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Hot Water Diversion Update 2023!

Hot Water Timers and Hot Water Diversion has been a topic surrounding solar systems since the option became available. The idea is simple; when installing solar you remove your electric hot water system from your off-peak meter, and instead run it on your main meter – T11 (which is what the solar is connected to) – and time it’s heating to coincide with the solar production hours. This used to be done simply with a hot water timer – the dumb method, but now can be done using an inverter’s “Load Management” function – the smart method. There are other options, but we’ll touch on them in future posts. This post simply aims to cover both methods, and why, as a result of increased feed-in tariffs, Solar hot water timers, and the Fronius Hot water relay, are dead.

I wrote this article way back in 2018, and a lot has changed. I would say hot water diversion – if done right – has made a huge comeback. This is due to three main reasons:

    • Reduced Feed-In Tariffs
    • Single Phase Export Limiting
    • Newer, smarter, cost-effective options

In this updated post I’ll keep the original concept of hot water diversion intact, but the end of the post is where the 2023 update comes in.

The Solar Hot Water Timer

With a hot water timer, installers set the timer up to come on for a set amount of hours during the period when they expect solar production to be at its highest, and when they expect the homeowner will be sending the most power back to the grid. The problem here is, it’s not guaranteed that period will always be the time of highest production due to rain or clouds, and the homeowner may have different usage habits on different days. If the period where the timer flicks on, is not when enough surplus power is being generated, the hot water will be heated from the grid, at the increased T11 rate. In this case, you can often lose money installing timers, hence, the dumb method. Surprisingly, many sales companies in Brisbane are still selling hot water timers as load control. I’ll give an example later in this post of why it’s not an ideal method.


The Fronius Hot Water Relay

Now for the smart method; using the Load Management Function of an inverter. The best one on the market is the Fronius Inverter’s Data manager card connected with a third-party relay. For simplicity, we refer to this as the Hot water Relay, and it’s the method we use (well, used, but I’ll get to that). The way it works is when a Fronius hot water Relay and Fronius Smart Meter are integrated into a solar system, they have the opportunity to smartly decide when the hot water unit turns on. The hot water relay is able to use the information from the smart meter to identify when a system is sending a large excess back to the grid. When that excess exceeds the kW demand of a hot water unit, it tells the hot water unit to switch on. When the excess is under the kW demand of the hot water unit, it turns off and tries again later. Below is a nice example of a hot water relay in action:

A Fronius Relay working well

The green is our solar production, and the filled-in grey is our household load. The large spikes are the hot water unit turning on, and you can clearly see the hot water relay controlling the unit to only turn on when the solar production is at its highest, and when it knows it won’t need to draw from the grid. This is very beneficial on cloudy days, on days that may have morning rain, or basically for any household that has varying day-by-day usage habits. However, the hot water relay, like a hot water timer, still requires excess solar production equal to the full capacity of the hot water unit (meaning a 3.6kW hot water element will require the full 3.6kW of solar production all at once), and as such on rainy days, when the excess is not there, it will need to draw a portion from the grid to ensure the hot water unit receives heating just like a hot water timer.

Below is a good example of the hot water unit working well early, but then it hits a time when it can no longer wait for excess solar production, and it needs to draw from the grid. The unfilled section is bought from the grid at the highest rate ( T11, 27c/kWh) :

Similiar to a hot water timer


Who killed the Fronius hot water relay?

Using a portion of T11  power from the grid used to be fine, as it is far superior to a hot water timer, and even with this occasional draw from the grid at the increased T11 rate, they still made financial sense. A hot water timer may help a hot water unit achieve 50% coverage from solar, while a hot water relay may achieve 70%. They both cost the same, and the hot water relay is actually more reliable. However, as good as relays are, since July 1st 2017, they rarely make financial sense.

Feed in tariffs

On July 1st, 2017, feed-in in tariffs greatly increased, in some cases from 6c per kWh to 14c per kWh, so the math behind hot water diversion becomes more complicated. Below is an example of an Excel spreadsheet calculation of a hot water relay’s payback period on a 6c Feed In Tariff – what it used to be. Most of the values we can read directly from a power bill, but the section we estimate is the percentage of the excess hot water kWh draw that will be covered by the solar + relay combo. In the below case, we estimated the hot water relay will account for 70% of the heating, and the remaining 30% resulting from rainy days, higher base load etc, will need to be drawn from the grid. The calculation importantly takes the feed-in tariff into account, as we have to remember the excess used to heat the hot water unit could have been sent back to the grid for 6c per kWh:

Hot water relay

$34.20 better off a quarter than the off-peak rate, $136.80 better off a year.

