Advice re Cape Town compliant grid-interactive (NO feed-in) battery backed up system

[cpbotha]

Dear all,

Together with an installer here in Somerset West we are looking at options for a grid-interactive PV install, compliant with current City of Cape Town regulations, with battery backup but no feed-in. (Cape Town wants you to pay R11k for the new smart meter, which they own, as well as a R14.90 / day levy. This, together with the advantages of battery backup in the context of load shedding, leads me to remove feed-in from the list.)

The main problem is that even when NO feed-in is required, the inverter maximum output is limited to a maximum of 3.5kW (see page 18 in http://resource.capetown.gov.za/documentcentre/Documents/Procedures%2c guidelines and regulations/Requiremenst for Samll-Scale Embedded Generation.pdf -- my house has a 60A breaker), and this usually has implications also for the maximum PV input.

The config which we are currently looking at consists of:

• 16 x 275Wp panels for 4.4kWp. GoodWe is limited to max 4.6kW.
• The GoodWe 3.6kW EM series hybrid inverter see https://thepowerstore.co.za/products/goodwe-em-3-6kw-hybrid-inverter-2-3kw-backup (this is on the CoCT list, with 2017 NRS certification)
• 2 x PylonTech US3000B lithium ion batteries, see http://www.pylontech.com.cn/pro_detail.aspx?id=121&cid=23
• PV roof and DB are well situated relative to each other. However, wiring up separate panels for geysers and maybe upgrading to PTC elements, although a good plan on paper, is going to be tricky due to location.

With 6 inhabitants, we use anything between 25 and 35 with peaks of up to 50kWh per day. Major consumers are the geysers (already all on GeyserWise timers), a big 3kW aircon and of course our old friend the 1kW swimming pool pump, which I do limit quite severely. (the recent 50kWh day was super hot, main aircon + running pool pump did most of the damage)

The config above could work, but I have a great north-facing inclined roof which definitely has space for more panels. However, the only other inverter (as far as we know) which satisfies CoCT inverter output limit (through a firmware configuration) is the SolarEdge SE5000H, see https://www.sustainable.co.za/solaredge-se5000h-5kva-hd-wave-grid-tie-inverter.html

This does require power optimisers on each and every panel, but the main deal-breaker is that it only works with high voltage batteries such as the Tesla PowerWall 2 or the LG Chem RESU batteries, which will take this project into impossible budget territory for me.

Do any of you experts have any suggestions w.r.t. inverters or inverter configurations (or other system changes) which will 1. satisfy cape town's 3.5kW inverter output requirement and 2. enable me to get a kWp or more extra generation capacity on the roof?

Thank you very much for reading this far!

 

[Guest]

Hi CP, Welcome.

Also look at the Victron Multiplus II. It ticks all the boxes.

And you can add multiple controllers to split the arrays better over the day.

FWIW. We are also 6 in the house, back filled the pool, 3 x geyser, 1 on a timer, other one too small with the main one on EV tubes which being in Cape Town, is a good idea, and we are on about +-R700-800 pm to Eskom, and that is on a 2.2kw array.

Edited January 11, 2019 by Guest

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1 hour ago, cpbotha said:

Together with an installer here in Somerset West

Hi there fellow CFMer! What the wind hasn't blown away in any case...

1 hour ago, cpbotha said:

GoodWe

 

1 hour ago, cpbotha said:

SolarEdge SE5000H

I know a guy here in CFM, a good acquaintance of mine, who deals in specifically those two inverters. He is quite a fan of the SolarEdge. I am personally not such a big fan. The technology is interesting, maybe even awesome, but even at a low failure rate you still have multiple optimisers on the roof which increases the odds of losing a single module on the roof (usually one in the middle, to make life difficult) unacceptable in my opinion. So unless you have a big problem with shade... don't bother. Also, forget about the high voltage battery idea. Tesla won't bring in anything until next year (maybe) and all the options are insanely expensive in any case.

1 hour ago, The Terrible Triplett said:

Also look at the Victron Multiplus II. It ticks all the boxes.

As I understand it, the problem is that with only 3.5kwh on tap, and average 5 hours full sunshine, he can only offset about half his consumption. I know in some countries you are allowed to install a larger inverter as long as there is some way to limit the part that goes into the grid: In other words, you can put up 10Kwp, as long as no more than 3.5kw makes it into the grid. I don't think that is allowed in Cape Town. I think the only thing you are allowed to do is oversize the array... as long as the inverter is only capable of the allowed max. I also think you are allowed to use a larger inverter and configure a lower limit (you can do that with Fronius for example, there is an option in the Profi menu), but you'd have to check this: I'm not sure.

