How the solar cuts out in a power cut

_Brian

I’m wondering what is the mechanism the system uses to cut out during a power cut.

If it’s already feeding power back through the grid, when there is a power cut how does it detect that ??

bullit_dodger

https://www.boards.ie/discussion/2058331161/how-the-solar-cuts-out-in-a-power-cut

Couple of different aspects to your question. The solar panels themselves have a spring loaded switch, which is held closed when there is grid power. When the grid drops, the spring opens the circuit and cuts the power coming from your panels into your inverter.

The inverter itself is a "grid-tie-in" inverter (general case here), and it's constantly looking at the voltage and frequency of the power coming in from the grid. It's not different from your telly, or oven in respect to that it's powered from the grid, not the solar panels themselves. So when the grid goes, it's got no power, so it shuts down.

graememk

Inverters don't need the spring loaded switch though. It's more of an issue of isolation (generally fire) where the DC cabling usually is coming into the attic, and hard to get to.

It does not actually form part of the anti islanding function on the inverter

bullit_dodger

https://www.boards.ie/discussion/comment/121613045#Comment_121613045

100% mate - and that why I was saying there's a couple of different aspects to answering the question.....

I’m wondering what is the mechanism the system uses to cut out during a power cut

The edge case is as you know the inverter can be powered in a limited capacity via the batteries etc, (EPS feed, or even the whole switchover that some people have to their consumer unit) but that's probably outside the scope of the question. The main thing is that it's powered by the grid itself, so when the grid is gone......it goes dark itself.

con747

https://www.boards.ie/discussion/comment/121613240#Comment_121613240

I'm not sure what you mean, I had a power cut earlier and with my change over switch and batteries I ran what I needed. When you say "so when the grid is gone......it goes dark itself" what are you referring to? The inverter?

bullit_dodger

Ach, I didn't really want to get into the specifics......it was more just trying to answer the original question and I'm sort of sorry I attempted it now. But yeah, there are a couple of different "areas" for lack of a better word inside your inverter. Most hybrids have 2 inverters inside the box. When the grid goes down, a lot of the inverter box (as a unit) is dark. Yes, many of them as I mentioned have an EPS outlet, and people have hooked that into the consumer unit via a changeover, but it's an edge case.

95+% of people don't have a changeover switch that or use the EPS - so for them, when the gird is down, the inverter is effectively down as it's powered by the grid.

Quantum Erasure

As someone who's half thinking about installing solar but knows nothing about it, this surprised me when I heard about it happening a neighbour.

Why would it ever be set up that way?

con747

https://www.boards.ie/discussion/comment/121613314#Comment_121613314

What surprised you? Don't half think about solar it's a no brainer. Best investment you will make unless you are aged 85+!

Ubbquittious

Most people dont have an alternative power source for the spring loaded switch. There might even be some rule against having such a set up

_Brian

https://www.boards.ie/discussion/comment/121613306#Comment_121613306

I suppose what I was asking is what measurements does it use ??

Voltage and frequency??, if the inverter is feeding back on the lines coming into the house how does it know if the grid is down ?, there’s nothing feeding into the house but rather the house is energising these lines.

is it looking at impedance on the supply side ??

graememk

https://www.boards.ie/discussion/comment/121613906#Comment_121613906

It's both voltage and frequency. On very windy days I find mine shutting down. I don't know if it's because of the frequency or voltage, my monitoring isn't catching it.

It's likely the inverter will shut off before the grid actually goes down, once the grid falls out of spec, inverter will shut off.

When there is a power cut, there will be a transient when the voltage/frequency drops, the inverter will see that and disconnect.

Generally inverters are DC powered (directly from PV)

It's built into all grid tied inverters.

MicktheMan

When the inverter shuts down either during a grid power outage or excess wind, does it power itself back up again automatically when power is restored or is manual intervention required?

graememk

https://www.boards.ie/discussion/comment/121614731#Comment_121614731

Restores automatically

allinthehead

https://www.boards.ie/discussion/comment/121613332#Comment_121613332

I don't know for sure but what I was told by an installer, and I read it somewhere too, is that you shouldn't feed the fireman switch with the batteries.

Ubbquittious

https://www.boards.ie/discussion/comment/121615776#Comment_121615776

They must be worried that people will get a taste for living off the grid 😂

graememk

https://www.boards.ie/discussion/comment/121615776#Comment_121615776

Afaik it's an seai rule.

allinthehead

https://www.boards.ie/discussion/comment/121615788#Comment_121615788

You could probably manage it with a modest setup for maybe 7-8 months of the year?

https://www.boards.ie/discussion/comment/121615806#Comment_121615806

I think you're correct, I'll see if I can dig it out.

allinthehead

https://www.boards.ie/discussion/comment/121615806#Comment_121615806

Found it.

