Questions to the City of Cape Town: SSEG installs / sign-off

[SilverNodashi]

13 hours ago, Elbow said:

I don't think you are understanding.  It's not about the feed back, it's about the stopping of the feedback. 

Let's say 100 10kw sseg systems in a neighbourhood.  Pushing 1MW into the grid.  Maybe there are 1000 homes behind that transformer and drawing average of 2kw each, so 2MW of load. 

Half the load is being carried by the solar systems. 

Oops - brown out. 

All those inverters follow all those fancy requirements.  So klunk klink klunk, they all drop off the grid at the same time. 

But all those houses didn't get the memo and the stoves keep stoving, and the geysers keep geysering, and etc. 

So suddenly that transformer has to double its output. 

Since a Power grid is an ac system - a very very low frequency tuned circuit - it is not going to enjoy that sudden change. 

I guess the result could be bang for that transformer, a trip for the whole area, or...? 

 

I hear you. And I do understand. 

 

What I am saying is that under a brownout condition the inverter should not feed back. 100x 10Kw systems or 300x 3.5Kw systems will both contribute to the same 1Mw (rounded off) on the grid. This is a different problem. The grid, at any point, has limits and can handle certain loads whether up or down (I know, there is more technicalities but let's keep it simple). 

 

I am trying to say, the inverter on your premises, regardless of the size (1Kw can kill as well) need to stop back feeding as soon as a brownout of fault occurs. 44

 

I don't live in Cape Town so these things don't affect me at this stage. But how do you deal with a shop / factory / office / etc for whom 3.5KW is just not enough. Not closely enough. Do they simply say "sorry you are too big a client, can't have solar" ?
 

Edited March 8, 2019 by SilverNodashi

[Guest]

21 minutes ago, GreenFields said:

Maybe best to match the energy consumption to production and make peace with the fact that grid tie means remaining dependent on the grid.

I keep on saying in different words that the focus must not be on the blerrie peaks for minutes per day, it is the constant draw that costs the most, which tends to be below 1kw.

And also to consider, most people cook food when they get home late afternoon / early evening.

Let me expand ...

14 hours ago, SilverNodashi said:

 Our washing machine uses 3Kw. The tumble dryer (... cloudy days) uses 2Kw. Make coffee while the tumble dryer is on you are above 4KW. 

If that is a worry, then don't boil the kettle (2kw) when the washing machine (3kw) is on and you are tumble drying (2kw).  
Stagger them, but it is troublesome.

Don't stagger keeping in mind that the total draw of +-7kw is not +-7kw but more like +-4kw on a good day as the panels then produce the savings of +-3kw - and the +-7kw peak is for minutes, not the whole day either.

And the tumble dryer on cloudy days, think about the savings the house does get if it is grid tied, savings that would never have been there if the solar array watts was not fed into the home overall. Or being off-grid, you cannot run the tumble dryer on cloudy days.

Is the glass half full or half empty?

To sum up:
Grid-tied peak watts is like "Relax bro, you are saving on Eskom with every single watt generated" ... from first to last light every single day, cloudy or not. 
Versus off-grid where the peak watts are VERY important as it counts in heaps and bounds towards a "blissful marriage", with cloudy days a huge challenge.

Go grid tied and be done with the worries.

[Guest]

38 minutes ago, SilverNodashi said:

But how do you deal with a shop / factory / office / etc for whom 3.5KW is just not enough. Not closely enough. Do they simply say "sorry you are too big a client, can't have solar" ?

Businesses can apply for different rules, see the solar panels on some of the businesses roofs.
And they tend to have larger breakers than homes ... 

We shall not confuse the two.  

And don't forget that with any business where the breaker is max 60amp, the 3.5kw savings is immense per annum versus not having it.
Get a bigger array that can produce for longer hours in the day.

[Guest]

44 minutes ago, SilverNodashi said:

... need to stop back feeding as soon as a brownout of fault occurs.

We know that.  

The one and only burning question all over today is: Does the inverter one has installed, have the "papers" to prove that? 