However, the calculation becomes worse the higher the feed-in value becomes. Below is the exact same estimate, but calculating off a 14c feed-in Tariff instead (Origins Solar Boost rate as of July 1st 2017):

Solar hot water relay

With a whopping $2.40 a year in savings, you’d have to be a pretty good (corrupt) salesman to convince someone to proceed with this kind of payback period. And just for an extra laugh, let’s look at a timer’s current payback period:

Hot water relay calculations

I’m probably being generous anticipating a hot water timer to cover 50% of the hot water heating, but even if it does exceed expectations to say 60%, you’re nearly always guaranteed to lose money if you install a timer.

Is the Fronius hot water relay dead?

No, I’d say it’s more like semi-retirement.

(Incidentally, its role has been replaced by the Fronius Ohmpilot, but that’s for another post).
But there are still plenty of situations where the Fronius hot water relay may be of use. For example:

    • Feed-in rates are not guaranteed
    • Off-peak rates may increase
    • If you have a 10kW system, your solar may cover more than 70% of the hot water heating.
    • It may not be viable to connect your hot water system to off-peak.

However, it’s still important to have a chat with a solar consultant, work out your household loads and times they’ll come on, run through your bill, and work out if removing an off-peak meter in favour of a relay is worth it. This is what we’re here for, and we’re constantly re-evaluating market changes to ensure when we come out to quote, we are offering the best, up-to-date advice.

Update 14/10/2021 – Solar feed-in tariffs have been dropping lately and so the “Fronius Hot Water Relay” or “Ohm Pilot” is getting closer to being a smart option again. Since feed-in tariffs go up and down all the time, it’s probably still a better choice to keep your hot water on off-peak!

And remember, if anyone tries to sell you a hot water timer, run for the hills.

2023 Updates – Let’s begin the resurrection! 

Reduced Feed-In Tariffs:

Looking through the above article, it’s quite clear to see that the whole idea surrounding the viability of hot water diversion was attached directly to the feed-in tariff. My sums above show 14c feed-in tariffs to discredit hot water diversion, a tariff rate that is quickly becoming a thing of the past. Brisbane is currently seeing an average 3-8c feed-in tariff offer, which when you refer to my first calculation, would result in $138 yearly savings with a hot water relay. So, tariffs are reduced, install relays on every job again, right? Well, not quite…

Cold Showers:

Hot water relays are much smarter than timers when it comes to optimizing your solar energy. However, it’s their smarts that cause their #1 problem – cold showers. One day you could have your hot water system fully heated by 11 am via perfect solar conditions. Then the night-time showers commence, and the hot water system does not heat up because, well, it’s night time and there’s no excess solar generation to pull from. Then the next day it’s cloudy and overcast, and your relay does not kick in hot water heating until its default “emergency heating” parameters are met by 5 pm. This means you have gone for 30 hours of no hot water heating, something few households can withstand. I’m also apparently told if you have any teenage girls, you’ll be hard-pressed to even survive the night!

Cold Shower Fix:

The fix would be to restrict the parameters of the relay to ensure it always heats by 10 am, but then by that point, you might as well go for a simple timer – it’s cheaper and does the same thing. It also has the added benefit of a “boost” function (something absent in the relay) allowing for nighttime heating. However, this nighttime boost will come at the cost of standard electricity rates – 29c – as opposed to the much more attractive off-peak electricity rates of 18c. So if you require frequent nighttime boosts, haven’t you just defeated the point of changing your hot water optimisation?

As you can see, feed-in tariff changes alone do not completely resurrect the hot water timer or hot water relay. On paper, their new calculations look good, but in reality, boosting and cold showers really defeat the purpose. This is where we enter, export limiting.

Export Limiting:

I wrote an article a while back on the grid regulation changes to system sizes on single-phase premises. In short, you can exceed 5kW inverter limits as long as you don’t send any more than 5kWh of solar back at any one time. This means if you have an 8kW system that is producing 8kW, and no loads for the solar to power, it’ll produce and export just 5kW. So in this instance, you would need to have an average load amount of 3kW (8kW minus the 5kW export limit) to financially justify the installation of this 8kW system. Most households since the impact of Covid-19 have been able to do this via more days of working from home, and average solar system sizes have skyrocketed as a result. However staying on topic, export limiting on a single phase has also opened the door for hot water timers and relays. Why not activate hot water heating at precisely the time your system is hitting an export limit of 5kW?

