Solar/battery use during power outages

Zenith74 · 30-01-2020 12:59PM #1

I did a quick search and came across some older threads on this subject, I'd like to revisit it though now that inverters have presumably evolved etc.

I recently got a GivEnergy hybrid inverter with some batteries and panels installed. As it happens our power was being turned off today to allow the ESB run in fibre for SIRO, so it got me thinking about what would be required to use the power in the batteries and potentially the panels.

The standard setup that was put in for us has an automated switch to isolate the panels from the inverter if the grid supply goes offline. The inverter itself will also stop sending out AC power if it sees the grid offline. However I emailed GivEnergy out of curiousity, having seen mention of "Backup power up to 2.5kW during power outages" in the spec sheet for my inverter. Turns out there is an "Essential Loads" output on the bottom of the inverter that will provide up to 2.5kW of AC output even when the grid goes offline. Of course the panels will be disconnected during a grid outage, so you will only have access to the batteries, so you'll need to charge them up in advance (possible from the online portal of this inverter).

Long and short of it is that I got a dedicated socket hung off the "Essential Loads" output of my inverter and am typing this message from my PC which is connected to the wifi and my cable broadband, and the gas central heating is operating, all from my battery with the grid being off for the day today. Pretty cool.

But it's a bit of a bummer that the panels would actually be generating enough to keep the battery topped up if they weren't isolated. The SEAI documentation talks about ways to allow for the solar system working during a power outage, so it doesn't seem to be illegal once it is done right. So I'm just curious what others have done? I'm not really too bothered about getting the whole house live, though that would be cool, a couple of Essential Loads sockets is enough, but I'd love the panels to be able to feed in.

Zardaz · 30-01-2020 01:17PM

Zenith74 wrote: »

...
The SEAI documentation talks about ways to allow for the solar system working during a power outage, so it doesn't seem to be illegal once it is done right.
...

To allow generation of solar power during a grid outage, the DC Solar Safety isolator (aka the "fireman's switch") would need to be manually bypassed.

This should not be done, unless in conjunction with a manual interlock to an additional physical isolator on the incomming mains grid supply.

Kind of tricky to do, with the incommer in the meter box and the solar isolator up near the roof.

See:

Sections 4.7 and 4.9

And the firemen need to know about it, and be able to shut the whole thing off before they enter your burning house.

It's similar to the rules for connecting any standby generator to an electrical installation.

"In order to ensure that parallel operation with the electricity network is not possible, a standby generator must always be connected through a change-over switch."

i.e. "don't be trying this at home, folks, with a pair of jump leads up in your attic in the dark."

see: https://www.seai.ie/publications/Code-of-Practice-Solar-PV-Grant.pdf, sections 4.7 & 4.9 for more details.....

Zenith74 · 30-01-2020 02:29PM

Thanks for the reply!

So the SEAI requirement states -
This system of isolation shall automatically isolate the DC circuit (or 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.

If I'm reading that right it's saying that to avail of the grant, the only way they'll accept you meeting the Building/SafeElectric regs is with an automatic isolator, which makes sense, nice and simple. Assuming that you've already availed of the grant and are now in-life, or perhaps you have not used the grant for your install, then I assume you're governed by the Building Regs themselves which state -
where Photovoltaic (P.V.) panels are provided on buildings, provision should be made for the isolation of the panel array externally and in accordance with ET101, 2008.

For completeness, Section 537.4 (Emergency Switching) of ET101:2008 states that -
Emergency switching is required;
- For all live conductors where a risk of electric shock is involved
- Must act as directly as possible on the appropriate supply conductors
- Accessible, readily identifiable and convenient for intended use

So again if I'm reading that right there needs to be a way of isolating the panels, and this needs to be accessible externally for fire safety. (I know this is probably what you already said, just writing it out for myself/clarity

). So we're talking some sort of big red firemans switch out on the side of the house that remotely operates the DC isolator in the attic? What does one of those look like out of interest? In our case anyway, it really would not be that big a deal to get from the current automated isolator down to the side of the house where the fireman switch would go, just across the attic, out the soffit, down behind a drain pipe and voila.

