2 minutes ago, Tsa said:

So as long as the charge current to batteries is capped at 15A this should be fine as an off-grid system?

Nope. It has nothing to do with the battery charge current.

The feature we're discussing is something rather specific to the Victron Multiplus inverters (Multi for short). You can limit your grid connection to some number, yet have larger loads than the grid connection would support because the difference can be taken from the batteries.

As I wrote earlier, this feature is meant for people with boats/yachts. Sometimes, when you moor up in some smaller marinas, your shore supply might be rather weak. This feature allows you to power your larger appliances without tripping the shore breaker. The idea is that these peak loads run for short periods only.

This feature also works with ESS (Victron's grid-tied implementation). When feeding power into the grid, it won't exceed this configured limit.

You can therefore use this feature to ensure that you never feed more than 15A into the grid at the point of connection (the input of the Multi), but because the Multi controls this on the INPUT side... you can have much larger loads on the output. This means you can install more PV, and power more loads without exceeding the 25% rule. But it also means that whenever you do exceed the 15A limit... your batteries must be able to carry the difference.

So because of this battery requirement, putting the "whole house" on the output would not be feasible for everyone. They will have to decide how to split it. i would think that if you left 3.5kw on the grid side and moved everything else to the output, then provided you don't have more than 3.5kw on the output (7kw total), this is not going to be a problem at all. It only becomes a problem when your backup loads exceed 3.5kw.

 

4 minutes ago, PJJ said:

Of course I made sure the killers (Microwave / Kettle / Hairdryers) where kept away, but I guess one man's non-critical load is another man's critical

If one has extra space in the DB, one can install an extra changeover switch so that the non-essential loads can be switched over to the Inverter Output.  You must then carefully manage the loads so that you don't trip the inverter, but this could be really helpful in the case of an extended power outage.

19 minutes ago, PJJ said:

I don't think people realize how much 3.5KW is, its plenty, I ran all my house lights, networking equipment, TV, 1 PC and fridge on a 800VA Multi for 2 months with no issues.

After the move three weeks ago, the new place sadly did not have a "simple" wiring layout, so this time it was not possible to split out the kitchen as I did the previous time. I could split off the laundry room, and the pool pump, and that was about it. The plugs of everything else ended up as essential loads. But 1) no electric geyser, and 2) gas stove makes the difference here. Without those loads, I rarely go over 2kw, and almost never over 3kw. A 15A limit would work perfectly well in this place.

Edit: At the moment I have a 25A limit configured (50A transfer switch in my Multi), because that's the limit of the cabling/breaker. If I do go over 5.7kw on the output, the difference would come from my batteries... up to almost 9kw... and then the Multi would give up and breakers would start tripping.

Edited February 25, 20206 yr by plonkster

4 minutes ago, Pietpower said:

But we do have heavy load items connected to the backup side of the inverter. Microwave, hairdryer, snackwich maker, clothes iron, toaster. Just using common sense not to use these during load shedding.

Of course, but if you limit the Multi's input to 15A, then some common sense may have to be applied even when there isn't load shedding. If you start enough loads on the backup side, and you go over 15A, the difference is supplied from the batteries. If your batteries cannot handle this extra load, or if such loads are sometimes used for long periods of time (running the batteries down), then this solution might not be for you.

Of the appliances you mention, a combination of microwave plus hairdryer would put you close to the limit (hair dryers are around 1.8kw - 2.0kw, microwaves as much as 1.5kw). Irons can be as much as 2kw, but are used for short periods only. Toasters are around 1kw, the kettle is around 2kw. Basically the risk is when a combination of these are run, then for that short period the battery might have to do the difference.

Not everyone has the same setup as my own, but at least in my house it would not be a problem.

6 minutes ago, calypso said:

3.5kw is plenty of power while in a backup phase. Its just the limitations of not being able to use many services at the same time while grid is running and connected. dishwasher/washing machine and tumble dryer can hit 7kw together if the timing is unlucky. 

