Circumventing the COCT 3.5kVA limit

[PierreJ]

I'm planning a grid-tied zero feed-in system based around the following hardware: Multiplus II 5kVA, Pylontech batteries, 16 x 400W Solar panels, SmartSolar 250/100 MPPT

Given that the installed PV capacity is 6.4kW and I'm on a 60A breaker, would COCT sign off on it if the "Maximum Inverter Power" software setting on the MultiPlus is set to 3.5kW?

I'm not really concerned about any "wasted" solar power, since (a) the MPPT can still charge the batteries if the inverter is maxing out at 3.5kW and (b) solar panels are cheap (at least compared to the batteries).

Thanks,

Pierre

[Fuenkli]

8 hours ago, PierreJ said:

would COCT sign off on it if the "Maximum Inverter Power" software setting on the MultiPlus is set to 3.5kW?

based on my experience they will. To make sure you are not running into problems I would however contact the CoCT to confirm.

[email protected]

[PierreJ]

2 hours ago, Fuenkli said:

based on my experience they will. To make sure you are not running into problems I would however contact the CoCT to confirm.

[email protected]

Thanks, I have sent him an e-mail. When/if he responds I will post his reply here.

[PaBz0r]

This webinar mentioned that a bigger inverter will be ok, but it seems they also have a view on the PV size for the particular system, which could end up being another story:

https://arepenergy.co.za/city-of-cape-town-webinar-nov-2019/

https://arepenergy.co.za/city-of-cape-town-webinar-nov-2019/

[root]

See the irradiance report that @Rautenk kindly agreed to publish. 

https://powerforum.co.za/topic/2109-is-your-system-legal-capetonians-have-till-28-feb-2019-to-register-their-systems/?do=findComment&comment=64401

Edited February 18, 2020 by root
Additional info

[PierreJ]

So I haven't been able to get a authoritative answer on this question, since my e-mail to CoCT went unanswered.

It seems reasonable to me and many others that the amount of DC you generate is not relevant, as long as the inverter is limited to producing 3.5kVA AC. However, according to an installer I talked to the amount of leeway you have will depend on which office deals with your application, and thus where in CoCT you live. Apparently the eastern office is much less lenient, and a system with more than 3.5kWp on the roof is very unlikely to be approved.

I think what I'm going to do is to proceed with the application process and see what transpires.

[Fuenkli]

49 minutes ago, PierreJ said:

since my e-mail to CoCT went unanswered.

disappointing . @Rautenk do you maybe have Ryno's tel number? 

below are the contact details of the people who handled my registration:

 

Shiraaz Swartland (Pr Tech Eng)
Principal Professional Officer: Service Connection Planning (SCP) – North

Tel: 021 444 2177 | Fax: 086 696 6068 | Cell: 083 324 2908 |  Email:      [email protected]  | Web: www.capetown.gov.za

 

Fadeelah Kenny

Service Connection Planning PPO - East

Tel: 021 444 0064 | Email: [email protected]

 

Yonela Makuleni
Distribution Systems Development - EAST

Electricity Services Head Office, Bloemhof Complex, Bellville

Tel: 021 444 8532
cell: 073 605 7988

 

[PierreJ]

On 2020/02/18 at 9:40 AM, Fuenkli said:

To make sure you are not running into problems I would however contact the CoCT to confirm.

[email protected]

I have received the following response from Ryno (I've also attached the PDF he refers to):

"The maximum total generation capacity is the maximum active power capacity of the generator at the utility point of connection (POC). For PV systems in particular, this refers to the maximum active power generation capacity of the inverter as limited either by hardware [typically a 15 A MCB for the 3.5 kW system] or by software settings at the POC, whilst the inverter rated power could be higher than the maximum total generation capacity.  Refer to attached ‘Residential generation capacity (2019 10 24).pdf’."

It looks like a canned response, so I've asked him to exlicitly confirm that this means:

1) The kWp on the roof is irrelevant, provided the DC-AC inverter will not produce more than 3.5kW while grid-tied.

