Inevitability

Yeah, and I suspect that’s why it’s relatively efficient. From first light the geyser is already getting heated. Every watt goes into the geyser. And no management needed.
Different to using an inverter as if Pv is low and battery is dead then the geyser gets nothing.
The last 2 days had bad weather in JHB. The only thing I had to worry about was my battery charging. I didn’t have to choose between geyser and batteries. This is especially important for me being offgrid without a generator.

Thanks @Denns
Yea that helps a lot so in short the geyser will get heated with whatever PV there is from sunrise until you switch on the AC side and AC will only pull power if still below the thermostat cut off. Same goes for when AC is turned off to sunset, as temps drop below the thermostat setting it will heat up again from PV as long as AC is off.
As I have a smart switch and temp sensor already on my geyser link to HA this opens some interesting avenues to explore with automations to optimize avoiding grid usage.

The controller uses a timer to determine whether to use AC or DC. Any timer of your choice will work. If its input sees AC it bypasses PV and uses AC only. When your timer goes off and its input doesn't see AC, It switches to PV. So during non PV times you can use AC if you manage to finish all the hot water at night. During the day, your timer will be off to let the PV be the only source to heat the geyser. That's basically how it works.

The DC is not converted to AC. Its a high frequency pulse DC from the panels to allow it to work with your standard thermostat.
Your thermostat controls the heating. If the geyser is up to temp and you have the thermostat set at 55 (should be 70 to maximise solar) then when the thermostat opens the controller idles until the thermostat opens again. Same as when your geyser is being supplied by the grid.
Your next question, if you have a 2kW element the controller will feed whatever is available (whether its 200W or 1500W etc) to the element. The element doesnt care or know what its getting. A 2kW element operates at that power when it sees 230VAC. The resistance is fixed at 26.45 ohms. If you lower the voltage then the power it pushes into the geyser is lowered also. You cant go over 250 or so otherwise you burn out the element. That is why I have 1.34kW of panels and my geyser still gets heated. The element is running at half its rating pretty much.

Because of the above that is why I said I will be able to get more out of a 3kW element than a 2kW because a 3kW element has a resistance of 17.6. So if your panels have a voltage of say 150V, your element can operate at a higher current than if it was at a higher resistance. So with a 2kW element like I have now I am only getting about 66% of the power that I would otherwise get from a 3kW at the same voltage. By that reason that is why Geysertech has 2 controllers, I have the cheaper one which is designed to a max of 3kW elements. The bigger brother goes as high as 4kW elements and takes more panels and have temperature monitoring etc.

Hopefully this answers your questions.

@Denns the Geysertech PI2R controller you got, can you just clarify how it works as it mention a timer on the AC side. Am I correct in assuming that the DC is "converted" to AC and then fed to the geyser and the output is a combination of AC and DC input reducing AC side by the available DC input. This makes sense when AC is on but if AC is off how does the system work. Does it feed DC input "converted" to AC to the element irrespective as long as the temp is below the set value. E.G. the AC is off and DC is only producing 1000w and the element is a 2kw unit will it run the element at 1000w or is it only operating when the elements required draw is reached? From my limited knowledge the element in a geyser is standard resistive heating element and will try and pull the required 2kw or is it a case of 1000w in 1000w heat out (kind of like a passive system until AC is turned on and if DC is more than the 2kw or temp is above set value now AC is used)

Unless the inverter is disconnected from the municipality, or you only use a 48V charger, you will have to engage with the municipality... And probably you may have to register off grid inverters also.

Oh I didnt see this.

450 includes the geyser yes. So my House uses about 250kWh which is on the 2 inverters and battery banks. The geyser averages 200kWh a month.

To cover 450kWh isnt hard to be honest. My personal take though is aim for at least a 8kW inverter, About 6kWp of panels (10x600W or 10x590) and 10kWh of battery. If the geyser is on your Elon then you can drop the panels for the house to 4kWp, a 6kW inverter with good passthrough capabilities (A Solis or Lux power) and still keep the 10kWh of battery.
I have seen solar ways sell packages like these for 50k or so . The 8kW systems typically go for 60k or so. Installation is typically around 15 to 25k. A quote a friend of mine sent recently was for 85k. It was a 8kW Deye inverter, 10kWh of batteries but can't remember the panels.

