Advice for order/install for Australia

During summer I tend to have showers in the morning AND in the evening, but use a lot less hot water. Under normal circumstances I feel like we use most of our hot water during the day as we have dinner and wash the dishes by 3pm.

The hot water system was installed 3 years ago but it was a like for like replacement for a system installed in 2000. It’s a single element Vulcan Electric 3.6Kw.

I think there might be a CL11 (or something like that) closer to the rate you mention. I don’t know why we’re on CL33 but that’s the way it’s always been and I’ve never been able to find any details on how it works other than power is only available at certain mystery off peak times.

I’ve been unable to find any information on time or kWh caps on the FIT. But AGL can of course change their rates at any time and often do so twice a year.

Oh sorry, that should have been 1,000kWh.

I wish electricity providers didn’t obfuscate as much as they do. Won’t be until I have an IoTaWatt that I’ll have a better understanding of when and on what we actually use most of our power on.

Speaking of which I just got a notification that my IoTaWatt has just left Hong Kong. Hopefully it won’t take too long to get to me.


I have just ordered a IoTaWatt system today, looking forward to getting it and setting it up!

I live in Canberra and you are not legally allowed to (I am sure some do but) hook up solar to heat hot water and have a controlled load. I am going to get a timer installed.


Tarriff 33 provides at least 18 hours of ‘on’ time per day and you pay a higher rate. The tariff 31 rate provides less ‘on’ time but is much cheaper and is probably all you need for hot water.

You will likely save a lot more money changing tariffs than you will using solar to charge your hot water but you can do both.

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Got my IoTaWatt yesterday… EXCITED!
Solar installation in 6 days.

Have all the parts ready. Just need to arrange with the electrician to drill a hole, put in some conduit (for the CT’s) and install the dual GPO’s.

Hopefully there won’t be any problems.


P.S. Also found out today that the electric hot water system was set to 70C. Had it set down to 60C and limited to 50C to the bathrooms. Should save on some electricity, though I don’t know if it’s significant.

Standby heat loss in a modern electric HW tank (foam insulation) is about 2kWh/day. Unlike a heat pump, where the energy needed to add heat is a function of the delta, resistance heating is linear. So as long as you are using mixing valves to control the output temperature, the standby loss reduction will be proportional to the reduction of tank temperature vs ambient temperature.

If you don’t have mixing valves, it’s likely to save more.

I believe there is a mixing valve, but I also know this system is 20+ year old technology (replaced 4 years ago with an identical system that was installed more than 20 years ago).

I don’t know if that classifies it as modern.

You will be able to accurately measure your standby loss with IoTaWatt. Plot a period of time when you are away or can be assured there is no usage. Note the time between heating cycles and the Wh of the later cycle. Wh/time is the heat loss.

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I am not sure how well you will be able to measure standby loss, unless you don’t use water for a long period. I have a heat pump water heater and it has sensors inside. Here is a plot of temperature and water usage:

You can see the last water usage was just before 1:30AM. The top and bottom sensors show the water is at 141-142 degrees. It takes a little over an hour to go down 1 degree (from 2:00AM to 3:40AM). It takes a little over an hour to down the next degree. At just before 5:00 things start changing dramatically. That is when the recirc pump starts (4:50AM according to IotaWatt, looks like I need to adjust the timer again, or work on a control system to control it better). You can see how the bottom of the tank has dropped 2 degrees in less than an hour, but the top of the tank is still the same.

Anyway, when I did another test many months ago, I discovered that measuring the heat loss of the tank was really hard even with two tanks and one bypassed. The water heater timers don’t really save much energy because the difference in heat loss of a few degrees is not so much. They probably save some by providing slightly less hot (temperature) water for the first usage in the morning. Now, the recirc pump is a huge energy waster. The pump itself uses very little energy, but the heat loss of a whole house’s worth of pipes (even when well insulated to R3) is quite large. But, having hot water without needing to wait is very nice.

I’m doing some reconfiguration of the IoTaWatt and have connected the VT, however it seems like it’s display US voltages?


Or am I misunderstanding?

The VT appears to have been configured correctly OOTB.


I have not used that VT - i used the ones from Jaycar - but at the bottom of that plug pack is says DS-12-09 - in the selection it is a 10-09 - sure you have purchased the right unit ?

Try clicking the reverse and see what that reports ?


According to this link here the model looks wrong ??


Just looked on the RadioParts website and there only seems to be one on there for 9v ac so i guess it nust be right.

Try the reverse option on the input


Based on this page:

It looks like the 2nd option, which is the E6. Reversing didn’t seem to affect anything.
Changing it to the model without E6 also didn’t seem to do much. Generic240v makes it show around 220V which is also off, but much closer.

I made the purchase by following the link on the Aussie bundle page. It points to.

For what it’s worth the voltage it’s showing seems like half of what it actually is.

EDIT: Hang on… This power board is connected via a UPS. I don’t know if that would have any effect on it but I will try elsewhere.

EDIT2: Nope… Made no difference at all.

The E6 in the list is a 120V primary, so if you select that, you have told IotaWatt that your primary is 120V. So, the numbers you see are expected.

I would use DCSS AC910 (Aus). That should get you close and if your want to get closer follow the calibration process.

What the HELL!? I had to rub my eyes… I COMPLETELY missed that looking through the list.

Apologies for being blind.

Voltage is working thought it disagrees with my calibrated smart plugs.

However, I assumed I could get a reading from a CT if I put it on a power cable. I put it on the cable feeding the power board in my office (all the power in this room save for lights goes through this) and I get 0 Watts.

The smart plug on the same socket reads 220Watts - 320 Watts depending on power usage at the time. I’ve tried multiple sockets on the IoTaWatt and two of the CT’s I bought with it (the AccuCT 50A variety).

What could I be doing wrong?

Look at the docs. You can calibrate the voltage if you have a meter or other standard.

The CT goes on only one of the two conductors of a circuit. Are you clamping on a sheet he’d cable with two conductors? They would cancel each other out.

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That makes perfect sense. Thank you.

Slipped my mind that in a meter box the wires are all seperate. Was worried there for a minute.

I guess in my communication I implied that the Smart Energy Meter was capable of this and this was the response I received:

It’s not the Smart Energy Meter that does that, though it is required, it is a Fronius relay WITH the smart meter. We don’t recommend them. They are about $500 with a 12 month warranty and not manufactured by Fronius. A standard timer is cheaper and more reliable.

Yes you can use anyones Contactor/Relay - the Relay output from the Inverter is just a 240v low amp output - do not buy the Fronius one - a timer is going to be OK 90% of the time (if you do not want to go down the inverter path - but you will have to decide if you are going to run it from Solar or from your controlled load - if running from Solar - on days where you do not get enough solar and/or have a big power draw you will be paying to reheat the water from Grid power.

Your choice how you want to do it - many ways to skin the cat.

When i move our instantaneous gas hot water on and get an Electric HWS i will be getting one with dual element, Bottom element will be on mains that will be on a contactor that i can initiate based on excess solar production (courtesy of Iotawatt) and will be handled through Node Red.

The top element will be on a seperate lower temp thermostat that will be on the mains only - if the tank has not reached temp from Solar by 3PM (also taking into account some other metrics) i will then kick the top element in for a quick boost prior to the evening loads coming on