How To Use a Fronius Smart Meter To Solar Power Your Hot Water

fronius hot water diversion

Note to installers: Don’t wire directly in to bathtub or the duck will die.

Over the past week or so I’ve been politely prodded  by a plethora of people pushing me to provide information pertaining to solar hot water diverters.

A ‘hot water diverter’ is a box of power electronics that that sucks up your homes’ surplus solar electricity and diverts it to an electric hot water system instead of exporting it to the grid where it would earn a feed-in-tariff.  If the whole system is well designed and installed it will  greatly reduce or even eliminate using grid electricity for water heating.

Feed-in tariffs have recently risen — well, not for Westies1, but for the rest of us — so really, interest in diverters should have remained restrained, because the more you can get paid for exporting your solar, the lower the rate of return will be on investing in diverter hardware.

But, as fate would have it, a fairly sensational ABC News story has stoked curiosities across the country and caused countless cadres of curious citizens to kindly clamor for me come up with more information.

I fully intend to write about hot water diverters in depth — just as soon as I am done convincing someone else to do most of the actual work for me.  But before I get around to doing that, I will tell you what I know about another method for increasing the amount of solar electricity used to heat water that can be done by people who very wisely own, or who are going to own, a Fronius inverter.

By using a Fronius smart meter and connecting a Fronius Energy Management Relay2  to their electric hot water system, Fronius inverter owners can use their Fronius3 datamanager, which came with their inverter, to turn their hot water systems on when there is a surplus of solar energy that would otherwise be sent into the grid, and turn the hot water system off when solar output falls.

Update 21st August:  I have learned that while most Fronius inverters come with datamangers installed, there are versions called “light” that do not.  So if you are buying a Fronius inverter and want to use their relay and smart meter, check that you are not buying a light version. 

fronts smart meter

A Fronius Smart Meter (3 phase model shown)

It is also possible use just the relay without the smart meter.  It will still work, but won’t be nearly as smart.

The Fronius relay will either switch your hot water element 100% on, or 100% off4. It isn’t able to send small amounts of surplus solar power to the hot water system as a diverter can, so it is not as effective at using surplus solar electricity, but may be considerably cheaper.  Fronius makes a hot water diverter, called a Fronius Ohmpilot, that is not available at the moment in Australia.  They say its installed cost in Europe, at the current exchange rate, will be from $1,600 to $1,940.  In comparison they say the European cost of installing their relay will only be from $300 to $520.

Fronius Ohmpilot

The not-available-in-Australia-but-totally-available-in-Austria Fronius Ohmpilot

The good news is, as part of a Fronius inverter installation, it is possible to have a relay installed in Australia for $220.  At the same time a single phase Fronius smart meter can be installed for $340 or the more expensive 3 phase smart meter for $680.  So for a home with single phase power, having a Fronius relay and smart meter installed can add under $600 to the cost of a Fronius inverter installation.

Update 21st August:  There are versions of Fronius inverters called “light” that don’t come with datamanagers.  If you are buying one of these and need to install the datamanager separately it may add approximately $380 to the installation.

What The Hell Is Fronius?

Fake Austrian Family

A fake Austrian family in fake Austria, with a fake Austrian castle in the background.

Fronius is a family owned Austrian company, founded in 1945 in an Austrian army hut by Gunter and Friedl Fronius.  The company also makes welding gear, but Down Under they are most famous for their high quality solar inverters.

Fronius inverters come with a 10 year warranty, which is better than the 5 years most have, but the warranty only covers the cost of installing a replacement for the first 5 years.  For the second 5 year period they will provide a replacement inverter, but won’t pay for installation.

How Does The Fronius Smart Meter And Relay Work?

When the Fronius smart meter is installed and a Fronius relay is wired up to your electric hot water system, you are ready to rock and roll!  Or rather, monitor and control.  I guess, when you think about it, that’s really the opposite of rock and roll… but I’m sure it’s still lots of fun.

The Fronius datamanager, which is the monitoring software all their inverters come with, can now be used to set the hot water system to only turn on only when there is enough surplus solar electricity to run it.  This makes it possible to never use grid electricity to heat your water again.

But unless you have a giant beast of a solar system, you may end up taking quite a few cold showers in winter when hot water use is at its highest and solar output is at its lowest.  Fortunately, if, like Jeremy Clarkson,  you are not a fan of pneumonia, you can avoid this by programing the datamanager to turn on the hot water system for a period each day even if there isn’t enough surplus solar electricity to run it, which is very likely on cold miserable days with no sunshine.  So even with this system installed most people will still use at least some grid electricity for hot water.