[GreenFields]

27 minutes ago, SilverNodashi said:

I don't live in Cape Town so these things don't affect me at this stage. But how do you deal with a shop / factory / office / etc for whom 3.5KW is just not enough. Not closely enough. Do they simply say "sorry you are too big a client, can't have solar" ?

Just speaking from NMBM's setup (see extract), but I'm assuming CT and elsewhere could be similar. The maximum amount of solar is estimated as about 25% of the maximum notified demand for the specific premises. In this table, on line number one, if your premises are on a on an 80A service breaker single phase, having a maximum notified demand of 18.5kVA at 230V, then your maximum allowable generation capacity is 25% of that, which is 4.6kVA.

Larger premises have larger notified demand, so should be able to install greater generation capacity.

Extrapolating this table to the smaller end of the scale, if your premises are on a 60A breaker with around 13.8kVA maximum demand, you're only allowed a quarter of that in generation capaciy, being around 3.5kVA. It's so that the embedded generation does not overwhelm the grid that it depends on.

[SilverNodashi]

6 minutes ago, GreenFields said:

Just speaking from NMBM's setup (see extract), but I'm assuming CT and elsewhere could be similar. The maximum amount of solar is estimated as about 25% of the maximum notified demand for the specific premises. In this table, on line number one, if your premises are on a on an 80A service breaker single phase, having a maximum notified demand of 18.5kVA at 230V, then your maximum allowable generation capacity is 25% of that, which is 4.6kVA.

Larger premises have larger notified demand, so should be able to install greater generation capacity.

Extrapolating this table to the smaller end of the scale, if your premises are on a 60A breaker with around 13.8kVA maximum demand, you're only allowed a quarter of that in generation capaciy, being around 3.5kVA. It's so that the embedded generation does not overwhelm the grid that it depends on.

And this is the problem. 

 

Our home based office (not my house, another house we use as an office) average on about 4.2KW since we have an air conned server room, laser printers, servers, PC's, CCTV, etc all running the whole time. We don't need to upgrade to 80A or 3phase but again we're above the 3.5Kw allowable limit. The office has solar panels to ensure uninterupted power first and secondly to save money. 

Now if I am limited to 3.5Kw then it means I will be paying more for Eskom than I wanted to, but also that some of the equipment won't have power in the event of a power failure during the day. 

 

 

 

 

Somehow the logic behind all of this just doesn't make sense. Same as with large shops who keep their lights on during the night but houses get load shed 

[SilverNodashi]

19 minutes ago, The Terrible Triplett said:

I keep on saying in different words that the focus must not be on the blerrie peaks for minutes per day, it is the constant draw that costs the most, which tends to be below 1kw.

And also to consider, most people cook food when they get home late afternoon / early evening.

Let me expand ...

If that is a worry, then don't boil the kettle (2kw) when the washing machine (3kw) is on and you are tumble drying (2kw).  
Stagger them, but it is troublesome.

Don't stagger keeping in mind that the total draw of +-7kw is not +-7kw but more like +-4kw on a good day as the panels then produce the savings of +-3kw - and the +-7kw peak is for minutes, not the whole day either.

And the tumble dryer on cloudy days, think about the savings the house does get if it is grid tied, savings that would never have been there if the solar array watts was not fed into the home overall. Or being off-grid, you cannot run the tumble dryer on cloudy days.

Is the glass half full or half empty?

To sum up:
Grid-tied peak watts is like "Relax bro, you are saving on Eskom with every single watt generated" ... from first to last light every single day, cloudy or not. 
Versus off-grid where the peak watts are VERY important as it counts in heaps and bounds towards a "blissful marriage", with cloudy days a huge challenge.

Go grid tied and be done with the worries.

Why should I not be able use my kettle, or any other appliance for that matter, cause the municipality decided that everyone should only use a little power? Just cause your usage is X doesn't mean everyone else also use X. I use Y, my neighbor use Z, etc. 

