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ATS on AC coupled grid tied system.
#1
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



My hope is that the supplies will switch fast enough that the micro inverters won’t 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.
UK Southwest.

7 kWp Solar Panels (28 x 250Wp Shinetime Mono).
14 X APS YC500i Micro Inverters.
28 X 40P 18650 cell packs/modules configured as 14S 80P.
Sofar Mass Energy ME3000SP AC coupled charger/inverter.
Still sourcing and processing cells for powerwall.
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#2
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.
The Ultimate DIY Solar and build place
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#3
(08-25-2019, 07:32 PM)daromer Wrote: 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.

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.
UK Southwest.

7 kWp Solar Panels (28 x 250Wp Shinetime Mono).
14 X APS YC500i Micro Inverters.
28 X 40P 18650 cell packs/modules configured as 14S 80P.
Sofar Mass Energy ME3000SP AC coupled charger/inverter.
Still sourcing and processing cells for powerwall.
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#4
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.



(08-25-2019, 08:42 PM)chuckp Wrote: 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.

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 ?
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#5
(08-25-2019, 09:16 PM)Sean Wrote: 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.

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.
UK Southwest.

7 kWp Solar Panels (28 x 250Wp Shinetime Mono).
14 X APS YC500i Micro Inverters.
28 X 40P 18650 cell packs/modules configured as 14S 80P.
Sofar Mass Energy ME3000SP AC coupled charger/inverter.
Still sourcing and processing cells for powerwall.
Reply
#6
I meant bidirectional - in/out on an AC feed.
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#7
(08-25-2019, 11:45 PM)Sean Wrote: I meant bidirectional - in/out on an AC feed.

So basically what the ME3000SP does.
UK Southwest.

7 kWp Solar Panels (28 x 250Wp Shinetime Mono).
14 X APS YC500i Micro Inverters.
28 X 40P 18650 cell packs/modules configured as 14S 80P.
Sofar Mass Energy ME3000SP AC coupled charger/inverter.
Still sourcing and processing cells for powerwall.
Reply
#8
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 Tongue
chuckp likes this post
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#9
(08-26-2019, 09:51 AM)daromer Wrote: I have seen gear blow up due to doing it without thinking Tongue

Definitely wouldn’t do anything without being 100% certain first.

My house is worth more than having a power loss.
UK Southwest.

7 kWp Solar Panels (28 x 250Wp Shinetime Mono).
14 X APS YC500i Micro Inverters.
28 X 40P 18650 cell packs/modules configured as 14S 80P.
Sofar Mass Energy ME3000SP AC coupled charger/inverter.
Still sourcing and processing cells for powerwall.
Reply
#10
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.
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