Emergency Power option - Automatic Switch

[nowty]

Nice set up and about as "automatic" as most will achieve.

What happens if there is a short outage in the region of 5 to 10 seconds? We get lots of those in migrating bird season as the bird strike the power lines causing them to short out and trip the "auto-closers" Power goes off then back on a few seconds later. At certain times of year we get at least one of those "events" per day. It was another factor in having a 3kW UPS running all the "tech" stuff (routers/wifi/weather station etc.)

So if the power comes back the system still stays in Off Grid Mode for a few minutes so if its a frequent intermittent fault like every few seconds or even every minute, that's OK, it will stay in off grid mode. But if its an intermittent fault, like every half hour it can be a right pain as sometimes when we have a storm the lights occasionally flicker but everything would normally still run OK.

But with my system its sometimes too sensitive, and cuts the external power when it did not need to. In these situations I manually cut the live grid feed with the grid isolator to force myself off grid until after the storm.

So its not without its downside but when we have had several extended power cuts due to cable faults in the street its been just magic.

[openspaceman]

I use my SMA Sunny Island battery as an EPS, so if the external power fails I lose the power for 2 or 3 secs whilst the Sunny Island cuts the live grid connection with a 100A power contactor and it also cuts my EV charging circuits with another 63A power contactor. These contactors are failsafe in that they are in the OFF state if un-energised.

The power then comes back on automatically to the house via the 6kW Sunny Island battery inverter using all the same wiring and the neutral is still connected to maintain a PME. The PME is also backed up with a local earth rod so even if I lose the external TNCS PME because of a cable fault in the street, the system turns into a TT earthing system.

The short outage switches off several WiFi sockets which switches off other high power circuits such as the heatpump, storage heater boosting and immersions heaters so I don't get an instant overload on the sunny Island when running in Off Grid mode.

The beauty is the solar PV inverters still reconnect and are then throttled to avoid overvoltage by the Sunny Island through frequency shift control. So in summer I could run for months with a grid outage.

When the external power comes back, the Sunny Island senses this and has to match the grid voltage, synchronise with the grid frequency and shut down the solar PV inverters if they are being throttled as they will operating at a slightly higher frequency than the grid.

Then the live grid feed and the EV charger circuit are then re-connected and shortly after the solar PV inverters reconnect. So I don't lose power again on re-connection with the grid.

That's fascinating and all new to me; ignoring the automation basically your sunny island battery and inverter replace the grid by supplying a correct wave form so that the normally grid connected PV system still works. I was thinking more on the lines of an engine powered generator to do this.

As long as the load from the house is less than the limit of the inverter then the solar system stays up as long as there is daylight AND/OR charge in the batteries?

Could you explain the bit about the solar PV inverters being throttled a bit more?

[nowty]

I use my SMA Sunny Island battery as an EPS, so if the external power fails I lose the power for 2 or 3 secs whilst the Sunny Island cuts the live grid connection with a 100A power contactor and it also cuts my EV charging circuits with another 63A power contactor. These contactors are failsafe in that they are in the OFF state if un-energised.

The power then comes back on automatically to the house via the 6kW Sunny Island battery inverter using all the same wiring and the neutral is still connected to maintain a PME. The PME is also backed up with a local earth rod so even if I lose the external TNCS PME because of a cable fault in the street, the system turns into a TT earthing system.

The short outage switches off several WiFi sockets which switches off other high power circuits such as the heatpump, storage heater boosting and immersions heaters so I don't get an instant overload on the sunny Island when running in Off Grid mode.

The beauty is the solar PV inverters still reconnect and are then throttled to avoid overvoltage by the Sunny Island through frequency shift control. So in summer I could run for months with a grid outage.

When the external power comes back, the Sunny Island senses this and has to match the grid voltage, synchronise with the grid frequency and shut down the solar PV inverters if they are being throttled as they will operating at a slightly higher frequency than the grid.

Then the live grid feed and the EV charger circuit are then re-connected and shortly after the solar PV inverters reconnect. So I don't lose power again on re-connection with the grid.

That's fascinating and all new to me; ignoring the automation basically your sunny island battery and inverter replace the grid by supplying a correct wave form so that the normally grid connected PV system still works. I was thinking more on the lines of an engine powered generator to do this.

As long as the load from the house is less than the limit of the inverter then the solar system stays up as long as there is daylight AND/OR charge in the batteries?

Could you explain the bit about the solar PV inverters being throttled a bit more?

Yes your correct in what you are saying.

As far as I know SMA is the only company which seems to do this function and I think its a legacy thing where you did not need any comms between the battery inverter and the PV inverters to allow this to work. If there is no where for the PV generation to go, the voltage increases and the SI increases the frequency from 50Hz to between 51Hz and 52Hz and the PV inverters sense this and drop their own generation proportionally. If the SI goes all the way up to 55Hz, that causes the PV inverters to disconnect at 54.5Hz. So after a power cut, when the grid returns, the SI increases the frequency to 55Hz to disconnect the PV inverters, before dropping back to synchronise with the grid before re-energising the live grid connection contactor. Thereafter the PV inverters re-connect as normal.