This is huge. Suddenly we’re not talking about feed-in tariffs of 14c, and we’re not even talking about feed-in tariffs of 6c. We’re talking about potentially 0c tariffs. If you export limited to 5kW but have a system capacity generation of 8kW, you’re missing out on 3kW (for multiple hours in the middle of the day) which can easily be soaked by a hot water system. Now, as you might know, I’m a visual kind of guy, so let’s try to explain my excitement with some images:

The above is actually an 8kW system, but export is limited to 5kW. As you can see, the system is unable to reach its full capacity because there is no household load to stop it from reaching the 5kW export cap. The grey section is not allowed to be greater than 5kW due to Energex grid restrictions. Let’s say this household also has an off-peak electric hot water system. They have a 3.6kW element which is heating for roughly 2 hours at night, for the reduced tariff rate of 18c per kWh. That’s $1.29 a day, or $120 a quarter – just for the hot water! Now, let’s pretend we add a hot water timer to this household:

Although the graph is different, it’s important to note this is the exact same system. It’s producing more power because the household has a hot water load coming on in the middle of the day, so our restrictive grey section is able to reach its full capacity of 8kW, as the 5kW limitation has shifted. Once the hot water has reached its desired temperature by 12pm, you’ll notice the system ramps itself down again to adhere to the 5kW export limit requirement again. In this instance, the hot water was completely covered by the solar generation that it otherwise would not have been able to utilise, effectively saving the full $120 per quarter. 

Of course, this is a perfect example for simplicity’s sake. You are going to get rainy days, periods of high usage, etc., so the savings won’t be this consistently high. However, even if we go as far as to halve these savings (as I did in my original hot water efficiency calculations) that’s still $60 savings a quarter, or $240 a year – well above my high-end 2018 example of $136 a year.

It’s important to note the ability to capitalise on export limiting hours must be achieved by a timer, not a relay. A relay, while optimal, uses your solar data for the entire day to maximise the hours it heats up the hot water unit. This means it could be using hours before export limiting has taken effect, or after export limiting has taken effect. Basically, morning or late afternoon. These are the hours you could be exporting for 6-8c. So, the calculations and savings are not as optimal as the hours of export limiting, when the feed-in tariff is effectively 0c. Also, as previously mentioned, the timer has the added benefit of boosting itself for nighttime heating in times of high hot water usage. This is something a relay cannot do. While you’d want to minimise this nighttime heating to increase savings, there is still a lot of leeway in doing so now compared to before, as our savings are looking well above $200 annually. 





The Dilemma

Of course, we enter the dilemma of installing a large size simply for the sake of hot water heating. Why not save money and go smaller? To a size more suited to your other electrical appliances, and retain the off-peak hot water rates? This question has no generic answer, it will vary from household to household. In short, if you have a roof that is easy to increase from 5kW to 8kW~, and therefore the cost to do so is small, then it’s probably a good idea. However, if your roof makes the design from 5kW to 8kW difficult, and therefore extremely costly simply for the sake of covering a hot water load, then it’s probably not a good idea.

Putting it All Together

So now we have export limiting, on top of the reduced feed-in tariffs. I don’t feel one or the other would justify a hot water timer by itself, but combining both together it’s hard to ignore hot water diversion is making a comeback. However, I can’t help but feel the story of hot water diversion is not complete yet. We are forced to install a “dumb” timer to make sure we don’t have cold showers. This dumb timer also has a very limited warranty, which feels disconnected from a high quality system. We’re forced to use it in the hours of export limiting without any room to adapt to your usage habits. Seems a waste of how smart the future is supposed to be. Watching your solar system un-optimally power such a large, expensive load. What if there was a device that could:

    • Turn on when you hit the hours of export limiting
    • Respond to load and weather changes to draw optimally from your solar, and
    • Boost at night to ensure the water stays hot

Well now in 2023, there is – The New Catch Power Relay.

This is the device we’ve been waiting for, and after some testing / financial analysis, we’ve added it to our range, and are installing them on nearly every single phase household that has an electric hot water system. I’d recommend reading this article for more information, or the below video if that’s more your thing:

We acknowledge the landscape for hot water diversion has improved over the years, but it wasn’t until now that we’ve been satisfied with the answer. Export limiting, reduced feed-in tariffs, and now this new Catch Relay, have all come together to provide the answer. Those looking to maximise their solar system, and save even more money on their power bills by optimising one of the largest electrical loads, can now do so. Stay tuned, and as always, feel free to leave any comments below and I’ll be happy to answer.

Ben Neville

Sales Designer / Estimator

MC Electrical


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58 Comments on The Death of Hot Water Timers and the Fronius Hot Water Relay

Ray said :Guest Report 4 months ago

I have 12 kw solar system. My heat pump has just failed after 14 yrs and I replaced it with a std electric hot water system, definatly not as efficient as heat pump, so I need to do something.

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Ian a said :Guest Report 6 months ago

Its time for a smart catch power with a timer as well as restricting hot water diversion to the otherwise wasted pv production above the 5kw limit, add in wifi and some smart home integration as well. So far this stuff is tech from the stone age!

    Devina Rogers said :Guest Report 6 months ago

    Hi Marcus, Mark recently reviewed heat pumps as they use 1/4 of the power an electric tank uses and he found his results surprising:

      Davina2022 said :Guest Report 8 months ago

      Hi Sunny, give us a call on 3268 3836 and our service team will do their best to advise you on your options.

