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.

Here’s a schematic from Fronius for the technically minded:

Update 21st August:  I have learned that while most Fronius inverters come with datamanagers 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 to 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 and is a contact that needs to be connected to a second, third-party relay that is rated to switch your hot water element.
  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

Joining SolarQuotes in 2015, Ronald has a knack for reading those tediously long documents put out by solar manufacturers and translating their contents into something consumers might find interesting. Master of heavily researched deep-dive blog posts, his relentless consumer advocacy has ruffled more than a few manufacturer's feathers over the years. Read Ronald's full bio.


  1. Bret Busby says

    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.

    • Finn Peacock says

      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.

      • 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

          • 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. Bret Busby says

    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

  14. Tom Martin says

    I am interested in connecting the Fronius relay to electric HW heat pump. Will it work with any heat pump? Where do the wires from the Fronius relay connect to in the heat pump?
    Thanks for the great article!

  15. Hi Tom, Ronald, the heat pump is not actually connected to the inverter, nor is it connected to the fronius relay. The diagram is a bit simplistic.The fronius relay is a switching relay,(low power only) it receives information from the inverter, and then controls a power relay (15 or 20 amps) (also installed into your box) this is what your heat pump is connected to, a little relay controlling a big relay, then through a dedicated circuit breaker. If you are doing this setup, make sure your electrician sets up the “load management page” properly for a heat pump. Minimum “on” time should be at least 15 minutes, heat pumps don’t like turning on and off 15 or 20 times an hour, think cloudy day and a breeze. Then there is the time clock to think about too, don’t set it too late in the afternoon. Tell me how you go.

  16. Ken Young says

    Hi Ronald,

    I am about to install a Fronius Primo 5Kw single phase Inverter (5.0-1AUS) and a Fronius Smart Meter (63A-1), along with 6.6Kw of Solar Panels. Could you please advise:-

    That this inverter is not designated as a light version and therefore has the Data Manager included in the Inverter or, how I can confirm that it is not the light version?relay

    Can I add a Fronius Energy Management Relay as mentioned in this article to my new system when installed, even though I have no immediate use for it as currently I have a Rinnai instantaneous natural gas booster on my Solar hot water system or, should I wait until I change over to an electric hot water booster before installing this Relay?

    Thanks for the great Blog.

    • Ronald Brakels says

      Hello Ken

      Looking at what is being sold, as far as I can seel, the Fronius Primo 5 kilowatt inverter comes with the datamanager. But it would still be best to check with whoever you are buying it from that it comes with the datamanager. For inverters where there is an option of buying an inverter without the datamanager they tend to be roughly $170 cheaper without.

      There is no reason why you cannot add an energy management relay for future use. I don’t see an advantage in getting it before you are ready to use it as you will need someone to do the installation anyway and they may as well put it in then.

    • Ronald Brakels says


      Mark has pointed out below the Fronius 5.0-1AUS is only a 4.6 kilowatt inverter and so can only have a maximum of 6.118 kilowatts of solar panels. There is a basically identical inverter, the Fronius 5.0-1 without the AUS which is 5 kilowatts and approved for use in Australia. It is sold in Australia, but not everyone might stock them.

  17. Hi Ken, Ronald, how’s the horse ?
    The inverter that you are talking about (5.0-1AUS) is not rated for the number of panels you want to install, it’s too small, as it is only rated to 4600 watts, not the 5000 you think it is !!, check the specs. Go to the 5.0 international instead, and it has the data manager as well.

    • Ronald Brakels says

      Good catch, Mark! Thank you.

      I’m afraid my horse may be feeling a little depressed. He’s pretty long in the face.

  18. Greg Hudson says

    The wiring note to installers is probably wrong…
    It says not to wire up the bathtub because the duck will die, but the duck is probably rubber, and is insulated from the electricity 😉

  19. Hi

    If i have gas hot water and no real need or want to change to storage IS a FRONIUS smart meter a waste of money and one better of to just use the supplied Data manager to monitor power use/ exported ?

    Installing a system this month with Fronius Primo inverter so only cost is the smart meter at $250 if done with installation

    • Ronald Brakels says

      Personally, I would say that if you are not planning to use the Fronius smart meter with a Fronius relay for hot water or another purpose it is not needed. If you were planning to get off gas entirely, then it might be worth considering.