2) That the inverter may produce more than 3.5kW when it is not connected to the grid, e.g. during loadshedding.

Will post his response here when I get it.

Residential generation capacity (2019 10 24).pdf

[___]

If we use a Victron Multiplus oor Goodwe in this example, the POC (point of connection) would be the input of the inverter. This must be limited to 3.5kw.

So the example i used elsewhere, of a 5kva multi with 3kWp of PV... that would be problematic, because the maximum power at the PoC is 4kw (it gets the rest from the batteries). But... software limits are allowed, and you can limit your Multiplus's inout to  15A. Then it will never feed in (or draw!) more than 15A on its input. The downside to this config, is any load over 15A also comes from the batteries. The upside is that the inverter can be larger, and loads on the output can benefit from it.

[PierreJ]

1 hour ago, plonkster said:

If we use a Victron Multiplus oor Goodwe in this example, the POC (point of connection) would be the input of the inverter. This must be limited to 3.5kw.

So the example i used elsewhere, of a 5kva multi with 3kWp of PV... that would be problematic, because the maximum power at the PoC is 4kw (it gets the rest from the batteries). But... software limits are allowed, and you can limit your Multiplus's inout to  15A. Then it will never feed in (or draw!) more than 15A on its input. The downside to this config, is any load over 15A also comes from the batteries. The upside is that the inverter can be larger, and loads on the output can benefit from it.

The optimist in me reads "maximum active power generation capacity of the inverter" to mean the amount of power the inverter can add to whatever it draws from the grid. The Multiplus II 5kVA model can transfer 50A from input to output, so if my interpretation is correct then you could legally power a 65A load from it (drawing 50A from the grid and 15A from battery/PV). That kind of setup would be acceptable to me, since the Multiplus can only sustain about 4kW (17A) of generation anyway and I like a bit of safety margin. The Multiplus has a "Limit Inverter Power" setting that could be set to 3.5kW for this purpose. This setting is also conveniently ignored if grid power goes down. 

However, if your interpretation is correct and I effectively have to slap a physical (or virtual) 15A breaker before the inverter then that would mean I cannot ever have a load greater than 3.5kW after the inverter. That would truly suck.

Edited February 25, 2020 by PierreJ

[PaBz0r]

 

1 hour ago, plonkster said:

But... software limits are allowed, and you can limit your Multiplus's inout to  15A. Then it will never feed in (or draw!) more than 15A on its input

So like the shore power settings and not actually setting the inverter output to 3.5kw? 

 

1 hour ago, plonkster said:

The downside to this config, is any load over 15A also comes from the batteries.

So for instance in my case, this won't be problem:

[PierreJ]

I have asked Ryno whether the statements below are accurate, and he responded "yes" to both:

1) The rated capacity of the solar panels on the roof may exceed 3.5kWp, as long as the grid-tied inverter that converts the DC from the panels and/or batteries to AC will be limited in software or hardware to producing no more than 3.5kW.

2) If the grid is down (e.g. during loadshedding) and the inverter is islanded, it may make maximal use of battery and/or solar power up to its capacity and not be limited to 3.5kW.

[___]

1 hour ago, PaBz0r said:

So like the shore power settings and not actually setting the inverter output to 3.5kw? 

Exactly. The AC-input limit that Multis and Quattros have for the last decade or so, mostly used by people in boats and yachts who have limited shore supplies. You can use that for this purpose.

The limit works in both directions, both for current drawn but also for current fed back. The reason is simple: For its intended use, the point of the feature is to prevent the breaker on the other end from tripping. That breaker works in both directions, so you have to apply the limit in both directions too.

This limit can be used to limit your feed-in to 3.5kw, simply by setting an AC-input limit of 15A. The problem is that it also limits your draw from the grid to 3.5kw. The rest has to come from the batteries. If you can live with that, then you can use this feature very effectively to have more power available for your own loads, without feeding it into the grid.

The other option is the Maximum Inverter Power setting in the ESS menu. You could install a 5kVA Multi, and limit it to 3.5kw. In theory this gains you 1.1kw, since the 3kVA unit is limited to 2.4kw grid-tied. And again, if the grid fails, you have the full 5kw available for backup loads.

[PierreJ]

3 hours ago, plonkster said:

If we use a Victron Multiplus oor Goodwe in this example, the POC (point of connection) would be the input of the inverter. This must be limited to 3.5kw.

So the example i used elsewhere, of a 5kva multi with 3kWp of PV... that would be problematic, because the maximum power at the PoC is 4kw (it gets the rest from the batteries). But... software limits are allowed, and you can limit your Multiplus's inout to  15A. Then it will never feed in (or draw!) more than 15A on its input. The downside to this config, is any load over 15A also comes from the batteries. The upside is that the inverter can be larger, and loads on the output can benefit from it.

More Q&A with Ryno:

The 15A limit, is that a hard limit on the inverter grid input (e.g. a 15A breaker) or a generation limit? [Yes, e.g. for the 60 A single phase service circuit breaker at the POC as per feedback below.] Some grid-tied inverters are able to pass through substantial AC current from the grid through to the load - 50A for the 5kVA Victron Multiplus, for example. What I am asking is whether a 65A load on the inverter output would be legal (50A from grid [No, 15 A max from the grid POC for the 60 A single phase supply] + 15A generated [up to the limit of the inverter rated power]), or whether the maximum permissible load on the inverter output would be 15A.

(The black text is mine, and the red text is his response.)

I was really hoping you were wrong in your interpretation, but it seems you're on the money. This completely stymies my plan to put all the loads after the Multiplus, since I won't be allowed to make use of the 50A transfer facility.

So I guess the best option still on the table is this:

1) Leave all the non-essential loads connected directly to the grid

2) Add an energy meter immediately after the mains switch of the main DB so that the Multiplus can be configured to prevent feed-in.

3) Software-limit the Multiplus to 15A of bidirectional "shore" current.

Is it possible to configure the Multiplus to do (2) and (3) simultaneously? If so, this means that solar and batteries will be able to contibute up to 15A to my non-essential loads, but if the sun is down and the batteries are flat the essential loads will be limited to drawing 15A from the grid.

Also, it seems clear to me now that you can put as many solar panels on your roof as your MPPT can handle. That's some good news at least.

[___]

3 minutes ago, PierreJ said:

I was really hoping you were wrong in your interpretation, but it seems you're on the money. This completely stymies my plan to put all the loads after the Multiplus, since I won't be allowed to make use of the 50A transfer facility.

There must be a misunderstanding here. What they want to avoid is the massive spike that results from charging batteries after an outage. Whether your loads are all on the output or not doesn't matter... after an outage they all pile back onto the grid anyway regardless of where they are connected. The one variable is the battery charging.

But indeed, if you use the AC input limit as described earlier, then you wont be able to use the full 50A capacity of the transfer switch. It will never draw more than 15A from the grid, and never push more than 15A into the grid. For some houses this will work fine, but for some it won't.

[PierreJ]

1 minute ago, plonkster said:

What they want to avoid is the massive spike that results from charging batteries after an outage. Whether your loads are all on the output or not doesn't matter... after an outage they all pile back onto the grid anyway regardless of where they are connected.

I suspect that they are worried that if the loads are on the other side of the inverter that a minor surge or brownout in the grid could cause the inverter to trip and suddenly remove a fairly large load. If there are enough such inverters in a neighbourhood and they all trip at the same time then it could cause problems for the stability of the grid.

I could ask Ryno to clarify the reasoning behind it, but I think he's growing tired of me now, so perhaps someone else should.

[FixAMess]

What does all the above mean for those with a 5KW Goodwe? Would we have to get an 80Amp feed?

[PJJ]

9 minutes ago, calypso said:

All just sounds like a massive pain in the ass for CT folk. I have a tiny house and it doesnt sounds like nearly enough power. 

Its only on the AC Input side, as stated above, once you are islanded the sky is the limit.

[PJJ]

1 hour ago, plonkster said:

mostly used by people in boats and yachts who have limited shore supplies

Its also VERY useful in preventing you from accidentally tripping your mains supply in a house with big loads and charging batteries after a grid outage.

We have one farm house with 2x Big geysers elements multiple aircons, swimming pool pump etc, and watching the Multi throttle its AC charger to ensure it keeps within the AC input Limits (Or even take power from the DC bus with power assist) is a thing of beauty!  

[NigelL]

48 minutes ago, plonkster said:

But indeed, if you use the AC input limit as described earlier, then you wont be able to use the full 50A capacity of the transfer switch. It will never draw more than 15A from the grid, and never push more than 15A into the grid. For some houses this will work fine, but for some it won't.

This is true if one uses the transfer switch in the Multiplus-II, however one does not need to do this. You can always use the alternative method shown below 

 

In this case the Non-Essential loads are not limited by the 15A breaker and you can still make use of the full 5kW to Essential loads if needed.

[___]

28 minutes ago, PJJ said:

We have one farm house with 2x Big geysers elements multiple aircons, swimming pool pump etc, and watching the Multi throttle its AC charger to ensure it keeps within the AC input Limits (Or even take power from the DC bus with power assist) is a thing of beauty!  

Indeed, it is a beautiful solution, but not for the small-battery-folks(tm)*. If you have a large enough battery to carry the >15A loads for as long as they need carrying, this solves the 25% CoCT issue neatly and efficiently.

I suspect what most people want is an AC limit that works only in the one direction (feed-in) while allowing the full 50A (or whatever) of the transfer switch through on import. But I think @Pietpower is spot on with his guess that with such a setup, a tripping event also disconnects a potentially large block of loads, which has a possible equal destabilising potential.

* Small battery folks. Those are the people who ask for support, and when you drill down you find out they broke the rule of common-sense-proportion and they have a really small battery. Then they make their problem yours and expect a solution. I have nothing against small batteries, I do understand they cost money, but with them comes certain limitations that you have to accept

 

 

[___]

8 minutes ago, NigelL said:

In this case the Non-Essential loads are not limited by the 15A breaker and you can still make use of the full 5kW to Essential loads if needed.

I suspect that carefully balancing your loads might be the key here.

If you put around 3.5kw of your loads on the output, and 3.5kw on the input, you can install an 8kw Quattro, A carlo gavazzi meter on the input side (or the current sense CT as indicated), and limit the input to 15A. While the house's load is under 3.5kw, it does not matter where the load is (input or output), the Multi will power it. If you have more than 3.5kw on the input side... well then the difference will have to come from the grid. And if you have more than 3.5kw on the output side... then the difference will come from the batteries.

I suspect very few people with a single-phase 60A connection in a 3-4 bedroom house will have more than 3.5kw of loads that need actual backup!

Edit: Of course the 8kw Quattro isn't on the CoCT list... so you cannot actually do that... but in theory you could.

Edited February 25, 2020 by plonkster

[Tsa]

OK, so I have read through most of this and still not sure. Can someone please try and explain it using crayons.

So running panels with 2kw capacity, Growatt SPF 5kv hybrid and 2x 2.4kw Lithium batteries. All loads via inverter, excluding stove & geyser. Grid input only used to charge batteries when PV not available. 

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

[NigelL]

1 minute ago, plonkster said:

II suspect very few people with a single-phase 60A connection in a 3-4 bedroom house will have more than 3.5kw of loads that need actual backup!

Indeed!   

[PJJ]

8 minutes ago, plonkster said:

I suspect very few people with a single-phase 60A connection in a 3-4 bedroom house will have more than 3.5kw of loads that need actual backup!

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.

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

Edited February 25, 2020 by PJJ