        Devina Rogers said :Guest Report 8 months ago

        Hi Marek, you may find Mark's recent comparison of hot water management options helpful:

          Devina Rogers said :Guest Report 8 months ago

          Sure James, Ben's latest post may provide you with more information and options:

            Devina Rogers said :Guest Report 8 months ago

            Hi Andrew, give our service team a call on 07 3268 3836, and they may be able to advise what may be best based on your solar system's production and consumption levels.

              Devina Rogers said :Guest Report 8 months ago

              Hi Jon, we do Catch Power as an add-on to new solar installations, occasionally as a stand-alone service if we're not too busy. For those smaller jobs, we recommend Julian Saxby from Brisbane Solar Repairs.

                Marcus said :Guest Report one year ago

                We have a 4.8 solar. Hot water heating is hugely excessive cost wise and drains sola batt o/night. 11pm to 7am. On sunny days am now setting boost button to ‘on’ which when element reaches temp max should turn off. Will the boost charge be at peak cost or come from the solar produced ? Any other options you suggest ? We live in the foothills of the Victorian Alps. … (senior pensioners)

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                Jon Douglas said :Guest Report 2 years ago

                Hi Ben - I’m very interested to read your 2022 update regarding hot water diversion. We’re just about to transition to a new power plan with lower FIT and export limits, and consequently we’re keen to make smarter use of our excess power, instead of selling it for 5c/kWh (fir the reasons you’ve outlined). The “Catch Power” product looks like a good solution, so I’m wondering if MC Electrical is able to install one (I noted you’ve advised you’re moving towards install them next year…..)

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                Sunny Phillips said :Guest Report 2 years ago

                Hi Ben, MC Electrical are installing an 7.8KW system(Fronius 6KW inverter) for me in Oct, 2022. I am also moving HW off gas to electric but doing that now. Couple of questions: - HWS comes standard with 3.6KW element. DO you recommend changing down to 1.8 or 2.4KW......plumber said easy to do? - Timer only $200 installed. Catch Power or Fronius Ohmmeter cost vs benefit. Any thoughts? Regards Sunny Phillips

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                Ben Neville said :administrator Report 2 years ago

                Hi Michael, Apologies for the late reply. For something that turns on after house requirements are met, you would need a smart load diversion option. In this instance, I think a Catch Relay would work well, but it all depends on your available excess load, element size, feed in tariff, etc. I would recommend you discuss with your original installer the best device to use based on your individual circumstances.

                  Ben Neville said :administrator Report 2 years ago

                  Hi Terry, In short, timers are lot simpler, and are less likely to cause call back problems for the installer if parameters aren't set correctly. So I can understand why this option is sold by installers, but of course don't agree with it in most circumstances. The conversation has become a lot more complicated since I originally wrote this article, so I'm going to post an update soon - stay tuned!

                    Terry said :Guest Report 2 years ago

                    Hi Ben, great comments and advice however amidst the mountain of information (and misinformation) surrounding solar, for a newcomer like myself, I missed this article (and Finn's) relating to HWS timers. The 'dumb' method of control is still being advocated as the choice over HWS diverters. I bought Fronius (2x5) and therefore bought the SmartMeter with it for export control (and monitoring). I wasn't aware of its Load Management feature and wasn't told about it. I was sold the 'dumb' method for $200, as a better (only) alternative to the more expensive diverters, but came across your write-up (and Finn's and also YouTube by Gold Coast Solar Power Solutions) and am astonished that the Fronius relay was not highlighted or offered at sale. An integrated solution, with full configurability for about the same price. FIT is 6.5c here and with 3.8kW element I'm sure it will more frequently pull grid power as winter comes around. Of course to get this remedied I'll have to pay another $400. Your write-up was fairly comprehensive, and blunt, however if you have anything additional to add I would certainly appreciate it.

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                    Andrew Holden said :Guest Report 3 years ago

                    Hi guys. You installed a 7.8kW system at my house less than two months ago. At the time, we did not make any changes to our current hot water system setup. A large system is on off-peak, and a small system for an ensuite heats on demand. This was acceptable before. However, Energex has now introduced a demand tariff based on your peak usage on any day in a month between 4p and 9p, and charge you that extra amount for the whole month. If the oven and hot water system were used at the same time in the evenings, which is a likely scenario, it could lead to a hefty bill. Does this bring the discussed options in this article back into play in this case? Any suggestions on how to manage this? Thanks. Andrew.

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                    Michael Farrell said :Guest Report 3 years ago

                    I have just signed a contract to instal 8kW Trina Vertex S panels with a Goodwe GW8500-ms inverter. How do I get the hot water heater to turn on when there is surplus power (after house requirements are met) being generated please?

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                    James Hampson said :Guest Report 3 years ago

                    We had the off peak meter removed and timer installed some time ago. It appears that this is a better way. Can you give me more information please.