  20. Thank for quick reply Roald

    If the standard suppled monitoring works okay to monitor input/output ill keep the $250

  21. As an aid to those who may be trying to follow the maths in footnote 5, the resulting number is an easier more direct multiplier to use
    ie 1.16 Wh per degree per litre. or if you prefer roughly 1.2.

    eg for the example in the article
    Half of the 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 degrees

    energy required: 1.16 x 125 x (60-10) = 7250Wh or 7.25kWh

    so, time in hours 7.25 / 1.8 = 4.03h

  22. Tony Morrison says

    I’m on the North Coast of NSW (Essential Energy Region) and have a 5.5 Kw solar PV system with a Huawei single phase inverter recently installed . I also have an existing solar HWS electrically boosted on Controlled Load 2, controlled by a ripple controller. I was told during the PV install that it was not possible (illegal) to feed my excess solar to the hotwater electrical boost circuit (ahead/upstream of the ripple controller). As a result during the day I’m exporting my generated power to the grid, while at the same time I’m importing (the same power!!!) at a higher cost to energise the element in my HWS..

    I was told that the only way that I could use my generated solar to power by HWS was remove the HWS from the ripple controlled circuit to the general house hold power circuit.

    Can anyone confirm that this wiring configuration is the norm and in fact the only one that is legal as it seems quite daft? Or do I need some sort of diverter.

    • Ronald Brakels says

      Hi Tony

      I’m afraid that’s my understanding of how it works. The rules are quite strict about how controlled loads can be used. An option would be to put your hot water system on the general household power circuit and put it on a timer so it will switch on in the middle of the day. But because cloudy winter days are when your hot water system will need the most boosting it may end up using a lot of full price grid power as your solar output will be low at these times. As a result it may be best to leave it as it is, but just what is best will depend on what you currently pay for your hot water controlled load, if there are usually people at home during the day using electricity, and the element size of your hot water boost.

      You can get a diverter for your hot water system. Again, you’d have to look at what you are paying for hot water control load and your solar feed-in tariff and decide if the difference between the two is large enough to make it worthwhile. But since it’s for a solar hot water system boost I doubt it would be worth the expense.

      • Tony Morrison says

        thanks for the confirmation, seems daft (or delusional) to be exporting at the same time that I am importing, I’m sure that they are the same electrons given the proximity. I’ll have to think up something clever to overcome this once I have more data on how the system is performing.

  23. Ronald,
    i am in west Australia with a flat rate for imports of 25.75 cents per Kw and a FIT of 7.135 cents per Kw. There are only too of us in the house and we are home most of the day as we are both retired.we have a 80lt storage electric hot water system, which we have just had fitted with a 1200 watt element, it was 3600 watts before, on our roof we have a 6.625 Kw solar system with a 5 Kw Fronius inverter with data manager and a rely for the hot water system.i have just set the dater manager to turn on the hot water rely at 1800 watts and of at 1600 watts with a minimum time of 1 minute run time.i use to track our usage etc and have noticed that in the last 2 weeks since its been installed we have used an average of 4 Kw less per day imported from the Grid, therefor saving us 0.75 cents a day and as the rely cost fitted $220 then in only 9 months or so it will have paid for itself, we did it this way as a smart meter and a power diverter would have cost about 8 times as much and therefor had a payback time longer that the warranty on the diverter, we are very happy with the setup and look forward to see how much it saves us in the next 12 months.

  24. Hi Ronald,this may not be suitable for this site to use,but its a good listen to and so very right in my view about the CURRENT lack of thought about the environment by our government, cheers. Jim Dixon

  25. Hi Ronald,

    Would the Fronius Relay work with a Sanden Eco Heat Pump?

    We are in the process of a new build in Melbourne and looking to work around the VBA requirements for a Gas boosted solar HWS. This requires that the heat pump has no connection to the mains electricity. See details below.


    Do heat pump water heaters comply as a solar option? A: Yes, only under limited conditions. If a reticulated gas supply from a gas company is available for connection to the building, the solar water heater—

    1. Must be a gas boosted solar water heater if it incorporates booster heating and is not a heat pump water heater; and

    2. If it is a heat pump water heater, no part of the heater that is capable of heating water can be connected to the mains electricity supply for that part of the heater to operate.

    • Ronald Brakels says

      Hi Sam

      A Fronius Relay will work with a Sanden Eco Heat Pump, but it would be connected to the mains electricity. But if you have a solar system that will count as a solar option and there should be no need for your head pump hot water system to count as a solar option — as far as I understand.

  26. Hi there,
    I am not sure if this will be a doublt post, I am not sure if my inital post worked.

    I am looking at a new system.

    Ideally I want the fronius primo 8.2kwh with 10+kwh of panels (brands currently being determined by size as trying to make the most of it) and a fronius smart meter and hot water relay.

    My hot water system is 3.6kwh (I just checked).

    I am being told at the moment that the fronius can only take 2 strings, with 14 on each string. We have been trying to work out how people actually get 10+kwh on the 8.2kwh primo (it just does not seem possible).

    Other quotes I have gotten did have the full system of 10+kwh but I cannot tell if those quotes are mistaken? I want to do this right?

    Is it correct we are limited to 14 per string and 2 strings?

    Obviously, I would like the larger system to reduce our power consumption. Hopefully also to power our larger hot water system.

    However if I cannot make this work, I will need to downgrade to the 5kwh fronius with 6.6kwh… This would obviously reduce my outcome, and possibly make the 3.6kwh heating of our hot water pointless because it would never produce enough to do so (and changing it right at this moment will not happen).

    Ideally, I would like the 8kwh with the 10kwh. Do you know how this may be achieved?

    Thank you in advance.

    • Ronald Brakels says

      Hello Stevie

      I’ve had a quick look at the Fronius configurator:

      And it indicates that if 305 watt panels are used then the Fronius Primo 8.2 can only accept a total of 14 panels per MPPT. (An MPPT is a Multiple Power Point Tracker and the inverter has 2.) This allows for an 8.54 kilowatt system. However, it says it can accept 22 of these panels on one MPPT and 11 on the other for a 10.065 kilowatt system. So I suspect those who told you it could only accept a total of 28 panels (14 + 14) simply looked at what it could accept with the same number of panels on each MPPT and were not flexible enough to consider the other options.

      Provided your roof has suitable space you should be able to get about 10 kilowatts of panels in total, but the exact capacity and number of panels will depend on their characteristics and how they can be arranged.

      • Stevie Raines says

        Oh no. Now I’m more confused. I just sent through requesting 11+22… is this the correct thing? 9.9kwh on the 8.2 inverter.

        They’re 300w Seraphim Blades

        • Ronald Brakels says

          Jim Dixon explains it in his comment below. I am not a solar system designer so don’t be certain this is correct, but with 300 watt panels you can have 2 parallel strings of 9 panels connected to each of the Fronius Primo 8.2’s MPPTs. This will come to a total of 36 panels and 10.8 kilowatts of panel capacity, which is very close to the maximum you can have and still receive STCs. This may not suit your roof, so it is possible to change the number of panels connected to each MPPT so long as the DC voltage on the roof doesn’t exceed 600 volts.

  27. Jim Dixon says

    hi in Australia its not about the total amount of watts on the inverter, the 8.2 will take 12.3 kw of panels, its about the fact we have a 600 volt DC limit for installs so you can have have.40 X 305 watts 2 strings of 10 X 2 parallel on each MPPT for 6100 watts and 18 amps. 14 standard panels is very close to the 600 volt limit, so if you have room for them its better to have to sets of parallel strings. as you can only claim for the rebate for 133% of the inverter size you could have too strings of 300 watts of 9 X 2-= 360 volts -=-5400 watts and 18 amps on each MPPT for a total of 10800 watts and 18 amps input. the reason you can only have 14 panels in one string is 14 X 38 v =570 volts. were as in series parallel of 9 X 2 its only 360 volts, well within the inverter specks.

  28. Hi,

    What about solar panels in real time producing 3kw, Fronius dividing (balansing) each phase to grid:
    L1 – 1kw
    L2 – 1kw
    L3 – 1kw
    But the electric heater consumes one phase L1 – 1.5 kW, two phases are supplied to the grid.
    So how to make FRONIUS more efficient and allow the L1 phase to consume all the energy it needs?

