Comparing Solar Hot Water Diverters Available In Australia

Update: since publishing this article commenters have made us aware of 2 other hot water diverters on the Australian market, the ‘Dimplex Free-E’ and a unit from SolarEdge. We’ll add these to the comparison table as soon as we have enough info. If you know of any others let us know.

I recently wrote about solar hot water diverters.  These devices use your surplus solar electricity to power your hot water cylinder.

They can cut your electricity bills provided your solar feed-in tariff is less than the cost of the grid electricity used to heat your water — which is not always the case.

I am going to assume you’ve read my earlier article, done your research, and decided a solar hot water diverter is for you.  You’ve either determined it will save you money or it was love at first comprehension of the concept and you’ve realized you can’t live without one.  So the question becomes, which diverter should you choose?

To help you with your decision, here at SolarQuotes, we1 have tried to track down every diverter on sale in Australia. For the ones we’ve found, we’ve researched their retail price and specifications and put the results into our Solar Hot Water Diverter Comparison Table.

Diverter Comparison Table

See details of every solar hot water diverter available in Australia in our new diverter comparison table.



The iBoost Is Not Available In Australia

The iBoost is a diverter from the UK that was marketed in Australia, but has since disappeared and we have been unable to contact the company.  As there is no evidence they have a presence in Australia, they are not included on the table.

About Controlled Load and Economy Tariffs

Devices on controlled load or economy tariffs must be hardwired2. They cannot be connected to any other power source except the controlled load/economy tariff meter.  So a hot water element connected to solar via a diverter cannot also be connected to a controlled load or economy tariff3.

A workaround is to use a dual element hot water system. Connect the upper element to a diverter and the lower element to the controlled load/economy tariff.  The latter is set to a lower temperature than the diverter element. This reduces the amount of grid electricity used to heat the water. But the lower temperature set point should be at least 60 degrees to control the growth of Legionella and other dangerous microorganisms.  20-30% of hot water systems have 2 elements and they are more common in colder areas.

Comparing Diverter Features

The diverter information came from the companies that supply them, or in the case of the Powerdiverter, it was scraped off the internet.  I will go through the details of the four different diverters on the comparison table and see if I can arrive at any firm conclusions about which diverter will  rise triumphant from the solar electric hot water Thunderdome:


Price:  The number of dollarydoos they cost.  Catch Power gives the installed cost of their diverters while the others just give the hardware cost, so you’ll need a separate quote for installation.

If a company claims their diverter only takes minutes to install, don’t get optimistic about the installation cost.  Technically, my beard only took minutes to grow.  While diverters do not need an accredited solar installer, they do need a qualified electrician and so you will probably need to pay at least $200 for installation.  I expect the real cost to be from $250 to $350.

Single Phase or 3 Phase:  Most homes have single phase power, but an increasing number have 3 phase.  If your home has a large ducted air conditioner4 that serves multiple rooms there is a good chance you have 3 phase power.  Three phase diverters are more complex and so cost more.  They also take more effort to connect, increasing the installation cost.

Maximum Heating Element Capacity:  The electrical power diverters send to hot water systems is variable and depends on the amount of surplus solar electricity supplied.  This variable output can only be used for heating elements.  If used with anything that has pumps, motors, or electronics there is a very high risk the magic smoke inside that makes them work will escape5.

The biggest element in a normal household hot water systems is 4.8 kilowatts.  Only two of the four diverters can cope with an element that large, but they can all handle a 3.6 kilowatt element, which is the next step down.

Number of Heating Load Outputs:  Most people will only want to use their diverter for a single hot water system and nothing else.  But if you want to run a second hot water system using the same diverter, or potentially another device with a heating element, such as a bar heater or floor heating, then you’ll want a diverter with two variable heating load outputs.

Sensor Connection:  All diverters have a Current Transformer (CT) sensor  that goes just after the electricity meter to measure when surplus solar is being exported.  This sensor is normally connected by a wire to the diverter, but some can use a wireless link. Handy if your meter box is a long way from your hot water cylinder.

Timer:  If a diverter has a timer it can use off-peak electricity rates to heat water.  This feature won’t save most solar households money, as they are usually better off on a standard tariff, but some solar households may benefit from a time-of-use tariff, especially those with battery storage.