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                    Mark C said :administrator Report 3 years ago

                    Hi Wayne, sorry for the delayed reply. It probably still isn't worth it if you have your hot water is on off-peak tariff.But you could look into connecting your Fronius inverter to SolarAnalytics for about $130. They have a new feature being released this month where you can upload your power bill and it will tell you the best retailer! Let us know if you'd like to try it out. Or wait a few months and we'll know how well it works.

                      Wayne fletcher said :Guest Report 3 years ago

                      We bought a 6.6kw system with 5kw fronius invertor from you guys back in 2018. I was told back then it wasnt worth conecting up the hotwater smart meter side of things due to the 14c fit rate. Thats now been cut to 8ckw fit Is it worth connecting the smart hotwater meter now that the fit is 8c. Or still not a great idea. The solar works very well and am very happy with it, but do wish we had of gone to a bigger system like say 10kw Regards Wayne

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                      Chris Sharkey said :Guest Report 3 years ago

                      Could someone let me know if it is worthwhile getting a timer and please give me a quote

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                      Marek said :Guest Report 4 years ago

                      Just confirming what the best solution is: 1. Using the data management relay in the Fronius Primo Load Management to switch on a contact for the Hot Water during daylight hours 2. Using the Fronius Ohmpilot and configuring the same as above You get the same results?

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                      Mark C said :administrator Report 4 years ago

                      Hi Michael. It depends where you live but we're still getting 16c with some retailers in QLD. We had a lot of issues with customers running out of hot water with relays. We've gone back to using timers and a contactor with export limited systems - because export limited power gives you zero cents :)

                        Michael said :Guest Report 4 years ago

                        Not sure where you are getting 14c net feed in from. 8c seems to be the "max" these days (and 6c in some cases). I'm still of the view that some kind of HWS relay would be a worthwhile investment for us...assuming it can be integrated into our system (which uses a Sungrow inverter).

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                        DB said :Guest Report 5 years ago

                        I have a 5kw system with 3.6kw hot water element and the Fronius relay works great for me. Of course it's not advised to turn off the minimum hours per day because of legionaries disease. But when you have a hot water element that big, you've generally got a tank that's large - mine is around 300L. It takes several days for it to go cold when switched off. Which means in queensland with the odd rainy day, it's unlikely to ever be an issue. So at my place, using the relay, the hot water system is 95+% solar powered (~+/-5% for clouds that come over whilst heating). Because of the size of the element, it only takes 1hr to heat up if it was heated the day prior, and on the odd rainy day when you don't hit 3.6kw, it might take 2 hrs to heat. Most of the time it gets enough sun throughout the day and wouldn't use the 3 hrs minimum anyway. On the very odd day of total overcast darkness, it waits for the next day. That's my experience anyway

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                        JD said :Guest Report 5 years ago

                        Thanks Ben for your reply to my earlier query re pool heater, that tallies with where my thinking has got to also (but with more technical nous!). I think I'll stick with the timer on the heater (which is separate to the filtration timer) and override it (i.e. switch the heater off) if it looks like it will be a (rare) Queensland sun-free day! And also adjust the timer so it runs at peak solar output times generally.

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                        Ben Neville said :administrator Report 5 years ago

                        Hi JD, Thanks for the kind words. While you could use an appliance relay to regulate a pools' heating and filtering, it's generally more suited to a timing method. The reasoning is the relay parameters are yearly, while the variances in the pool heating and filtering requirements are seasonal (more heating in winter, less in summer, etc.) This means you would need constant parameter changes, depending on the circumstances and time of year. I guess you could manually override the relay during rainy days, but currently there is no automatic feature for this yet. So yes, it's possible, but it's generally not suited to the heating variances of a pool.

                          JD said :Guest Report 5 years ago

                          Hi - great post, and I'm just trawling through all of the various articles on your site - thank you for making this information so clear, and available! I am just getting my head around usage/consumption kWH etc. The main energy usage culprit in my home (most probably) is the swimming pool heat pump which we keep running for c. 6-8hrs/day throughout the (Brisbane) winter (more or less). So my (slightly off topic) question is, is there a relay type system which would switch the pool heater (and its pump) on when there is solar power, but not when it's rainy etc (pool temp is not so critical as a shower, won't be swimming anyway...) Very indulgent, but when the capital outlay on the pool was so much it's nice to get use out of it. Adding PV should help ease the environmental conscience... Thanks!

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                          Mark C said :administrator Report 5 years ago

                          Hi Sheila. It's not a new concept. It's called a solar hot water diverter. SolarHart has just integrated a diverter into the tank. Fronius has one called the "ohm pilot" (i have it at my place) and CatchPower is another brand. It's a great concept as long as the diverter is warranted for at least 5 years, and I'd always buy a stainless steel tank. Work out how much it will save you. (Around about 20cents per kWH x how many kWh you in hot water per quarter. Your solar may only heat 80 percent of your hot water and the rest will draw from the Grid. I would tend to keep the tank and diverter as 2 separate devices and I'd recommend a Catch Power (cheaper) or Fronius (premium).

