Hello World!

Can someone please check my understanding and my solution:
The Elon Smart will allow me to skip any inverter and battery cost and put PV straight into my existing Kwikot geyser. I was saving money for a Geyserwise MWS (which works on the same idea, but a more "proper" solution), but the price went up by 50% in 1 year so now it's waaaaaaay over my budget.
Anyway ... Elon Smart allows max input DC Voltage of 230V and max current of 15A.
Being in Durbs, winter sunshine is not good, so I want to maximise the panels to get nearest to the Elon's max.
So I tried to find panels that get me near to the limit of the Elon, but in all my searching, I see that panels up to 590W have Isc under 15A but then panels above this Watts all have Isc past 15A.
So I settled on choosing 4x Jinko Tiger Neo Bifacial 590W. Voc is around 52V and Isc is 14.49A.
I have a white roof so the bifacial will do something, but I'm not expecting much... 5 to 10% extra will still be super useful on cloudy days and in winter.
This past week, my geyser used around 11 kWh per day for water heating (I plugged the geyser into a Killawatt ... Yes, yes, I'm dodgy like that).
Family splits between early morning or evening showers.
No money for a proper solar+inverter+battery solution.
I didn't post specific prices or link to listings, just in case that breaks any rules , but panels + Elon add up to around R11k.
Still need to account for mounting hardware, cabling stuff, and labour.
What I am here to ask and learn is : Does all of this look about right? Have I missed something obvious?

Edited August 7Aug 7 by Inevitability

On 2026/08/07 at 8:48 PM, Inevitability said:

Isc under 15A

I am not sure how the Elon converts DC to AC but I would guess it makes a modified sine wave. If this is the case, Isc is not as important as Imp and the most important is maximising Vmp. Your geyser element size will probably determine the current draw.

On 2026/08/07 at 8:48 PM, Inevitability said:

Killawatt ... Yes, yes, I'm dodgy like that

Well done.

On 2026/08/07 at 10:48 PM, Inevitability said:

Hello World!

Can someone please check my understanding and my solution:
The Elon Smart will allow me to skip any inverter and battery cost and put PV straight into my existing Kwikot geyser. I was saving money for a Geyserwise MWS (which works on the same idea, but a more "proper" solution), but the price went up by 50% in 1 year so now it's waaaaaaay over my budget.
Anyway ... Elon Smart allows max input DC Voltage of 230V and max current of 15A.
Being in Durbs, winter sunshine is not good, so I want to maximise the panels to get nearest to the Elon's max.
So I tried to find panels that get me near to the limit of the Elon, but in all my searching, I see that panels up to 590W have Isc under 15A but then panels above this Watts all have Isc past 15A.
So I settled on choosing 4x Jinko Tiger Neo Bifacial 590W. Voc is around 52V and Isc is 14.49A.
I have a white roof so the bifacial will do something, but I'm not expecting much... 5 to 10% extra will still be super useful on cloudy days and in winter.
This past week, my geyser used around 11 kWh per day for water heating (I plugged the geyser into a Killawatt ... Yes, yes, I'm dodgy like that).
Family splits between early morning or evening showers.
No money for a proper solar+inverter+battery solution.
I didn't post specific prices or link to listings, just in case that breaks any rules , but panels + Elon add up to around R11k.
Still need to account for mounting hardware, cabling stuff, and labour.
What I am here to ask and learn is : Does all of this look about right? Have I missed something obvious?

As @frivan said, ISC is not the parameter to look at but the Imp. Very few panels have an Imp over 15A. Highest I have seen is about 17.7A.

Only concern I see is the VOC of the panels would get up to 210V which is fine but cutting it a bit too close. I would aim for total VOC from the 4 panels below 205V. Ideally 200V. Give it head room for cooler weather and cloud flares.

To maximise heating set the geyser to 70 degrees. Use a thermo mixing valve if worried about people burning themselves in the shower but I have never had that issue, even with a 10-year-old that stayed with us for a month.

I didn't use panels as big you but you would be better off with bigger panels definitely. I used 4x340W and they have been excellent for our geyser at the house. Its worked so well that I can easily add a second 150 litre geyser and use the thermostat of the main geyser to allow the controller to start heating the second geyser (which will feed the main geyser) when the first geyser is up to temp. Considering my first geyser hits 70 around 1pm, I am sure the second geyser should be able to hit around 50 degrees by sun set. I will have much more hot water available and use up all the solar from those 4 panels. But that's a project for when the hot water requirements go up.

I don't know how the Elon works but to answer @frivan question regarding the output, my Geyser tech unit is a pulsed DC wave (contrary to what the manufacturer rep told me). It is not a modified sine wave. I know this because when I measure the output from the Controller on AC the meter reads 0 volts. Implying that the voltage waveform isn't crossing zero and stays positive. When I switch the meter to DC i measure about 135V whereas the DC from my panels is about 155V. This corresponds to a pulsed DC wave and not an AC wave. It's just high-speed switching of the solar panel.