SMA explain it better here,

[cojmh]

That is a really neat setup .... something to aim for!

Do you have a post which outlines how you have everything setup? Do you have a single Inverter running all 12KW of your panels or do you have these setup across more than one inverter?

The bit that always seems to be difficult (perhaps it is just me) is how to get multiple things to work together in a manner that is not going to cause in-fighting between the devices and in my case (and I am sure many others) how to avoid issues with the FIT scheme.

[openspaceman]

Thanks for that nowty.

How do you make use of the charge in the sunny island battery when normally connected to the grid?

Is it likely my growatt inverter and battery will react similarly to the sunny island?

My chief reason for asking is I am interested in a small chp system to provide a few kWh in the winter gap rather than worried about grid outage.

[nowty]

Do you have a post which outlines how you have everything setup? Do you have a single Inverter running all 12KW of your panels or do you have these setup across more than one inverter?

The bit that always seems to be difficult (perhaps it is just me) is how to get multiple things to work together in a manner that is not going to cause in-fighting between the devices and in my case (and I am sure many others) how to avoid issues with the FIT scheme.

There was loads about it on the old defunct forum but not on here. Its quite a long story how I got to where I am now.
I have 3 SMA PV inverters (Sunny Boy v21) and 1 SMA Sunny Island (v12) battery inverter and an SMA Sunny Manager 2 controller and grid point monitor. Two of the three PV inverters go through separate generation meters for FIT purposes.

All inverters and the Sunny Manager are internet hard wired and can be monitored and controlled via the SMA Sunny Portal website or phone APP.

How do you make use of the charge in the sunny island battery when normally connected to the grid?

Is it likely my growatt inverter and battery will react similarly to the sunny island?

The Sunny Island operates exactly like a standard AC coupled battery inverter and balances the house loads to achieve zero import if possible.

Example of phone APP monitoring from a few days ago when I was charging the EV and had the heatpump on.

[smegal]

There was loads about it on the old defunct forum but not on here. Its quite a long story how I got to where I am now.
I have 3 SMA PV inverters (Sunny Boy v21) and 1 SMA Sunny Island (v12) battery inverter and an SMA Sunny Manager 2 controller and grid point monitor. Two of the three PV inverters go through separate generation meters for FIT purposes.

Do you know what the threads were called? I tried to download the old forum (with limited success) but as cojmh is a close friend in real life, I am happy to spend some time and trawl through my archive to find the information.

[nowty]

There was loads about it on the old defunct forum but not on here. Its quite a long story how I got to where I am now.
I have 3 SMA PV inverters (Sunny Boy v21) and 1 SMA Sunny Island (v12) battery inverter and an SMA Sunny Manager 2 controller and grid point monitor. Two of the three PV inverters go through separate generation meters for FIT purposes.

Do you know what the threads were called? I tried to download the old forum (with limited success) but as cojmh is a close friend in real life, I am happy to spend some time and trawl through my archive to find the information.

I actually pulled off copies myself before it all died.

I re-wrote my heatpump project and am part way through my lithium battery balancing one. I'll get to it in the end but what's lost in re-writing up historic stuff is all the questions and answers on the way through a project.

[openspaceman]

The Sunny Island operates exactly like a standard AC coupled battery inverter and balances the house loads to achieve zero import if possible.

You have lost me a bit there, easily done with things electric, I cannot quite see how the sunny island can work as a normal battery storage and as an eps unless all your consumer units are downstream of it, even then I cannot visualise how the changeover switch can cut the supply plus switch the sunny island as an eps. Perhaps you would expand a bit in simple terms.

[nowty]

The Sunny Island operates exactly like a standard AC coupled battery inverter and balances the house loads to achieve zero import if possible.

You have lost me a bit there, easily done with things electric, I cannot quite see how the sunny island can work as a normal battery storage and as an eps unless all your consumer units are downstream of it, even then I cannot visualise how the changeover switch can cut the supply plus switch the sunny island as an eps. Perhaps you would expand a bit in simple terms.

I'll try and draw something up soon.

But think of it like a battery inverter that has a separate EPS output on it, where you need a change over switch or you just use the EPS output as an emergency socket.

Instead of having the emergency socket, the change over switch is integrated into the system so it isolates the live grid but then turns on as an off grid inverter on the same grid tie circuit it normally operates when the grid is there. But now the grid has been cut off with a G99 anti islanding relay.

So yes all consumer units are downstream of it but they always have been. The only difference is in normal operation it operates as a battery grid tie inverter and in the grid fault condition, it cuts off the live grid feed and turns on as an off grid inverter.

If the grid comes back it simply resyncs with the grid using a low power monitoring feed and then re-energises the G99 anti islanding relay.