    • Ronald Brakels says

      Hi Lorens

      The good news is there is no need as it won’t change the amount of energy electricity meter registers your home as using or exporting and it won’t increase the amount of solar energy generated. So if it could be done it wouldn’t improve your situation.

  29. Dominic Wild says

    Simplest solution is timer and relay to switch H/W in at max. expected feed-in times, cost about $200 + labour.

    Fronius Smartmeter 3-phase: Fleabay cost is about $500, dealers will charge $700-$800 for installation, but no-one will quote for additional H/W connection without site visit. The Smartmeter has CTs (Current Transformers) and works out how much solar production and how much grid use is and minimizes solar feed-in by switching in consumers based on PV-Surplus. What is the payback time??

    Ohmpilot ($1,400 quoted) goes one step further and uses electrickery via PWM to send energy parcels to the consumers. What is the payback time??

    With WA having dropped feed-in to 3c/kWh and upped it to 10c after 3PM, Solarquotes tells me my payback time has been extended now from 3.8 years to 4.6! in my new build I have decided to use my 6.6kW solar with three-phase 5kW Fronius Symo for H/W, but I need your help as I am sure my electrician and I will need to “pool our ignorance” to come up with a solution as he/she may not have connected many H/W systems to a Fronius in WA, so I have a few questions for my proposed solution:

    Have asked builder for a Rinnai H/W tank with 1.8kW element (smallest), as that is best to ask for less but longer time switched on, but they could only supply 2.4kW, sad.

    To save myself the Smartmeter expense and work on PV-Production rather than PV-Surplus, I intend to use the existing Datamanager plug-in card, which is part of Fronius single- and three-phase inverters. It has four digital outputs I/O 0 – I/O 3 to drive relays, but the Datamanager 2.0 manual on page 60 talks of “The output I/O 1 can be used to control an actuator (e.g., relay, contactor) via the “Load Manager” function”; why I/O 1 only?

    Another sketch in a different manual shows an external power supply (10.7 – 24VDC) connected to connection Uint and GND and a load connected to I/O 0, a bit confusing as another manual talks of I/O 1 only. A Finder series 19 relay with a 24V coil and driving up to 16A and giving me Auto/On/Off manual setting seems to be ideal. Auto will switch H/W on at my setting via Energy Manager at a threshold of 2,400W (?) and off at ?W for a duration of ? min ?max minutes and desired duration per day of ? minutes and finish by ? PM. Any suggestions there?

    Fronius is recommending Finder for relays. The Finder relay I found is model 199190244000, series 19 and 24VDC coil giving me 16A, which should be good enough for a 2.4kW element. If the water is still cold in the shower, I must go outside in the nude and switch the relay to ON from Auto.


    1 “When the supply is via an external power supply, the external power supply must be galvanically isolated.” On the DIN rail, a 24VDC transformer will be installed, but what does “galvanically isolated” mean?
    2 Settings – Energy manager allows me also the option “by power surplus (in case of feed-in limits)”. In WA I am limited to 5kW feed-in, does that mean my 6.6kW panels could ever produce more than 5kW, which would go to waste?
    3 “That option can only be selected if a counter has been connected”. What does that mean?
    4 If the grid reaches 256VAC, then my $5,000 system will be switched OFF, so I have always been dreaming of installing a voltage sensing relay to switch my H/W system on to drop the voltage. I would have to watch the voltage in that suburb to see if gets exceeded frequently. Have you thought of doing something like that?
    5 A competitor flogging Huawei inverters is claiming Fronius will soon start charging for the privilege of letting the inverter talk to the web, which you can also see and store. Is there a trick to switch in consumers if feed-in is excessive, similar to IFTTT??

    So many questions, so little time!

    • Dominic Wild ,
      Hi i fitted a relay to my fronius inverter over too years ago,to heat my hot water tank.only a 80lt storage tank so i only fitted a 1200 watt heater element to it, as i have a 6600 watt solar system which would be able to heat the water a mim of 4 hrs per day even during winter,the fronius dater manager with the latest software is capable of running 4 different relays. my system is just a fronius inverter,relay driven by 24 volts DC from the I/O port in the inverter,powering the relay with a manual override switch, the dater manager center has a load management section were, i have set the start watts On–1250– min run time 1 Min and the off watts of 1200,there is also a desired run time per day, and a minimum run time per day—so there is no chance of running out of hot water ever as this last one is in effect a run timer.also you can have any size element fitted to your tank you wish,from 1200 watts up, just because it not the standard fit for the size of tank just means you have to replace the standard one with what size you want.mine has saved me about 4 kwhs per day and also helps to keep the output line voltage down, in WA you can ask to have your inverter output voltage wound up to 258 volts as well, total cost for the rely and fitting was $185 JIm

      • Dominic Wild says

        Thanks Jim Dixon for advice. Looks like your parameters are:

        On 1250 W
        Off 1200 W
        Min. 1 minute
        Max. 4 hrs
        Probably switched off at 5PM or so.

