EMS - Single point of failure?

General Everything Else
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Hi All
I’m considering installing a second AC coupled inverter with the new EMS to enable easier control of the two systems and also provide more power to the home especially in winter when there is more power required such as the heat pump needing more energy for heating.

These are all positive reasons to install the EMS but

What are the Negatives
Is the EMS a single point of failure ?

For instance:
If the EMS unit fails there is no way to control the inverters or use the battery system so the system is down and offline.

If it is - can 2 devices be installed in high availability mode
Ie active standby setup

Just going through the pros and cons of the solution
before spending more cash on another inverter and batteries

I’ve currently got 2 x Gen2 9.5kwh units with the single 3kw AC coupled inverter

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Triple AC3 + EMS owner here. The EMS is really good, seems to have been very reliable for me, but you are correct in your suspicion that the EMS is a single point of failure. Essentially if the EMS turns off/breaks/crashes you’ll lose all your inverters/batteries and won’t be able to use them individually as the wiring and firmware is EMS specific so will not work.

There is the alternative of having a second inverter and more meters so effectively 2 separate systems and then balance them with homeassistant and pre-built scripts if you’re handy with that and they’ll continue to work if you have 1 inverter go down.

Bit of 6 of 1 half a dozen of the other if you ask me.

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I have two Gen 1 hybrid inverters, one with a 9.5 and one with a 5.2 battery.

Big pro is the increased throughput of having two inverters being able to discharge, meaning on all bar a really cold period I can run house load alongside the heat pump and not worry too much about grid importing.

Disadvantage is cross charging which in my case predominately happens from one inverter to the other when the inverters are in Eco mode, so often overnight.

I have now managed to all bar totally eliminate this by putting the inverters into pause charge mode when the sun goes down and back to normal Eco mode at sunrise. This is done with Home Assistant automations (wrapping around Predbat that controls my actual battery charging/exporting).

Personally I was on the fence about whether I would get the hybrid inverter EMS (when it comes out), figuring it would cost £1000 or so for the device and having it fitted and whether I would see the value in it or not. I’m now pretty positive I won’t.

If you have an EMS fitted then there’s a new firmware installed on the AC3’s which will only talk to the EMS, so in effect they become brain dead. So they can’t be independently controlled any more and as Chris confirms, the EMS is a single point of failure.
One additional disadvantage of the EMS is that they are slower to respond to changing house load because the EMS has to identify the load and then instruct the inverters to respond.

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Hmm I read with some interest the responses , some factual and some well we won’t go there.

is it a single point of failure yes and no, yes if the EMS stops working because it has developed a fault then yes, but you can recover this by utilising inverter 1 turn on eco mode and set meters to 1, and set up your normal charge and discharge routines until you have replaced the EMS. you might have to restart the Inverter or get support to do a grid code reset to remove the alarm

So how many EMS units have completely failed 1 and that was at install and I suspect that was because the installer tried to change the MSN File and removed it but couldn’t put it back on.

most issues are inverter or battery related and you would have suffered those EMS or no EMS, the EMS continued to work as long as it could see a grid meter and ignored the faulty Inverter, Predbat and balancing software can not operate as quickly as direct Modbus connectivity, I don’t care who you are it’s a fact I know I built it tested it and do this sort of thing day in and day out.

The EMS makes decisions every 300ms and changes every 1200ms you can not do that with API/ or Modbus over TCP, people get a little confused because the out put you see is every minute , that’s a snapshot, go look at the meter data, like any other piece of equipment you need to set it up correctly.

Ask valiant, we ran a house project with them and the overall cost to run the house with two EV’s and a heat pump was £-135 for the year, valiant published a white paper on it, two ac3 inverter and two 9.5kwh batteries

feel free to not use an EMS but two inverters on same cct is not supported, unless they either go via an EMS or are designed to work in Parallel, the general cost in energy for running the EMS is approx. 800w for two inverters over a period of 24hrs, so it is more efficient that just running the inverter without the EMS again that’s been measured. this is due to ramp up and ramp down speeds of the EMS.

biggest problems I see is installation getting some to understand that in Modbus terms efficient communication requires good connectivity so no wago connections on the cat5/6 cable, two pairs doesn’t work better that a single twisted pair, use the best spec cable for the Meter and inverter communications .

so you can now go away and make an informed decision.