Grid Power Boost:  If a diverter doesn’t receive enough surplus solar electricity to heat water it will boost its temperature using grid electricity.  While all diverters can all be manually boosted with the twist of a knob, they can also ‘intelligently’ choose when to boost.

Special Features:  One diverter offers internet monitoring and takes advantage of weather forecasts to optimise time-of-use tariffs.

Another diverter offers ‘threshold power’ to appliances that don’t mind their power being cut and reconnected multiple times per day (such as a pool pump or hydroponics heater). This feature allows you to configure the diverter with the power draw of the appliance, and only power it when there is both surplus solar, and your hot water is at temperature.

Warranty:  The length of the written warranty.

Hype:  An example of a ridiculous or over the top statement a company has made about their diverter.

Catch Power: Green Catch And Blue Catch

Catch Power Green

Can you guess which Catch Power this is? (Hint: It’s not Catch Power Blue.)

I am going to proceed in alphabetical order.

Catch Power makes 2 diverters, Green and Blue, which are both manufactured in Australia.  The Green Catch is single phase. The fancier Blue Catch has a single phase version and a 3 phase version should come out this month.  The characteristics they have in common are:

Maximum Heating Element Capacity:  4.8 kilowatts6.

Number of Heating Load Outputs:  1

Timer:  Yes.

Warranty:  5 years.

The Catch Power Green

Price:  The installed cost of the Catch Power Green is given as $1,000.

Phases:  Single phase.

Sensor Connection:  Wired.

Grid Power Boost:  The Catch Power Green will boost the hot water system’s temperature for a set period each night.  The time period can be reduced in summer and increased in winter.  It can also adjust the period automatically.

If the hot water system doesn’t reach its maximum temperature for two days will heat the water at night using grid power until it reaches the system’s maximum temperature, which will be at least 60 degrees.  (A common setting is 65 degrees.  Higher than this greatly increases the risk of serious scalding injuries if the system doesn’t have a tempering valve.)  This will prevent dangerous microorganisms such as Legionella from getting a foothold in the tank.

It can also be manually boosted by twisting a knob.

Special Features:  Nope.  It’s just a diverter.  And that’s fine.

The Catch Power Blue

Power Catch Blue

Price:  The installed cost of the Blue Catch is given as $1,700 for the single phase version and $1,950 for the 3 phase version.

Phases:  Single phase or 3 phase.

Sensor Connection:  Wired connection from the meter sensor to the diverter with a wireless connection to its communicator which plugs in to your modem or router.

Grid Power Boost:  The Blue Catch is internet connected and monitors the household’s energy consumption and hot water use.  It receives a weather report at 11pm every night and uses that along with the information it has gathered to intelligently decide how much grid electricity it will need to use to boost the hot water temperature.  It will do this at night so households on time-of-use tariffs can make use of off-peak rates.

Catch Power says they do not know who much more efficient this is that the Green Catch, as they have not had enough time to make a reasonable comparison.

Special Features:  The internet connection allows remote monitoring by Catch Power to detect any problems.

Both the weather forecasting and monitoring are dependent on Catch Power’s servers staying in operation.  The possibility of servers going offline is important to keep in mind when purchasing anything that makes use of the cloud and isn’t a monkey god.

Catch Power’s Warranty Is Catch-22

The Catch Power Green and Blue both come with 5 year warranties.  I will juxtaposition two sentences from their warranty documents to highlight a problem:

A troublesome juxtaposition

Under Australian Consumer Law you are entitled to claim compensation for consequential losses from a product not working as it should if the losses are reasonably foreseeable.

I’m no lawyer, but I would say having to pay an electrician to remove a faulty unit and replace it with a new one is a loss resulting from the failure of the original unit. The resulting cost is very foreseeable by anyone who is even only slightly reasonable.  This makes me believe a consumer would be entitled to compensation for those losses[1. Manufacturers and installers not understanding their obligations under Australian Consumer Law is a problem in the solar (and many other) industries. I will cover this in a future post.].