Anyways, dont want to take this off subject. 

This is exactly what the problem is, if you limit it to 15A then you can only supplement the 7kw with 3.5kw from the Grid, in the case where you don't have enough PV or Battery to cover, or in the case where you have hit the inverter limit and it needs to pass the rest through.

*EDIT*

Ok based on Plonkster's reply below, this is only an issue untill passthru is triggered, then normal operation can continue, depending if you have installed a smaller breaker or not

 

 

Edited February 25, 20206 yr by PaBz0r

Oh, and one more thing: If you do exceed the input limit while the battery is low (below the minimum SOC configured for ESS), then the Multi will go into passthru and simply pass the power through. This is because the Multi cannot powerassist if the battery is too low.

For people who actually use power-assist for its indended purpose, this is a problem (because it trips the breaker). For people who want to use it for the alternate purpose discussed here... this is actually what you want. At night, when "switching back to the grid", you have the full capacity available again.

1 minute ago, plonkster said:

Oh, and one more thing: If you do exceed the input limit while the battery is low (below the minimum SOC configured for ESS), then the Multi will go into passthru and simply pass the power through. This is because the Multi cannot powerassist if the battery is too low.

For people who actually use power-assist for its indended purpose, this is a problem (because it trips the breaker). For people who want to use it for the alternate purpose discussed here... this is actually what you want. At night, when "switching back to the grid", you have the full capacity available again.

This is now if they haven't forced you to install a 15A breaker.. as per some diagrams we have seen.

14 minutes ago, calypso said:

But with no inverter in place you could pull 60A from the grid all day everyday if you wanted to. But more than a 3.5kw inverter is seen as risky. 

Well you could but you won't, because your demand would be whatever it was before. (predating your install)

In the install that I mentioned earlier where the AC Input limit works so great, that house never had a event where the main breaker tripped due to drawing too much power.

But after the install, maxing the 70A charger of the 5kVA Multi you will see that your grid power draw now goes up by a additional 3.7KW+- because of the AC Charger.

Now multiply that by potentially thousands of homes and you will see that you might have a peak demand problem right after a loadshedding event.

12 minutes ago, PJJ said:

Now multiply that by potentially thousands of homes and you will see that you might have a peak demand problem right after a loadshedding event.

Also, repeat after me. The 25% rule isn't about the capacity of the cable connecting your house to the grid, it is about the TIMING of events!

When the inverter disconnects from the grid, and when it reconnects, it tends to do so in tandem. If there is some anomaly on the grid (low voltage, a vector shift), all the inverters in the neighbourhood disconnect simultaneously. They then all start their countdown timers (because the regulations say 60 seconds after things stabilise), and they reconnect at the same time.

In some countries there are ramp rates for this same reason. When you connect to the grid, you have to slowly ramp up the power you feed in, or the power you draw for charging batteries.

Edited February 25, 20206 yr by plonkster

3 minutes ago, Pietpower said:

Then the Ryno reply mention: "The maximum total generation capacity is the maximum active power capacity of the generator at the utility point of connection (POC)." Which is effectively how much you can feed back into the grid.

But software limiting is allowed. When this limit is configured, the maximum power capacity of the Multi at the point of connection becomes 15A. The total capacity could be more (which is the point of the thread), as long as the grid never sees any of it.

Edit: Or more specifically, as long as you never expect the grid to PICK UP more than 15A, then you comply. That's the point of PowerAssist. It stops the upstream breaker (which is too small) from tripping. It does this in both directions (import and export). This is what the regulations require.

Right?

Edited February 25, 20206 yr by plonkster

Out of curiousity...  the 25 % rule is for the breaker connecting your property to the grid?  In a complex, we have a 600A breaker - so I can merrily have 33 kilowatt of generation going on here?

3 minutes ago, plonkster said:

Also, repeat after me. The 25% rule isn't about the capacity of the cable connecting your house to the grid, it is about the TIMING of events!