Austrian cyborg

It switches individual consumers on or off?  Sounds like Austrian cyborg technology is more advanced than I thought.

The Relay Can Be Used Alone

I spoke to MC Electrical in Brisbane about the Fronius relay and smart meter.   You can read the blog post they wrote on them here.  They told me it is possible to use the Fronius relay without the smart meter.  It just won’t be nearly as smart.

The relay will be cable of switching on a hot water system when rooftop solar output exceeds a preset amount, but without the meter to guide its way, it won’t be able to take the amount of electricity the household is using into account.  In other words it will be operating blind and won’t be able to tell if activating the hot water system will result in electricity being drawn from the grid due to electricity consumption occurring in the home at that time.

People who are normally out of the house during the day may be happy with just using a blind and dumb relay, but they should still expect to use significantly more grid electricity to heat their water than when used in combination with the smart meter.

To prevent cloudy weather keeping solar output low and resulting in no electricity being sent to the hot water system during the day, the relay will make the hot water system turn on anyway for a period and use at least some grid electricity, so people won’t be caught without hot water.  MC Electrical said they adjust the parameters of relay’s operation according to the customer’s situation.

The Fronius Relay Can Be Used On Other Appliances

Fronius smart meters and relays aren’t limited to conventional electric hot water systems and can be used on other devices including energy efficient heat pump hot water systems, pool filters, and pool heaters.  Multiple appliances can be controlled through the datamanager, but a separate relay will need to be bought and installed for each one.

The Fronius Smart Meter Can Export Limit

The Fronius smart meter can be used to export limit a system, which is something often required in rural areas.  If a smart meter is required anyway for export limiting, then getting a relay installed at the same time won’t cost a great deal more and will allow surplus electricity, that might otherwise go to waste, be put to good use.

Getting The Most Out Of Fronius Hot Water

Just how much a household can save on their electricity bills, if anything at all, from using a Fronius smart meter and relay depends on a range of factors including, solar system size, hot water consumption, heating element power, location, controlled tariffs, feed-in tariffs, and electricity plans.

When It Comes To Solar, Bigger Is Better

Larger rooftop solar systems will produce more surplus electricity and so reduce the amount of grid electricity required to heat water.

The More Hot Water You Use, The Better The Economics

The more hot water a household uses, the more likely investing in a Fronius smart meter and relay will be worthwhile.  Larger households tend to use more hot water, as do those in colder parts of the country.

Smaller Hot Water Elements Are Better


Here we see an Austrian about to work on a switchboard.  As the member of a safety conscious culture, he is taking the precaution of wearing a reflective vest in case it actually turns out to be a Deceptikon and shoots lasers at him.

I have a very small hot water heating element.  It’s only 1.8 kilowatts.  Personally, I think anything more than that is a waste.  Sure, some people boast about how quickly their big, 4.8 kilowatt heating element can make the contents of their storage tank go from frigid to steaming hot, but when it comes to maximizing solar self consumption, trust me, bigger is not better. This is because the smaller the element, the more likely it is there will be enough surplus solar electricity to run it without needing to draw on grid power.

For a variety of reasons a solar system with 5 kilowatts of panels may rarely or never produce more than 4 kilowatts of power, even under perfectly clear skies.  But if a hot water system’s heating element is only 1.8 kilowatts, that can be small enough for surplus solar electricity to heat water without the need to draw on grid power, provided there is sufficient sunshine.

If a family uses half the hot water in a 250 liter hot water system in winter and the fresh water that enters the tank is 10 degrees, then with a 1.8 kilowatt heating element it will take over 4 hours of heating for the water temperature to raise to 60 degrees5, which is the minimum temperature hot water systems are normally set to.

But if their heating element draws a hefty 4.8 kilowatts then it would only take 1.5 hours to do the same job, but with 5 kilowatts of solar panels it will be virtually impossible to avoid using at least some grid electricity, even on perfectly clear days.

Location Counts

A 5 kilowatt solar system will only produce around 1% more electricity through the year in Brisbane than in Adelaide.  But the output in Brisbane is much more constant, with electricity production in the worst winter month averaging 61% of the best summer month.  But in Adelaide, output during the worst winter month is only 36% of the best summer month.

