Hi All

I am a but distrusting of the PTC element tech that seems to be only offered by Geyserwise in South Africa (haven't really been able to find other sources).

Geyserwise have a decent solar controller product (ugly as all sin), but I find it really clunky and needs much more quality development - So I am very skeptical when they are the only ones that have come up with this PTC technology with some quite impressive claims. It seems fairly pricey compared to a standard resistive element, so I would like to hear others thought and possibly experiences.

Regards

KLEVA

PTC stands for positive temperature coefficient. The element itself is usually a ceramic material instead of the usual nichrome wire used for resistive heating. The ceramic material's resistance increases as the temperature rises, thus lowering the power used. The downside of that is that it heats less as it gets warmer and at some point the losses and the power used will equalize and the temperature will stop increasing - the elements on the market don't advertise this set-point, and it is sometimes too low to be considered safe. The upside of that is that you don't need a thermostat, which is a common failure point for geysers.

The claims with regards to energy efficiency is nonsense, as both PTC elements and normal nichrome elements are resistive heating devices and both have the same ~100% efficiency numbers.

One possible advantage in PV solar installations is that instead of switching a 2-4kW element on and off, the power draw lowers until it matches the geyser losses when it comes up to temperature, which could help with managing your loads.

4 hours ago, KLEVA said:

Hi All

I am a but distrusting of the PTC element tech that seems to be only offered by Geyserwise in South Africa (haven't really been able to find other sources).

Geyserwise have a decent solar controller product (ugly as all sin), but I find it really clunky and needs much more quality development - So I am very skeptical when they are the only ones that have come up with this PTC technology with some quite impressive claims. It seems fairly pricey compared to a standard resistive element, so I would like to hear others thought and possibly experiences.

Regards

KLEVA

If you Google PTC heater you will find some heaters using it. A number of years ago I bought such a heater. We actually like the heater as it does not produce the intense heat an element heater would. This is a safety feature. No or few things will catch fire. The Goldair heater is a common brand in the shops.

It is not strange to see the PTC units only producing and using 50% of their rated power once they heat up. With this in mind they can never produce double the heat compared to an element using the same power.

Edited August 8, 20223 yr by Scorp007

Just now, Scorp007 said:

If you Google PTC heater you will find some heaters using it. A number of years ago I bought such a heater. We actually like the heater as it does not produce the intense heat an element heater would. This is a safety feature. No or few things will catch fire. The Goldair heater is a common brand in the shops.

Some info on Wikipedia.

In the 1980s, some manufacturers were making advertising claims that critics such as New York Times writer Matthew L. Wald found dubious. In particular, manufacturers claimed ceramic heaters produced more heat than conventional ones, even when both were rated with the same heat output.^[6]

Consumers Union has not found significant differences between ceramic and conventional heaters. However, in its 1989 review, the testing organization did treat ceramic heaters as a separate category, as a response to manufacturer claims. The only significant difference it found was ceramic heaters were substantially more expensive. As a category, the conventional heaters it tested that year slightly outperformed ceramic heaters in the areas of evenly heating all parts of a room and at holding the room at a steady temperature. Consumers Union did find ceramic heaters' characteristic of sharply reducing heat output when airflow was blocked to be a useful safety feature. However, it found that the tip-over switches and overheat-protection sensors included in many conventional heaters also provided good safety.^[4]

 

 

A friend of mine had the element on his geyser fail. The plumber convinced him that a PTC element will last longer. A year later the geyser started leaking and had to be replaced. If I didn't remind him, the PTC would have been gone with the old geyser. I like the Geyserwise control but would stick to common and cheap geyser parts.

Thank you all for the comments.
I now have a decent idea of what a PTC element is vs a resistive element in a geyser

Hi @KLEVA

I use the PTC element because it can use both AC and DC power.

The DC powered by 2x solar panels ensures that in the day I do not have to top-up because of heat losses. My AC power applied to the geyser is purely to supply for consumption. Furthermore, the element seems much more durable.

Thank you all - I think I now understand the pros vs cons - In my personal installation it doesn't seem to make a difference - but hopefully it will help others. Also you gave me an idea into new tech out there that I wasn't aware of, thank you.

2

1 hour ago, Pieter Lourens said:

Hi @KLEVA

I use the PTC element because it can use both AC and DC power.

The DC powered by 2x solar panels ensures that in the day I do not have to top-up because of heat losses. My AC power applied to the geyser is purely to supply for consumption. Furthermore, the element seems much more durable.

