ace

I removed my geyser's conventional thermostat years ago and replaced it with a digital controller using ntc probe fitting right where the mechanical thermostat use to be. This digital unit has a auto tune function and a ramp soak program very accurate. I use it with a 25a SSR that you can get in AC,DC or ACDC. When up to set temperature the unit pulses the element to keep it at set temperature no more switching on and off. The CAL 3300 that i am using is expensive but their is other digital options that could work for you.

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

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. 

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 

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 am a very big fan of low voltage DC.  I define low voltage as anything less than 50V nominal.  I think all small power consumers under 100W or 150W should be run from DC.  The world is also slowly moving into that direction.  The USB3  specification goes up to 5A 48V - that is 240W.

However, for high power appliances needing a few hundred watts or more, DC doesn't make much sense.

Another thing to consider is that the overall inverter efficiency is not very good at small loads.  With zero load, your inverter has 0% efficiency.  Best efficiency is normally attained at around 70 - 80 % of rated power, but this can vary depending on the design.

For people that do not have an inverter, using 2 or 3 solar panels dedicate to geyser heating, then running a geyser at 140 - 150VDC would also make a lot of sense to me.

Not sure that there is a gain going DC, including the additional cost of purchasing a DC element, running additional cabling to your geyser, let alone the compliance side of it.  As mentioned above, if you have your batteries full by 12PM, might as well just use AC. Can control it via a smart switch to only power at certain times or based on SOC. Most inverters are 90% + efficient between DC>AC

I agree with @Bobster.and @WannabeSolarSparky your battery and inverter is more than capable of running the geyser from the inverter just manage the geyser consumption and add geyser insulation(jacket) and all hot water pipes. Drawing 30 odd amps via a seperate load from the battery might interfere with you comms between batt and inverter also extra wiring and fuse.

That's great, will save on the wiring.
DC is a dangerous beast, be careful. Also suggest if you go this route to put the wiring in metal conduit and use decent DC fusing and breakers to reduce the risk of fire.
Other than that I suppose dc to power the geyser direct from the battery could be ok.
Also check compliance with the electrical code to ensure your insurance is not compromised.

Unless your geyser is very close to the battery bank the wiring could end up costing quite a bit.
48 volt 1500 watt dc element would be drawing over 30 amps from the battery bank.

Hi everyone, as the title suggests....  I'm looking for some input regarding a way that I am "thinking" of powering a dc geyser element.
Before I start, I think some basic info is probably a good idea: I am completely off-grid, have about 5kw of solar, 3x100ah Lithium Batteries, gas geyser, gas stove & oven, energy efficient appliances (tv, fridge, washing machine etc.), lights all converted to 12v led (supplied by high efficiency meanwell dc-dc converter). My average consumption ranges from 350-450w after sundown (according to the inverter anyway). My batteries are at about 49v in the morning & hit float (51.5v) at about 12 each day. I feel I'm in a very good space regarding my power situation (although I've read that I perhaps should discharge my batteries a bit more for better longevity - input on that is welcome too).
Anyway, I have been thinking about putting my traditional geyser to use, considering that the for at least half the day, the majority of my solar power is pretty much wasted. I am considering using a 48v 1500w geyser element to heat up water in the geyser prior to the gas geyser. Now I have seen the commercial geyser kits which includes a mppt controller & panels etc & connect to a dc geyser element. However I struggle to see any reason why one could not simply buy & hook up the dc element directly to the battery bank (obviously with the correct thermostat etc). I already have a mppt charging my batteries, the batt's already have a bms built in, the bank is more than capable of providing the voltage & current required. So why not just connect the element directly? Why don't more people do this? It seems logical, is there something I'm not taking into account?
So just to clarify.... I want to hook up the dc geyser element directly to my battery bank, this will only be turned on during the day after batteries have hit float voltage & will be turned off again after sundown. Does anyone know a valid reason for this not to be done in this way? Does anyone foresee any potential issues? Any knowledgeable input will be greatly appreciated. 

I guess I should say thanks, but this is really bad news.
I know R1500 is cheap, but x 16 is a lot of dough I just dropped on something that will only last me 8 months!!
I've had them for about 2 weeks now. It's too late to take them back. I even threw away all the boxes.
If you hear about about the murder of a battery rep tomorrow............ it wasn't me!

Thanks for the welcome Chris.
Also thank you for your input on my system. I will definitely get myself another panel as soon as funds are available again.
My batteries aren't on busbars, so I will be sorting that out asap too.
I'm not at all familiar with battery balancers or battery monitors, although I have been hearing them mentioned quite frequently here on the forum.
I will have to do a bit of research into that. Before I buy anything I will try get some guidance here first though.
I think I will rather start a new thread with my other questions. 
Thanks again.