Sorry if it wasn't clear in my post, but that is exactly what I tried to illustrate, its not the capacity of a single home that is the problem, its this added load that potentially thousands of inverters could all add to the grid following a loadshedding event, on top of the already big strain the system would face from just geysers/fridges etc all kicking in as well.

18 minutes ago, PJJ said:

Sorry if it wasn't clear in my post, but that is exactly what I tried to illustrate, its not the capacity of a single home that is the problem, its this added load that potentially thousands of inverters could all add to the grid following a loadshedding event, on top of the already big strain the system would face from just geysers/fridges etc all kicking in as well.

If I had the time I'd make a video about this 🙂

 

10 minutes ago, plonkster said:

If I had the time I'd make a video about this 🙂

 

You should!

You could also even cover the potential role we solar + storage folks can play in helping with grid services

43 minutes ago, admiral said:

Out of curiousity...  the 25 % rule is for the breaker connecting your property to the grid?  In a complex, we have a 600A breaker - so I can merrily have 33 kilowatt of generation going on here?

More seriously though 🙂  Is this the truth?

1 hour ago, Pietpower said:

I can add another geyser that will have 4kW to pick up when the grid goes on

That's still a bit different. Inverter/chargers that comply with NRS097-2-1 wait 60 seconds and then connect to the grid and start charging. Grid operators know how to pick up those instantaneous loads that all switch on immediately, but I think they want to put a lid on the things that happen 60 seconds later.

At least, I think that is the INTENT, and I agree with you, that helps us to understand why it is like it is.

I think what additionally makes this harder is that there are people who install 6kW and 10kW PV systems on a single phase connection. That's already a significantly larger "disturbance" than an extra 4kw (or more likely 3kw these days) geyser. Presently, this is not a big problem, because there's likely one such guy per neighbourhood, but in time... who knows 🙂

 

1 hour ago, admiral said:

More seriously though 🙂  Is this the truth?

Above a certain power level, you need a dedicated feeder line 🙂

 

28 minutes ago, Pietpower said:

staggered

Not necessarily. The regulations say wait 60 seconds, and if the measured parameters are stable within that window, then reconnect. So it is in fact not staggered, anything that complies will in fact reconnect more or less at the same time 60 seconds later. The are actually synchronised around the event.

Let me just be clear, I am speculating. I am assuming there is a good reason for the rule, and speculating about what it could be. I know there are people out there who are dead convinced that the authorities just want to make life difficult for everyone, hate solar, and are making up all these rules to make our lives difficult (not you @Pietpower, but I've met such people in the past 🙂 ). I find that even more silly... it's too elaborate a plan, it would be much easier to just outright levy a tax of some sort, or say "no unauthorised" connections and then authorise nothing...

 

13 minutes ago, Pietpower said:

my opinion is mechanical ventilation requirements in the building regulations

Sounds like the story for the American railway gauge (it is a nonsense story but funny enough). Why is it that particular size? Well, apparently the Americans did it that way cause the Brits did, and the brits did it that way cause the track had to fit in the same existing spaces, which in turn was determined by the size of a Roman chariot, which was determined by the size of two horses side by side. So the size is literally twice the size of a horse's arse.

(As I said... not true... but kinda describes how it happens).

Edited February 26, 20206 yr by plonkster

1 hour ago, Pietpower said:

Many of the items require 10 fresh air changes

Fun fact about these, the amount of air changes required will be dictated by the maximum CO2 concentration you would want on the inside of the building.

So the best way of actually designing this would be to have a CO2 sensor inside the building monitoring ppm, once the concentration goes above say 600ppm you start ventilating, once you reach 450ppm you stop.

But the reason why I think we have bigger systems in the first place is because our mall experience is different to the ones in the developed world, in the developed world, you have fewer shoppers going to more malls, but each shopper also has much higher purchasing power than the average South African shopper.

So fewer people with more money = the same as more people with little money.