Catch Power’s Hype

I am going to confine myself to addressing one piece of hype for each diverter and for Catch Power I will stick to one simple statement that strikes me as misleading:

Free Hot Water

Apart from a few exceptions7, no one on-grid can use a diverter to create free hot water.  If a household uses one kilowatt-hour of solar electricity to heat water that kWh is not sent into the grid for a feed-in tariff. The cost of that kWh is equal to the forgone feed-in tariff.  It’s not free.

There are plenty of people in Australia receiving a feed-in tariff higher than their controlled load tariff, these people would lose money.

Claiming a diverter will let you create free hot water from your excess solar power is like your boss claiming she provides free soft drinks at work when she actually deducts $1 from your pay for each can you drink.  You may be happy to pay only $1 a can and think it’s a good deal, but it’s not the same as free.

The Paladin-2

Paladin-2 Diverter

The Paladin-2 is a solar hot water diverter designed and manufactured in New Zealand.  This version is modified for Australian conditions and temperatures.  Unless you live in Tasmania, make sure you have the Australian version.

Price:  $790 uninstalled.

Phases:  Single phase.

Maximum Heating Element Capacity:  4 kilowatts.  In practice this means the largest standard sized heating element it can use is 3.6 kilowatts.

Number of Heating Load Outputs:  1

Sensor Connection:  Wired sensor.

Timer:  No.

Grid Power Boost:  A heat sensor installed at the bottom of the hot water tank tells the the Paladin-2 to use grid electricity to heat water if the temperature falls below 40 degrees.  Because hot water rises, this will result in the water at the outlet being above 40 degrees, which is enough for showering and general use.  (In cold weather the most common shower temperature is 41 degrees.)

If the hot water system doesn’t reach a minimum of 60 degrees for 3 days it will automatically use grid power to boost the temperature to that level to control Legionella and other dangerous microorganisms.

It can also be manually boosted via use of a knob.

Special Features:  The Paladin can be used to control a compatible electric vehicle charger called the JuiceBox. It does this by communicating with the vehicle charger advising it when it can charge. It does not use the diverter output. Any attempt to use variable diverter power that is only suitable for heating elements to charge an electric car would result in a great deal of magical smoke being set free.

Warranty:  Its warranty is the shortest of all the diverters at 2 years.  Hopefully, it will soon be increased to at least match the 5 years of the others.  Paladin says none of their diverters have ever failed.

Hype:  The information provided on the Paladin website is generally well grounded.  This is a pleasant contrast to some of the hyperbolic claims made by other diverter suppliers.

The Powerdiverter

Powerdiverter contacted us and provided lots of information. Unfortunately due to unforeseen circumstances we didn’t receive the information until after the deadline for this post. We’ll update this post to reflect the new information shortly.

Powerdiverter Diverter.

Price:  $900 uninstalled.

Phases:  Single phase.

Maximum Heating Element Capacity:  4.8 kilowatts.

Number of Heating Load Outputs:  1

Sensor Connection:  Wired sensor with wireless option available.

Timer:  Yes.

Grid Power Boost:  Unknown.

Special Features:  None that I know of.

Warranty:  5 years.

The SunMate


The SunMate is a hot water diverter supplied by Australian Wind and Solar.  While the very literal-minded may think a SunMate is a sure way to get plasma burns8, it is a very interesting device because it is the only diverter that can provide 240V AC to devices once surplus solar generation reaches a preset threshold.  This feature is given the somewhat unsurprising name of threshold power.

Price:  $850 uninstalled for the single phase version and $1,250 uninstalled for the 3 phase version.

Phases:  Single phase or 3 phase.

Maximum Heating Element Capacity:  3.6 kilowatts.

Number of Heating Load Outputs:  It has two outputs which can be used as two variable heating load outputs, two threshold power load outputs, or one of each type.

Sensor Connection:  Wired sensor with wireless option available.

Timer:  Yes.

Grid Power Boost:  A timer allows the hot water system temperature to be boosted up to three times a day using grid power.  If it is set to do this in the mid to late afternoon, then provided the system gets to its maximum temperature using solar, it will be unlikely to use grid electricity.  If an optional temperature sensor is installed it can boost with grid electricity until a set temperature is reached.

The SunMate also has a Legionella control function that will raise the temperature of the system to its maximum temperature, which will be at least 60 degrees, to kill potentially dangerous microorganisms every few days.

It can also be manually boosted by turning a knob.