In locations where solar output is especially low during winter, which is when the most hot water is used, the more likely it is grid electricity will be need to be used.  The coldest parts of Australia tend to have the worst winter solar performance, while the the warmer parts of the country tend to produce considerably more solar electricity in winter, but use less hot water overall and so gain less benefit from having a Fronius smart meter and relay.

It’s a Catch-11 situation.  It’s like Catch-22, but only half as bad.

The Cost Of Controlled Tariffs And Feed-In Tariffs Matter


If your goal is to save money it is important to consider how much controlled tariffs cost.  These tariffs are often referred to as “off-peak hot water”.  The lower they are compared to your feed-in tariff, the less money you will save using solar electricity for water heating.

For example, looking at the Origin Solar Boost plan for South Australia, I see it has a feed-in tariff of 18 cents and a controlled load tariff of 21.175 cents.  This means if a household on this plan used a fairly typical 1,500 kilowatt-hours a year to heat water using a controlled tariff and then changed to using a Fronius smart meter and relay and managed to use 100% solar electricity for their hot water, they would only save $48 a year on their electricity bills.

If just 15% of the electricity used to heat their water came from the grid, then because the standard tariff is twice as much as the controlled tariff, they would lose money.  Since a hot water system using a Fronius relay is likely to average more than 15% grid electricity use over the year due to poor solar production in winter, I would say it is not be a good idea for a household sticking to that particular electricity plan to use a Fronius smart meter and relay for hot water, even if they have a teeny weeny little heating element like I do.

Because feed-in tariffs and controlled tariffs can vary significantly between electricity retail plans, it will be important to carefully examine them to decide if it is worthwhile to change to a different retail plan or if it is a good idea to use a Fronius smart meter and relay at all6.

Three Examples

I have taken three different locations in Australia — rural Queensland, Sydney, and Adelaide — and estimated how much money could be saved on electricity bills each year by using a Fronius smart meter and relay to heat water.  In the Sydney and Adelaide examples I have assumed the households use an above average amount of hot water and for every example I have assumed the households have large solar systems, small 1.8 kilowatt heating elements in their hot water systems, and are using the relay and smart meter in combination and not just the relay alone, so little grid electricity will be required for heating water.

Example — Rural Queensland

In rural Queensland electricity prices and feed-in tariffs are fixed.  The warm climate results in households using less hot water than in most other states and solar output is more constant.  If a household that uses 1,000 kilowatt-hours a year to heat water with a controlled tariff switched to using 100% solar electricity they would save  $73 a year.  If 10% of the electricity used to heat water came from the grid they would save $62 a year.

Example — Sydney

For Sydney I’ve assumed the household is on the AGL Everyday NSW Residential Electricity Market Offer retail electricity plan (AGL366955MR).  If they use 2,000 kilowatt-hours a year to heat water with a controlled tariff and change to using 100% solar electricity instead, they will save $47 a year.  If they use 20% grid electricity to heat water they will instead lose $11 a year.

Example — Adelaide

In the Adelaide example the household is on the People Energy7 Standing Offer retail electricity plan (PEO227399SR).  If they use 2,000 kilowatt-hours a year to heat water with a controlled tariff and change to using 100% solar electricity, they will save $174 a year.  If they use 20% grid electricity to heat water they will instead only save $106 a year.


Typical savings per year if 100% of solar is diverted to heat hot water.


Typical savings per year with hot water PV diversion if 10% of your hot water energy still comes from the grid.

Adelaide Comes Out Ahead, Sydney Loses

Both the Queensland and Adelaide examples were better off using the Fronius smart meter and relay to heat water. However, in the Sydney example the household was worse off.  So while using the Fronius smart meter and relay can appear to save households money under the right circumstances, extreme care will have to be taken to ensure it won’t end up costing money.

Because the amount of grid electricity used needs to be minimized for it to be worthwhile, households with less than 4 kilowatts of panels or a hot water system heating element larger than 1.8 to 2.4 kilowatts will need to be especially cautious.


  1. Western Australia’s feed-in tariff is still 7.1 cents, the same as it was a year ago.
  2. A ‘relay’ is a fancy name for a remotely controlled switch that switches stuff on and off. The ‘Fronius Energy Management Relay’ is built into most Fronius inverters
  3. Okay, I’ve written the word Fronius so many times it’s starting to get weird.  Now whenever I try to say the word “pony” it comes out as “froni”.
  4. Finn informs me that engineers like to call the use of a relay ‘Bang Bang control’ as opposed to the more precise ‘proportional control’ employed by a diverter
  5. It takes 4.1868 joules to raise the temperature of 1 gram of water by 1 degree.  125 liters is 125,000 grams of water and 1 kilowatt-hour of electricity supplies 3.6 megajoules of heat.
  6. Unfortunately, it is not permitted to have a solar hot water system that is attached to a relay to also be on a controlled tariff.
  7. I hope People Energy is like people using treadmills and not just straight biomass.
About Ronald Brakels

Many years ago now, Ronald Brakels was born in Toowoomba. He first rose to international prominence when his township took up a collection to send him to Japan, which was the furthest they could manage with the money they raised. He became passionately interested in environmental matters upon his return to Australia when the local Mayor met him at the airport and explained it was far too dangerous for him to return to Toowoomba on account of climate change and mutant attack goats. Ronald then moved to a property in the Adelaide Hills where he now lives with his horse, Tonto 23.


  1. I disagree with the proposal and the effectiveness. I am in Western Australia, and, for the past (about) 20 years, in order to 1) replace the bodgy water heating systems that were here when we bought this house (two solar water heaters – one of which leaked through the roof – and a wetback on a box fireplace that smoked out the house when a fire was lit in it, and, an instantaneous gas fuelled water heater, all at low water pressure, using those copper pipe gooseneck things), and 2) to make the water heating more efficient and environmentally friendly, have been using a water heating system designed by me.We have a large solar water heater with an electric booster element (which virtually never gets turned on), and the water outlet from that, feeds in to a large gas storage water heater. Valves allow both water heaters to be bypassed, should they need to be disconnected/replaced, as has happened over the years. I believe that such a water heating system is more efficient, and more cost-effective, than what is proposed in the article. Between about September/October and March, the sun provides our hot water heating. I believe that surplus electricity generated by a photovoltaic system, is better directed to battery storage (when we can afford it), especially with the unstable electricity supply that we have here.

    • Yeap I agree. I have a solar hotwater system and as above from about Sept -April the sun heats my water. And the rest of the time gas booster if needed. If I have to switch to elecrtic booster I would consider an effcient heat pump system together with solar hotwater.

  2. Aaron Murphy says:

    Can an existing hot water system be retrofitted with a smaller element, or can the element be cheaply turned down?
    Ours has a 3.6kW element and wreaks havoc as we have a timer on it and it only runs from 11am to 2pm every day. When the hot water system is on, we can’t run anything else other than the idle house load otherwise we draw from the grid.

    • Hi Aaron,

      I’ll find out what your options are for replacing the element with a smaller one.

      But a good solution for people with big elements is the hot water diverter that uses power electronics to power an element from 0-100%, so you can get your element to only use the surplus solar whether it is a few hundred watts or a few kilowatts. We should have that post ready next week along with a comparison table of the different devices available in Australia that achieve this.

      • Natalie H says:

        I am following this intently also as we also have a large hotwater service with a 3.6kW element, but we have not yet installled our solar system. Any advice on how to best not draw power from the grid would be great!

        • Ronald Brakels says:

          You may be interested in solar hot water diverter and I will write about them soon. A diverter can take surplus solar electricity that is less than 3.6 kilowatts and feed it to your hot water element in little 3.6 kilowatt chunks, so you can heat water without drawing grid electricity. But, using the money to get a larger solar system or invest in energy efficiency may be more cost effective than getting a diverter at the moment.

        • Mark Archos says:

          Hi Natalie, if you have a rheem, I know you can retrofit a 2400W heater. I have the exact setup that Ronald is writing about, works a treat, 6.6 kw of panels & a 5 kw inverter. Mark A QLD

          • Natalie H says:

            Hi Mark,
            I have a thermann water heater. Do you know if that option is available for them too?

      • Aaron Murphy says:

        Thank you Finn, I will look into a hot water diverter, but I have heard they are expensive.

  3. Thanks for a great article Ron.
    Can the same approach be applied for those considering installing a hydronic water heating system for their house? (ie. using excess elec from Solar PV panels to heat hydronic radiators instead of potable hot water). My question is mainly in relation to the energy requirements rather than the logic of the approach. Not many people seem to have gone down this path at least here in Melbourne which surprises me – perhaps b/c energy requirements for hydronic are generally too high relative to avail. solar PV energy in winter without a huge system (or high cost of a heat pump). But that’s what I’m hoping to do.