But having more shoppers = More CO2, and that CO2 needs to be taken out, whatever they are spending R10 or R10K at the mall.

I saw this firsthand in the US, the malls where quite empty compared to what I am used to, I don't know how it is where you guys live, but here in Limpopo, if I go the local mall over a weekend the mall is guaranteed to be packed, however its mostly just people coming in to buy 1 shirt, or even just to buy a R15 Pie at the King Pie in the middle of the mall.

6 minutes ago, calypso said:

Too late to edit now. But IE: is it a once off inspection or annual etc. 

I doubt anyone would ever visit you again, unless the transformer on the street corner blew up and they're hunting for the cause.

If the option to override the current limit via a GX device is disabled, then you would need the (expensive) VE.Bus to USB cable in order to change the current limit. So your installer could make it hard for you to change the limit if he/she was so inclined.

5 hours ago, calypso said:

Well if its something like a Multiplus 2 3000w then you wont need any limits as it cant invert over the limit. Then just push more grid it to max out the 32A transfer switch. 

If a 5000w unit then yes you would need to put in the software limits. 

CoCT looks at the maximum current at the point of connection between the grid and the inverter, so even if you have a 3kW Multiplus you would still have to limit the AC transfer to 15A.

I strongly suspect that this interpretation is contrary to how they interpreted their own regulations previously, but this is the way things currently stand. There is no restriction on the amount of power you may generate for the loads connected to the inverter output, as long as you stay under the current limit between the grid and the inverter.

Edited March 11, 20206 yr by PierreJ

11 hours ago, PierreJ said:

CoCT looks at the maximum current at the point of connection between the grid and the inverter, so even if you have a 3kW Multiplus you would still have to limit the AC transfer to 15A.

Again, I go back to basic principles. I was told this is about the pick-up. When you install the inverter, you should not make the situation WORSE than it is.

There are two kinds of pickup that needs to be considered (do tell me if I am missing something).

1. The first is the kind of pickup that happens when an embedded generator disconnects. In other words, this happens when there is a disturbance on the grid but it is not a full-blown outage. The embedded generators trip and all loads pile back onto the grid.

2. The second is the pickup that happens after an outage, when everyone's geyser and freezer turns on immediately.

Now let's consider the case of a 3kVA Multi that does not have its AC-in limited to 15A. This means that it can feed in 2400W into the grid, which means the maximum pickup in situation 1 above is 2.4kw. After an outage this inverter will wait 60 seconds, and then bring all the loads on the output back online. These loads cannot exceed 3kw... because the inverter would have been overloaded during the outage in that case. Requiring that these loads must be limited to 15A is impractical and adds nothing.

What does make things worse is if the inverter/charger immediately starts charging the batteries. Now it has to pick up the full 3kw load plus the charge power (35A times roughly 50, not even 2kw).

But what makes this really interesting, is that UPS setups are not required to register, not subject to these rules... and they are the ones most guilty of adding battery charging load to the grid.

So I'm really not sure about this overall 15A limit. Limiting the AC input on a 3kva is not necessary as far as I can see, since it is not making the pickup worse. With a 5kva it would be necessary, because you'd run into trouble with the first item above.

Edited March 12, 20206 yr by plonkster

I think the municipality is opportunistic with their approach. They move the control to the home owner instead of being able to supply the maximum amperage we require - which is lot more than 15a. It will be utopia for them if they can reduce the home demand automatically to 15a max per connection. Just think, no more transformers tripping on overload.

When a stove, geyser and kettle are on simultaneously they far exceed the supposedly allowable 15 amps. And if the power trips you will hear the women complaining. My wife will definitely.

Something is wrong with their approach.

 

 

28 minutes ago, plonkster said:

I was told this is about the pick-up.

All the regulations to limit the inverters to 3.5kW yet if I dont have solar and want to install a second 4kW geyser there is nothing stopping me.

Now the grid has to pick up my 4kW geyser plus whatever else I have running which can go up to 13.8kW on a 60A breaker.