New Solar PV System - Connection to Consumer Unit

[JohnW2]

I rather think that electrical industry procedures will assume that a system is live until it's been proved dead and earthed - on the assumption that anyone can make up a widowmaker and backfeed the network, or an embedded generator could have faulty protection, or ... I doubt that anyone in their right mind would just switch off and then assume that the circuit is dead and safe to touch !

Exactly - which makes me wonder a bit why 'we' are seemingly getting so excited about the technology for making PV inverters shut down when they should (something they'll almost certainly do fairly quickly, even if not 'immediately').

Kind Regards, John

 

[bernardgreen]

If the section the DNO want isolated has a high load when the DNO fuses / breakers are pulled then the connected solar PVs cannot supply that load and voltage in the section drops and this drop is detected by the solar PV invertors and they shut down.

If the section has a very low loading, loading less than the supply from the solar PVs feeding that section of the grid can supply then there is no voltage drop on the section and solar PVs are left on line. Sometimes the voltage on the section will increase when the DNO fuses are pulled and this increase trips the solar PV invertors to shut down.

 

[JohnW2]

If the section the DNO want isolated has a high load when the DNO fuses / breakers are pulled then the connected solar PVs cannot supply that load and voltage in the section drops and this drop is detected by the solar PV invertors and they shut down.

Indeed, I've said that - and I presume that, in practice, that is going to be by far the most common situation.

If the section has a very low loading, loading less than the supply from the solar PVs feeding that section of the grid can supply then there is no voltage drop on the section and solar PVs are left on line.

I've also discussed that, which is really the main issue we are discussing (since the 'common' situation described above is easily understood). At first sight one might think that what you say would be the case, but it seems that the inverters are probably designed to shut down in the event of loss of grid power even if the PVs are able to supply the load in the local 'islanded' part of the network. Techniques such as discussed in the recently-cited paper can probably achieve that, particularly the rate of change of frequency after loss of the grid supply 'reference'.

I haven't yet had a chance to read that paper properly, but I think that it may well provide a better explanation of some of the possibilities. What I wrote in post #36 may well have a lot to do with it.

Kind Regards, John

 

[ericmark]

For the DNO line worker he/she should know by now one needs to short out supply before working, where the problem arises is where some one doing other works hits a cable, we want the system to fail safe as soon as possible. Be it road works, digging the garden, or something hitting over head lines may be as simple as a tree falling we want that made safe ASAP.

they told me it will use a spare fuseway in the distribution board

My consumer unit has a split bus

So he has stated the consumer unit fitted does not have three neutrals so will not accept a RCBO and the intention is to supply one of the bus bars with the power from the inverter rather than fit a new consumer unit. So it seems what ever should be done, in this case it seems it is not being done.

 

[RCZ]

Hi…newbie here….what a great site…shame it wasn’t around 30 years ago! Regarding the tails from the inverter to the consumer unit…I’m having a AC unit between the inverter and my consumer unit…it will facilitate the inverter powering the house even when I have a power cut from the grid…But I have a question if I may…can the tails going into the consumer unit go straight into the main switch rather than a MCB…same difference, no?

 

[JohnD]

…I’m having a AC unit between the inverter and my consumer unit…it will facilitate the inverter powering the house even when I have a power cut from the grid…

No, it doesn't work like that. The inverter shuts down in a power cut. You might be able to get an inverter with a standby emergency outlet. You must not connect it to a grid circuit.

 

[RCZ]

Hi John…a company here called Allo.Solar advised this, I had a choice between 2 AC units, one would not power the house in a power cut the other would…what can I say….

 

[JohnD]

You must not allow your inverter to supply power to the grid during a power cut. There are various ways to achieve that. Some more expensive than others. Imagine a linesman sitting in a trench repairing the cable that comes out of your house.

I don't know what regulations you have in your country equivalent to the Electricity Act.

 

[RCZ]

I will clarify this with Allo.Solar and get back to you…I get what your saying…thanks…

 

[RCZ]

Does this help…

 

[JohnD]

It looks to me like it has some stand-by emergency outlets, which you could plug your boiler or your dialysis machine into, that are not connected to your ordinary house circuits and therefore do not make your consumer unit live.

Quite useful if you are in an area prone to power cuts or if you have some essential equipment, but will not power your house.

 

[ericmark]

My solar inverter can supply a maximum of 5 kW, so I can not have whole of the house supplied by solar and battery, I can have one 3 kW circuit which is battery backed, in my case the central heating and freezers only. The rest of the house will fail with a loss of the DNO supply. This is in a way good, as don't want to run out of power due to lights being left on.

But the inverter has to be designed specially to do this, on the loss of DNO supply it also connects earth and neutral together for example. And I need an earth rod of course, as can't rely on DNO earth if supply cut.

The requirements vary country to country, and there are a load of DIP switches to set the inverter for the country it is installed in. And one also needs paperwork to confirm it complies, so this can't be done as DIY. On the 4th April 2018 I did not have solar panels and battery, so I may have made mistakes, and the same applies to anyone else, best if you start a new post, as also what may be correct in your case may not be correct for @Geflugenmitt plus things have moved on since this thread was started.

 

[Why Not Indeed]

You must not allow your inverter to supply power to the grid during a power cut.

I believe there are some air conditioning systems designed specifically to integrate with PV [ie, they run off DC not AC]. This might be what RCZ is talking about.

 

[RCZ]

This may clarify things about the AC unit, here’s the blurb on the site….

In the event of a power failure, the batteries integrated into your photovoltaic installation take over and provide emergency power to your home. This feature is similar to that of a dedicated backup power line, and ensures vital energy continuity.

When a power failure is detected, the switching box safely disconnects the photovoltaic system from the power grid. This avoids energy returns, which can be dangerous. The switch box also provides backup power to your home from the battery park.

This ready-to-connect and pre-tested solution is easy to install and use. It allows you to benefit from a reliable and secure backup power supply in the event of a power failure.

 

[Why Not Indeed]

I think you have a specific technical question which is best addressed to the supplier of the equipment or the person installing it.