Your application is surely working for yyou Great to have the option of using the AC or DC element.  I always thought that 2-3 panels should be good to top up during the day and keep the temp at a certain level. One has the whole day to do it provided not a lot of hot water is used during the day. The problem of using a AC thermostat is then solved via the geyser wise controller?

We read a lot about normal elements burning out. I have only replaced 1 element in over 45 years so it seems my water has always been of low lime content. Yes I have my share of steel geyser tanks rusting and normally they last about 6 years. Keeping me busy between the 2 I have in use. The one burnt out only tripped on the DB once and burnt open circuit. I was quite shocked when going to investigate to find the whole isolator also burnt quite badly which could have been a fire hazard. I was sure the connections were good but the result did not look good.

2 hours ago, Scorp007 said:

Your application is surely working for yyou Great to have the option of using the AC or DC element.  I always thought that 2-3 panels should be good to top up during the day and keep the temp at a certain level. One has the whole day to do it provided not a lot of hot water is used during the day. The problem of using a AC thermostat is then solved via the geyser wise controller?

Hi @Scorp007

Yes, it works very well for me. However, I implemented a solution differently than the default GeyserWise package.

Firstly, my expense was less than 10G per geyser. With home automation I can top-up the geysers from the inverter if the geysers are not sufficiently warm at a given time. With home automation I can also spread my load so that the two geysers does not consume electricity concurrently.

Secondly, having the two geysers on their own systems allows them not to be impacted by load shedding. The AC top-up capability is on my inverter's non-essential load.

I need to officially measure my DC values. However with 2x panels on a geyser I get more than a 5 degrees Celcius increased heat in an hour. The DC power does more than just maintaining the temperature.

Why is it not possible to simply connect 50v solar panels directly to the geyser if you install a 50v 1 Kw element into the geyser. You can leave the thermostat as the means to avoid overheating. If you have a 300l geyser once the water is hot you easily have sufficient hot water for all purposes overnight and the geyser will re heat the water from sunrise to sunset?

On 2023/05/09 at 4:00 PM, Chris Symons said:

Why is it not possible to simply connect 50v solar panels directly to the geyser if you install a 50v 1 Kw element into the geyser. You can leave the thermostat as the means to avoid overheating. If you have a 300l geyser once the water is hot you easily have sufficient hot water for all purposes overnight and the geyser will re heat the water from sunrise to sunset?

I am doing just that right now. 620Watt 48Voc panel directly connected to the Geyserwise 900Watt element. Victron SmartShunt inline to monitor. (no MPPT, no PWM)

Edited November 10, 2025Nov 10 by AndreFvdM

41 minutes ago, AndreFvdM said:

I am doing just that right now. 620Watt 48Voc panel directly connected to the Geyserwise 900Watt element. Victron SmartShunt inline to monitor. (no MPPT, no PWM)

This can work during sunshine but what about rainy day like today in Gauteng. Normally 500W will take a whole day after a morning bath. If a PTC element perhaps you can get it to work if no hot water is needed during the day. 150L geyser at 25 deg would need 6kW of power to get to 60 deg.

46 minutes ago, AndreFvdM said:

I am doing just that right now. 620Watt 48Voc panel directly connected to the Geyserwise 900Watt element. Victron SmartShunt inline to monitor. (no MPPT, no PWM)

5 minutes ago, Scorp007 said:

This can work during sunshine but what about rainy day like today in Gauteng. Normally 500W will take a whole day after a morning bath. If a PTC element perhaps you can get it to work if no hot water is needed during the day. 150L geyser at 25 deg would need 6kW of power to get to 60 deg.

true, energy in -> energy out. If you don't have solar power then you won't have hot water. Sure you can overpanel in series use a MPPT to buck it down. On cloudy days my HomeAssistant would start the heatpump as soon as batteries SOC reach 100%. The heatpump draws 1100Wat and hear the 2x150l geysers (in series) is just over an hour. But the heatpump is my backup. The PTC is pushing 550Watt into the geyser as we speak. Sure it will take 12hours to heat 150l from 20 to 70. But I can connect another panel, or even insert another PTC into the other geyser. Point is that the energy is for free, and it works without a R4000 MPPT controller.

58 minutes ago, tony Lampard said:

"I use the PTC element because it can use both AC and DC power." I think someone may be taking you for a ride.

