Teltech

Dr. Pieter Groenewald will love the support ☝

AFAIK he is well and still recovering.

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Good evening Fellow Forumites
Good news - we managed to get the generator to charge the batteries without tripping the unit. Thanks for the help and advice and to the team @Solis Inverters SA who was very helpful and making my friend happy again (it was his 50th birthday too). Turns out a software update and a few minor adjustments on the input side was all that was needed. COC was issued and his system is working better than expected.

Good evening Fellow Forumites
Good news - we managed to get the generator to charge the batteries without tripping the unit. Thanks for the help and advice and to the team @Solis Inverters SA who was very helpful and making my friend happy again (it was his 50th birthday too). Turns out a software update and a few minor adjustments on the input side was all that was needed. COC was issued and his system is working better than expected.

Hi Emma, and WELCOME to the Forum.
You already have two options for your geyser - I am controlling mine via a CBI Astute smart controller such as this: https://www.voltex.co.za/product/cbi-astute-smart-controller-asc-wifi-enabled that works via Wi-Fi. As long as my home router is on, I can access the controller from work and switch the geyser on or off as I like. I can also check the power used for the day, and check daily historical power usage for some months.
Best way to learn is to ask questions right here on the Forum.

The calculator previously did not include the cost of insuring the solar system; I have now added this feature.

Thanks for all the feedback, really appreciate it.
The 0.5% default comes from the NREL field studies, which track what installed panels actually do over decades, and the median lands right around half a percent a year. The datasheet curves on new Tier 1 panels are lower, around 0.4%, but those are warranty floors rather than measured performance, so I kept the field number as the default.
That said, it's a slider, not a fixed assumption. You can set anything from 0.3 to 0.8, so new BC or bifacial panels can run at 0.3 or 0.4 and older poly at the top end. I've also updated the note under the slider to explain exactly this, what the default is based on and when to move it.
On bifacial gains, the cleanest way to capture those is the yearly output override box. Put in the kWh per kWp your system actually achieves and the gain is baked in, without me having to guess your reflective surface.

Indeed, but now we are comparing two totally different metrics 🙂 and yours has a whole lot more variables.
My best month this year was May, then again I have been off grid since December. But I also upgraded my battery bank in March, and started deeper cycling (and evening usage) in May.

Here are my Port Elizabeth weather station's graphs, for the year to date (1 Jan 2026 to 24 June 2026):

Ignoring the dip in March/ April and the spike in May (due to various comms issues), you can clearly see peaks of well over 1000W/sqm in January vs barely over 500W/sqm in June.

Here is a graph of the last 12 months (25 June 2025 to 24 June 2026):

So in my experience, with both coastal and inland installations, it is generally a drop of around 50%.

The 4000W solar power rating is not really important.
I have seen my inverter pull 4000W and no more. The extra 550W on it it’s there for extra generation during cloudy days that’s all. His would do the same, just pull up to a max of 4kW when he installs the 8 panels on it.
Even if he had 6000W on his 4000W MPPt it would be fine.

Most solar calculators online quote you a payback that never matches reality. They assume you use every kilowatt your panels make, that prices stand still, that your battery lasts forever and that the cash you sank into it could not have earned a cent anywhere else.
So I built one that does not pretend. You put in your real numbers and it shows you two figures side by side - the rosy payback a salesman quotes and the realistic one you are actually likely to get - then it breaks down exactly what eats the gap. Wasted daytime generation, panel degradation, the battery you will replace once down the line, financing interest and the higher fixed charge some municipalities slap on solar homes.
It is free and there is no signup. Set your own tariff off your bill rather than the presets and be honest about how much you use in daylight and you will get a sensible answer.
Anyone interested can have a look here:
https://southafricafacts.co.za/solar-savings-calculator-south-africa/
Keen to hear if the numbers line up with what you are actually seeing. Share your own setup and payback if you are up for it.

@TaliaB is still in high care and sedated while getting some rest. He breathes normally and DR would like his oxygen level to pick up to over 94%.

I am not on this forum very frequently and hence only yesterday by chance I had learnt of @TaliaB's medical condition and hospitalization after having tried to contact him about something completely different😥
I was also informed that by the Grace of God he is doing better now.
My heart goes out to him and his wife, and I wish him a very speedy recovery to absolute excellent health in the future.🙏
God Bless you @TaliaB

I wouldn't do that as a first choice. The inverter can in theory connect up to 10,400W of panels. Now I understand that it's a mixed bag of panels, but I'd start by maybe listing what you've got by make and model of the panels, and then seeing if one can come up with a configuration that could allow you to add that 4kW of panels without resorting to another MPPT. If it's a forlorn hope, if it doesn't work, then so be it, or if you've already gone through the thought process and concluded that you need the MPPT solution, that's something else, but from what you've written, I'd at least ask if this is an option.

