In the case of a heat pump the water circulate in the tank and mix while the heatpump is working, so this is not an issue as it would be for a normal element inside the tank heating the water.
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I’m also wondering, with no heat pump, just normal tap usage drawing hot water from the top of the geyser, if that will not suffice to mix enough?
A vertical geyser complicates matters even more cause the temp sensor is at the wrong spot. Bleh.
Benchmark is if the wife can happily shower in “boiling” water with the geyser temp is like <30 deg C.
BUT!!! It depends on how warm the ENTIRE geyser was and who showered before her … Russian Roulette I tell you, Russian Roulette.
To solve the risk to my health… I showed her the “red button” on the Geyserwise display.
But so far I think I got it, use the hot water taps a few times in the afternoon so that the geyser can “mix better” … so far I have missed early morning “shouting matches”. 
Some of them are indirect systems, where something like propylene glycol is circulated through a copper coil where the element goes. Others should work by drawing water from the bottom, heating it and returning it to the top. If you do the process slow enough (heating the water to more than the others at the top) it works in the same way.
Depends somewhat on the brand of heat pump. Your ITS pumps come with a valve (kinda like a tempering valve, same tech) that feeds the output from the heat pump back into the heat pump. This is because a heat pump only raises the water temperature by a few degrees, and if you pumped it directly into the top of the tank, you’d slowly mix the whole tank down to luke-warm before you start slowly mixing it back up to “the wife is happy” temperature.
This valve keeps the water in the loop until it is hot enough, then it starts mixing cold water into the inlet (causing some of the hot water to push into the tank), and in this way some of the mixing is avoided. Of course the constant flow must disturb the layers, but it is not as “thorough” as it would be without that valve.
On my unit there is something wrong with the valve. 90% of the time it doesn’t bother us. It seems the issue is intermittent. Or something. In the coldest two weeks of winter, we switch the heat pump off before we start showering to prevent the mixing effect. But when that valve sticks, you can put your hand on the return pipe from the heat pump… the water is ice cold!
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I added some non return valves and a small 12v reticulation pump (with 40w panel) to my system to circulate the water from output to input (a loop) - works during the day so to maximise the water mixing and heating off the PV.
My heatpump normally only run at times before we do our normal showers, but a while back I was in the shower earlier than normal and the hot water suddenly dried up as the heatpump started it’s cycle. Surprise 
This only happens if most of the house has already showered before you and a while earlier.
Not only does this add some kW to the geyser but it will also circulate the water…
I haven’t heard of a temperature sensor being installed on the hot water outlet… 
Those extra kW’s, pennies compared to flip side of not spending them.
No idea about temp sensors on the outlet, only got the one that comes with the geyser, the vertical one, I think it is at the bottom, hence the <30deg C yet “boiling” hot water females require.
I’ve witnessed this myself. These vertical geyser thermostats don’t reveal the water temperature that comes out of the hot tap… Crazy!
Tell the wife to run the hot water until it gets as hot as it’s going to and then she can decide if it’s hot enough: No instrumentation needed! 
here some more details.
I’m wondering if this box of tricks is all it is??
It needs 230V DC input, thats what my DC is from my panels to run my house.
Or am I mistaken here.
Surely the geyserwise dc element is a better option then.
Geyserwise DC
Yes, it might be. It will require 6 PV panels in series to produce this voltage.
But if they are 350W panels (or greater) then that’s way more power than what Geyserwise recommend. I have 4 panels on my system and it copes well with a 150l geyser.
I can’t see what the reason is to use 220V except if they want to use the standard element in the geyser and not need a DC/DC converter (or inverter) to convert the PV voltage to 220V.
And we don’t know if there’s a MPPT in there somewhere…
Matching a standard element is actually not that simple. You would think that it’s as easy as putting up panels until you get roughly 230V, but it turns out to be more complex.
Your standard 3kW element (in a 150 liter tank) needs 3000/230 ~= 13A, ie the element (when hot) has a resistance of 230/13 ~= 18Ω.
If you put up your usual 350W modules that make 10A at roughly 36V Vmp (yeah I know I’m fudging the numbers a little ), then even if you put up 7 such modules, in practice it is going to pull it down to 180V (10A times 18Ω), and you’re going to get 1.8kW worth of power out of it.
The options available would be 1) accept the lowish efficiency of just 1.8kW, 2) swap the element for a 2kW element, or match the panels to the required current, 3) DC/DC converter.
Ok! All the more of a mystery about what they’ve got under the hood…
I was amused by the AC and DC terminals in the photo… 220V AC is the same power as 220V DC so why the separate connections??