ATS on AC coupled grid tied system.

chuckp

chuckp

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Jul 29, 2018
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So the plan is to install an ATS on my grid tied system so that in the event of a grid power failure I can keep the power to the whole house on.

My solar system has AP System YC500i grid tied micro inverters that supply AC from the panels direct to the house. Batteries will be connected to a Sofar Mass Energy ME3000SP AC coupled bidirectional charger/inverter.

The ME300SP has EPS functionality that can supply a critical loads board but not sure how I could use this to my advantage.

The plan is to use these ABB contactors as the ATS


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My hope is that the supplies will switch fast enough that the micro inverters wont notice the power failure and remain on.

Not sure if this is possible so any help greatly appreciated.

I will draw a wiring schematic of how the system is connected up and post later.
 
You should not connect any microinverters or grid-tie inverters to any inverter at your home alone. This is Only doable if the grid-tie inverters are made to work with a isolated off-grid system.

With that said some microinverters and grid-tie system can operate in parallel with an off-grid inverter but you need to investigate this first. Generaly its a bad idea. Off-grid is in most cases not working with a grid-tie system. You need to find a Hybrid system to do that.

Just 15 seconds google didnt show me that your micro-inverters have this function at all.
 
daromer said:
You should not connect any microinverters or grid-tie inverters to any inverter at your home alone. This is Only doable if the grid-tie inverters are made to work with a isolated off-grid system.

With that said some microinverters and grid-tie system can operate in parallel with an off-grid inverter but you need to investigate this first. Generaly its a bad idea. Off-grid is in most cases not working with a grid-tie system. You need to find a Hybrid system to do that.

Just 15 seconds google didnt show me that your micro-inverters have this function at all.
Click to expand...

I thought that would be the case. So the best option will be to use the EPS function of the ME3000SP to supply a critical loads only board as this will be totally isolated from everything else and the micro inverters will shut down as usual.

Was hoping that the ATS would isolate the systems from the grid to prevent any back feeding in the event of a failure, the ME3000SP would then supply the house from the batteries leaving the micro inverters on producing power during the day to supply the house and charge the batteries. Also use a load dump to get rid of any surplus generated power once/if the batteries are fully charged. As the ME300SP is bidirectional it should only discharge batteries if the solar is not sufficient. At night the micro inverters would not be generating any power so the system would run on the batteries only until sun up and the micro inverters started to generate again.

Well that was a dumbass idea.

a hybrid would involve a complete rewire of my panels and taking down the micro inverters.
 
Having a GTI on the critical/UPS output side of a hybrid inverter is a very common configuration - just maintain the 1:1 rule of matching battery inverted power to PV power - there's zero reason why micros can't also be used either.


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chuckp said:
Was hoping that the ATS would isolate the systems from the grid to prevent any back feeding in the event of a failure, the ME3000SP would then supply the house from the batteries leaving the micro inverters on producing power during the day to supply the house and charge the batteries. Also use a load dump to get rid of any surplus generated power once/if the batteries are fully charged. As the ME300SP is bidirectional it should only discharge batteries if the solar is not sufficient. At night the micro inverters would not be generating any power so the system would run on the batteries only until sun up and the micro inverters started to generate again.

Well that was a dumbass idea.
Click to expand...

Nope not at all dumbass, you just need to use the incoming grid supply to close a suitable interlocking contactor that connects the grid to your entire house (with your ESS sitting parallel to your meter tails) - when the grid fails your house, along with your ESS is islanded (leaving the house powered by the ESS)

Unless you get very frequent outages I'm not sure the above is worth the effort ?
 
Sean said:
Having a GTI on the critical/UPS output side of a hybrid inverter is a very common configuration - just maintain the 1:1 rule of matching battery inverted power to PV power - there's zero reason why micros can't also be used either.
Click to expand...

Doesn't a hybrid require a DC input from the PV.

I only have DC directly at the PV panels the micro inverters mounted under the panels give me an AC supply at the panels. This is then bought into the house via AC trunk cables.

I could swap out the micro inverters for optimizers but then I would need to rewire the trunk cable's to make them suitable for the DC.

The grid is very stable during the summer months, but in recent years we have been getting more frequent power cuts during the winter months especially during very bad weather.
 
Sean said:
I meant bidirectional - in/out on an AC feed.
Click to expand...

So basically what the ME3000SP does.
 
Its for sure not a dumb idea but you need to make sure the gear you going to use support it.

I have seen gear blow up due to doing it without thinking :p
 
daromer said:
I have seen gear blow up due to doing it without thinking :p
Click to expand...

Definitely wouldnt do anything without being 100% certain first.

My house is worth more than having a power loss.
 
Looking at the specification (from the manual) for your unit, DO NOT CONNECT ANY PV INVERTERS TO THE CRITICAL/UPS OUTPUT.

The inverter stage is a high frequency type (in the manual) and does not allow backfeed of any PV power, unlike the design of the Victron units which are a low frequency type setup.

The design of the unit is such that one of three things will happen :

1. The unit would burnout as the PV inverters fight the frequency following of the inverter
2. The unit would shutdown with over voltage when there is insufficient load attached
3. The PV inverters would shutdown on over voltage when there is insufficient load attached

Best case, the supply would be at the maximum voltage range when you have insufficient load (which will make all EU specific tollrance based, 220V, appliances fail before thier time).

This is effectively your inverter design :
48V Battery -> DC Boost only stage -> HV Capacitor -> Inversion stage -> 240V AC

The other interesting bit in the spec for the unit is the short circuit handling capability (100A 1uS) which with a typical fuse/breaker as protection any short near the unit will likely result in the output inverter stage blowing (FET replacement fix). Just be carefuls as to what and how much you attach as suirge handling from some appliances may be an issue.

In terms of ATS by using relays/contactors you will always have to have an outage to re-connect to the grid because the unit would run the risk of being out of phase when switching back to grid.

Switching time when the unit loses power would still result in a half or full cycle power loss so some appliances will not like it and reset anyway.

Within the power grid the system is setup so that the initial fault is auto reset within 100-500mS so a lightning strike instigated trip (when no physical damage) would switch back on within a second. If you have an ATS that is a latch type arrangement you could find that you end up islanded a lot more frequently than intended with a manual reset back to grid.

Unless you use the critical circuit side for everything that is critical only (i.e. lights) islanding and returning to grid for the unit you have will be a bit more complex and a manual changeover at some point.

The reason for the manual stage is you may have to consider how some appliances will react if they are switched on and off too briefly (fridge compressors).

My setup at the moment is suicide lead and have only had to use it once for a few hours after bob the builder put an excavator bucket through the power cable down the road.

Separate issue with islanding, double pole isolation from the grid is a must, due to potential issues with the neutral line. When isolated, earthing is then a key issue and laso making sure residual current circuit breakers are going to work as intended.
 
completelycharged said:
Looking at the specification (from the manual) for your unit, DO NOT CONNECT ANY PV INVERTERS TO THE CRITICAL/UPS OUTPUT.

The inverter stage is a high frequency type (in the manual) and does not allow backfeed of any PV power, unlike the design of the Victron units which are a low frequency type setup.

The design of the unit is such that one of three things will happen :

1. The unit would burnout as the PV inverters fight the frequency following of the inverter
2. The unit would shutdown with over voltage when there is insufficient load attached
3. The PV inverters would shutdown on over voltage when there is insufficient load attached

Best case, the supply would be at the maximum voltage range when you have insufficient load (which will make all EU specific tollrance based, 220V, appliances fail before thier time).

This is effectively your inverter design :
48V Battery -> DC Boost only stage -> HV Capacitor -> Inversion stage -> 240V AC

The other interesting bit in the spec for the unit is the short circuit handling capability (100A 1uS) which with a typical fuse/breaker as protection any short near the unit will likely result in the output inverter stage blowing (FET replacement fix). Just be carefuls as to what and how much you attach as suirge handling from some appliances may be an issue.
Click to expand...

Yeah

Ive resigned myself to the fact that Im only going to use the UPS or as they call it the EPS for a critical
loads board as intended.

Im going to fit an additional consumer unit and put a couple of lights, maybe a couple of socket outlets for fridge etc and the heating controls onto it.
 
Take a look at my build. I did exactly what you're looking to do. However, my inverter does allow power to be backfeed from the output into the battery and my Micros support curtailment so the inverter can shut them off by rising the frequency above 62.5hz (although this can also be accomplished with a contactor on the solar backfeed breaker)

https://secondlifestorage.com/showthread.php?tid=7743

Here's the document on curtailment for my micros
https://enphase.com/sites/default/f...Considerations-AC-Coupling-Micros-Battery.pdf

I would also stay away from load sinks. If the device you're using as a sink fails that power has nowhere to go, I primarily use freq shift, if that fails my controller detecs power still being produced and it'll open the contactor for the solar shutting down all solar production and if those 2 fail the BMS will disconnect the battery if voltage goes above 4.1v per cell.

It's all about having redundancies to prevent a fire.
 
The inverter in the link (12kW) in the thread is a low frequency type driven by a H-Bridge (8 FET's x 4) arrangement, which work quite well charging (back feeding) or supplying loads. The inverters I have put together are the same principle.

Using frequency deviations to switch the solar off (causing automatic over frequency disconnection) requires the house to be running fully off the inverter at the time, so the house grid de-syncronises from the mains and then re-syncronises back so the inverter runs in line mode.

Not sure I would implement this type of control method because it is relying on the inverters automatically disconnecting and may be repeatedly emergency disconnecting under full load, which would not do the relays any good and may cause early failure depending on how the shutdown is implemented within the inverter firmware.
 
I'm out of my depth here - but what about a 'manual solution' where if the grid goes down
1) you disconnect from grid (switch the main breakers off)
2) feed in 'simulated' grid power from a generator or independent battery/inverter - to enable your system to think it has grid and keep active.

This would not be automatic but maybe a manual method is better than none?
 
completelycharged said:
The inverter in the link (12kW) in the thread is a low frequency type driven by a H-Bridge (8 FET's x 4) arrangement, which work quite well charging (back feeding) or supplying loads. The inverters I have put together are the same principle.

Using frequency deviations to switch the solar off (causing automatic over frequency disconnection) requires the house to be running fully off the inverter at the time, so the house grid de-syncronises from the mains and then re-syncronises back so the inverter runs in line mode.

Not sure I would implement this type of control method because it is relying on the inverters automatically disconnecting and may be repeatedly emergency disconnecting under full load, which would not do the relays any good and may cause early failure depending on how the shutdown is implemented within the inverter firmware.
Click to expand...

Why would the whole house need to be on the inverter for freq shift to work? If you have a sub panel with only the loads you want backed up it would also work.

I see your point about repeated disconnections. Maybe I should have said "Use an energy diversion but have a failover that will kick in if your diversion fails."
 
My initial thought was to keep the micro inverters online to charge the Powerwall during daylight hours with the solar surplus power being generated that's not used by the house when a grid failure occurs.

I have now decided that I'm going to fit a separate consumer unit to supply some lighting a few socket outlets for frigde/freezers, phone chargers etc. and maybe the heating system.

The Sofar ME3000 has a EPS built in so makes it very easy to do with the just one contactor.
 
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