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The latest is they intent fitting a filter in the largest vein in the body to catch the blood clots before they get to the lungs. This should happen tonight. This is after consulting a specialist in PTA.
Will keep you guys informed. 🙏🙏

In my opinion, if you cannot afford more panels now, I would install 2 strings of 6-8 panels each with both strings facing north. If there is space for a 7th or 8th panel on one, or both of these strings, get your installer to allow for their addition with this installation (add the mounting rails now)... then it will be very easy for you to just add those panels later on if you discover that it is necessary. The same goes for your third string, allow for the trunking, cabling, isolators, surge arrestors, etc and have that all installed now, making things much simpler when you install the east string at a later stage.
Regarding your second question: That would depend on your power consumption and lifestyle. My wife and I have averaged about 17kWh used per day for so far in 2026, and my 20kWh batteries have only dropped below 70% SoC (thus used more than ~6kWh through the night) twice this year - with such a light night-time load the batteries are fully recharged (99-100% SoC) by 10:00 at the latest, with the 2kW geyser then heating between 10:00 and 14:30. My 14 x 575W panels easily handle these loads, plus normal living consumption (coffee, toast, cooking, ironing, etc.) at the same time, and can still also run either a 2kW heater, or the oven, between about 10:30 and 15:00 - but not both at the same time... If your "after dark" consumption if much higher (thus dropping your SoC to say 40%) then your daytime battery charging will take longer to fully recharge the batteries, which might limit your daytime usage of other high-consumption devices (such as a geyser or an oven) whilst the batteries are charging. Fortunately, if you have allowed for the installation of a third string on the east-facing roof, as I suggested above, it will be an easy and quick operation to install that third string if you find that the two north-facing strings cannot cope.

These are very important questions that you are asking, and have a much wider "audience application" than just adding a second battery - perhaps you should change the title of this thread...
In my mind, you have the final say in what you want to buy, and who you want to work on your system - unfortunately most of the manufacturers, wholesalers, retailers and installers are running a type of protection racket (the "solar mafia") in this industry. The manufacturers & wholesalers are protecting their loyal installers, and threaten to not honor their guarantee if someone other than the original installer work on the system. I've had such a run-in with a wholesaler who was a Sunsynk agent at the time, that insisted I use the original installer when I had a problem with one of the batteries, else they would not repair the battery under warranty...
I did insist, before accepting the installers quotation, that I will be the sole controller of my system, and that he had to transfer the "owner" in the app to me. I think that you are fully entitled to insist that the installer be removed from sharing your system. The only "con" in this regard is that the installer cannot remotely visit your system to check it if it develops a problem, and you are thus forced to really understand the system and all the settings.
Apologies to the decent, professional installers who are not part of this mafia (and there are many of them on this Forum) - no offense meant to you.

@Aartappel your problem is quite a generic one and I have seen a few different solutions that the farming community is deploying...Direct Solar panels on VFDs, some farmers creating micro Grids large in size and then installing their own MV transmission lines and then disconnecting the various Eskom incomer points. I have at least 3 users completed these projects & have done it in a staged approach but the savings and the benefits are there to witness. Those unreliable expensive Eskom points are worth shutting down & pocketing the ongoing costs into your own infrastructure.
I have been involved with especially ATESS and more recently over the last 2 yrs Megarevo Transformer based Hybrids and AC coupled Grid ties and DC coupled ATESS topology. The largest plant at 1.5MW carrying a base load of 700kW is in a factory with massive HVAC and high inductive loads. The Atess equipment is really robust and honestly can take a heavy punch with large motors starting and stopping...
Its just my personal opinion that the High frequency non transformer based inverters won't last long for the irrigation environment or SAs farming environment because we have harsh conditions and we require equipment that will last the next decade that is serviceable in the field.
If you need basic advice and user cases please PM me. I can definitely point you in the right direction as well as share plants with you that have proven themselves in the field. The farming community are ripe to reap the rewards of solar power & with Diesel pricing very volatile id imagine it's going to accelerate...

Well, this is morphing into a very interesting discussion...
If the object of installing solar is ONLY to save money then I agree with you... however, many of us have installed solar PRIMARILY to not be dependent on a corrupt and inefficient government "state owned enterprise" (Eksdom), compound further with living in a crime infested country where having the municipal and/or Eksdom power cables stolen has become the norm (and leaving users of the utility without any power for extended periods...), and not the exception... So, many people like me would rather pay more to be able to have reliable power when we need it.
Again, this statement would be applicable to many modern city dwellers who go through life just buying and replacing things (that's what modern living is all about...) - but there are still a number of people who believe (as I do) in fixing things, or (heaven forbid...) actually making things themselves. Now, in my workshop I have (amongst others) a metal lathe with a 3kW motor, and before my recent retirement I could only work in my workshop during the evenings (still do, when it's not too cold...), and this absolutely needed to drain power from the batteries. I also have a good collection of power tools, TIG welder, etc. etc. - and that's why I opted for an overkill 12kW inverter and 20kW of LiFePO4 batteries, rather than having to rely on the unreliable Eksdom... my money, my choice.
I too would like to spend my money well, and have great ROI - but within context of the above... So, having "wasted..." money on a larger than needed for "normal" living system, would it not make ROI sense to deliberately discharge some of the batteries' capacity at night to heat the geyser between 04:00 and 05:00, thereby creating additional "storage space" to harvest more PV during the day (that would have been wasted otherwise)? By the way, in terms of actual ROI, I've recovered slightly more than 27% of my original investment in just more than 1.5 years, and with the utility rate increasing at the rate that it has over the last few years the return is bound to accelerate...
The above is not meant to insult or infuriate anyone other than our national power supplier - merely to point out that one should not judge (or assess) everyone using the same criteria 😇

