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Experience getting City of Cape Town to sign-off a zero feed-in system with inverter maximum output greater than 3.5kVA ?


cpbotha

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Based on my initial reading of Cape Town's "Requirements for small-scale embedded generation" [1] (see page 18 for the limits) I interpreted the maximum inverter output limit (3.5kVA for a 60A breaker) as holding even when ZERO feed-in / export was configured in a grid tied system.

However, when I read through NRS 097-2-3 [2] (see around 4.2.2 for example), I'm starting to doubt my earlier assumption. Could it be that the "generation limit" does refer to what is fed back into the grid, and NOT to total inverter output?

Does anyone have actual experience with successfully signing off an inverter with a rated output larger than 3.5kVA on a property with a 60A breaker, where the feed-in to the grid has been limited using an approved mechanism?

[1] http://resource.capetown.gov.za/documentcentre/Documents/Procedures%2c guidelines and regulations/Requiremenst for Samll-Scale Embedded Generation.pdf

[2] http://pqrs.co.za/wp-content/uploads/2015/03/NRS-097-2-3-final-2014.pdf

Edited by cpbotha
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3 minutes ago, cpbotha said:

However, when I read through NRS 097-2-3 [2] (see around 4.2.2 for example), I'm starting to doubt my earlier assumption. Could it be that the "generation limit" does refer to what is fed back into the grid, and NOT to total inverter output?

I believe Cape Town errs on the side of caution (from their perspective). They want to be sure you won't be able to do more than allowed, so they are going to cap you on generation capacity. It might also have something to do with grid-tied inverters, where you pretty much have no choice: If you're off on a holiday, then you're pretty much going to feed all of it into the grid.

In some countries they do allow Hybrid setups to be larger. With Victron you can even set an AC input limit which is adhered to in both directions, that is if you set it to 16A it will never import more than 16A and never export more than 16A. This is however a user-alterable setting... so unless it could be somehow locked, I sort-of already know CoCT will not be okay with that 🙂

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1 hour ago, plonkster said:

I believe Cape Town errs on the side of caution (from their perspective). They want to be sure you won't be able to do more than allowed, so they are going to cap you on generation capacity. It might also have something to do with grid-tied inverters, where you pretty much have no choice: If you're off on a holiday, then you're pretty much going to feed all of it into the grid.

In some countries they do allow Hybrid setups to be larger. With Victron you can even set an AC input limit which is adhered to in both directions, that is if you set it to 16A it will never import more than 16A and never export more than 16A. This is however a user-alterable setting... so unless it could be somehow locked, I sort-of already know CoCT will not be okay with that 🙂

Interestingly, the SSEG requirements document states on page 18: "Generation Capacity refers to the total output capacity of the generator. For PV systems in particular, this refers to the maximum output of the inverter as limited either by hardware, or by software settings."

So they do explicitly support software limiting of the maximum output.

With the GoodWe ES, if you want to limit grid export, you install the so-called EzMeter and CT clamp (included) on the house supply. Now you can export limit to anything, also 0.

I would still very much like to hear if anyone has experience with getting the city to sign off (or not!) larger than 3.5kVA inverters which have this sort of export limitation.

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28 minutes ago, phil.g00 said:

For the life of me, I don't understand the rationale behind this limit.

NRS 097-2-3 states the following in section 4.1a: "An individual limit of 25 % of NMD will typically support a penetration level (percentage of customers that install a generator) of 30 % to 50 %, which is considered a reasonable and acceptable compromise between restricting individual generator sizes versus restricting penetration levels."

I am not sure in which interpretation of this statement is the correct one.

Further down under 4.2.1 we have: "The maximum individual generation limit in a shared LV feeder (see figure 1) is approximately 25 % of the customer’s NMD, up to a maximum of 20 kVA (generators greater than 20 kVA should be connected through a dedicated LV feeder)."

... which sounds like they are concerned with how much a customer generates back into the public grid.

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1 minute ago, cpbotha said:

With the GoodWe ES, if you want to limit grid export, you install the so-called EzMeter and CT clamp (included) on the house supply. Now you can export limit to anything, also 0.

Aaah yes, but a grid limiter isn't "instant". It always plays catch-up. So say you have 10KW capacity installed, you are presently using 5KW, and your grid limiter has it balanced so the grid is at zero. Suddenly the geyser turns off just as te kid in the garage turns off the table saw and your load drops from 5kw to 1kw. For around 500mS (sometimes more) you will feed 4kw into the grid before the modbus meter takes another reading, and then it might take some more seconds before the inverter pulls back (some, like the Fronius, are quite fast). So it sort-of matters whether the engineers are concerned with continuous throughput, or with peaks as well. I'm pretty sure a 15kw peak on a single-phase system is going to be a problem, while a 5kw one might not be.