Our electricity is very stable here, so I won't be doing this, I'm just curious!

Zardaz · 30-01-2020 03:33PM

It requires a multi-way, multi pole mechanically interlocked switch for full safety.
Regarding "remotely operates", I think using a contactor/relay wont cut it, the various switches for the AC and DC basically need to be on the same mechanical shaft, and should be break-before-make.
Which means that AC and DC cabling will need to be brought to the same switchgear, so a lot of high voltage/current cables will need to be routed around the place.

This is really out of the realm of normal domestic electric installations, and something that a commercial/industrial electrician should be doing. (and certifying)

Bacically, you would need some sort of 3 Position manual switch:
1) All OFF - AC: the incoming grid live and neutral is disconnected. DC: the Automatic DC panel isolator is NOT bypassed, and that automatic isolator will be Open Circuit since the main AC grid power is off. Backup sockets feed from the inverter will still be live though until your battery runs down. (unless you switch off that feed as well)
2) Grid-Tie: the incoming grid live and neutral is connected, the Automatic DC panel isolator is NOT bypassed, and that automatic isolator will be closed-circuit (if the grid is live), or open-circuit (if the grid goes down). (normal everyday mode)
3) Off-Grid: AC: the incoming grid live and neutral is disconnected. DC: the Automatic DC isolator IS bypassed.

If in Off-Grid mode, the Isolators near the inverter will still need to work independently, i.e. be able to disconnect the panels/house AC/Battery DC as requested even if the panel isolator is bypassed by the big switch.

In reality, the power grid is very reliable in this country, so all this is probably not worth the cost and hassle to cover infrequent and short power cuts, unless you have an Ecto-Containment System in your house.

old_house · 30-01-2020 04:20PM

Tesla is making an automatic switch for that purpose called "Tesla Backup Gateway 2". It's not seamless though and I don't know if it's available or even legal in Ireland, but somebody explains it here: https://www.youtube.com/watch?v=gP51JjnWvLo

Edit: I'm not sure if the panels would actually be able to recharge the battery with this setup. It looks like it just reconnects a tesla power wall back to the house circuit to provide baclup power after having disconnected the whole system from the grid in case of a power failure. No mention of panels working on the data sheet, but still a useful solution for some I guess...

Zenith74 · 30-01-2020 05:04PM

Zardaz wrote: »

It requires a multi-way, multi pole mechanically interlocked switch for full safety.
Regarding "remotely operates", I think using a contactor/relay wont cut it, the various switches for the AC and DC basically need to be on the same mechanical shaft, and should be break-before-make.

Is the 'automatic' DC isolator not already being effectively remotely operated? It's operated by pulling the fuse in the meter box, or disconnecting on the poll or however the fire-service normally do this, which remotely triggers the DC isolator to break the DC circuit?

There's two independent things going on here right?

First we need to be sure that AC power is not fed into the house and out onto the grid from the solar setup to protect guys working on the local power lines during a power outage - this is handled by the inverter which monitors the AC supply, if it goes off then it stops sending AC power out as well. Isolating the DC from panels isn't in-scope here I guess, because the inverter handles it further downstream. If the DC supply from the panels was relevant, then the DC supply from the batteries should also be relevant and an auto-isolator for them would be specified, which it isn't.

Secondly you want to ensure that if there's a fire/emergency in the house, when the firemen enter they can pull the fuse outside and know that there aren't live cables knocking around that could harm them or extend the emergency. Pulling the fuse in the meter box will stop the incoming grid power, stop the inverter sending AC into the house and also cause the DC isolator from the panels to open.

I think it's only the second one that we would need to deal with to try and get the panels providing DC to the inverter during a power outage, the inverter would continue to self-isolate anyway. If the automatic DC isolator had a second sets of inputs on it and would allow DC to flow if there was continutity on these inputs, then you could just run a pair of wires to a big red firemans switch out on the side of the house beside the meter box labelled "Switch off to isolate PV array DC output".

Again just shooting the breeze here, no intention of doing it, as you say the grid is very reliable here.

Solar/battery use during power outages

Comments