    • Ronald Brakels says:

      Floor heating, hydronic or dry, could be an excellent use of Fronius relay. However, since heating won’t be used all the year and solar output is lower in winter, many people may decide a controlled tariff would be a cheaper option, depending on their circumstances.

      I think a major reason why floor heating hasn’t caught on is because if the floor isn’t insulated, as they generally aren’t here, the ground can suck out the heat fast, resulting in high energy consumption. This makes it difficult to retrofit floor heating in an existing home.

  4. Hi Finn,
    Great post. Got a quote from one of the 3 installers you recommended. Looking at 12 x Trina 270W Honey panels + Fronius Primo 3.0-1 inverter. I asked about the smart meter to which they replied they can install, but it would require the purchase of the DataManager. I thought the inverters came with the data manager installed?

    Just waiting on clarification from them, but are there two versions of inverter?

    In Tasmania this is a bit easier, looking at ToU tariff in conjunction with hot water timer to turn on during daylight off peak hours when power is cheap, that way my hot water can utilize a portion of my solar, even if generation is under my element size as it’s all one tariff for power/heat.


    • Ronald Brakels says:

      Hello Hayden.

      Ronald here.

      I believe I made a bad mistake writing the article. Because of the information in the Fronius brochure:

      “Thanks to the integrated Fronius Datamanager, our inverters offer a communication package with fully integrated datalogging, WLAN, Ethernet, energy management, a web server and a range of interfaces as standard. For you, this means no additional components and no hidden extra costs; simply a complete solution.”

      I thought Fronius inverters now came with the datamanager, but this does not appear to be the case in Australia.

      The people I spoke to about the Fronius relay and smart meter didn’t mention the datamanager, but then I didn’t ask.

      I have updated the article, and I will double check what the situation is on Monday.

      • Thanks Ronald.
        Seems strange. why would Fronius not include the Datamanager in the Australian models? The documentation online is very ambiguous… says it is standard in the inverters. Anyway, please let us know how you go, the company quoting me might be correct.

        • Ronald Brakels says:

          Hi Hayden,

          I have some good news and I have some bad news.

          It turns out that most Fronius inverters come with the datamanager already installed.

          Unfortunately, there are “light” versions that don’t have it. It appears the one you have been quoted for is a light version.

          The reason why your quoted inverter might be light is because it is only a 3 kilowatt inverter. Provided you have the space on your roof, you may be better off spending the cost of the datamanager, relay, and smart meter on expanding the size of your solar system. Unless you are normally out of the house during the day and only have a 1.8 kilowatt element in your hot water system, you are likely to still be forced to use a considerable amount of grid electricity for hot water, especially in winter.

          A hot water diverter is another option, and I’ll soon have an article or two up about them.

          • Thanks Ronald,
            Once the company gets back to me, I’ll ask them about my options. Perhaps the 4kW or 5kW has the module for not that much more? Either way I wanted the smart meter so I can monitor household consumption in realtime, along with production. We are out during the day, but were going to schedule things to run during this time – heat pump, hot water on timer etc and move to a ToU tariff.

            We have a 2.4kW element.

            Cheers thanks for the info

  5. Mark Archos says:

    Natalie, from what I have found on the web, yes there are 3 units available,1800,2400 and the 3600, dux tells me they are interchangeable.Get your solar guy to fit it while he’s there.

  6. Chris Winter says:

    The castle up there is not fake Austrian, and it’s not this one It’s which is highly Austrian indeed. 🙂

    • Ronald Brakels says:

      Thank you very much for that Chris. Clearly I got my castles confused. It’s embarrassing because I have been there, but it’s just a hazy memory of endless chicken dinners and gunshots.

  7. Andy Webster says:

    So many variables and permutations that confusion can easily reign! (it might be early dementia)

    I recently installed 6.6kW of panels and a 5kW Fronius Primo inverter (which I was told is the ‘international’ version of that inverter)..

    Does the Primo I.V. have the abovementioned data manager?

    I shelled out the extra few hundred for the Fronius smart meter, not really knowing why I should at the time, but I’m glad I least..I think I am..

    The relay was never pitched to me… but seems a good idea.. (I was going replace our leaking Saxon HWS with an Apricus , but my wife had a new electric storage system installed while I was at work! )
    Being able to use the Solar PV to ‘superheat’ the tank in the daytime seems wise.
    I always wondered why you cant have say, a solar WHS that will heat up to 90*C+ in the daytime, but wont kick in the element at night unless it gets below a set-point or unless manually activated. I’d like to do this with my electric HWS & PV system. Legionella wont be an issue at lower temps as it will be ‘pasteurised’ daily.

    • Ronald Brakels says:

      Hello Andy.

      There are versions of Fronius inverters called “Fronius light” that don’t have datamanagers, but I would say your new 5 kilowatt inverter probably has one. With 6.6 kilowatts of panels it’s likely you will be able to mostly power your hot water system with solar electricity. The smaller the element, the easier this will be, but even if has a large 4.8 kilowatt element, I think you’d probably be able to mostly power it with solar electricity on clear and partly cloudy days.

  8. Regarding the post by Andy Webster, timestamped 2017-08-30:1725,

    1, Pasteurised involves being heated to a specified temperature, and then being cooled rapidly to a specified temperature, not just being heated to a particular temperature. Whilst being heated to a particular temperature can seemingly kill most bacteria, and, whilst I do not know whether the same test applies now to milk produced for human consumption, I know that. some years ago, milk was tested for thermoduric bacteria, with counts being done of the number of thermoduric bacteria surviving extreme heat. So, don’t be fooled into thinking that, simply because water is heated to a particular temperature, it is completely fee of harmful bacteria – it is simply, more likely to have less harmful bacteria.

    2. Regarding your text “I always wondered why you cant have say, a solar WHS that will heat up to 90*C+ in the daytime, but wont kick in the element at night unless it gets below a set-point or unless manually activated.”, after we bought and moved into this house, and found the electrical wiring to be unsafe (unfortunately, electrical work by electrical contractors, is not properly regulated), with the substantial rewiring that was needed, I got the outside fuse board replaced by an inside circuit breaker board, and thence, the electrical booster element for the solar water heater, has its own circuit breaker, which means a convenient on/off switch for the solar water heater electrical booster element.All households should have circuit breaker boards (inside the house), rather than fuse boards, for many reasons, and, this convenience, is only one of the many advantages. In a built up area (city or town), household security is improved by having an inside circuit breaker board, rather than an outside fuse board, and, with circuit breakers, frantic searches for the correct fuse wire (incorrect fuse wire can cause fatal house fires), are eliminated.

    3. With your system, and, the capital expenditure involved, why do you not have a system like our one that I described, involving a large solar water heater system, with its own storage tank (as part of that system) with the booster turned off, and, the water output from that, feeding into a large storage water heater, which the fuel source heats only when the solar water heater output is not sufficiently hot?

  9. Hi Andy,the 5kw primo international does have a data manager, if it’s a brand new system, give your installer a few days to send you the link,(solar web, all the history and tools you’ll ever need ), as well, you have the smart meter which can be accessed directly through your router, it updates every three seconds and allows you to adjust all the settings. Connect your.water system, change down to a 2.4kw element, will run a treat, as mine does. Your installer should have walked you through all this, ringem up.

  10. Hi,
    I have a instantaneous hw service but it takes too long for the hot water to reach the kitchen tab. I was thinking to install a 50 ltr electric HW service near the tap and run it with a timer over my 5 kw solar. Can I just use one of those plug in timers?Thanks

    • Ronald Brakels says:

      Hello Rudi.

      You can get a 50 litre hot water system with a 1.8 or 2.4 kilowatt element that can be plugged into a normal power point, so you could just use it with a normal plug in timer. The smaller element is less likely to use solar electricity when it is on and if you get one with a 2.4 kilowatt element, you won’t be able to run anything else off that power point when the hot water element is on.

      In addition to 50 litre systems, 25 litre ones are also available. It will take 17 minutes for a 1.8 kilowatt element to heat 25 liters of water from 20 degrees to 60 degrees and 33 minutes for 50 litres.

      I think in all states new storage hot water systems must now have a tempering valve, so the cost will be more than it was. (But well worth it if it prevents a nasty burn.)

  11. South Australia

    Speaking to a few solar installers in SA, it may be possible to have the Fronius Primo Inverter divert surplus PV during the day and have it still attached to Controlled Tariff to switch on at night for re-heating.

  12. Hi,

    I’m a little confused – is the Fronius Smart Meter a substitute for the smart meter required to be installed so the energy supplier knows what to charge (or pay for FiT) or is it additional and possibly already inside the Primo inverter?

    • Ronald Brakels says:

      Hi Brett

      The Fronius Smart Meter will work as your household electricity meter.

      Here is the Fronius page on it with its specifications:

      Update: Apparently it doesn’t act as a household electricity meter.

      • Thanks Ronald,

        I currently have a Controlled Load 1 for HWH and a Peak Load for everything else. These are old meters and about to get changed for my new installed PV system with Fronius Primo inverter.

        I assume my inverter is on the peak load circuit. Could you describe how the smart meter(s?) fit into that arrangement to achieve sending surplus to the HWH on the controlled load circuit?

        I asked my sparky these questions, but he has no idea about the Fronius gear…

        Thanks **enormously** for your advice!!

        • Ronald Brakels says:

          Hello Brett

          Generally you can’t put a relay on a hot water system that is on a controlled load tariff, although it may depend on where you are. It is forbidden in Queensland. I know that.

          If you have a Fronius datamanager, smart meter, and a relay connected to your hot water system, the smart meter will say, “Hey! We’re exporting 3.6 kilowatts of solar electricity. You can turn on the hot water system now.” And the relay will say, “Okay,” and turn it on. Later, when the solar surplus falls below 3.6 kilowatts, the smart meter will tell the relay to turn it off.

          That’s assuming the hot water system has a 3.6 kilowatt element.

          One thing you should do before you go ahead is compare your controlled load tariff and your feed-in tariff. There is no economic point to not using a controlled load for hot water if your feed-in tariff is the same or greater than what you pay for the controlled tariff.

          • Ok, thanks for describing that. It seems I need to know whether the use of a relay is permissible in NSW to pull the tank onto the peak circuit (assuming single element).

            After that I’m sure there’s some serious maths to around this to determine whether it’s worth the cost vs. trying to discipline my kids to use less hot water 🙂

      • By the way, I realise that the controlled load 1 rates are pretty close to the FiT rates I would get back. The negligible saving is not the reason I want this arrangement.

        CL1 is only overnight, so having an extra boost during the day from the PV system guards against running out of hot water at the end of the day, i.e. when my kids have used it all up and I want a shower!

        • Ronald Brakels says:

          Ah, right! I just mentioned this in my last comment. You could try just hitting the boost button. That’s not a very elegant solution though.

          • Boost button – is that implying I need a dual element tank? I’m about to get a new tank, so wiring the 2nd element into the peak load circuit could take advantage of the surplus as is needed.

          • Ronald Brakels says:

            The boost button will turn a on a hot water system that’s on a controlled load tariff for two hours and you will be charged for the electricity it uses at the standard rate. They might not exist everywhere, but in Queensland it is on my parents’ electricity meter and you just hold it down for a few seconds. (Or that’s what you are supposed to do. It’s never been used.) With a 3.6 kilowatt element it will raise the temperature of the water in a 250 liter tank by 24 degrees and if you pay 30 cents a kilowatt-hour it will cost $2.16. As you can see, if you use it all the time, the cost will soon add up, but if you only need to do it rarely it might be an acceptable approach. (Because hot water rises to the top of the storage tank you won’t need to wait 2 hours to take a shower, but you will need to wait.)

            Things you might want to consider is washing clothes with cold water and installing water conserving shower heads, if you haven’t taken these steps already. If you don’t have low flow shower heads, simply replacing them could be your cheapest option.

          • Thanks again Ronald, very good info.

            I don’t see a boost button option on the Fronius Smart Meter. If that’s right, I think the no-relay-over-CL-connected-HWH options are:

            1) A boost button on a Controlled Load 1 meter. Although the boost is drawing peak rates, this is cheapest if only very occasionally needed and is a little inconvenient to have to wait an hour or so for reasonable heating, OR

            2) As per 1) but on Controlled Load 2. This adds about ~$120 more per year (based on my historical 4800 kWH usage per year and has much less chance of needing to push the boost button, OR

            3) A dual element tank, lower element on CL1 or 2, upper element on Peak. This adds about $300 more outlay for tank and $100 for an additional peak circuit to tank location and higher running costs, but no chance of running out, OR

            4) As per 3) but with a Fronius setup to pull only surplus PV output to the upper element when needed. This ensures peak time heating on demand at *potentially* only FiT rate, so same as 2) but cheaper operationally.