5. Shunt and battery back up  The shunt must isolate the solar panel array on loss of mains and cannot be re-energised from the battery backup. The shunt circuit must disconnect the solar array automatically when the AC power is removed and automatically reconnect when the AC is re-energized. The position of the shunt switch must be within 1.5M of the array. This also applies to external systems where the inverter is located outside and the shunt needs to be within 1.5m of the array, taking care to ensure the DC cable is appropriately protected from external forces i.e., use of conduit or SWA cable etc. Where a “back-up system” i.e., battery storage with auxiliary supply is in use, the shunt switch operation must not be compromised and cannot be re-energised from the back up supply. In the event emergency services are called to a property and the mains electricity supply has been disconnected the shunt switch must maintain the disconnection of the solar DC supply and must not be re-energised by the auxiliary output as this will lead to a health and safety risk to emergency services.  

https://www.seai.ie/grants/home-energy-grants/solar-electricity-grant/SPV-Contractor-Technical-Bulletin_2022_08.pdf

con747

https://www.boards.ie/discussion/comment/121615896#Comment_121615896

It's only needed for the grant though, the North and UK don't bother with them and that's why I had mine removed so the panels work in power cuts.

allinthehead

https://www.boards.ie/discussion/comment/121615917#Comment_121615917

I don't believe that's correct, my understanding is that it's to conform to Is10101 and Building Regs part B.

Through these requirements of Part B of the building regulations and I.S. 10101, all domestic PV installations installed under this Scheme must:

• Provide an automatic (i.e., automatically operated by disconnection of the main AC supply to the building) shunt (or interlocked) isolation of the circuit (whether AC or DC, and two pole) from the solar PV modules into the building, as close to the solar PV modules as possible, and a maximum of 1.5m internally from the point of cable entry to the building. 

• Where the circuit from the solar PV modules does not enter the building, this point of automatic isolation must be within 1.5m of the solar PV modules. • For ground mounted system the shunt (automatic isolator) must be within 1.5m of the solar PV modules.

• This system of isolation shall automatically isolate the circuit from the solar PV modules when the AC supply is disconnected to the building, i.e., a shunt or interlocked isolation function. 

• ‘Shunt’ or ‘interlocked’ isolation of the DC circuit is the only acceptable manner of meeting the Building Regulation TGD B – Fire Safety (2017) for the purposes of this Scheme. 

• For the avoidance of doubt the disconnection of the circuit from the solar PV modules must be automatic and operated by removal of AC supply to the building and must not be operated by means of a dedicated switch, pushbutton, ‘fireman’s switch’ or other manner. 

• For the avoidance of doubt an isolation of the supply from the PV modules is required in ALL cases, whether micro-inverters, DC optimised inverters, where the inverter is within 1.5m of cable entry or any other configuration is used.

• This system of isolation must automatically reconnect upon restoration of AC supply to the building. A warning label must be applied to the main external AC connection point to the building 

con747

https://www.boards.ie/discussion/comment/121615966#Comment_121615966

Beyond my pay grade that!

allinthehead

https://www.boards.ie/discussion/comment/121615981#Comment_121615981

Ignorance is the best defense🤣

con747

https://www.boards.ie/discussion/comment/121615988#Comment_121615988

Everyone is ignorant about something.

Ubbquittious

https://www.boards.ie/discussion/comment/121615846#Comment_121615846

For the rest of the time you could have an extension lead to the neighbours keeping the battery topped up.

One neighbour could stump up the 300 a year standing charge for a dozen houses with solar. The powers that be are probably sharpening the feck out of their legal instruments to stop that kind of cord cutting situation arising

Ubbquittious

The FUD monger aer out in force tonight 😂😂

allinthehead

https://www.boards.ie/discussion/comment/121616054#Comment_121616054

I know, I was joking. If ever you're asked plead ignorance.

_Brian

Last question on this.

Say I had access to another renewable source like hydro and the power was coming in at 240v.

is there a unit I can get to do same process, disconnect the power in event of a power cut ?

it’s just a fanciful notion in the back of my mind. What would I call such a device if I were looking for one.

graememk

Hydro for instance would normally be three phase, then rectified into DC, and back to single phase AC with a grid tied inverter.

_Brian

https://www.boards.ie/discussion/comment/121617250#Comment_121617250

But if it were already entering the property at 240v an inverter isn’t what would be needed. I was wondering if there were a unit that would take 240v and cut it when there is a power cut.

graememk

https://www.boards.ie/discussion/comment/121617271#Comment_121617271

If it's coming in at 240.. from what?

Hydro/wind is a motor spinning. At x voltage, y frequency and z current. 3 phase

Faster it spins more voltage. Also more frequency.

It is then rectified to a stable DC and either with a charge controller (for batteries) with a DC DC converter or a grid tied inverter can also be used.

_Brian

https://www.boards.ie/discussion/comment/121617887#Comment_121617887

From another renewable source 100m away so converting to 240v at source would mean less loss over the distance.