                            Mark C said :administrator Report 5 years ago

                            Hi Sheila. It's not a new concept. It's called a hot water diverter. SolarHart has just integrated a diverter into the tank. Fronius has one called the "ohm pilot" (i have it at my place) and CatchPower is another brand. It's a great concept as long as it is warranted for at least 5 years. And work out how much it will save you. Around about 20cents per kWH and work out how many kWh you in hot water per quarter. Your solar may only heat 80 per cent of the

                              Sheila Donaldson said :Guest Report 5 years ago

                              Hi Mark, Wondering about your views on the Solahart Powerstore Hot Water system, which as a variable heating element and hence claims it can use any amount of spare PV solar power. Also we are in Ergon territory - current FIT is a measly 7.8 c/ kw. Many thanks Sheila Donaldson

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                              Ben Neville said :administrator Report 5 years ago

                              Hi Edd, One of the setups via the energy manager, is to provide some form of heating regardless of the weather conditions. This means, if you've had a cloudy miserable day and not enough solar excess was found, the relay will still trigger the hot water unit to heat. The graph shows this happening, using solar where it can, and drawing the rest from the grid. This is important to ensure the household still has hot water. An Enphase MicroInverter setup does not have a load management function as far as I'm aware. A catch power would be an ideal solution in this scenario, but more on that in another blog!

                                edd said :Guest Report 5 years ago

                                Hello Ben.... I dont quite get this sentecne "Below is a good example of the hot water unit working well early, but then it hits a time when it can no longer wait for excess solar production, and it needs to draw from the grid", so the SHW will not do as what has been set up through the energy manager ? why will it force to run ? do Enphase Micro Inverter have their own smart relay too ? or they need to pair up with some third party relay Thankyou

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                                Mark C said :administrator Report 5 years ago

                                Hi Sean, I'm not sure, but probably - I've only installed one (at my place). Best to contact Fronius.

                                  Sean said :Guest Report 5 years ago

                                  Is it possible to alter the threshold at which the OhmPilot starts feeding the surplus to its loads ? - I have one, along with an 8kW Primo, and have just installed a Victron grid parallel self consumption ESS system, which is working well - apart from the OhmPilot gradually increasing its diversion, and thus increasing the battery loading. I can alter the point at which the Victron ESS starts feeding from the battery, but I cant see if it's possible with the OhmPilot - anyone offer any wise words ?

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                                  Mark C said :administrator Report 6 years ago

                                  Hi Chris. I have the Fronius ohm pilot at my place. Not only is it expensive to purchase, but it is also expensive to install if your hot water is remote from your switchboard. We had ours connected wirelessly and had some issues so I hardwired the ohm pilot back to the smart meter. Once it is working, it is a great product - rock solid. I can't see the economics working out in most cases.

                                    Chris N said :Guest Report 6 years ago

                                    Are you able to give any update on the OhmPilot and temperature sensor you mentioned in your blog? It is certainly a more costly addition than a "smart" relay, but it maximises usage even on cloudy or rainy days or even early/late hours of the day.

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                                    Ben Neville said :administrator Report 6 years ago

                                    Hi Quido, I believe we are on the same page here. Timer and Relays do not "ramp up" depending on the spare capacity, they require solar + grid equal to the full capacity of the hot water unit. Your Sunmate is different technology, similar to the Ohmpilot or Catchpower (a blog for another day). Because of this type of technology, your hot water diversion is able to cover a higher % of hot water heating, and therefore make more financial sense. You are also in a State with a favourable FiT to off peak ratio, where here in Brisbane the FiT equals the off peak rate - making no financial sense even with 100% hot water coverage.

                                      Quido said :Guest Report 6 years ago

                                      Forgot to say I've got 7.8kW of panels on a 6kW inverter which is probably the minimum right size for the 100% diversion-powered HWS scenario to be viable incl. winter months. But a smaller system could still do it at say 90% with minimum grid topups during consecutive cloudy winter days.

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                                      Quido said :Guest Report 6 years ago

                                      The misleading failure of this article is that it calls the Fronius relay 'smart' and that it assumes that under the diversion smart scenario the "excess solar production [must] equal to the full capacity of the hot water unit (meaning a 3.6kW hot water element will require the full 3.6kW of solar production all at once),". In have had an AustralianWindAndSolar Sunmate 2.0 diverter installed for 2 years on a 3.6kw heater with 315L capacity (young family of 4) and never had to boost from grid import, i.e. 100% covered by my excess solar production. The diverter has a wireless meter in the meter box and ramps up from 50W to 3600W depending on spare capacity. I understand the Ohmpilot now does the same, 2 years later. So even on a 11c FIT and say 19c off-peak here in VIC I'm still approx. 8c better off diverting into the 16kWh hot water "battery". Diverter cost was around $800.

