@Modina

It would be interesting to know on what basis or how you have measured input vs output to dispute the % on a broad sample of inverters. 

These are standard efficiencies according to CEC test procedure (developed by Sandia National Laboratories), and must be tested by an independent laboratory.  Weightings are also specified in the test procedure, so are fixed for all inverters.

https://pvpmc.sandia.gov/modeling-steps/dc-to-ac-conversion/cec-inverter-test-protocol/

You may be thinking of good old 50Hz transformers. But most modern inverters use HF transformers, where 99% is easily achievable.

But the basic fact is that losses will be LOWER with a modern inverter, than using the thinnest legal DC cabling.  You will need to use pretty thick DC cables to get lower losses than an inverter at high power levels.

 

14 minutes ago, chrisc said:

Its 30% more efficient than a conventional element 

I don't know what the guys that make such claims smoke.  I think someone changed the definition of efficiency while I was not looking.  But this wouldn't be surprising, because most words have their historic meaning changed by exactly 180 degrees, or like German Foreign Affairs Minister Baerbock would say, 360 degrees. 🙄

An electric heater is the only thing that has nearly 100% efficiency.  As measured with the standard meaning of efficiency.  In other words all energy you put in, is converted into heat.  Depending how hot, a very tiny amount could be changed to light, mainly infrared. 

20 minutes ago, chrisc said:

Did you consider a PTC element, sold by Geyserwise?  It uses a 72 volt PTC solid state heating device and is a direct swap to a hot wire element, which design is about 100 years old 

I have no personal experience with these, but yes, PTC elements are very good.  The best part is that they are self regulating.  They will go high impedance at a certain designed for temperature as to practically pass no meaningful current.  It still would need a thermostat of sorts, to allow the end-user to down turn his hot water temperature and not always have to run the system at the PTC designed set-point. 

2 hours ago, hoohloc said:

Please explain more on how drawing from a battery via a separate load might interfere

Let me try an explain what i actually meant. Fair enough your bms will communicate the soc via comms to the inverter. Looking at hybrid parity inverters when blending power from battery solar and grid. Say you are drawing 500 watts on your essential loads you will blend for example 250w from solar and 250w from battery all good but actually you are consuming 30amp x 50v=1500watts+ 250watts= 1750watts from your battery so now your data reporting on your inverter is not accurate. If the 1750w was part of the inverter blending calculation and you had enough solar available it would use the solar power to heat the geyser instead of using the battery to drive the 1750w. Charging the battery will consume more power than what you have used from the battery due to losses.

2 minutes ago, TaliaB said:

Let me try an explain what i actually meant. Fair enough your bms will communicate the soc via comms to the inverter. Looking at hybrid parity inverters when blending power from battery solar and grid. Say you are drawing 500 watts on your essential loads you will blend for example 250w from solar and 250w from battery all good but actually you are consuming 30amp x 50v=1500watts+ 250watts= 1750watts from your battery so now your data reporting on your inverter is not accurate. If the 1750w was part of the inverter blending calculation and you had enough solar available it would use the solar power to heat the geyser instead of using the battery to drive the 1750w. Charging the battery will consume more power than what you have used from the battery due to losses.

Ok, data reporting on the inverter will definitely not include the 1500w but that does not stop you from  including that in your calculations because you know that you have 1500w which is being used by the geyser and the period which the geyser was ON. As for blending solar grid and battery, surely you can prioritize solar first and when you have enough solar, all that will go to your loads including charging the very same battery you are drawing from and will only take from the battery when solar is not enough. I guess it all depends on the type of inverter one uses. Bottom line, what OP was asking is if it will be possible to run directly from the batteries, the answer is YES, most definitely. he can power his DC geyser element directly from the batteries. It is practical and I'm doing it without any issues, nine months now and counting. I would choose that over the accuracy of inverter data recording because having hot water in the morning without putting a hole in my pocket is a bliss. Happy wife, happy daughter makes a happy home hey! plus I get to save on gas water heating. If I had done this before installing the gas water heater, I would have never installed it because I hardly hear it switching ON and it has been cold these past days and was expecting to be boosting my hot water every now and then with gas 

19 minutes ago, hoohloc said:

Happy wife, happy daughter makes a happy home hey!

Fair enough like i always say the key to a happy marriage "Yes dear" 😜

45 minutes ago, Modina said:

I don't know what the guys that make such claims smoke.  I think someone changed the definition of efficiency while I was not looking.  But this wouldn't be surprising, because most words have their historic meaning changed by exactly 180 degrees, or like German Foreign Affairs Minister Baerbock would say, 360 degrees. 🙄

An electric heater is the only thing that has nearly 100% efficiency.  As measured with the standard meaning of efficiency.  In other words all energy you put in, is converted into heat.  Depending how hot, a very tiny amount could be changed to light, mainly infrared. 

I have no personal experience with these, but yes, PTC elements are very good.  The best part is that they are self regulating.  They will go high impedance at a certain designed for temperature as to practically pass no meaningful current.  It still would need a thermostat of sorts, to allow the end-user to down turn his hot water temperature and not always have to run the system at the PTC designed set-point. 