3 minutes ago, cpbotha said:

I am not sure in which interpretation of this statement is the correct one.

Sounds like the one justifies the 25% decision (it is a simple "automatic approval" value that is good enough for as much as half of your customers), while the other one reiterates this value and states that 20kva is the max before you need a dedicated transformer for that stuff.

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4 minutes ago, cpbotha said:

... they are concerned with how much a customer generates back into the public grid.

That is my understanding. If everyone who can was to go grid tied, the grid is not designed for that.

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4 minutes ago, cpbotha said:

... which sounds like they are concerned with how much a customer generates back into the public grid.

It also assumes that customer uses zero of the power he makes.

Really it should take into account penetration and average own usage into account. This limitation is so unrealistically small that it all but rules out generating back into the public grid.

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3 minutes ago, phil.g00 said:

Really it should take into account penetration and average own usage into account. This limitation is so unrealistically small that it all but rules out generating back into the public grid.

The document does say 30%-50%. For myself... 3.5kw is plenty. With a bit more effort, I could go off-grid with that. But then I have what is called an energy-conscious household, not as advanced as the one TTT has, but well on its way. Though I must say, not having a pool pump... bliss.

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2 minutes ago, plonkster said:

For myself... 3.5kw is plenty. With a bit more effort, I could go off-grid with that. But then I have what is called an energy-conscious household,

That's my point, your at capacity, being energy-conscious and there's nothing left to export.

They stick a number on future solar penetration, something that's a complete thumb-suck.

But no number on average usage,- something they have decades of historical usage facts to support.

It just seems wrong, that there is zero incentive to send a watt out to the grid, (so who's going to do it?) and yet the cap is set so low that people can barely enough for their own usage.

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12 minutes ago, phil.g00 said:

That's my point, your at capacity, being energy-conscious and there's nothing left to export.

Most people hear they can save on solar so they invest in it. Note: Most are not electrically inclined, like my Dr, mechanic, family. It must just work.

So here is the thing. Most are at work during the "sporting event:" and one cannot assume the majority would not go to the lengths we go here, to use every single watt wisely, daytime, to not "waste" any of that power. My Dr, mechanic, family do not care. Works, yes, cool. On they go with their lives.

Solar is a lifestyle.

 

25 minutes ago, plonkster said:

The document does say 30%-50%. For myself... 3.5kw is plenty

With my 2.2kw array, and I struggle to justify 700w more, it is pretty easy to go "open taps" and feed a lot back into the grid during a day.

Now lets use 5kva systems and multiply that by 500 - 1000 - 10 000 grid tied systems in an area.

When dealing with large groups, in this case all going solar, you have to "dumb down" the rules ... and that will irritate the much smaller more conscientious groups, like us.

 

12 minutes ago, phil.g00 said:

... zero incentive to send a watt out to the grid, ...

The constitution / NERSA makes it illegal to sell electricity to anyone unless you are Eskom.

So the Munic can only buy from Eskom, not the home users. Till that is changed, we are stuck.

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9 minutes ago, The Terrible Triplett said:

So the Munic can only buy from Eskom, not the home users.

And here's the thing. IF the law is changed, Munic can buy from home users, from anyone, then the grid must be prepared for that, as it was never designed for that in mind.

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If you want to export you will need to upgrade your metering.

In CoCT it just isn't worth it to export, doesn't make financial sense as the Daily Connection charge for EGs with Net Metering is so high that you will need around 6kW system before you break even on the daily costs. Not to mention the additional metering install costs etc. 

I am sure a few people have made the calculations, feel like sharing?

And back to the original topic, I can confirm. CoCT will not sign off if you are out of the range defined by NRS097-2-3, BUT you can ask special permission to exceed!

 

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4 hours ago, Rautenk said:

And back to the original topic, I can confirm. CoCT will not sign off if you are out of the range defined by NRS097-2-3, BUT you can ask special permission to exceed!

If what exactly is out of the range? Maximum rated total inverter output, or output to the grid? :)

Also, do you have experience with the "asking special permission" bit?

If you can share anything with regard to your CoCT sign-off experiences, I would be most grateful to hear!

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22 minutes ago, cpbotha said:

Also, do you have experience with the "asking special permission" bit?