Special Features:  The SunMate has 2 outputs and these can be used to provide variable diverter power to:

  • two heating elements, or
  • ‘threshold power’ to two appliances (that are tolerant of intermittent power), or
  • variable power to one heating element and threshold power to one appliance.

No matter what arrangement is used, the maximum amount of power that can be supplied will total 3.6 kilowatts, although this can be increased to 12 or possibly 16 kilowatts per output using optional hardware.

The ability to provide both variable power and threshold power makes it possible for the SunMate to provide a hot water system with surplus electricity and also a device such as a pool pump.

Warranty:  5 years.

The SunMate warranty states the following:

SunMate Warranty Exceptions

So, “This warranty will not apply” if “The product has been used and maintained according instructions provided by the company.”  I find this really refreshing because it’s the exact opposite of what most warranties want you to do.  But while I would like to believe they are reenvisioning the entire concept of warranties by embracing anarchy, what I think has actually happened is they have just severely under invested in the word “unless” and there is supposed to be one at the start of each of those statements.

The warranty also says that if you want to make a claim, then you have to send them:

SunMate Claim Condition

This makes me wonder what happens if you only send them 4 good quality resolution pictures of the problem.

It also makes me wonder if the unit is prone to failures so dramatic it actually takes at least 5 good quality resolution pictures to convey the full extent of the disaster.

In these days of easy digital photography it is not unreasonable to send a photograph showing any error messages that may be displayed or damage that may be visible, but you are protected by Australian consumer guarantees and companies are not permitted to reject warranty claims because you did not jump through pointless hoops to their satisfaction.

Hype:  I will force myself to only give one example of hyperbole:

My parents in rural Queensland pay 17.4 cents per kilowatt-hour for their hot water system’s economy tariff and their solar feed-in tariff is 10.1 cents.  So in order to save $400 a year they would have to use 5,479 kilowatt-hours a year for heating water.  That is a ridiculous amount.  The average Australian family of 4 only uses around 1,500 kilowatt-hours a year for heating water.  If my parents used that much, a diverter would save them around $110 a year, provided 100% of their water heating was done by solar electricity.

Diverter Thunderdome

A battle royale9 is now beginning in my brain, as I consider all the information and attempt to select an overall champion.

While I can’t actually know which diverters are the best without extended real life testing, based on the information I do have, I think I can pick a couple of winners.

Value For Money

If it is assumed the cost of installation is $300 and you just want to power a hot water system with solar electricity, then the Catch Power Green diverter with an installed cost of $1,000 and a 5 year warranty is the winner.  It also has the advantage of being able to work with the largest standard hot water element.

But if you want to run a device such as a pool pump off ‘threshold power’ in addition to supplying variable diverter power to a hot water system, then provided your hot water system’s element is 3.6 kilowatts or less, you can have that option for only $150 more with the SunMate diverter.  (Or a little more than $150 if the extra work of adding threshold power capability increases the installation cost.)

These two systems appear to offer the best value for money at the moment.  But if you want a 3 phase system, then unless you are a really big fan of online monitoring, the SunMate 3 phase version appears to provide the best value.

My conclusions are subject to change as new information comes to light and I will endeavour to keep you up to date with new diverter developments. If you have real world experience of any of these devices, please let us know in the comments.


  1. I say we, but actually it was Jono.
  2. Pool filters are an exception to the hardwired rule.
  3. QLD explicitly prohibits it. I’ve been told that Tasmania allows it. My interpretation of the rules everywhere else is that it is not allowed.
  4. A refrigeration air conditioner, not an evaporative one.  Swamp coolers are very energy efficient and so even very large ones can get buy with just single phase power.  Their drawback is they need water and aren’t very effective in humid climates.
  5. Some people say electronic devices don’t actually contain magic smoke that makes them work.  But if that is the case, how come no electronic device has ever continued to work after I’ve made smoke come out of it?
  6. The Catch Power diverters can only send a maximum of 4.6 kilowatts to a 4.8 kilowatt element, but this will make no practical difference for the large majority of households.
  7. properties on zero export that are unable to send surplus solar electricity into the grid for a feed-in tariff
  8. As far as I am concerned, what happens between a consenting adult and a five billion year old ball of plasma is no one’s concern.
  9. I’ve never actually seen the Japanese movie Battle Royale, but I did quite enjoy the Japanese movie Howl’s Moving Castle, so maybe I should check it out.