True, they are very good and worth every penny. For the AC supply, I use the normal thermostat that came with the geyser but the DC supply has no thermostat. Still looking for a solution to that one but for now, SONOF is doing the trick. I have the AC supply on CBI Astute  and DC supply on a SONOF/timer. when I want to power the geyser the whole day I use both AC and DC and when the AC switches off/ no current flow, I know that the temperature is ok and I switch off the DC supply.

5 hours ago, hoohloc said:

Bottom line, what OP was asking is if it will be possible to run directly from the batteries, the answer is YES, most definitely. he can power his DC geyser element directly from the batteries. It is practical and I'm doing it without any issues, nine months now and counting. I would choose that over the accuracy of inverter data recording because having hot water in the morning without putting a hole in my pocket is a bliss. Happy wife, happy daughter makes a happy home hey! plus I get to save on gas water heating. If I had done this before installing the gas water heater, I would have never installed it because I hardly hear it switching ON and it has been cold these past days and was expecting to be boosting my hot water every now and then with gas 

Thanks Hoohloc. A straight up answer from someone who has actually done this is invaluable. I still can't quite understand why not more people do it like this. Some are saying there's not be a big advantage (power wise) over just running the geyser directly from the inverter, but as far as off-grid solar is concerned, I feel that every little bit counts. And although my inverter should be able to handle the load of a geyser (I think geyser is 3kw). I feel the less stress put on my budget synapse inverter, the better. I personally prefer not to risk it damaged by my wife accidentally using the microwave & my daughter the hairdryer together while the geyser is on. 

6 hours ago, chrisc said:

Did you consider a PTC element, sold by Geyserwise?  It uses a 72 volt PTC solid state heating device and is a direct swap to a hot wire element, which design is about 100 years old 

Its 30% more efficient than a conventional element 

I use one with a Geyserwise ECO controller which can also be run off a DC source

I'm not familiar with this at all, so I'll def check it out before I proceed. Thanks for the info.

The book is still not closed how the PTC element can heat water using less power. This link about the Extend element using 33% less power. Similar to the Geyserwise. 

Kwikot does not agree. 

https://www.4x4community.co.za/forum/showthread.php/365812-Xtend-Replacement-Geyser-Element

Edited June 8, 20233 yr by Scorp007

12 minutes ago, Scorp007 said:

The book is still not closed how the PTC element can heat water using less power.

Well if you close your physics book and open the marketing book, sure it can!

A heat pump operates on the sound principals of an open physics book, even with 8 degrees ambient air my heatpump uses about 2kWh to heat water from 25degrees to 53 degrees (Celsius)

1 hour ago, iiznh said:

Well if you close your physics book and open the marketing book, sure it can!

A heat pump operates on the sound principals of an open physics book, even with 8 degrees ambient air my heatpump uses about 2kWh to heat water from 25degrees to 53 degrees (Celsius)

A heat pump does not use electricity to heat water.  It uses electricity to move heat from the air to the water.

Both conventional elements and PTC elements directly convert electricity into heat, and that conversion is very nearly 100% efficient.  The only difference can be in how efficiently the heating element transfers that heat to the water.  A very heavily scaled conventional element could potentially be marginally less efficient at heat transfer than a PTC element - but a properly maintained conventional element will have nearly identical performance to a PTC element.

20 minutes ago, JustinSchoeman said:

A heat pump does not use electricity to heat water.  It uses electricity to move heat from the air to the water.

Technically the electricity drives an electrical compressor, it compresses a gas (often called refrigerant) into a liquid, once it turn to liquid the temperature rises, the (hot)water is then used to cool down this liquefied gas, it then flows through a capilary tube to the heat-exchanger where the pressure is lowered allowing it to evaporate again, which means that it becomes extremely cold again (zero or below) since we took a lot of the energy out of the system. Normal ambient air is used to heat up the cold side and once it reaches close to ambient temp it is re-used for the next cycle. Pretty much how a fridge works, except we are using the hot cycle and a fridge uses the cold cycle. For the most part it uses a lot less electricity harvesting heat from the air than converting the electricity directly to heat. A PTC element cannot bend the laws of physics and generate more heat from the same energy. The salesman has done a good job selling the 30% claim

Your geyser leaks energy ,easily 1.5-3KWh+ per day... if you want to save a lot of money, do not get a different element, get the best insulated geyser on the market and insulate your pipes as it will save you large amounts of cash over it's 8-10 years lifespan.

2 hours ago, iiznh said:

Well if you close your physics book and open the marketing book, sure it can!

A heat pump operates on the sound principals of an open physics book, even with 8 degrees ambient air my heatpump uses about 2kWh to heat water from 25degrees to 53 degrees (Celsius)

We can both agree on these 2 items. I run my 1.5kw draw heat pump only 2 hrs a day and it's works fine for nearly 10yrs now. Only repair was one pump replaced at R12000 due to installer not fitting a strainer. 

But buy ever. 

5 hours ago, ace said:

I'm not familiar with this at all, so I'll def check it out before I proceed. Thanks for the info.