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                                      Ben Neville said :administrator Report 6 years ago

                                      Hi Dez, Thanks for the kind words. Electric hot water is still viable compared to gas, even if you remove solar from the equation. Only recently we had a councilman out to check the gas mains, and he advised against gas hot water due to the costs alone. Also, if off peak rates rise and your situation deems load diversion viable again, you'll be prepared with an electric hot water system along with a solar system to make the change. So, an off peak electric hot water system is not only cheaper, it gives you more options in the future.

                                        Dez said :Guest Report 6 years ago

                                        These blogs are really very good. I've got a question re solar relays vs gas instant. Given that feedins are up, would electric hot water be viable at all? Would it make more sense to just go a large solar array, export and use credits against gas bill?

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                                        Mark C said :administrator Report 6 years ago

                                        Hi Dave. I'm not a fan of solar hot water. The plumbers I know don't like it for reliability, and that has always been my experience. Either way, my take is that if you use that roof space for another 4 panels, and then gleaning Solar excess with the likes of a Catchpower or Ohmpilot, would not only be cheaper, but it would be making use of 1 reliable type of technology for all your energy needs. (We don't often see booster elements in QLD.)

                                          Ben Neville said :administrator Report 6 years ago

                                          Hi Pete, Just curious why you were looking towards a relay when you already have a solar hot water system? As per my understanding, if there's not enough sun for the solar HWS to heat, then a relay hooked up to an inverter is also not going to find enough excess solar. So any boosting you do will still be from the main tariff regardless of if you have a relay installed or not. I believe you're far better off having the booster connected to a night rate tariff, so if the sun is lacking that day, the night boost will give you the heating you require at a much better rate. I'm unfortunately not sure about the charges to have that work done, might be worth an inquiry with Essential Energy and an electrician. Those are also some hefty supply charges, if you didn't already have solar hot water, a relay in your circumstance would make sense just to avoid paying those charges.

                                            Pete said :Guest Report 6 years ago

                                            Hi Ben, Out of curiosity, how do the numbers stack up with Essential Energy which currently has a 14.85c/day daily supply charge for a controlled load meter. This works out to be $54.75 per year just to have the meter whether it's used or not. I have solar HWS and have the booster on for around 6 months of the year consuming around 1600kWh. The booster is currently connected to a single tariff meter. I don't have solar yet, but are planning on getting a 5kW system in the very near future. I was originally looking at the fronius relay, but I'm not sure now. I assume I can get a controlled load meter, but I'm unsure what the up front cost would be.

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                                            Ben Neville said :administrator Report 6 years ago

                                            Hi Mark, This is something we thought about as soon as the tariff increases came through last year - our existing customers. For those who were installed well prior to the price increases, the relay installations on the old 6c FiT would have paid for themselves by now. You were installed just before the FiT increase, so you fall in that transitional period and would have a combination of both exceptional payback period, and minor payback period. Fortunately in your situation, I can see by your solarweb data you are utilising your relay effectively, even throughout winter. You have a north facing array, with a minimal base load during times when the relay wants to heat. I estimate the relay is saving you $90 a year, based on a 10.6c FiT, a 28c T11 charge, a 18.7c T31 charge, and 500kW hot water usage a quarter. The savings between May - July last year would have been even higher. Going forward we are advising against hot water relays for our customers, unless their situation is ideal and they meet some of the criteria listed in the closing lines of my post.

                                              Mark C said :administrator Report 6 years ago

                                              Hi Sean, if you are talking about Origin's Solar Boost 20c feed-in tariff, then only use a relay if you can not get an off-peak tariff. If you can get an off-peak tariff of around 20c, then use that instead. Then 100 percent of your water will be heated with cheap power. With a "Fronius relay" controlling hot water, you only heat water with solar when there is enough excess solar. On rainy days you revert to using expensive T11 grid power.

                                                Sean said :Guest Report 6 years ago

                                                I don't currently have a PV system but certainly plan to shortly (6.6Kw). I log both my consumption Tariffs with an Efergy and PVOutput (this has been eyeopening and very educational in itself!). The numbers show pretty accurately my smallish HWS costs me 50c daily, $185 yearly including all supply and taxes. Would you recommend the relay if selecting 'Solar Boost' ? P.S. Would love to see more articles like this from people who do this stuff day in day out.

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                                                Mark C said :administrator Report 6 years ago

                                                Hi Sean, Yes, it's about $550 for a single-phase Fronius Smart Meter and relay. Add about $300 if your switchboard is 3 phase. However, in reality, I would always recommend a smart meter anyway. Having consumption monitoring will help you understand your usage patterns and will help size a battery. A single-phase smart meter is about $330 installed. So you are only looking at about $220 to add a relay. It's not so much about the initial outlay, it's just that using low off-peak rates 100% of the time is often better than using 14c solar some of the time.

                                                  Sean said :Guest Report 6 years ago

                                                  So many numbers to crunch. Roughly speaking whats the going rate to install the Fronius Smart Meter + Relay? $5-600ish?