Your comments mixes a few practical truths with some assumptions that don’t always hold up technically or economically.
I agree with the first part smallest battery that meets your actual use case usually gives the best ROI. Especially in grid-connected systems, batteries are often the most expensive kWh you’ll ever “buy,” so oversizing them for things like geysers or daytime loads doesn’t make much sense when you can rather push that load into solar hours.
Where I differ is the jump from 10kWh to 20kWh being a “problem.” That’s more a system design and brand limitation than a universal truth. Many modern rack systems (Pylontech, Hubble, Dyness, Freedom Won, etc.) are inherently modular at ~5kWh per unit, so expansion is incremental by design. If someone installs a monolithic 10kWh battery, then yes they’ve locked themselves into larger expansion steps, but that’s a product choice, not a battery principle.
On the second-hand argument:
In theory, 5kWh units might be more liquid but in practice, the second-hand battery market is still very immature, and buyers are far more concerned about:
●Cycle count
●State of Health (SOH)
●Brand reputation and BMS compatibility
A 10kWh unit with good telemetry and warranty traceability will often be easier to move than multiple smaller units of uncertain history.
Also worth noting: more small batteries = more parallel strings, more comms complexity, more potential imbalance issues over time. There’s a real engineering trade-off there, especially in systems that already push multiple parallel packs.
The “phone two friends” comment is funny, but practically speaking, installation logistics shouldn’t drive system design. Most 10kWh-class batteries are still manageable with proper handling, and installers deal with this daily.
Get yourself one of these:

For me the bigger picture is this:
Size the battery for night load and outage requirements only use solar + load shifting for high-energy loads (geysers, pool pumps, etc.)
Keep the system modular where possible, but not at the expense of unnecessary complexity. If anything, I’d argue the real optimisation is:.Spend on panels first, battery second especially if the grid is available.
That’s where the real ROI difference sits.

To answer @MuneebK question 1 x 10.6kWh or 2 x 5.32kwh batteries? Installing 1 battery module makes more sense less wiring less components much simpler.
As for the rest of the discussion my 2 cents. Try not to use high resistive loads(geysers) from your batteries.
Let us compare two very different cost models: PV generation vs stored energy.
Additional solar capacity (R/Wp) is still far cheaper per kWh produced over its lifetime than LiFePO⁴ storage (R/kWh usable).
Using batteries to run a 2–3kW resistive load like a geyser is one of the least efficient uses of stored energy (high discharge rate + unnecessary cycling).
If utility/grid is available, it generally makes no financial sense to size battery capacity for occasional cloudy periods just to support non-essential loads like water heating. That’s an expensive way to avoid a relatively cheap backup source(Eskom) used a few days a year. A better approach is load shifting + thermal storage: Heat the geyser during peak PV hours (10:00–15:00) and set thermostat to ~70 °C to increase stored energy capacity. Use a geyser blanket + pipe insulation to reduce standing losses. Let stored thermal energy carry evening demand (mixed down at the tap).
This effectively turns the geyser into a low-cost energy storage system, avoiding battery cycling and preserving stored electrical energy for essential loads..Also consider load staggering only one geyser active at a time..Prioritise based on SOC or excess PV.
Hierarchy should be:
1.Use PV directly
2.Shift loads to sun hours
3.Store as heat (geyser)
4.Use batteries for essentials
5.Use grid as fallback
Oversizing batteries to run high-power thermal loads at night is usually a capital inefficiency, not a system optimisation.

They say a picture paints a thousand words... here's two power graphs from this morning to illustrate the point I made in my previous post:
Picture 1. After a number of really cloudy & rainy days, finally some sunshine 😊. At 08:05 my panels were producing 2.79kW, and my batteries were charging at 2.3kW. At this point in time, there was sufficient PV power to run my geyser's 2kW element, should I have elected to prioritize the geyser, but with only minimal power going towards charging the batteries. There was still not enough PV to power a 3kW element.

Picture 2. At 09:00 the panels were producing 4.81kW, the batteries were charging at 2.1kW, and the load (including the 2kW geyser that was switched on at that time) was drawing 2.3kW. I prefer to keep the batteries' charge rate low, and have set the inverter to not supply more than 3.1kW to the batteries, and it is thus clear from these figures that the PV supply was maxed out at that point in time. It would still not have been possible to start a 3kW geyser element at this time whilst maintaining a +2kW battery charge at the same time.

I have the Sunsynk 10kW unit with 4 Dyness BX51100 batteries and I used the comms cable that came with inverter. Was plug & play, been working flawlessly for the past 2 years.