FYI. Rautenk is an engineer, one that is going to sign off my install, when I can finish it. :-) 

His list of checks are quite comprehensive I must add.

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30 minutes ago, cpbotha said:

Also, do you have experience with the "asking special permission" bit?

This I actually do not have experience with, however it is stated in the CoCT requirements document:

"Note: The generation size limits in the table apply to normal residential connections on a shared low-voltage (LV) network. Customers who wish to apply for an installation with a generation capacity exceeding the limits in the above table should consult with EGD before commencing with their formal application."

SO there is that option.... But how effective it is, that is a question on its own. 

And the CoCT guidelines are quite clear, it is Generator installed capacity regardless if you are feeding to the grid or blocking it. 

Best is to attempt and contact the CoCT's energy department, it may take a few weeks to get a good enough response. 

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9 hours ago, Rautenk said:

Thanks for the advertisement TTT, I am looking forward to seeing your system.

I also found you on Facebook, after a post on the SolarPV group, and discovered that we have two friends in common. That means I now implicitly trust you with everything and you will hear from my shortly IRL 😛

(I'm kidding about the trust thing... but not about hearing from me).

Edited by plonkster
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On 2019/01/21 at 8:37 AM, cpbotha said:

However, when I read through NRS 097-2-3 [2] (see around 4.2.2 for example), I'm starting to doubt my earlier assumption. Could it be that the "generation limit" does refer to what is fed back into the grid, and NOT to total inverter output?

So I has a bit of a more in-depth read of NRS097-2-3 and I found the one thing we all love to read past.. the Definitions at the start... 

It is VERY clear that NRS097-2-3 states Generation size and not export limits:

From NRS097-2-3:

"generator size
maximum change in active power flow at the point of utility connection for a generator trip (or rapid
reduction in output) when generating at full active power output


NOTE Some or all of the power generated may be consumed by the customers’ local loads. Where there is no
local storage the generator size is the active power rating of the installed generation. In cases with local
storage, the storage can be used to reduce the effective size of the generator by compensating for variations in
generation output, hence the definition used above."

From this it is clear that this is then to limit the trip currents in case of fault conditions.

I hope this helps a few people

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40 minutes ago, Rautenk said:

maximum change in active power flow at the point of utility connection for a generator trip (or rapid
reduction in output) when generating at full active power output

So as a practical thought-experiment, one might conceive a 5KVA hybrid inverter that is powering some large load in the home from a combination of PV and battery, with a 3KWp array on the roof. Let's say the load is exactly 5KW, so the power draw on the grid side is zero. Now imagine something goes wrong and a breaker trips, and for a second or two the entire 5KW pushes back into the grid, that is to say, the maximum change in active power flow is 5KW. This exceeds the limit.

It then follows that you can't fit a 5KVA inverter even if you only have 3KWp on the roof.

It should also follow that I can put 6KWp on the roof, as long as I use a 3KVA inverter.

Do I understand that correctly?

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1 minute ago, phil.g00 said:

So not that you'll feed in suddenly, but they'll have to pick up your shortfall suddenly.

I think you're right, but the answer is going to be the same. This is actually a common scenario, let's say the BMS on the battery disconnects. That will cause the hybrid inverter to turn off in many cases, again creating an instant delta of 5KW.

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1 minute ago, phil.g00 said:

@plonksterI think it .means a generation trip not a load trip.

So not that you'll feed in suddenly, but they'll have to pick up your shortfall suddenly.

I Agree with Phil, if you read this with the specific note on Hybrid Inverters then one should look at the Type Test certification etc. for how they react in that regard you explained. That would be bad for your circuit breaker.

NRS is more focussed on Grid:

It is less to do with 1 inverter and more to do with the 25% limit on the Transformer, so looking at this it is if the Transformer is fully loaded with Embedded Generation and a fault condition on the grid causes all of the inverters to simultaneously disconnect it should not affect the grid.

And 

8 minutes ago, plonkster said:

It should also follow that I can put 6KWp on the roof, as long as I use a 3KVA inverter

Yes, that is 100% correct there. the Inverter will be limiting the generation possibility. 

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33 minutes ago, Rautenk said:

It is less to do with 1 inverter and more to do with the 25% limit on the Transformer, so looking at this it is if the Transformer is fully loaded with Embedded Generation and a fault condition on the grid causes all of the inverters to simultaneously disconnect it should not affect the grid.

Again, something that is not uncommon. A brown-out below 180V would cause them all to disconnect in one smooth sweep, potentially making things much worse 🙂

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