking in now but there is negligible generation. In the absence of a timely response from the supplier/installer, does anyone have any suggestions?

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10 minutes ago, Jeremy Harris said:

Is the power back on now?

 

If not, then the PV will not start to generate, as it must grid lock before the inverter can turn on.

different invertor then if OFF GRID system ?

 that is a pain --would have thought there should be some sort of overide switch for just this situation 

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7 minutes ago, scottishjohn said:

different invertor then if OFF GRID system ?

 that is a pain --would have thought there should be some sort of overide switch for just this situation 

 

 

Cannot be an off grid system, as it's AC coupled and grid tied.  The inverter has an auxiliary backup output, but that is asynchronous.  The inverter still needs to be grid tied to start up.

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The power isn't back on yet. My choice was to have the DNO digging outside at gone midnight or manage till this morning, so I chose the latter.

 I was unaware of needing to lock back to the grid - that seems logical so I shall wait and see.

 

Thanks, all.

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8 minutes ago, vivienz said:

The power isn't back on yet. My choice was to have the DNO digging outside at gone midnight or manage till this morning, so I chose the latter.

 I was unaware of needing to lock back to the grid - that seems logical so I shall wait and see.

 

Thanks, all.

 

 

Yes, the inverter needs not only to have grid power available to start up, but that supply has to pass the inverter power-on test parameters.  Most inverters check at least the loop impedance and grid frequency during startup, and will only turn on when both are within limits.  Some inverters display the measured parameters during startup (ours does) so that any out of tolerance measurement can be seen.

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Whenever there is a fault, your inverter will enter 'islanding' mode, whereby it cuts itself off from the grid, and prevents generation, the intention of this is for the safety of the DNO, so that when they start touching cables they aren't live because someones PV is inputting power into them.

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Not a subject I know much about but on a simplistic level I would have thought the inverter could disconnect from the grid if the grid conditions are not correct but still be able to generate into your batteries?

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Just now, joe90 said:

Not a subject I know much about but on a simplistic level I would have thought the inverter could disconnect from the grid if the grid conditions are not correct but still be able to generate into your batteries?

 

If there is even a small chance that power could leak into the grid, there is danger to the workers, so the inverters are programmed to shut off.

 

You may see Battery inverters with UPS functions, but I'm pretty sure all of them require a dedicated circuit, which doesn't lead back to your CU.

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4 minutes ago, MikeGrahamT21 said:

You may see Battery inverters with UPS functions, but I'm pretty sure all of them require a dedicated circuit, which doesn't lead back to your CU.

that seems a good idea 

what it does highlight is if someone was wanting to add PV because their supply is prone to outages ,then std system cannot cope with that once batteries gone down --no power even if sunny

 EG lots of snow and power lines down for days in winter.

 so for those  better to have a stand by generator in  first place

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8 minutes ago, joe90 said:

Not a subject I know much about but on a simplistic level I would have thought the inverter could disconnect from the grid if the grid conditions are not correct but still be able to generate into your batteries?

 

An off-grid inverter can do this, but cannot then be connected to the grid directly.  It is possible to build a battery system that has two inverters, with no AC connection between them.  There are a few ways to do this, but none of the commonly available domestic battery storage systems currently have such a capability.

 

 

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I see tesla make such a device to addo not your powerwall --which gets round this problem 

and allows your pv to keep on working

 

n March 2019, Tesla released the ‘Backup Gateway 2’ which allows you to use the electricity stored in your Powerwall in the event of a power-cut.

 

Edited by scottishjohn
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2 hours ago, Jeremy Harris said:

The inverter has an auxiliary backup output, but that is asynchronous.  The inverter still needs to be grid tied to start up.

I dimly recall discussing this previously - seems daft that you cannot always use your PV in case of a power cut and charge your battery again. I guess it could be solved with some clever switch gear on the DC side and an alternate inverter just feeding the batteries although they also need inverter services to run the appliances.