[___]

20 minutes ago, The Terrible Triplett said:

Businesses can apply for different rules, see the solar panels on some of the businesses roofs.

Businesses are three phase usually, so immediately you have 10KVA rather than just 3. And again, that is just the easy no-extra-homework option. If you want to put in more, you apply, you get the impact study done, you pay the big-time engineer to design it and sign it off. This is likely exactly what the big shopping centers do.

At some point (I think it is 100KWp) you must have your own dedicated feeder. As you get to 1MWp you need your own transformer(s) and switch yard.

1 hour ago, SilverNodashi said:

I am trying to say, the inverter on your premises, regardless of the size (1Kw can kill as well) need to stop back feeding as soon as a brownout of fault occurs.

And it does that... which is what causes the issue. But I think my brown-out example might be confusing things.

Let's consider a condition where there is no power failure, but some disturbance causes all the PV-inverters in your area to disconnect. A distant lightning strike causes a momentary spike for example.

If you're feeding in 100% of your capacity (a full 13kw on a single phase line), then the supplier sees 13kw less of the loads because you are powering those loads for them. Then a momentary disturbance on the grid (or a cloud, or even a rise in voltage, or a nuisance trip on a circuit breaker) causes your production to drop-out. Now the supplier suddenly sees 13KW extra load because you stopped powering that for them.

This might be your own loads... or other people down the street. The grid now has to "pick up" these loads. They want to have a means of estimating the amount of pick-up.

Now imagine this effect multiplied over a large area of many embedded generators. To plan for it, you have to know how much the pick-up might be. Of course this is also an inverse function of solar uptake (how many people get into it). I would imagine that if every single house in my town installed the allowed 3.5kw array, and a cloud moving over the town causes a sweeping 15% "mexican wave"... that's going to be bad enough!

It would be interesting to see how they got to this number, because it must have made certain assumptions about uptake as well.

Perhaps another thing to think of is that not everyone lives in a neighbourhood with 50 houses on a large transformer. There are places where you have 10 or less houses on a transformer. You may well get into a situation in such cases where the last guy in the neighbourhood who wants to install solar will be told he cannot because the transformer isn't big enough for more...

[Guest]

3 minutes ago, SilverNodashi said:

Why should I not be able use my kettle, or any other appliance for that matter, cause the municipality decided that everyone should only use a little power? Just cause your usage is X doesn't mean everyone else also use X. I use Y, my neighbor use Z, etc. 

That is not the point I am making. Use how much you want, but you are going to be regulated.

It is not about YOU.
It is about YOU and EVERY OTHER user sharing the same transformer in YOUR area.

If people don't like that, the answer is simple, go off-grid and you can do as you please. 
IF you don't want to or cannot afford that, then there are rules to be adhered to. Rules that are intended to safe guard OUR collective grid.

 

[SilverNodashi]

2 minutes ago, The Terrible Triplett said:

That is not the point I am making. Use how much you want, but you are going to be regulated.

It is not about YOU.
It is about YOU and EVERY OTHER user sharing the same transformer in YOUR area.

If people don't like that, the answer is simple, go off-grid and you can do as you please. 
IF you don't want to or cannot afford that, then there are rules to be adhered to. Rules that are intended to safe guard OUR collective grid.

 

I know it's not ME. I made a general statement about power usage. 

but OK, I get the point. This is how it is and that's it. 

[Rautenk]

3 hours ago, SilverNodashi said:

Our home based office (not my house, another house we use as an office) average on about 4.2KW since we have an air conned server room, laser printers, servers, PC's, CCTV, etc all running the whole time. We don't need to upgrade to 80A or 3phase but again we're above the 3.5Kw allowable limit. The office has solar panels to ensure uninterupted power first and secondly to save money. 

Now if I am limited to 3.5Kw then it means I will be paying more for Eskom than I wanted to, but also that some of the equipment won't have power in the event of a power failure during the day. 