My entire offgrid installation was 85k. This included the 3.6kW inverter, 5kW inverter, 12kWh of GEL batteries, 5kWh of Lithium battery, 8x650W panels, 4x340W panels, the Geysertech. All the extras like cabling, breakers, DB etc is included. Along with replacement of lights etc.

When it comes to solar panels, being in Durban you should get a quote from ARTsolar - they manufacture in Pinetown and when I bought earlier in the year they were the cheapest option by a significant margin, especially because I could collect myself. Paid R8k for 6 x 600W panels.

As Frivan mentioned, grid-tied is your cheapest start. Either look for an inverter that can run without batteries, or another option is to try and find a second hand solis grid-tie only inverter. The big disadvantage with grid-tie only is they don't work if there is no Eskom grid, but loadshedding has been much better lately and is forecast to remain better, so it's worth the risk in my opinion.

I personally prefer having my geysers on my inverters (admittedly I have 10kw available) as it allows a lot of flexibility when weather is less than ideal. On good days, I heat the geysers extra, on bad days I rely on some extra heat from the day before and prioritize other loads. But there is definitely value in the simplicity of having your geyser on it's own system that you set and forget. The biggest thing is when making choices about what to buy now, is to think if these still have value in your future system, or is there enough value in them you can recover costs selling again later.

Her is a plan:
1 Connect 4 solar panels to your geyser
2 Run a 5kW Deye in grid tie mode
3 Install smart switches and controllers
4 Add four more solar panels
5 Buy a Shoto 5kWh battery
6 Add 8 solar panels
7 Add one more 5kW Deye in parallel
8 Add 2 more 5kWh batteries
Repeat steps 6 to 8 until you have taken over the world.

Yeah, I figured that the panel arrangement would be okay and it didn't make sense that it wouldn't work from the technical point of view especially with the 250V they claim in the manual. Now you have it in writing also so if any goes wrong, they will honor their warranty.

I am sure it just dumps the DC of the panels straight to the element as the unit replaces the thermostat if not mistaken. You can't dump DC straight onto the element through the normal thermostat without damaging the thermostat so that's why they are replacing it. Nothing really proprietary about that lol. Its contacts are rated for DC and AC switching and a micro controller that controls the relay and takes the measurements through a sensor. That's all. Guys have done this with DC contactors etc.
Where the Elon differs from my unit is that my unit makes use of the thermostat and element of the geyser. That is you don't replace anything on the geyser itself. They were able to do that by pulsing the DC from the panels at a very high frequency. This way you don't damage the thermostat as there is a zero point for the voltage waveform like AC.

As for your inverter vs controller internal debate. My rationale for using a controller is that I have all the AC capacity of the inverters available to the house and don't have to rob that capacity for a couple of hours a day for the geyser. Its also a zero management system, with your Elon since it reads the temp you can setup a nice automation system that automatically uses the grid to boost the temp up to whatever setpoint you choose. If you are using 11kWh from the grid (I assume you arent using a timer at the moment) then you will drop that to about 2 to 3 max. Thats a saving of 240kWh a month or about 720 rand plus a month.

When you decide to get an inverter and do solar you now dont have to worry about getting a huge inverter. If you pick a 6kW then all the 6kW would be available for your house and you can do the morning heating for 1 hour around 5am when most are still in bed. I would still save up for an 8kW and up just to bulletproof your system and cover the oven, etc on demand.
Goodluck with your Solar/Savings Journey!

I got a answer back from PowerOptimal (Elon Smart OEM). Barry was super helpful. He took my panel specs and ran it through a calculator they have to match the element to the panels. For my idea of 4x Jinko 590w bifacial in series, he came back with a 97% match for a 4kW element and 96% match for 3kW.
Either way it's looking good.
I asked him about how they apply and switch the DC to the geyser element. He said that was proprietary info 🙂
He also confirmed there's no MPPT and no AC-to-DC conversions.
He said they have done extensive testing.
Side note: Elon Smart has already been around for a few years.
So here's where I am:
- My idea for max-ing the PV input is compatible with the Elon and the geyser element
- Out of winter , I will probably end up with excess energy from the 4 panels that I can't use (...problem for another day, and the app will probably tell me exactly how much I am wasting)
- The alternative is to start with an inverter from day 1 , and power the geyser now without batteries, with the idea of expanding the solution and adding batteries and PV and eventually power everything in the house. No wasted energy from panels, and no wasted cost of the Elon. After giving this a (very) little thought, I don't think that a 5kW inverter will be enough for the end-state of my house (with that that we run at the same time), and to buy an 8kW or bigger inverter now is just too expensive for me.

So my mind is made up... no offence to anyone who doesn't agree.

I am gonna start proper price-hunting and will keep updating here as things move forward.
Thank you all for reading / commenting / questioning.
I really cannot thank you all enough.

And just to add, a lot of what I did is unnecessary in 2026.

Don't buy GEL, Lithium is actually cheaper now and lasts much longer.

Don't buy a cheap inverter like I did because brands like Solis and Luxpower are at most 1000 rand more than the Axpert clones and are NRS approved. NRS is required for grid connected inverters.
Solar has gotten so much cheaper now that the gap between "fancy" brand and "cheap" is very low now. So just do it right the first time. I wont buy a Deye or Sunsync in the future whenever I need to replace my inverters as I do think they are overpriced. But I would look at Solis and Luxpower because they go for around 7k. An equivalent inverter from Eco or Must is 5.5k. But you get more features on the Solis and Luxpower.
As for Geyser on inverter. I firmly believe don't add a geyser to any inverter less than 8kW. Also if you are grid connected then its also fine, you just pull from the grid when the clouds roll in. In my case I don't want to pull from batteries every time a cloud rolls over so that is why I used a Geysertech. 99% of the time the water is hot. The option to top up is there but I have never needed to.
Do I waste generation when the thermostat opens? Yes. But my batteries get full around 12 so I already waste generation on the main system as it is. In summer they are full around 10am. I overspecced for cloudy days and have no interest in making use of all the PV.

Thanks for the mention @Yellow Measure. I did go about going off-grid on a budget and DIY installed my whole system. You are definitely right that it was not a one shot thing that I decided to do and it was a gradual progression that kept changing over months to get to where my system is now.
I started off in 2024 December with a 24V 2kW inverter and bought myself 4 GEL batteries and 2 650W panels. The goal was basic load shedding protection. This was the cheapest route I could go without breaking the bank. In 2 months, my goals changed pretty quickly to wanting to cut my bills. I sold the 2kW to a family member at half the price and got myself a MUST 3.6kW 24V inverter which costed R3300. So very cheap. I then expanded my battery bank to 10 GEL batteries (I didnt have the money to outright spend 12k or so at the time for a LFP 5kWh battery). Each battery was 1100 rand so I spent 11k over 4 months on the battery bank. It took me 3 months to get the GEL batteries. I was also buying 1 extra panel at a time of the 650W panels until I got to 7 Panels. With this my GEL batteries were being drained on average only about 30% a day and have protection on them to ensure you cant pull more than 3kW from the bank. GEL batteries are a bit sensitive in that regard.
By then almost the whole house except the Oven, Kitchen and Geyser was on Solar. I then took a leap of faith (after getting a bill of 16k from City Power) to put the whole house on my 3.6kW and GEL battery bank. I made sure to tell none of my colleagues at work as that would have brought me quite a bit of scorn for having all these big loads on a small inverter. I made it work though running one kitchen load at a time but the geyser was a big problem. Even with load scheduling etc the geyser had to run for about 4 hours a day which with a bit of clouds would start draining the GEL batteries. My kitchen has a dishwasher, washing machine, 2 Ovens, microwave, etc. And all that was on a 3.6kW and GEL batteries lol. I also have a pool and 2 fish pond pumps that run during the day.

I investigated how to deal with the Geyser and settled on the Geysertech PI2R controller. This was around August last year. I got it for 3100 rand. Requires no batteries and works off panels. Because my goals had changed to not using any power from City power I bought 4 340W panels. I added so many to ensure the water would be heated to temp 99% of the days which it does get to. Geyser is set to 70 degrees and it was enough for myself and my wife pretty much every day. She would bath in the tub at night and we had enough hot water still for morning showers. It has the advantage that it accepts AC also so my inverter was wired to it but I never used that functionality as the geyser is always hot. In winter the thermostat opens around 3pm. In summer around 1pm. Cloudy days it still has very good performance.