 

 

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13 minutes ago, scottishjohn said:

I see tesla make such a device to addo not your powerwall --which gets round this problem 

and allows your pv to keep on working

 

n March 2019, Tesla released the ‘Backup Gateway 2’ which allows you to use the electricity stored in your Powerwall in the event of a power-cut.

 

 

 

It doesn't get around this problem.  The Gateway 2 just works like all the other battery systems that have a backup option.  It's one-way, in that the PV inverter still will not turn on unless there is grid power available.

 

Many battery storage systems offer a power cut backup supply option, either via a dedicated backed up output from the inverter/charger, or via a changeover switch and an inverter that has an islanding mode for output.  I'm not aware of any (other than dedicated off-grid systems) that will allow the inverter to start up without being able to sense the grid in order to frequency sync, do the required safety tests, etc.

 

It's possible to build a system that uses an off-grid type islanding inverter/charger, with an anti export protection device on the grid power changeover, but it's a bit of a faff to set up, plus there are not many approved anti-export devices available yet. 

 

2 minutes ago, MikeSharp01 said:

I dimly recall discussing this previously - seems daft that you cannot always use your PV in case of a power cut and charge your battery again. I guess it could be solved with some clever switch gear on the DC side and an alternate inverter just feeding the batteries although they also need inverter services to run the appliances.

 

 

 

You can use a DC coupled system to get around this limitation.  That works by using the DC from the PV system to charge the battery pack, with the batteries then used to run an inverter.  The inverter needs to be a model that can switch between islanding and non-islanding mode on the fly, plus there needs to be a grid power changeover switch, plus an export limiting device.  The inverter also probably needs to be sized to be able to deliver the full output from the PV system, if it's still going to export to the grid via the grid power export limiting device.  Not impossible to do, but probably not worth the hassle.  Most power cuts are of a short duration, so just having the ability to pull backup power from the battery pack is probably enough for the majority of people.

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3 minutes ago, MikeGrahamT21 said:

Doubt that will be approved for use in the UK!

 

 

It's not.  Having seen how it works, I'm not convinced that it will be approved any time soon, either.  Their current G100 approval only applies to their export limiting device, I believe.

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The fault was found and is fixed, tge DNO guys are backfilling where they dug out the cable now. It appears that a groundworker caught the cable when they were putting the rainwater drain in and just squidged it back in without telling anyone. The cable had a small split and has worsened over time.

On the plus side, it's the first time I've had a lengthy power cut situation, so it was interesting. The power cut started at about 5.30 yesterday evening. I switched off all non-essentials, leaving lights, some sockets and fridges and freezers running before switching over to battery power. The Sunamp was full and I had 50% charge in my batteries. There was no need for heating as the house is at a toasty 23C downstairs with the milder weather. We were frugal with lights and had no tv on. I charged my phone and we had tea and coffee this morning. The batteries finally ran out of juice at 8am this morning.

Overall, aside from the inconvenience of the power cut itself, the sunamp and battery backup system have worked out really well.

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1 minute ago, vivienz said:

The fault was found and is fixed, tge DNO guys are backfilling where they dug out the cable now. It appears that a groundworker caught the cable when they were putting the rainwater drain in and just squidged it back in without telling anyone. The cable had a small split and has worsened over time.

On the plus side, it's the first time I've had a lengthy power cut situation, so it was interesting. The power cut started at about 5.30 yesterday evening. I switched off all non-essentials, leaving lights, some sockets and fridges and freezers running before switching over to battery power. The Sunamp was full and I had 50% charge in my batteries. There was no need for heating as the house is at a toasty 23C downstairs with the milder weather. We were frugal with lights and had no tv on. I charged my phone and we had tea and coffee this morning. The batteries finally ran out of juice at 8am this morning.

Overall, aside from the inconvenience of the power cut itself, the sunamp and battery backup system have worked out really well.

what capacity is your battery storage

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