Well, here I would actually recommend the following:

1. Back-Up UPS system, to cover the entire premises (this should be 15kVA, with battery back-up as calculated by your usage)

Now if you DO NOT install PV panels directly onto the system, them it can be installed as a UPS systems as per SANS10142. There is no limitation on this and does not fall under the embedded generation gambit. So NRS097-3 does not apply (also 097-2-1).

For this I would even recommend Axperts, though a Victron might be better option.

2. Grid Tie inverter 

Install a 3.5kVA Grid tie system for reduction in energy usage, include a Grid Blocking function here as you don't want to give your energy away for free!

 

Then, (I still have to check if this is actually feasible, on Axperts), when you have load shedding event you have a MANUAL change over switch. One that will allow you to disconnect the Grid Tie system from the Munic Supply and break the munic supply and connect it to the "back-up" side of the UPS. Ensure that the gird blocking is also installed on the UPS system so that your Grid Tie unit do not push power INTO your UPS device (Victron and Fronius are integrated so you can use this).

 

 

[SilverNodashi]

1 minute ago, Rautenk said:

Well, here I would actually recommend the following:

1. Back-Up UPS system, to cover the entire premises (this should be 15kVA, with battery back-up as calculated by your usage)

Now if you DO NOT install PV panels directly onto the system, them it can be installed as a UPS systems as per SANS10142. There is no limitation on this and does not fall under the embedded generation gambit. So NRS097-3 does not apply (also 097-2-1).

For this I would even recommend Axperts, though a Victron might be better option.

2. Grid Tie inverter 

Install a 3.5kVA Grid tie system for reduction in energy usage, include a Grid Blocking function here as you don't want to give your energy away for free!

 

Then, (I still have to check if this is actually feasible, on Axperts), when you have load shedding event you have a MANUAL change over switch. One that will allow you to disconnect the Grid Tie system from the Munic Supply and break the munic supply and connect it to the "back-up" side of the UPS. Ensure that the gird blocking is also installed on the UPS system so that your Grid Tie unit do not push power INTO your UPS device (Victron and Fronius are integrated so you can use this).

 

 

There's a guy in our area selling LED lights with battery backups. His "sales pitch" is that it saves electricity. How, I don't know, since it has a transformer to recharge the battery.

The office already has solar panels inverters and batteries. But this regulation will force me to take it off. IF it ever comes to Ekurhuleni. The solar panels cut the day time electricity usages by about 60%.

 

 

 

It's cheaper to install a 15KVA backup generator than a UPS that could possibly last 6 hours.

[Guest]

2 minutes ago, SilverNodashi said:

IF it ever comes to Ekurhuleni.

You guys are aware, that if NERSA takes over, and they seem to be doing, this will become a SA standard, not CoCT interpretation anymore?

[SilverNodashi]

I am going to withdraw from this conversation as it's quite clear that no matter what one does you'll end up paying far more than the savings could have been and somehow or another it would be illegal.

I quoted a client R82K for an offgrid system with minimal battery backup last week. Was told, "sorry you are mad! You rip people off. Someone else quoted me R54,000".

And I sympathize with her as I know most people cannot afford an off-grid system. My mom's electricity bill is R300 average per month. No matter what system I install there, she'll never recoup her investment. My uncle's electricity bill is R120 average per month. Same thing, he'll never recover his investment. In both cases they got a R10K generator (a few years ago when they were expensive) as backups. They often fail to start first time since they don't get serviced that often. But it gives them electricity when needed.
A friend owns a trailer factory, was quoted approx R450,000 for a solar system to easy day-time eskom costs. For him it's just too much an upfront investment. So they down tools where there's no power. A genset to run his workshop would be about R140,000.
Our church's monthly bill is about R20k. They couldn't afford a solar system (I think it came to R340,000 a few years ago) so they brought a R80k generator to run essential loads during load shedding. I think they had to start it 4 times last year. Big investment with a minus figure return, for diesel / maintenance.

[Guest]

16 minutes ago, SilverNodashi said:

I am going to withdraw from this conversation as it's quite clear that no matter what one does you'll end up paying far more than the savings could have been and somehow or another it would be illegal.