I then decided to get a Victron MPPT as I could not add another panel to the 3.6kW so In total I wound up with 8x650W panels to charge the GEL batteries and supply the house loads. I tested my system since August last year till around January and I never needed the grid. The only issue I had was overloading of the inverter in December last year as my wife and I where used to only running one high draw appliance in the kitchen but we had about 6 people in the house and they were not too familiar with house the inverter worked etc but after a week or so they adjusted. The hot water was fine during that period and we had no issues with batteries being overly drained or anything.
In February this year I got disconnected by City power after I applied to go off-grid. Around March I got a recommendation from the guys over at MBB that builders was selling all in one inverter and battery systems so I managed to scoop up a brand new 5kW Omnivolt inverter with a 5kWh battery for 9500 rand. I since reconfigured the house now to make the 5kW the main inverter and it has solar. My 3.6kW still has its GEL batteries and gets charged from the 5kW inverter between 9am and 3pm. My DB is split so the 5kW supplies the kitchen and lounge. The 3.6kW supplies all the 3 bedroom plugs (3 bed house) and lights.
I do not have a generator installed as the house is very efficient (lots of work to replace lights etc). My consumption is about 450kWh a month with a system that can supply double that so that is the main reason. So yes, with patience, and a budget you can reduce your bill. I averaged by the way about 750kWh to 1000kWh a month before I did all of this. We changed a lot of our habits to get the house to be what it is now. The cheapest installation is the one that supplies the least load. If you continue to use a lot of power then you cant do this for cheap.
My solar panels were from a chinese shop called SunMagic. Fivestar panels. They are built very well so no issues there. My batteries are Navasolar. Got them from Takealot for cheap. They are almost 2 years old but have their original capacity so far as I looked after them and have balancers etc. Now with the 5kW and 5kWh battery they are barely working and only being drained about 10% a day. I foresee them lasting about 6 years easily. So @Yellow Measure is right, Get your objectives clear from the start and be prepared to do what you need to do to get your targets met.

One last thing, solar had caused a lot of arguments in my marriage. My wife was quite resistant to a lot of what I was doing. She eventually so the light when I showed her that I dont have to pay the 1500 a month in fixed charges anymore (COJ Postpaid). And we have power 24/7. My system is going to be fully paid off next year in June. Average saving of 35000 rand a year. I went off grid with a 3.6kW inverter and GEL batteries. Where there is a will there is a way.

After reading your posts, and understanding your approach (and limited budget), I think that it's worthwhile to think about the ultimate end-state as well as "systems thinking" in your visioning.
First-off: Good on you for focusing on the biggest culprit, and the area where the most possible gains can be realised.
Secondly, be mindful that you don't lose your peripheral vision in the process. People with limited budgets can rarely, if ever, create their dream system in one big bang. Each component is one building block of the bigger system, like a grain of sand in the mortar, the mortar holding one brick to another, a brick in a wall of bricks, a wall in a room, a room in a house, and a house in a home. Each component should be reusable. Even wealthier people make this mistake, and those that aren't as wealthy are prone to do so because of "sticker shock", or they limit their big-picture thinking because they are either 1) unable to prioritise their spending, or are 2) unable to see how the gradual spending / investment of smaller amounts eventually adds up to total independence from the Socialist Eskom / municipality. 6 years ago this wasn't my own goal, but in January the greedy socialist municipality forced me to choose it, at very little cost to myself because the foundation was solid.
Today you are solving one problem, but tomorrow will bring another, and so your solution needs to be extensible and not just a "point" or standalone solution. A parallel can be drawn to those that purchase Mecer trolleys to "keep the TV on" during loadshedding. It was a great solution at the time, for short periods of outage, but the downsides were that it was clunky, required a place to stay and trip-me-over extension leads, emitted explosive hydrogen gases, produced motor-killing square waves and was subject to the shallow cycles and maintenance requirements of lead-acid batteries. Woe betide anyone who had a surge-protector after the inverter, or who had plugged them into wall sockets when the power returned. When load-shedding intensified, some people simply bought more of them, so we found households with two or three of them. Those who were smart enough to realise that Eskom's inability to keep the lights on, as well as their constant billion rand bail-outs and price increases was endemic to Socialist agenda, went for solutions earlier on that were more extensible and could be upgraded without risk of the big BOOM!
Granted that point solutions have their place: a 10,000mAh power bank is useful and portable, and can be repurposed in hundreds of different ways, but it isn't a power or money saver.
Many who have had solar-powered geysers before installing a full-blown integrated solar system argue that in hindsight, precious North-facing roof space used by the solar geyser heating system would be better served if they could replace it with traditional solar panels, purely because the electricity generated could be redeployed to either charge batteries or service other loads
Someone who seems to have achieved his clear objectives (off-grid!) in record time, and very limited budget is @Denns in his post https://powerforum.co.za/topic/34183-exciting-long-term-review-new-hubble-energy-am16-am5-in-a-real-micro-grid-setup/#findComment-230500
You can bet that he didn't arrive at it all in one month though, so I leave it to him to expand on his journey and budget, which I am sure that you will find to be inspirational.