If this is indeed allowed (oversizing the array), then you can use something like the Victron Multiplus-II (as TTT said), which brings the PV in on the DC side. Since the inverter itself is only 3kw (closer to 2.4 when grid-tied), you're physical feed-in is limited to below the required 3.5kw. The remainder goes into the batteries and can be used at night.

[cpbotha]

 

 

Dear @The Terrible Triplett and @plonkster thank you very much for this!! ( @plonkster cool to run into fellow CFMer here! Let me know when you're in the neighbourhood of Paardevlei for good coffee (my office is there, different type of engineers, LOTS OF COFFEE going down))

4 hours ago, plonkster said:

If this is indeed allowed (oversizing the array), then you can use something like the Victron Multiplus-II (as TTT said), which brings the PV in on the DC side. Since the inverter itself is only 3kw (closer to 2.4 when grid-tied), you're physical feed-in is limited to below the required 3.5kw. The remainder goes into the batteries and can be used at night.

Wow, to my inexperienced ears this sounds like what I need to be able to get more panels on my roof. It will be easier to charge battery during the day AND feed AC into my home for longer. I can compensate for the slight hit in inverter output kW by staggering my geyser ON periods.

@plonkster Do I understand correctly that I can attach more than one MPPT to the MultiPlus II and further that you work for Victron (or have knowledge at least as deep as their own engineers?) :)

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13 minutes ago, cpbotha said:

 Do I understand correctly that I can attach more than one MPPT to the MultiPlus II and further that you work for Victron (or have knowledge at least as deep as their own engineers?) :)

This being a public forum and something I do in my private capacity, I generally don't advertise this much :-) Yes, you can attach multiple MPPTs to the battery bank. If you want to know how it all works, look on youtube for a video called "ESS Webinar".

[Guest]

Only a pleasure. Once you "get" into it, you will find that most of your loads are averaging <1kw over 24/7/365.

Next level, the loads that are on when all is asleep, to analyze and decide on.

 

14 hours ago, cpbotha said:

I can compensate for the slight hit in inverter output kW by staggering my geyser ON periods.

Ditto, you have timers on the geysers and stagger them to heat BUT ...

Geysers are probably 1/3 of your electricity use?

@phil.g00 makes a very eloquent point in asking why use PV panels and "waste" some of that regulated source if you can go big with EV tubes, which are not regulated. Rather use the PV power for where it has the most benefit than "wasting" the regulated resource on heating water. 1sqm of EV tubes can heat water up much faster than 1sqm of PV panels, and even more so under clouds, so EV tubes works much better in Cape Town than PV, especially in winter.

On EV tubes. If you can have the household change in that all shower evenings, or mornings, round about the same time, you could have even more savings as the geyser never has to use Eskom to heat water. We did that and with the water restrictions, I cannot recall when last we had to use Eskom to heat the EV tube geyser.

Another tiitbit, how far is the furthest warm water tap from the geyser? We found it to be the kitchen. We saw over time that the kitchen, when you wait for the hot water to reach the tap, takes quite a bit of water out of the geyser in the evenings when the kitchen is used most. When I had the chance I installed a small 50l geyser for the kitchen and 1 shower. That solved the "losses" of hot water at night. To heat 50l geyser is cents.

And, if you decided to go EV tubes, retrofit the exiting geyser/s. It is going to pop one day. So the day it pops it is an insurance claim right. At that time you ask for the money instead of the replacement geyser and get a proper solar geyser instead like say a Duratherm make, 10 year warranty. They keep the water longer on temp inside the geyser than any Kwikot.

That saves quite a bit on going EV tubes. :-) 

[cpbotha]

Just in case anyone else was also searching for this, here is the NRS 097-2-1: 2017 certificate of the Victron MultiPlus II: https://www.victronenergy.com/upload/documents/Certificate-NRS-097-2-1-17-18-320-00-MultiPlus-II-and-MultiGrid-II.pdf

Thank you very much @plonkster for that webinar, it really increased my understanding of how the Victron works, and just in general what my options are with battery-backed solar PV: