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Cape Town trade-offs


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Hi everyone,

I've been reading so many posts here trying to get myself orientated.

I've recently bought a new house and wanted to get some PV panels up and run some of my load from the panels - at least some of the time.  I had in mind the pool pump (which can run in the day) to start with.  Maybe the dishwasher which can also run in the day, and then some lighter loads depending on how things go.  I'm waiting on some openenergymonitor hardware to arrive so that I have good data on what draws what.

But the practicality of the PV system  does depend on how you make up the shortfall - ie load beyond available PV power

I had the opportunity to buy in Infinisolar 3KW hybrid invertor.  I grabbed that chance since it is very versatile and much under list.  But now engaging with the CTCC rules and all and the trade-offs seem very complicated. My new house has an old analogue credit meter.  It seems it not OK to connect my hybrid inverters grid input to that even if I program my inverter not to feed back. 

Do I understand that I either do not connect the grid input at all - so a completely off grid system, or I choose either:

  1. Switch to a prepaid meter (my cost), and add an isolator to prevent the feed in (what device, and how much?).  Now I can draw from the grid with no chance to feed back.  And I'd be on the standard pre-paid tariff. I'll probably need to buy some batteries ($$$) to "time shift" my daytime excess energy into the evening.  Or:
     
  2. Switch to a "both ways" meter (my cost - and how much?), switch to the feed-in tariff (R350-ish standing charge and probably well under R100 feed-in credit?). But I don't immediately have to buy batteries which is a big capital saving.  Do I also need a Ziehl or other sort of gear between my inverter and grid?

In both cases the expensive services of a PrEng are required to certify the install.

So it looks like a complicated calculation to figure the best approach, and in either case an expensive exercise to satisfy them.

So for other Capetonians what have you chosen to do?

Thanks,

Elbow

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13 minutes ago, Chris Hobson said:

 

The 3kVA Infinisolar is on the COCT list of approved inverters so that is the first hurdle. 

You may have seen this .

 

Thanks - I did see that the Infinisola is approved, though mine is branded Renesola so hope they agree that its obviously the same thing.

I did read other CTCC documents but I didn't see that document so thanks!

Elbow

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You have two options. You can remain on your current tariff and fit a grid-limiter device to prevent feedback. I'm unsure if you have to change the meter to prepaid but I don't think so. Or, you can change to the Embedded Generator tariff, which has a R400 (ish) a month service fee and requires the new meter. In general it's better to fit the grid limiter and stay on the domestic tariff.

In all cases you need the expensive PrEng. As I understand it the Cape Town list is a guide more than an absolute rule. If the inverter is on the list, there is less work to do. If it is not on the list, but a PrEng is willing to sign it off as complying with NRS097-2-1, it might still be okay. Don't quote me on this yet, that's how I understand it.

I can refer you to someone who can help you with that. Friend of mine finally managed to get the services of a PrEng to sign his systems off.

Edit: About the R400 service fee. It is not a dead loss. The simple truth is that it costs money to maintain the distribution network even if you don't use a single unit of electricity. In Cape Town, the connection fee is subsidised into the cost, so there is no separate connection fee. You do however pay almost R2/kwh because of that (and even more if you exceed 600kwh a month). When you use solar power, you will be buying less power, so there is less chance of subsidising the connection cost. In addition, you might also be selling them power using THEIR equipment to do it. So what they do is split the maintenance cost out into a separate fee, but they reduce the per-unit cost below 600kwh as well. So basically they ensure that you never pay less than R400. In addition, the first 600kwh after that is now so cheap that it's cheaper to buy it from them than to use battery storage, that is, it is an incentive to ensure you buy the first 600kwh from them. They make sure you spend at least R1200 a month towards the city coffers :-)

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8 hours ago, plonkster said:

I'm unsure if you have to change the meter to prepaid but I don't think so.

If under 100 Amps then a prepaid meter with grid limiter will be required. 

(The good news is the COC will cover the costs of the prepayment meter)

See extract from COC Requirements for small scale embedded generation dated 23/11/2016, Section A, 1.4 below:

"Metering and Tariffs Residential customers may adopt one of two approaches to connecting SSEG to the grid: i. Customers wanting to connect SSEG to the grid without being compensated for reverse power flow will be required to install reverse power flow blocking protection to prevent reverse power flow onto the electricity grid. Customers with prepayment meters may then, subject to the ruling policies for tariffs and metering, keep their existing meter and remain on the relevant electricity consumption tariff. Customers drawing less than 100 A with credit meters will be required to have their credit meter replaced with a prepayment meter at the City’s cost. Customers drawing more than 100 A will be required to either reduce their capacity below 100 A, or alternatively have a bidirectional AMI meter supplied and installed by the City at the customer’s cost and be placed on the SPU 1 tariff. In other words, conventional credit and prepayment meters are never allowed to run backwards."

 

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4 minutes ago, Carl said:

Customers drawing less than 100 A with credit meters will be required to have their credit meter replaced with a prepayment meter at the City’s cost.

Thanks, now I also know :-) I wasn't sure.

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Thanks for the input.  So - thinking aloud..., and using guesstimated numbers (who can help me with better estimates?)

Lets say I put up 10x300Wp panels or 12x255.  So in theory I have 3kWp.  Theoretically 15kW/h average per day? Reading here I think that's too optimistic, so lets say 12.  (The pros can help me with realistic figures?)

Option 1 is pure off-grid, no batteries:

If I think about a pure off-grid system with no batteries It seems to me it will be difficult to use all the energy.  Reason being that it must be used when the sun is shining, and we must stay within the available power at all times.

So I would guess that I could maybe use half (6kWh) in a day on average.  What do people think?

The advantage being that the system is relatively cheap.  I could even reduce the number of panels and maybe build a starter system with limited power for under R30k. But all the panels with inverter for maybe R40k?

To try to get the most out of it I would build a control system that measures available power (Openenergymonitor or data from inverter) turns things on and off as there is power budget.  (Using relays or Sonoff wifi switches).  What "things"? - non-critical items like the pool pump, maybe a low power geyser heating element?  Run the washing machine on a sunny day.  

If it is 6kWh saved per day then we are talking about something like 180kWh per month which is about R470 today.  R40k capital saved us R470 per month.  It'll look better later if electricity prices continue to rise faster than inflation.

Option 2 adds feed-in from the grid:

So I connect my inverter to the grid with the reverse blocking device. Still no batteries.  CTCC installs pre-paid at their expense.  Let's guesstimate we spent now R50k with the extra hardware and the PrEng signoff.

So now I don't have to worry so much about overloading the PV since the Infinisolar will "top up" shortfall from the grid.  So we can use all the daytime power we make up to the demand (rest wasted).  But still, daytime demand isn't that high, even with effort to move load to the daytime.  Let's guess we can now use 8kWh off the panels.  240kWh/month or R625.  R50k capital saved us R625.

Option 3 is full grid-tie:

So now we need the fancy new meter too.  But we don't need the reverse current blocker.  So R55k total?

We're on the SSEG tariff - so paying CTCC R400 standing charge, but our first 600kWh quite.a bit cheaper.

So how this turns out depends on total consumption.

We make 12 per day, use 8 ourselves so sell the excess 4 back. So 120kWh per month or R84 (whoop-de-do).

Assuming 800 kWh/month total consumption we are still buying 800-360=440.  That costs us R512.

So 400+512-84= R828.  800kWh at domestic tariff would have been R1580 so R750 saving having spent R55k.

So - a lot of abouts and guesstimates, but based on all that the option 3 has the best return.  But there's not much in it.

Next is to think about batteries.  I suspect that will push the balance back to option 2 - But another post...

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12 minutes ago, Elbow said:

If I think about a pure off-grid system with no batteries It seems to me it will be difficult to use all the energy.

I am tired tonight again so hope I make sense. One cannot be off-grid and have no batteries. You either need grid or batteries to augment the solar energy generated by the PV array when it is insufficient to supply the load.

15 minutes ago, Elbow said:

Lets say I put up 10x300Wp panels or 12x255.  So in theory I have 3kWp.  Theoretically 15kW/h average per day? Reading here I think that's too optimistic, so lets say 12.  (The pros can help me with realistic figures?)

In an off-grid system 12 would be a good average.

17 minutes ago, Elbow said:

So I would guess that I could maybe use half (6kWh) in a day on average.  What do people think?

If you can only use 6kWh then you are only going to generate 6kWh. (A little more if portion of that 6kWh comes from batteries as now battery charging is part of your load).

21 minutes ago, Elbow said:

So - a lot of abouts and guesstimates, but based on all that the option 3 has the best return.  But there's not much in it.

I think Option 2 probably has the best return especially if you could perhaps avoid PrEng sign-off. I don't think anyone on this forum with in the supply area of COCT is feeding back into the grid. Just too many hurdles with minimal return.

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Just remember that even a purely off-grid system needs sign-off nowadays. If it is completely disconnected from the grid, then you need no sign-off (as long as the wiring is done according to SANS), but if it has grid-fallback (where it switches back to the grid when the batteries are low) and it has solar panels attached, it is considered an embedded generator and you need to do the paper work. I'm pointing this out so you don't mistakenly think that is an easy way to avoid the red tape.

According to NRS097-2-1, if the  inverter has a suitably interlocking transfer switch (so that it is impossible for it to energise the line when the grid is down) and complies with the SANS regulations applicable to a UPS, it complies. But you still need a PrEng to say that it does. So there are no loopholes.

Lots of people have simply skipped the registration. They either spin their mechanical meter backwards (illegal of course), or they have a grid limiter in place and simply keep quiet. Cape Town have ways of finding you though. One way is aerial photography (theirs is much better than Google Earth!), the other is to look at your power consumption and if it is too low, they might investigate you for power theft only to find your unregistered equipment.

The fact that you cannot reply bypass the red tape means there is no point in going for pure off-grid if you can go hybrid or GTI for not too much extra money.

My choice in such cases remain a Fronius GTI. The Victron CCGX has control software for it, though I'm not sure if that can work without a Multi in the circuit. But I also know ExSolar sold a control unit for these inverters, though it wasn't much cheaper than a CCGX.

I can find out if the Fronius control works on its own if you want? There are several Fronius models on the CoCT list, you'd probably look at a Primo or a Galvo.

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  • 2 months later...

So....

Turns out that whilst the house has an old credit meter, it was just left there and there is also a prepayment meter and so I do have to deal with all the hassles of the SSEG stuff.

So wish me luck with all that...

Elbow

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On 7/29/2017 at 12:19 AM, plonkster said:

find out if the Fronius control works on its own

I did this by the way. The CCGX cannot work without a Multiplus or Quattro in the system, ie it cannot play grid limiter in a system with only a Fronius and a modbus meter.

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