What do you mean...? a PTC element can and does use both AC and DC separate or at the same time. They are sold this way - https://www.plumblink.co.za/product/geyserwise-element-ac-or-dc-2.0kw-230v-or-1100w-72v-dc-1.1-or-4-boss-ptc

1 hour ago, AndreFvdM said:

true, energy in -> energy out. If you don't have solar power then you won't have hot water. Sure you can overpanel in series use a MPPT to buck it down. On cloudy days my HomeAssistant would start the heatpump as soon as batteries SOC reach 100%. The heatpump draws 1100Wat and hear the 2x150l geysers (in series) is just over an hour. But the heatpump is my backup. The PTC is pushing 550Watt into the geyser as we speak. Sure it will take 12hours to heat 150l from 20 to 70. But I can connect another panel, or even insert another PTC into the other geyser. Point is that the energy is for free, and it works without a R4000 MPPT controller.

As one gets to hear how you manage the system makes a big difference. My post was really as an indication if there is not heat pump or grid connection then the single panel would not work great.

It's always different strokes for different folks. For the novice guy the R4000 controller should work fine and no automation involved. Instead of a dedicated controller one could also use a grid tied string inverter when there is stable grid that can use grid when the PV is low and for this the geyser works on AC being fed as per the way it was designed. I started my Grid tied this way by using only 2 small panels to run my 2 fridges during the day. Only later did I expand it to run more daily loads. This save me a lot over time without having to use batteries. The best ROI for inverters and then the heat pump for 14 yrs added greatly to my cost saving. My heat pump was subsidised at the time.

There are endless solutions these days to manage household water heating.

1 hour ago, tony Lampard said:

"I use the PTC element because it can use both AC and DC power." I think someone may be taking you for a ride. An electric heater is a resistive device; that is, it provides opposition to current flow when a voltage is applied to dissipate power in the form of heat, so it doesn't matter if its an AC element made from nichrome wire or ceramic - it will work when connected to DC.   .

Agreed. You dont need a fancy PTC element to supply it with DC. A resistor is a resistor.

52 minutes ago, Demo said:

What do you mean...? a PTC element can and does use both AC and DC separate or at the same time. They are sold this way - https://www.plumblink.co.za/product/geyserwise-element-ac-or-dc-2.0kw-230v-or-1100w-72v-dc-1.1-or-4-boss-ptc

A normal element will accept either AC or DC. Being supplied with both simultaneously though, that a normal element cant do.

47 minutes ago, Scorp007 said:

There are endless solutions these days to manage household water heating.

True. My Geysertech has been working perfectly fine. The current cloudy weather in JHB hasnt affected it too much. My timer is set to feed the Geyser with AC from the inverter for 30 minutes a day with a 2kW element. Otherwise the geyser is always hot and the Mppt controller is doing the rest just fine.

Edited November 10, 2025Nov 10 by Denns

2 hours ago, tony Lampard said:

Personally I prefer to have either 2 elements (1 on dc, the other ac from grid) or an inline supplementary instant gas geyser that is automatically set to boost if the water isn't hot enough. I think the latter is more attractive because it keeps it simple and that also takes care of high hot water demand.

I don't know if I am reading wrong but the "geyserwise" smacks a bit of magic of marketing, overcomplicating something that is essentially simple to make a quick buck?

Geyserwise is a bit too complicated for my liking personally. AC and DC elements need wiring for both; they need a special element. Too many things are required. Geysertech is just a controller. Feeds pulsed DC to the element. And if you feel your water isn't hot enough, just use ac connected to the geysertech and it supply AC to the element. Works with a basic 300 rand element from any manufacturer. PTC imo is a marketing gimmick.

Maybe useful for hard water areas but I see no other benefit but even then, you can buy 5 normal elements for the price of one PTC. So whats the benefit really if the PTC lasts 2x longer?

Edited November 10, 2025Nov 10 by Denns

1 hour ago, tony Lampard said:

The resistance element doesn't care if it's getting 200W or 2000W - it just converts whatever's available free to heat.

Thats the principle of my geyser controller. It feeds the element a constant 600W give or take throughout the day. Would have been higher if I had a 3kW element since it has lower resistance but my 2kW is friendly with the inverter so its a compromise I was willing to make.