        Four kWhs/day at 28c/kWh is a Dollar/day saving or $365/year. Thanks for the tip of winding up the voltage to 258V. Would Fronius have set it to 256V to stay legal in WA?

        The Finder relay costs about $50, a 24VDC DIN rail power supply is not too expensive, so $185 looks reasonable.

        It is going to be interesting to see if my suburb will sometimes switch my solar off due to over voltage, in that case a voltage sensing relay should trigger other consumers. The web tells me Fronius may start charging for the electricity figures sent to the cloud?

        • HI Dominic Wild,
          a couple of things you have not got quite right, the I/O pins are a 24 volt DC power supply for the relay, nothing else need to power the relay at all.
          the run time on the timer is a Minimum of 4 hrs per day your inverter would have been set in WA at 253 volts only, your electrician can get permission from western power to ramp it up to 258 volts legally. my timer runs from 10 am to 2 pm and i have a max desired run time of 7 hrs per day if there is enough PV output to cover the 1250 watts needed, if you had a 1800 watt element the you would need to add your house base load to the 1800 watts to set your start wattage, my inverter sends data to PVOutput, Jims maxim jinkos 6625. No cloud service needed, fronius inverters wind back output to the grid on high voltage to start with ,not just shut down, volts need to be above 260 for 5 sec i think to trigger a inverter shut down. jim

          • Dominic Wild says

            Thanks Jim for help. Is yours a relay or a contactor as a statement was made here that anything above 4A should be a contactor?

  30. Luke Butters says

    The inverter setup is a little complicated see for how to configure the inverter

  31. James Lockley says

    This is an old blog but I kept finding it while searching for how to setup a Fronius Symo in my quest for “free hot water” and the article and comments are helpful, so let me add my bit.

    As stated, I have a Fronius Symo with smart meter and data manager. This has the load management relay which I wanted to leverage to connect to my Steibel Eltron WWK302.

    This HWS has a heat pump only, there is no element. The compressor is 0.58kW. There are two temperature levels that water can be heated to, one is at 61 degrees. The second temperature setting is 65 degrees, and this is achieved when the compressor is activated by an external signal, in this case supplied by the Fronius load management relay.

    The Fronius load management relay was connected to an external relay that ended up being located inside the HWS and wired up per documentation from both Fronius and Steibel Eltron by my regular electician. The solar installers didn‘t seem interested in this small job.

    The Fronius load management relay was then configured to send a signal with 1kW exported, and turn off at 100W consumed, I set minimum duration of on signal to 1 minute and maximum duration at 720 minutes. I set no desired duration or other setting because if there is no excess solar, the hot water is heated as normal by the heat pump to 61.

    The HWS at 300L produces 520L at 40 degress if the contents are 61, and up towards 600L when at 65. The recharge is for 64% of the 40 degree supply, so the compressor shouldn‘t run until only around 300L of 40 degree water remaining. This should see most days the HWS does not recharge until the next day when initiated by the signal from the Fronius. Then if it doesn’t… no problem, water is heated as normal when required by the compressor.

    Nice and simple, the heat pump is fast enough and we (family of 4) don’t look like running out of hot water. Its great to see we are using more solar.

  32. Is it possible to have the top element on CL1 and the bottom element on general grid power in NSW?
    Also can you legally use a changeover switch to put the aircon on CL2 during the evening and general grid power during the day?

    • Anthony Bennett says

      Hi Chris,

      You’ll need to check but generally controlled load is cheap because the network has control, they don’t like you switching it. As far as I know the Greencatch diverter has a CL and General input so you can better harvest solar and fall back to CL. However the Queenslander’s are the only ones dumb enough to police the antiquated rules.

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