Edited August 9Aug 9 by Denns

On 2026/08/07 at 8:48 PM, Inevitability said:

Hello World!

Can someone please check my understanding and my solution:
The Elon Smart will allow me to skip any inverter and battery cost and put PV straight into my existing Kwikot geyser. I was saving money for a Geyserwise MWS (which works on the same idea, but a more "proper" solution), but the price went up by 50% in 1 year so now it's waaaaaaay over my budget.
Anyway ... Elon Smart allows max input DC Voltage of 230V and max current of 15A.
Being in Durbs, winter sunshine is not good, so I want to maximise the panels to get nearest to the Elon's max.
So I tried to find panels that get me near to the limit of the Elon, but in all my searching, I see that panels up to 590W have Isc under 15A but then panels above this Watts all have Isc past 15A.
So I settled on choosing 4x Jinko Tiger Neo Bifacial 590W. Voc is around 52V and Isc is 14.49A.
I have a white roof so the bifacial will do something, but I'm not expecting much... 5 to 10% extra will still be super useful on cloudy days and in winter.
This past week, my geyser used around 11 kWh per day for water heating (I plugged the geyser into a Killawatt ... Yes, yes, I'm dodgy like that).
Family splits between early morning or evening showers.
No money for a proper solar+inverter+battery solution.
I didn't post specific prices or link to listings, just in case that breaks any rules , but panels + Elon add up to around R11k.
Still need to account for mounting hardware, cabling stuff, and labour.
What I am here to ask and learn is : Does all of this look about right? Have I missed something obvious?

Two main concerns. First is is to understand the total energy requirements better regarding generation and storage ie. when does the Kilawatt show your current heating of 11kWh is taking place, day and/or night, and will the system be able to generate and store enough total energy you need, in whatever size geyser size you have on hand, to cover evening and morning hot water needs. Worst case if you've got say a 150l geyser and it gets heated up effectively for 1.5-2 hrs during the day, then emptied in the evening, and re-filled cold, and heated for another 1.5-2 hrs during the evening, you should check whether daytime-only heating is going to produce the real-world savings you're looking for.

Second concern, is why you are looking to use an unapproved panel configuration. Just reading through the Elon manual, it's quite extensive in its listing of recommended/prohibited/sub-optimal panel arrangements, and says that any alternative setups should be checked with them. My concern is, even if it works technically, that they may not support warranty claims on panels that they didn't agree to. Also, just looking through the manual regarding energy requirements for various cities, it seems you'd be better off in Durban to go with around 3kW of panels, probably in a parallel configuration as per the manual. Side-comment: Having 3kW of the same panels once-off is also "safer" to upgrade with, ie. to transfer to one MPPT of a 5-6kW inverter later, without having to mix and match panels.

I understand that financing is a constraint, and I love the idea of not paying a premium, but I also hate waste and risk.

29 minutes ago, GreenFields said:

Two main concerns. First is is to understand the total energy requirements better regarding generation and storage ie. when does the Kilawatt show your current heating of 11kWh is taking place, day and/or night, and will the system be able to generate and store enough total energy you need, in whatever size geyser size you have on hand, to cover evening and morning hot water needs. Worst case if you've got say a 150l geyser and it gets heated up effectively for 1.5-2 hrs during the day, then emptied in the evening, and re-filled cold, and heated for another 1.5-2 hrs during the evening, you should check whether daytime-only heating is going to produce the real-world savings you're looking for.

Second concern, is why you are looking to use an unapproved panel configuration. Just reading through the Elon manual, it's quite extensive in its listing of recommended/prohibited/sub-optimal panel arrangements, and says that any alternative setups should be checked with them. My concern is, even if it works technically, that they may not support warranty claims on panels that they didn't agree to. Also, just looking through the manual regarding energy requirements for various cities, it seems you'd be better off in Durban to go with around 3kW of panels, probably in a parallel configuration as per the manual. Side-comment: Having 3kW of the same panels once-off is also "safer" to upgrade with, ie. to transfer to one MPPT of a 5-6kW inverter later, without having to mix and match panels.

I understand that financing is a constraint, and I love the idea of not paying a premium, but I also hate waste and risk.

These are good comments @GreenFields but it’s concerning that they will void the warranty because of the type of panels and arrangement you use. As far as I’m concerned as long as you stay within that 250 volt limit with good margin it should be fine and any attempts to void warranty would be another case of the Pylontec battery issue many have here on this forum.

As for the 11kWh issue that is also valid but there isn’t much he can do about that. 4 panels like the ones he specced should be able to cover at least 8kWh a day without issues.

I averaged 7kWh a day on the geyser when grid connected. With 1.34kWp of panels (4x340) my geyser is heated up it half the day still remaining with the same shower usage. Their panel sizing is pretty large I must say. I don’t know if the Elon and Geysertech work similarly unfortunately but I can vouch that the Geysertech has been able to cover all our hot water requirements with zero bathing and showering changes like when we used about 7kWh from the grid.

