Hello again.
So I have a few, and ongoing, questions about the ESS. I’ll start with the simple ones.
Going through the manual and referencing on my VRM Remote Console I want to check…
In the menus “Settings<ESS<Grid feed-in”…AC-coupled PV - feed in excess is enabled. The manual seems to suggest (to me, at least) that this concerns devices like a Fronius inverter, which I don’t have. Am I mistaken?
Bit of dof question, but why do the numbers on the Dashboard not add up? That is the diffs between AC-out, PV, Battery discharge. Not crucial, just curious.
Is there a way to diminish the Grid-AC influence, ie, have most of the supply for my meagre loads come from my PV and only when it’s insufficient will grid-AC come flowing in?
(on Q:3 I have currently cut ties with the grid so as to utilize my PV and battery, up to that moment the grid had been bullying my installation taking up 58% of the supply, I want it to be less butch)
AC PV is for grid-tie ac inverters like the Fronius yes. They normally do not have batteries so their users normally have a arrangment to push excess power back into the grid. If you don’t have it, it will do nothing.
This would all be about effiecencies in the conversions. The heat that devices give when working is because not all the energy you supply is going into the thing that the device does. The rest is heat.
If your inverter can supply 800W of power and anything more will come from the grid, then to longer you can keep your usage to just under 800W the more power will be used from your PV and battery. So if you have a lot of loads using more than the 800W that will all come from the grid even if there is PV or battery available.
I find this to be exactly the opposite in my setup. My 1200VA inverter, when grid tied, rarely kicked out more than 200W, generally peaks at about 150-190W for fridge coming on-running once/hr, then runs for about about 15-20mins at 80W or so. Rest of the time it’s a computer, small load. And yet 58% of consumption came from the grid…hence my head scratching!
In fact, based on discussions had on this thread My Inverter's Capabilities...confused? - #12 by cattus I get the impression the ESS works as a support to the grid supplying the loads. Which leads me to think that if I attach my Installation to a large load (managed during the day eg heating geyser between 10am-3pm) I may then get more out of it. I may have misunderstood though.
Your inverter would only produce what it needs to. It wouldn’t feed back into the grid unless you’ve ticked that option. So if the loads in your house is low, it would only meet those loads.
Let’s say there’s a kettle turned on in your house, plus a few odds and ends, and your house’s total consumption is 2200W. Your inverter would supply 1200W (not sure if there’s limits while operating grid tied), meaning that 1000W would come from the grid.
When the kettle turns off, you have 200W for your house’s total consumption. Now the inverter would supply 200W and 0W would come from the grid.
In reality, you would have a grid set-point of say 50W, so your inverter would aim to always get 50W from the grid.
If you have a Multiplus and a grid meter, I think (don’t know the 1.2kW version) that it would feed back to take the grid meter to whatever the setpoint is, 50W say. So the geyser doesn’t need to be on the backup side of the Multi (and really shouldn’t be on a Multi that small, or even much larger).
Seeing that only a few items are on the inverter I would suggest your change your grid set-point to 0W. And if you know you have more loads being supplied before your inverter and that those are ALWAYS above a sertain point you could also use a setpoint of say -100W (that is the same as the grid meter saying it needs 100W for use before the inverter)
But if you only have small amount of load that is the only power your inverter will produce.
If your inverter output use too much grid power and there are no loads above 800W then it must be a setting.
So over the last few days we’ve had total blackouts, technical issues and then cable theft. This has left me fretting a little about my system effectively running off grid. I was concerned about my Battery SOC or ‘discharge’ to be precise, as in, how far would it go. When I looked at my Remote Console (when I could, because I cannot always) it showed this:
Now not being one to fiddle and actively do stuff to his system I tried to go online and read VRM Manuals and questions on the Victron.Community to learn more, this resulted in confusion. Seems there are settings behind settings I cannot see and the settings I can see are not setting per se but reflections of…sounds like ‘gevoelings’ to me.
Question:
How & where do I figure out, see, adjust whatever, how far my battery will discharge if the grid fails? (Honestly, I read and read and read and just ended up trapped in loops)
No, that is perfectly accurate. Although turning that setting on even if you don’t have a PV-inverter such as a Fronius can sometimes be helpful. In the rare case that a battery ends up slightly overvoltage, it allows the battery to deflate back into the grid. Why it works like that is somewhat technical… and I’m not getting into it now, just saying that leaving that ON does nothing bad, and potentially (in rare cases) something good.
They should be close, within a few percent. The reason they don’t add up is 1) propagation delays, and 2) conversion inefficiency.
You get power/voltage/energy values from various different bits of equipment, but you do not get them at the same time, nor are they a perfect snapshot. For example, if you have a grid meter (Carlo Gavazzi), the input-side loads is calculated by subtracting those numbers from each other, but there can be as much as a 1.5 second difference between the readings, which means any load that just stopped/started will be accounted for in one but not the other. For up to 2 seconds, the numbers will be grossly out of alignment (this is significantly better since Venus 3.00). This is what I call propagation delays.
But also conversion efficiency. If you look at the battery consumption, the Multi doesn’t have a measurement device on the DC side. It estimates it from the AC side, assuming a 90% conversion rate… which is often inaccurate. So the Multi can easily be off by 50W to 100W on the DC side.
Not perfectly clear on the question there. If I have to guess… very small loads, so the 50W ESS grid setpoint (or whatever you use) ends up being a substantial part of your import, and you would love that to be lower? Sadly, below 20W or so… it’s just noise. Not much room for improvement.
Newer (LifePO4) batteries generally have a Battery Management System (BMS) with their own shutoff value which is when the BMS effectively tells the inverter to stop using the battery at which point the inverter will switch off. It will then wait for it to be charged up from the grid (when it becomes available again) or solar (if you have an MPPT).
Pylontech’s USxxxxC models for example stops allowing it to be discharged at around 5% and others around 10%.
If you would like more control over it another option is in the inverter’s settings in VEConfigure where it specifies a voltage that it can use as well as a State of Charge (SOC) of the batteries:
So if you have for example a Pylontech that shuts down at around 5%, but you want to rather shut down at 10% then you can configure it there. You can then also specify at what % the inverter should switch on again. You can for example use 15% which will first charge up the batteries a bit before switching on the inverter and powering your loads.
I’d then stay away from the VEConfigure part and find out what the battery is and we can say that if it hits for example 10% it will shut down (and start back up around 11%).
So I believe the easiest answer to when will it shut down would be at around 5% SOC. But I would say that you should work with around 10%.
Once it’s shut down it will charge from the MPPT until the battery allows discharge again after which the inverter will switch on, but if the grid becomes available before then, then the grid will power your loads.
Keep in mind that the settings from my screenshot from VEConfigure (shut-down on SOC) is independent of the battery’s own setup which cannot be changed. But you can configure the inverter to shut down earlier and/or restart later if you’d like more control over it.
Thank you Fred.
At least I now feel my frustration after reading the VRM manual is not wholly unjustified; I kept having this feeling that the nugget I needed was hidden from me somehow.