            Hope I got that right! Who knew it would be like rocket surgery…

        • Ronald Brakels says:

          Brett, you may want to give the water saving discs I mention in the latest article a go:

          They might give you a fighting chance of having a hot shower.

          • Great article, very practical. I may be a sadist but I’m not a masochist, so a timer that only i can override might work 🙂

    • Hi Brett, I think you guys have your wires crossed, the fronius smart meter is not a substitute for you normal meters. Fronius should have called it, a programmable module with some smarts included. You will end up with both in your meter box, if you take the smart meter option.

      The other thing which you may not be aware of, rather than trying to make heating water so complicated, two circuits, two tariffs and two elements, the smart meter comes with a simple override switch on the board. Just don’t forget to turn it off afterwards. PS Buy a large storage system, they are not much more expensive, and all problems solved.

      • Ronald Brakels says:

        Thanks for that, Mark.

      • Thanks Mark.

        re: “not a substitute for normal meters”

        So if I understand you correctly, the diagram that is in Fronius manual (adapted to include a bath and duck at the start of this article) is then misleading? It should have another FiT meter between the Fronius meter and the grid?

  13. Hi Brett, it’s a simple diagram, yes your ausgrid meters would go on the right hand side of the smart meter in that diagram, to measure both incoming and outgoing power. As well as having an override switch (to manually kick in your hot water system) mounted in your fuse box (breaker box) the smart meter also has inside it, an intelligent time clock with user adjustable parameters, this little thing (and it is tiny, only two circuit breakers wide, single phase) was designed by engineers who understand all this stuff. Explaining how the intelligent timer works is an entire article in itself.

    • Ok thanks.

      So for *manually* rectifying running out, does the override switch
      1) enable power to flow from the grid on the CL1 circuit to the HWH at any time, OR
      2) change the HWH from the CL1 circuit to the peak circuit?

      I would have thought that 1) is illegal.

      In any case, if I want *automatic* handling of a low hot water occasion, I need a dual element tank, lower on CL & upper on peak. This seems true whether I use the Fronius smart meter or I don’t.

      Let me know if that’s dodgy thinking 🙂

      • Brett, when I got my system just on a year ago,( through this site ) I dumped CL1 and CL2, didn’t need them anymore, pool runs during the day for free, have not ever run out of hot water, the smart time clock works well, it took over three or four times in poor sun. Without knowing you or how many are in your clan, it sounds to me that, A, your hot water system is too small for the number of people in your home, or B, you have too many people for your HWS. That’s easy fixed, sell one of your children!! No only joking. Brett, mate, your over thinking this, this is the twenty first century, people don’t keep running out of hot water all the time, they buy a bigger system. It’s not like you can have too much storage, especially if it’s running on solar for free. I think you need to consult with a solar expert as I did, hi Nicole. Just remember, buying solar is not like buying a car or fridge, it’s a twenty year deal, get what you need to do the job once, properly. I fear too many people look back six months later and say to them selves, if only I had —— oversized.
        PS just got my winter power bill $8.11c.Outrageous. I do have an all gas kitchen and live in QLD.

        • Thanks Mark – I’m trying to understand the dynamics of it.

          One important closing point: Your cost for winter hot water was not $8.11c. Every kilowatt hour you sent to your HWH instead of the grid cost you your FiT … that’s not over thinking it – they are real dollars you didn’t get and your oversized tank only means that it cost you even more. Likewise, the pool doesn’t run “for free” either.

          That’s why the CL1 load makes enormous sense when its rate about the same as the FiT. It’s an insurance against both running out and paying more.

          • Brett,
            my electricity providers pricing in Qld may be a little different to where you are. My rates are : full time T11 33c
            off peak T33 30.8c
            night rate T31 27.6c
            feed in T40 16c
            Why would I feed into the grid @16c and pay either 27.6 or 30.8c a unit to heat water or run other heavy users of power, pool, air con? and yes it is legal in Qld to use off peak on air con as long as it’s wired in and each on it’s own circuit. But I’ve moved on now, as I wrote earlier, all I use now is T11 & T40 .
            Every home has different needs and different possibilities.
            The $8.11 bill is not for my hot water, that’s my full electricity bill for the three months of winter.

            google CLIShin244Ener1498831200 <–copy & paste works

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