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#solar #new-zealand
Reading @Joey Hess' recent post on solar PV for hot water, I was reminded that I have the above items, gathered when I was looking at a project for myself, but unused as I finally opted for an evacuated tube system:

Dual immersion heater element with standard thread/fitting for NZ hot water cylinders. This has two elements, the first marked 240V 2000W, the second marked 96V 1000W. The idea is that this replaces the standard 240V 3kW immersion heater, allowing normal mains operation with the first element, with the option of some sort of solar PV to the second element.

Combined thermostat and overtemp safety cutout. Most standard HW elements have the thermostat/safety built in. The above dual element does not, so this would do the job for the mains element. Note that it would probably not do the job for the solar element, which would be DC and so prone to arcing.

MPPT tracking controller for battery-less DC solar PV water heating. I got this from Techluck in the US, he hasYouTube demos:
It looks as though it works, though I have never tried it. As I recall, the solar array and probably the immersion element need to be reasonably matched to operating range of the PCB.
He doesn't post any operating/ connection details until you have purchased the unit.
I'd prefer to pass this to someone who has some basic understanding of electronics.
I would have to go back and see if I can find the operation/connection details.


Controller takes 2 x 24V panels at approx 220W each.

Water calcs are: (4.2 x Litres x TempRise'C)/3600 = kWhrs
or Litres x TempRise'C = (kWhrs x 3600)/4.2

So eg:(with no allowances for other losses) and at max output, 440W total for 5hrs gives 2.2kWhrs and would raise 47litres of water 40DegC.
Ambient cold water temperatures are generally 10 to 15'C, so that gives hot water at 50 to 55'C, which is approx the same temp as a normal domestic HW cylinder.

Actual sunlight hours will obviously vary hugely depending on location.

For those in NZ, there is a very good solar calculator at BRANZ:
This forecasts annual output for a given array size for a given location and orientation.

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I have the instructions for the MPPT controller installation.

@The Person You Have Called
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Re: %ogRkbe3JZ

@󠁪󠁯󠁥󠁹Joey Hess I'm quitting the solar PV parts I never used, including the Techluck controller.
No local response so far, I'll bump it a couple times, but you may like to look and see if you're interested in it: %vV/lP7P...

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And correction: I think the controller will manage additional panels, provided it is fitted to a larger heatsink...which is just the flat metal plate behind it. For anyone who is interested, we can dig into this further.

@Tom Cooks
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Final bump.
Does anyone anywhere have a use for this stuff???



Yes! My brother is really keen for this. He's keen to pay you some money too.

He's in welly and no hurry either, he doesn't have panels yet.


@Piet good!

And I'm not worried about the $$$: I have an evac tube solar HW system I am quite happy with, and this stuff is just gathering dust.
I contacted the manufacturer of the controller, and he re-sent the installation info. This includes discussion around various sizes/ratings of elements and size/configuration of panels.
It would definitely be a good idea to review this stuff before sourcing panels etc. I also think the whole thing needs at least some oversight from someone with some background in electronics, as the info is not as concise as it could be.

If you can give me an email contact (via Mix, if you prefer) I will copy you on what I have been sent.


Did a small dive on this thing, and the best guess I've seen is it's not a true MPPT. Developer is being very cagy about how it works, but the discussion in the FAQ about sizing heating elements slightly gives it away. Notice that some of the the examples don't have the panels running at full maximum power point.

Seems it pulses DC current to the water heater at ~100 HZ, to mimic AC (but without the inversion to negative voltages), so it can be safely used with AC thermostats without DC arcing, which is kind of elegant.


@󠁪󠁯󠁥󠁹Joey Hess I'm not sure what you mean by 'not a true MPPT'.
I'd agree it seems to be a fairly simple device.
Quite simply, for MPPT to work to heating elements in a non-battery setup, the elements have to be presented to the PV array as a variable resistor. In some early large setups, this was done by literally switching in and out some of an array of heaters, so as to arrive at the optimum resistance. I would guess that this device chops the DC and varies the mark space ratio of that, which would appear to the array as some sort of variable resistance. And I would further guess that it is constantly hunting to try and establish an optimum setting.
In such a circuit, with fixed value switching and smoothing components, there will be real limits both in capacity and and workable values; that is to say, I would think the PV and heater elements need to fall within certain ranges.

And yes, I agree he is cagey about how it works. But he seems to me to be very genuine. And he's been promoting these things for a long time now. If I had to guess, I would say that he is perhaps nervous of someone taking a simple design off him. There are also no shortage of folk who get their jollies by dissing other folks' efforts.

What I'm hoping is that we may yet get to find out: @Piet has expressed an interest on behalf of his brother, and would seem to have more than enough background to give definitive feedback!


This arrangement can only increase the apparent resistance of the element, it cannot decrease it. So if you have a lower wattage (higher resistance) element, and a lower voltage array, and they are ill matched, nothing this controller can do will match them well. I think that is what he is saying in the section you have highlighted.

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