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                                                  Ben Neville said :administrator Report 6 years ago

                                                  Hi Jaime, You have a good size array that should produce well, but being east/west your winter months will yield noticeably less. However, it's lucky you anticipate less daily usage in those months as this is when your array will also be producing the lowest. To keep relay contributions high, my advice would be to closely monitor your system, and make sure any daytime usage habits you have allow a window for your hot water unit to heat completely from the solar. As the blog form isn't the best for calculation formatting, I'm going to e-mail you my calculations so you can play around with a few projections.

                                                    Dave said :Guest Report 6 years ago

                                                    Hi Ben very informative article, however, would it not still be wisest to get Solar Hot Water Installed, as this alone will cull up to 80% of existing hot water heating costs. The smaller (ours are 2.4kw) booster heating elements only activate if required, so, the sun actually does all the work. The 3.6kw draw for Hot Water units is a myth, as most full electric only units have dual elements of 3.6kw or even 4.8kw units. For any more Solar Hot Water questions, please contact me. Cheers Dave BSE

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                                                    Jaime Workman said :Guest Report 6 years ago

                                                    Hi Ben, my array will be E/W with 1/3 of the panels east and 2/3 west. We have changed the design slightly and will increase to 8 kw. My water heater element is 3.6kw. We use about 20kwh during spring and autumn and 35 in winter and summer if we run AC. Our hot water usage ranges from 3 to 5 kwH per day. The water heater is 315 litres. I expect to use about 60% of the power during the day, though the percentage may be 70% in summer and 59% in winter. Thanks for your advice.

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                                                    Mark Blayney said :Guest Report 6 years ago

                                                    Thanks but this article has left me more than a bit confused !? You guys installed my system last May with the Fronius smart meter and I now get an 11 cent feed in tariff with AGL. So should I disable the meter or change the settings or what ?

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                                                    Ben Neville said :administrator Report 6 years ago

                                                    Hi George, thanks for your comment. I think your setup is a case in which a Fronius Relay works perfectly. Your inverter capacity is large enough, and your hot water kW draw is low enough to not be effected as much by rain or high base loads. This is where you could see the relay and smart meter combination account for over 85% of the hot water heating - making it worthwhile. A lot of the data and assumptions we made were based around a 3.6kW element and a 5kW inverter capacity, so my percentages are going to be lower than yours and therefore less financially viable. Happy to hear your setup is removing your bills!

                                                      George Roumeliotis said :Guest Report 6 years ago

                                                      The fronius relay installed here is feeding into a 1.7 kilowatt heater element of our hot water system. The solar system consists of 30 Jinko 270 W panels into 8.1 fronius inverter. By the way maximum p v output often exceeds panel specs 8268 W being the maximum. Our hot water system has been set to activate when there are 1500 Watts of excess and stay on for 30 minutes even if the panels drop below the threshold. End result in our case is that it comes on twice a day and still supplies all the hot water for the house. The panels are arranged in 2 strings of 15 North and 15 West both arrays function almost identical except for the expected bias 2 North in the morning the west in the afternoon. So far hot water and electricity bills have been eliminated. We use under 20kw a day... Not sure of this empirical outburst helps but the fronius smartmeter/relay has been fantastic here.

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                                                      Lindsay Mathieson said :Guest Report 6 years ago

                                                      Nice article, thanks. I bet it makes even less sense when you add batteries to the equation … I think people get obsessed with squeezing every last cent of usage out of their solar, without considering the cost of doing so.

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                                                      Ben Neville said :administrator Report 6 years ago

                                                      Thanks Jaime! Do you have a general idea of how your panels are going to be arranged on your roof? What do you expect your base load to be, and what size is your hot water in terms of it's kW draw? I can calculate your data, but the factors I've mentioned heavily decide the percentage of heating the relay will cover. If you are north facing, have a low base load, and a 2.4kW hot water unit, I'm calculating at least $68 a year savings for you (80% hot water heating covered by the relay). However, if you expect to use a lot of power in the day, have an inferior panel layout, and a 3.6kW element, you could be looking towards only $35 saving a year (70% hot water heating covered by the relay). The percentage of hot water coverage is the main component that influences the calculation, and is important to get right. I can show you my workings if you like, but any extra info you can provide on your base load, hot water capacity and panel layout will be helpful.

                                                        Jaime Workman said :Guest Report 6 years ago

                                                        Well written and thought provoking article. I wonder how those stats figure out for me? I am planning to install 7 kW of solar and use about 3kWh of hot water in summer and 5 in winter so I am well under your sample illustration. Feed in tariff is .10 and economy tariff is .175 and regular tariff is .285. I think in my case the Fronius smart meter with relay would save me a hundred dollars a year or so, but am I figuring correctly? We might lose some export in winter and are limited to 5kwh.

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