...if the temperature of the water in the geyser is insufficient. Otherwise it will do nothing.
...if the temperature of the water in the geyser is insufficient after a whole day of using the DC power from solar.

Any "smart" system is fallible, you always need an override.

So its just a timer built into the unit then. My unit has the timer external to it. All the scheduling and automation etc is done in Tuya which is free. Its pretty sweet, my Jojo tank and almost everything is connected to a smart switch. I can remotely turn and switch off everything basically in the house. My AC breaker into the unit is off though as I haven't needed to use AC for the geyser. The panels are sufficient.

On my unit default is Grid. So you use a timer to tell it when to use the grid or not. If no grid it just pushes all the PV available into the geyser until the thermostat opens at which point it just idles.
There is no fancy logic that decides whether to use grid or not. I am curious to know how the Elon does the decision making. Mine is stupid simple.

And that's how savings are achieved, whilst balancing lifestyle options. It uses the solar panels' DC in a super-efficient way to heat the water, but ensures that, regardless of solar conditions, you and you family will always have a warm shower (even if you have to pay extra for it).
It's still just a better mousetrap though, and will suffice if you have zero aspirations of becoming completely independent from the municipality for electricity.

The nice thing I saw about the Elon is you can see the water temp in the geyser. I can see him only needing 1 hour of heating in the morning the majority of days. If he determines that the geyser is getting up to temp fairly quickly off solar by around 1 or 2pm then I would push to add a second 150 litre geyser and use a contactor that is driven by the thermostat of the first one to start heating the second geyser. The second geyser being the input to the main geyser.

The hot water would definitely be enough then for morning showers without grid usage as the main geyser will get warm to hot water from the second geyser, reducing the temperature drop inside of it. That is my plan for when my hot water needs go up. Replace the element with a 3kW and add a second 150 litre geyser. From experience I know with 2 to 3 people the geyser is fully heated by around 1pm in summer and 2:30/3 in winter so I should be able to dump the excess solar into the second geyser.

My budget determines the limits of my aspirations here, and I'm not sad about that... I am a big fan of doing small steps to get to the eventual goal.


I am definitely keeping this idea on the list. Looks like a very neat way to use up all the energy coming out of the panels and will definitely help with lowering the amount of mains power that gets pulled.

Ah yes. I missed that part 🤦🏽‍♂️
Few years back I had a solar tube system... And on the DB board I had a basic timer... Allowing mains power for 1 hour around 5pm and again at 3am. And exactly as you say, it's just allowing mains to be used ... If the water is already hot, no mains power is used.

Ok... Brainfart moment... maybe I'm missing something obvious, but could I find a correct-spec MPPT and a "smart something" to handle the app monitoring and timing stuff, and that ends up being a better solution than the Elon?

Ok I realised what I'm missing... The thermostat needs to feedback somehow or the MPPT will keep feeding power into the geyser
Scratch all of that... Thermostat and DC switching are both obvious things I didn't even consider

Elon has a simple app toggle setting... Solar only / Mains only / Morning showers / evening showers / Morning and evening showers
Morning showers will use mains from 3am to 5am
Evening showers uses mains from 5pm to 7pm
There's also a manual tap on the app to use mains on demand

AI AI. Other than magic, if the Elon uses straight DC from the panels, the follow formula should apply:
Pdc = Pgeyser x ( Vstring / 230 )²

FYI: I am not the OP.
And according to the product write-up (which is publicly available BTW) it's a little more complex than that, apparently it analyses usage patterns, time of day and other factors.