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I have an EMS with 3x AC3’s. Overall happy with it. The only technical gripe I have is in the event of a grid powercut the unit does not hold time and when the grid comes back the system is idle until the time is set. If possible ask for a EPS socket to be added for the EMS to run off. Your installer can ask Giv for a wiring diagram on how to do this with multiple AC3’s.

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Thanks everyone for your response, I feel I’m a lot more informed now and wil make my decision on the information provided
Very informative

Thank you

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Hi Michael, I have a gen 2 hybrid and am looking to add a 2nd inverter to increase charge/discharge rate and add more storage. Is there an eta on the hybrid EMS and any news on which inverter combinations it will support? Many thanks

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Not at the moment, we have had to refocus the Hems unit towards Commercial at the this time, this is due to market pressure on commercial systems and a need to accurately monitor and run them.

When we have completed this requirement it will be back to completion of the Hems for residential systems, currently works for AIO, Gen2, AC3 and just needs the controls for Gen1 and Gen 2 adding and full testing to be completed.

can not commit to a release date at this present time

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9

I had an EMS added to my system last year along with a 2nd AC3 inverter
When I had my original system installed a few years ago (1 AC3 + 2 x 9.5kWh batteries) I also had a EPS manual change over switch installed for whole house use.
I’ve never had a power cut (until 2 days ago) so it was never tested in anger BUT I did test it once and it worked OK.
Since adding the 2nd ACS + EMS it had never been tested again and to be honest I hadn’t given it any thought.
2 days ago we had a power cut so I tried it, and it failed miserably
So.. my investigating started, why didn’t it work?
Once power was back
I remembered seeing a setting via the official web portal setting page appear sometime ago on each inverter for EPS enable/disable and I could not remember if I’d enabled it or not (I hadn’t)
So I enabled EPS on both inverters
The next day (yesterday) I safely shut all electrical & solar equipment down then isolated from the grid then switched over the EPS
NOTHING again!
So what am I missing? what has changed?
I’ve had the EMS installed and a 2nd AC3
I was starting to think that it might be impossible to have EPS with a EMS installed
Does the EMS need a UPS
Any information / advise will be greatly appreciated

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I have a similar setup to you: 2 x AC3 inverters, with 2 x 9.5kWh batteries attached to each, and an EMS to control the inverters. Each inverter has a socket connected to the EPS output and EPS is enabled on each inverter.

Prior to reading your post I had tested the EPS sockets by isolating the grid AC connection to the inverters and found that the EPS socket stayed live, so I assumed all was well.

Having read your post I tried the same test again but with the EMS switched off and in that scenario, which obviously mimics an actual power cut, the EPS socket is no longer live. It seems that the inverters shut down all power output when the EMS dies.

I tried plugging the EMS into the EPS socket but the time delay between the loss of mains and the EPS switching over to the battery is too long, so the inverter ‘sees’ the dead EMS and shuts down.

It looks like, as you suggest, it is necessary to use a UPS for powering the EMS, which seems ridiculous when those large GivEnergy batteries are connected up.

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Yes it does seem a bit mad.
So you need a UPS for the EMS to use the EPS… (can’t beat overuse of acronym’s)
I’m currently using a powerbank which works perfectly but doent look very professional so I’ve bought a couple of different very inexpensive DC UPS’s from AliExpress which should arrive later this week and a some 18650 batteries to power them which probably won’t arrive until a few weeks later.
I’m looking at setting 1 UPS up permanently for the EMS and another for my Raspberry Pi (Home Assistant)
Don’t take this the wrong way but I’m glad I’ve found someone else that can confirm my setup isn’t either faulty or unique.

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michael has sent me 2 wiring options for the eps option. But yes it is frustrating, the EMS isn’t a fire and forget user friendly box. Can’t get an installer to set it up and walk away we need to know how to set the time etc. OR new issue, if giv does fold and their servers go down, we then get a powercut… as far as i know the EMS pulls time from giv’s servers. I would like confirmation of what time server the box pulls data from.

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