I disagree. I have spent the monies on a inverter on "the list". If I was in Jhb or Pta or Dbn, I would have done the exact same thing if I knew about the list, and here everyone does.

All I now need is for CoCT to acknowledge the VDE certification of the Multigrid I have, and I should be home free, legally grid tied. Here is my latest email to the powers that be:

 

18 minutes ago, SilverNodashi said:

I quoted a client R82K for an offgrid system with minimal battery backup last week. Was told, "sorry you are mad! You rip people off. Someone else quoted me R54,000".

And I sympathize with her as I know most people cannot afford an off-grid system. My mom's electricity bill is R300 average per month. No matter what system I install there, she'll never recoup her investment. My uncle's electricity bill is R120 average per month. Same thing, he'll never recover his investment. In both cases they got a R10K generator (a few years ago when they were expensive) as backups. They often fail to start first time since they don't get serviced that often. But it gives them electricity when needed.
A friend owns a trailer factory, was quoted approx R450,000 for a solar system to easy day-time eskom costs. For him it's just too much an upfront investment. So they down tools where there's no power. A genset to run his workshop would be about R140,000.
Our church's monthly bill is about R20k. They couldn't afford a solar system (I think it came to R340,000 a few years ago) so they brought a R80k generator to run essential loads during load shedding. I think they had to start it 4 times last year. Big investment with a minus figure return, for diesel / maintenance.

What you describe above is the stock standard run of the mill everyday happenings around solar systems. THEY. ARE. NOT. CHEAP!!!

My parents are in the EXACT same boat ito monthly Eskom costs. Their geyser is on Eskom, 2 hours a day, they will NEVER recoup any PV or EV "investment" ever.

And not one of our friends or family can justify a solar system, not one even a generator. Eskom phases them not, as the lot of them are campers, so they can do without Eskom for extended periods.

Solar is at THIS point in time, for a "select few".

If someone asks me for advice on solar, I talk them out of solar. No jokes. The one or two that insists at the end they want it, by then knows EXACTLY what they are in for. And depending on budgets, I try and start them on a smaller systems, a system that is "on the list" and "future proof" ... grid tied.  

That is AFTER I have explained in great detail the NEED's vs WANT's vs COST's and the inevitable "lifestyle" changes that are coming.

I don't have to sell anyone anything ... so it makes it easier to walk away.

[cpbotha]

Hi there @GreenFields - have we recently been on the phone by any chance?  (green fields solar?)

I would like to underline @plonkster's point -- even if you have perfect reverse flow blocking (which does not exist), if your generator (inverter in this case) trips, all of a sudden the loads you had on your own inverter are now transferred to the grid, so your house is suddenly pulling e.g. 3.5kW of extra power FROM the grid.

This is why the NRS definitions mention specifically "instantaneous change in power flow" and "generator trips": This goes in both directions, and they want to ensure that the delta in both directions can never be more than 25% of the supply

All of that being said: Things are not looking bright even for my GoodWe 3648 plans. Judging by the answer @Fuenkli got, they might even throw out the 3.6kW Goodwe, because it's over 3.5...

[GreenFields]

1 hour ago, cpbotha said:

Judging by the answer @Fuenkli got, they might even throw out the 3.6kW Goodwe, because it's over 3.5...

That would be a real shame and probably unnecessary, considering the inherent inefficiencies of the system. On a nominal 3.6kW of panels, powering a 3.6kW Goodwe with say 97% efficiency, minus maybe losses in the panels and wiring, you're only barely outputting  3.5kW to begin with. And that's at the height of noon with 90 degree incidence angle of light onto the panels, probably right in the middle of summer on a bright and cloudless day, on a roof facing directly north, maybe at a standardised test temperature of 25 deg C. Time to look the other way, perhaps?

1 hour ago, cpbotha said:

Hi there @GreenFields - have we recently been on the phone by any chance?  (green fields solar?)

Sorry, no, not in the business, strictly a customer, just did a bit of research prior to buying, and I'm taking guesses based on observations on my own (different) system.