Yep, check out the Geyserwise PTC element, that is what I'm using. Mine is dual powered 

So a question I have. Will a PTC element not get a scale build up? 

3 hours ago, iiznh said:

Well if you close your physics book and open the marketing book, sure it can!

A heat pump operates on the sound principals of an open physics book, even with 8 degrees ambient air my heatpump uses about 2kWh to heat water from 25degrees to 53 degrees (Celsius)

ok, lets leave out the heat pump. Focus on the heating element because the prices are not comparable 😀

1 minute ago, Scorp007 said:

So a question I have. Will a PTC element not get a scale build up? 

According to their claim, yes but I'm yet to check. I'm currently running one now for a while and will check when I get a chance

6 hours ago, ace said:

Thanks Hoohloc. A straight up answer from someone who has actually done this is invaluable. I still can't quite understand why not more people do it like this. Some are saying there's not be a big advantage (power wise) over just running the geyser directly from the inverter, but as far as off-grid solar is concerned, I feel that every little bit counts. And although my inverter should be able to handle the load of a geyser (I think geyser is 3kw). I feel the less stress put on my budget synapse inverter, the better. I personally prefer not to risk it damaged by my wife accidentally using the microwave & my daughter the hairdryer together while the geyser is on. 

Doesn't this open the door to another problem? Say that the geyser, microwave and hairdryer are running at the same time. Now because you are feeding the geyser directly from the battery, your inverter doesn't trip. But you could still get the BMS alarmed.

Gap in my knowledge/experience: If my inverter trips and there is PV or grid, the inverter will reboot within a minute. But if the BMS trips? I haven't experienced that with the current battery (which can service a much higher load than my inverter, so the inverter will always trip first), but I don't think it will rest for a minute or so and then startup again.

So I think that at the least, any answers to questions about "can this setup work" have to be phrased so  that they are dependent on the brand and model of equipment being used. 

13 hours ago, Modina said:

Over 95% ?  I simply don't buy that.  Properly designed inverters will be typically 90 to 93%.  It will most likely need very exotic components to reach 95%
 

 

You don't have to agree but here are 2 loadings yesterday using the actual data points for input from PV and 230V output from the MPPT. Both over 97%.

Loading of 29 and 75% of the inverter output. Voltage and current readings shown on DC side and Watts output on AC side. 

If you are drawing directly from the battery, you run into a risk to overload the battery. Let’s say 1C battery - if the inverter is pulling close to the 1C rating and at the same time the geyser element draws additional power, you will discharge the battery above the specified safety rating. 

16 minutes ago, Bobster. said:

Doesn't this open the door to another problem? Say that the geyser, microwave and hairdryer are running at the same time. Now because you are feeding the geyser directly from the battery, your inverter doesn't trip. But you could still get the BMS alarmed.

Gap in my knowledge/experience: If my inverter trips and there is PV or grid, the inverter will reboot within a minute. But if the BMS trips? I haven't experienced that with the current battery (which can service a much higher load than my inverter, so the inverter will always trip first), but I don't think it will rest for a minute or so and then startup again.

So I think that at the least, any answers to questions about "can this setup work" have to be phrased so  that they are dependent on the brand and model of equipment being used. 

True, if you over load your inverter by powering all the loads at the same time knowing very well that you have a geyser on and running directly from the battery, you will be asking for problems. on the second statement, ''can this setup work'' the answer is Yes it does work. I'm currently doing that and at no point have I ever tripped my battery bank or the cheap growatt that I'm using. Both AC and DC are ON as we speak 😀

2 minutes ago, hoohloc said:

on the second statement, ''can this setup work'' the answer is Yes it does work. I'm currently doing that and at no point have I ever tripped my battery bank or the cheap growatt that I'm using. Both AC and DC are ON as we speak 😀

Sure, but it can work with batteries like yours and with an element rated at XYZ watts. That's what I'm saying. It's not as simple as "yes" or "no". It's "yes if..."

9 minutes ago, PowerUser said:

If you are drawing directly from the battery, you run into a risk to overload the battery. Let’s say 1C battery - if the inverter is pulling close to the 1C rating and at the same time the geyser element draws additional power, you will discharge the battery above the specified safety rating. 

I have never overloaded my 0.5C batteries and I'm powering directly from the batteries. You can have 1C battery connected to 3000w inverter, if you try to draw 4000w out of that inverter, it will trip. My point is, badly specd system will disappoint you at one point, but if you know what you want to achieve and spec your system to give you exactly that, then you have no risk of overloading the battery 😀

1 hour ago, Bobster. said:

Sure, but it can work with batteries like yours and with an element rated at XYZ watts. That's what I'm saying. It's not as simple as "yes" or "no". It's "yes if..."

It all boils down to specifics and not having a box approach. The details were given that the DC element portion of the dual element is a 900W element. Geyserwise drive it at 72V. If driven from 48V the current will be about 12.5A. I estimate at 48V the current is around 8.33A Few of the batteries we use will not be able to provide 8.33A?

Have I lost it somewhere? 

Edited June 8, 20233 yr by Scorp007