In my opinion if the Elon needs 3 to 4kWp of panels to heat the geyser as per manual and number of people then it’s not worth it. You mind as well get an inverter solution as the roof space would be used up just for the geyser.

And to add my 4 panel on the Geysertech are not North facing. They face south with a 10 to 15 degree tilt so suboptimal mounting and yet I still get a geyser heated up by 1pm.

His array should generate double mine especially if mounted true north and the right angle. I would contact Elon if I was him. I contacted the guys at Geysertech and they told me 2 high voltage panels would work fine or 3 normal panels.

The main thing they told me is that the most important thing isn’t the current but the voltage of the array. You get more power into the geyser the higher your voltage is. An element is a resistor basically so to get more current through the element you need higher voltage. Also a larger element has lower resistance and therefore will push more current though it.

I have the option of replacing my element with a 3kW as it currently is 2kW. So I can get an extra 20 to 30% more power into my geyser from the same array. I haven’t done it as there has been no need.

Edited August 9Aug 9 by Denns

5 hours ago, frivan said:

I am not sure how the Elon converts DC to AC

It doesn't, it uses a "smart" thermostat to choose whether or not to drive the existing element via DC, or to use AC from the grid.

Edited August 9Aug 9 by Yellow Measure

2 hours ago, Yellow Measure said:

choose whether or not to drive the existing element via DC

Well, then you could use a couple of diodes instead of the Elon.

2 hours ago, frivan said:

Well, then you could use a couple of diodes instead of the Elon.

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.

11 hours ago, Yellow Measure said:

analyses usage patterns

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

Wow ... thank you so much for the responses.
I have no idea (and the Elon manual doesn't say) how it takes DC from the panels and applies it to the geyser element. To be super honest, I didn't think I needed to understand it, since it's being sold like an OEM product. But now that you asked about it, you made me curious to know so I will ask them when I contact them.
Chat GPT also doesn't have any definitive answer, just guessing that it's something to do with duty-cycle manipulation.

The killawatt is in the ceiling and it's a pain to access, so I only read it twice ... 56kWh after 5-ish days and 91kWh after about 8 days ... There's no easy way of knowing what time the geyser is switching on/off. The kids prefer to shower in the evenings so they can sleep til the last moment in the morning, and the adults prefer to shower in the morning , so there's no room to change patterns there. Thing is , it's winter now and Durbs winters are short, so I don't expect this much electricity into the geyser after September. But I am not trying to make this completely off-grid. Very comfortable to use mains power to top up, but save enough to make it mostly use the solar ... 80/20 rule of thumb.

I must admit , this equation : Pdc = Pgeyser x ( Vstring / 230 )² needs more brainpower that I have at this moment 🤣 Cos I have no idea how PV panel voltage varies through a typical day... I will do some Googling and give it some thought to understand... Or just ask ChatGPT later.
The important point I do want to learn/understand more about is how much I lose with no MPPT.

On the point of the "unapproved panel configuration"... Before I started looking for panels, I did read the Elon Smart manual and what caught my attention was the maximum current and voltage inputs. I definitely read the section with the recommended configurations cos it was super useful. Then I started looking for panels, and didn't notice anything in my solution idea that would count as unapproved. The 4x 590W Jinko stays under 230Vdc and 15A, so I would be sticking withing the Elon Smart spec. But now since you mentioned it, I re-read that part of the manual and I see they specifically mention to contact them regarding bifacial panels. So I will definitely try to do that and see what they say. On this screenshot it shows Voc needs to be under 250V but other parts of the same manual say 230V , so this might be a typo.
https://poweroptimal.com/manuals/

Thank you guys so much for the feedback and questions ... I am learning so much more as I think about these questions and try to answer them for myself.

3 hours ago, frivan said:

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

How does that help the Elon decide on whether to use DC or AC to power the geyser?

1 hour ago, Yellow Measure said:

How does that help the Elon decide on whether to use DC or AC to power the geyser?

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.

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

Edited August 10Aug 10 by Inevitability

12 minutes ago, Inevitability said:

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

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.

Edited August 10Aug 10 by Denns

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?

Edited August 10Aug 10 by Inevitability

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

Edited August 10Aug 10 by Inevitability

6 hours ago, Inevitability said:

Morning showers will use mains from 3am to 5am

...if the temperature of the water in the geyser is insufficient. Otherwise it will do nothing.

6 hours ago, Inevitability said:

Evening showers uses mains from 5pm to 7pm

...if the temperature of the water in the geyser is insufficient after a whole day of using the DC power from solar.

6 hours ago, Inevitability said:

There's also a manual tap to use mains on demand

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

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.

26 minutes ago, Inevitability said:

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.

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.

7 hours ago, Yellow Measure said:

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.

9 hours ago, Yellow Measure said:

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.

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.

1 hour ago, Denns said:

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.

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.

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.

38 minutes ago, Inevitability said:

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.

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!

@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)

35 minutes ago, -cK- said:

@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)

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.

Edited August 12Aug 12 by Denns