[___]

19 hours ago, SilverNodashi said:

going to withdraw from this conversation

Things like this always bothers me... when emotion gets into a conversation

On a purely factual basis, without stepping on toes or anything, the "pick up" really is the official reason given for why the feed in limit is so low, why you cannot use your full cable capacity. You can accept this reason, or you can reject it and postulate some other reason why they might be going with such a low number, I mean it is entirely possible that deep down "they" are just hostile to solar power, want to protect their interests, and so on and so forth, and therefore they set a low limit. To prove such a thing, you'd then have to show that their official reason is flawed.

Personally I buy the official reason. Allowing people to use the full power the cable will sustain really isn't feasible. You have to put some kind of cap on things, or it will become unstable.

That however still leaves a massive amount of spectrum in the middle: Both propositions could still be true.  It is possible both that 1) there has to be a limit to protect grid stability AND 2) the limit they chose now errs on the side of being too restrictive. It is quite possible, and then one must argue for it.

That is why I said earlier that I'd love to see the math and the assumptions that went into that. Once you know what assumptions went into it, you can then see which one is the most vulnerable to attack... and then you can launch an argument for why the limit should be higher.

[Fuenkli]

15 minutes ago, plonkster said:

That is why I said earlier that I'd love to see the math and the assumptions that went into that

I agree. And then compare it to the experience and best practice of other countries who have gone through this already. There is a lot of countries with PV densities now higher than what we will probably ever achieve in SA. In addition I think smart grid management technology will become available to manage the challenge. We are also at the moment (and probably for quite some time) desperately requiring additional generation capacity.

 

[Coulomb]

5 hours ago, plonkster said:

Personally I buy the official reason. Allowing people to use the full power the cable will sustain really isn't feasible. You have to put some kind of cap on things, or it will become unstable.

Yeah. An unstable grid is a frightening thing to consider.

I like Germany's idea of using ramps instead of hard edges, though it took them a while to realise that hard edges are a bad idea. I mean things like how much power to reduce when the grid frequency increases to say 50.2 Hz. If all the PV inverters with their crystal locked timing drop their power 100% to 0% a milliHertz above say 50.2 Hz, then you get the "take up" problem you've been discussing. If however, they reduce to 90% at 50.21 Hz, 50% at 50.25 Hz, and 10% at 50.29 Hz (a simple straight line ramp), then if the spinning generators happen to overspeed a little, the PV inverters can back off and that will load the spinning generators more, slowing them down. But of course, this is a massive control system with delays due to the speed of light, inductance, and so on, so it could oscillate with larger and larger amplitude: instability. Control systems were never my strength. Kudos to those that design these things.

At some point (due to instability say), you do have to just trip off and start again. If the whole grid trips out, that's a big deal, worthy of their own Wikipedia pages. Restarting a large grid like in the USA, Europe, or Eastern Australia is a planning nightmare in itself. I imagine that South Africa has a relatively small grid compared to those, but that may not make it easier to control.

Edit: please pardon the topic drift.

Edited March 9, 2019 by Coulomb

[Elbow]

9 minutes ago, Coulomb said:

At some point (due to instability say), you do have to just trip off and start again. If the whole grid trips out, that's a big deal, worthy of their own Wikipedia pages. Restarting a large grid like in the USA, Europe, or Eastern Australia is a planning nightmare in itself. I imagine that South Africa has a relatively small grid compared to those, but that may not make it easier to control.

Apparently Johannesburg suffered a lot of trips yesterday - 10 substations tripped out leaving a LOT of people with no power.

 

[___]

3 hours ago, Coulomb said:

South Africa has a relatively small grid compared to those, but that may not make it easier to control.

As I understand it, there are a number of designated "black start" stations, stations that can start up without requiring external power (eg, Acacia is one such station in Cape Town). These are then used to start the next ones, and so on. The process apparently takes around 2 weeks if nothing goes wrong (not likely). During this time, some areas might have power while others won't, or you might only have power a few hours a day.