2 hours ago, tony Lampard said:

@Denns "Thats the principle of my geyser controller feeds the element a constant 600W - higher if I had a 3kW element since it has lower resistance but my 2kW is friendly with the inverter so its a compromise." My approach - even more friendly with the inverter reducing both capacity and draw; while it takes all your "overload" worries away as a soft load. When the geyser element is connected directly to a set of solar panels (connected to DC) the actual wattage of the element will vary according to the voltage supplied (no overload with low solar - just sorts itself out); you can keep the control circuit AC (those thermostat switch contacts tend to be flimsy and could arc closed with DC) so the DC switching is a big clunk (double break both + and - through your switch to reduce the risk of arcing); the control circuit load on your inverter is insignificant. The reduced wattage is a sort of "square of" so low voltage performance isn't great (equation in a previous post). It doesn't matter when you heat the water if the insulation is good so you don't have to dedicate panels to the geyser and can only bring in the DC circuit to heat the water when all your other needs are met "peak clipping" - if you generate solar and don't use it, its wasted. This takes your DSM front of pipe - feed the inverter for more pressing loads - feed the geyser when all other needs are met - feed the inverter when the geyser set temperature is reached; this can be done automatically with a time switch on your AC control circuit switching between contacts NC (de-energized the PV goes to the inverter) and NO (energized the PV leaves the inverter and goes to the geyser). Sorry its a scribbly sketch, hopefully you catch the drift The double break only on the + was a compromise in the sketch because that relay was a piggy back and only had 3 NC contacts.

Just a comment on the voltage changing the power fed with low PV. The voltage is relatively steady. It is the current that the panel provides that changes the wattage to the element with low irradiation. That's how I have found.

3 hours ago, tony Lampard said:

@Denns "Thats the principle of my geyser controller feeds the element a constant 600W - higher if I had a 3kW element since it has lower resistance but my 2kW is friendly with the inverter so its a compromise." My approach - even more friendly with the inverter reducing both capacity and draw; while it takes all your "overload" worries away as a soft load. When the geyser element is connected directly to a set of solar panels (connected to DC) the actual wattage of the element will vary according to the voltage supplied (no overload with low solar - just sorts itself out); you can keep the control circuit AC (those thermostat switch contacts tend to be flimsy and could arc closed with DC) so the DC switching is a big clunk (double break both + and - through your switch to reduce the risk of arcing); the control circuit load on your inverter is insignificant. The reduced wattage is a sort of "square of" so low voltage performance isn't great (equation in a previous post). It doesn't matter when you heat the water if the insulation is good so you don't have to dedicate panels to the geyser and can only bring in the DC circuit to heat the water when all your other needs are met "peak clipping" - if you generate solar and don't use it, its wasted. This takes your DSM front of pipe - feed the inverter for more pressing loads - feed the geyser when all other needs are met - feed the inverter when the geyser set temperature is reached; this can be done automatically with a time switch on your AC control circuit switching between contacts NC (de-energized the PV goes to the inverter) and NO (energized the PV leaves the inverter and goes to the geyser). Sorry its a scribbly sketch, hopefully you catch the drift The double break only on the + was a compromise in the sketch because that relay was a piggy back and only had 3 NC contacts.

interesting automation. What relays do you use ? I am weary of the high voltage DC spark on disconnect.

Would SolidState relays work ? which model number ? Maybe then I can make a MPPT(pseudo) to track the panel Vmp. Although that would add complexity. With direct connection my peak power is at ~36V, but the panel spec is Vmp=42V.

3 hours ago, Scorp007 said:

Just a comment on the voltage changing the power fed with low PV. The voltage is relatively steady. It is the current that the panel provides that changes the wattage to the element with low irradiation. That's how I have found.

Not what I have seen. For the panel to maintain the voltage, it must have enough irradiance to supply the load. If the load is higher than what the panel can output, you will see the panel voltage gets dragged down quite a bit. Similar to trying to supply a large load with a single battery. The voltage sags.

I have seen this on my geyser controller and the inverter. When there is a big load on the inverter and not enough sun, panel volts can go as low as 240V. If the sun is fully up and the same load is supplied, the voltage holds steady around 270. With medium load, almost 290V. The geyser controller also varies its voltage to a similar degree.

1 hour ago, tony Lampard said:

The "spark" you are risk averse to I called "arcing". First step is to take the thermostat to a control circuit - those typically flimsy contacts will arc in a jiffy I reckon. A really good clunk "big and strong" in the DC circuit break will reduce the risk of arcing with double break both + and - if possible. Double break is taking the wire through one set of contacts and back again through another set - doing this with + and - is a sort of belts and braces approach if one set of contacts arcs closed you still have another 3 in play. 2 years down the line I checked for signs of arcing using this approach - no sign, all good. In your calculations voltage drop from the element's resistance is a factor in your voltage measurements. I reiterate, this is the formula I have been using.. I don't know if that's iffy but its worked for me (mainly figured I don't want to exceed the rated voltage of the element "AC 240" as that might reduce the life of the element)

Basically P = V^2/R. R is just rated wattage/rated voltage. Your method just merges the whole calc.