About Ronald Brakels

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


  1. How does the SolarEdge Immersion Heater Controller compare?

  2. Hi Ronald,

    I installed a SunMate on my folks system and they have only had to boost their hot water system once for 2 hours (in dead of winter). The product works very well. They have not had to pay for off-peak grid electricity for 9 months since it was installed.

    It helped maximise the use of their 5kW system and improves their self-use consumption ratio by about 15% in the last 9 months.

    Their off-peak rate is only 6c cheaper than normal rates (Ergon), so it paid to have the hot water power diverter.

    On another note, Dimplex have a product called Free-E. Dimplex RRP is $999 but this could be different at retailers (Turks, L&H, Reece).


    • Just further info on Ergon off-peak rates, it’s now 22.5c/kWh on T33 tariff (1/7/2017 price) (18 hour rate). So, on $400 savings is about 1777kWh of hot water heating required So, that’s not suprising.

      100 litres of hot water to be raised by 45 degrees per day requries about 5.25kWh of energy.
      That at 365 days is about 1900kWh.

      That’s about 2 hot showers per day. Let alone, anything else needing hot water like washing. Plus any heat losses from Hot water.

      So, $400 savings is not really hype.

      • Ronald Brakels says:

        Ergon’s tariff 31 is 17.4 cents a kilowatt-hour and the feed-in tariff is 10.1 cents. So every kilowatt-hour diverted from being sent into the grid to heating water will saving only 7.3 cents. With 1,900 kilowatt-hours annual use that would come to a total saving of $139 provided all their hot water was entirely heated by solar electricity.

        Tariff 33 costs more but is provided for a minimum of 18 hours a day instead of 8, so if tariff 33 is required for the current hot water system to provide adequate hot water then if it put on a diverter it is likely to also need a considerable amount of grid electricity for heating. But even if this hot water system could be entirely solar powered it would only save $236 a year if 1,900 kilowatt-hours of tariff 33 electricity would otherwise have been used.

        While there are definitely families that use over 1,900 kilowatt-hours a year for heating water, most use much less than this, especially in rural Queensland where Ergon operates, so I have no problem describing a claim of $400 of savings from using a solar hot water diverter as being hyperbole at best.

    • Ronald Brakels says:

      I will have to look into the Free-E Dimplex and see what it is like.

  3. I do remember once meeting someone from PowerDiverter who was very much a salesperson… I believe they were a UK company trying to launch in the AU market – but had not really gotten their head around the differences in the AU grid… That would have been at least 2 x years ago – so if they still haven’t gotten the product right and are uncontactable, maybe they gave up!

  4. Hi Ronald,

    How did you calculate 5749kWh on $400 at 17.4c/kWh?

    By my calculation… $400 at 17.4c = 2298kWh required to offset the off-peak tariff rates.

    Granted, that’s a lot of hot water to heat, but that 2298kWh equates to about 120 litres of water per day requiring heating from 20C to 65C. That’s about 12 minutes of hot water running (assuming 10litres/min) but more likely 20+minutes with cold water mixing at tap. Obviously, if the water is colder than 20C, then more energy required to raise the temp. Or, if you wanted 70C water in the tank (definite instant kill for legionella), more energy required again. The hotter water will keep it’s heat retained longer to overcome less sunny days which I set my parents tank to so that cold water coming into the tank doesn’t reduce the temp as quickly if the tank was set to 60 or 65C. (Yes, I know that there is a formula for working out mixing water of diff temps to get final water temp). Getting free energy, so what not use it to raise the water temp a bit higher.
    PS> water tempering valve drops to “50C” mark, so some say it’s wasting energy to heat water to 70C but there are other good reasons for water heating to 70C (if you do not have a solar hot water system). e.g., legionella control and heat retention is longer.

    • Ronald Brakels says:

      Graham, If I have a choice between sending one kilowatt-hour of surplus electricity into the grid for 10.1 cents or diverting it to a hot water system where it will displace 17.4 cents word of tariff 31 grid electricity, then by diverting it to the hot water system I will only come out 7.3 cents ahead. That means to save $400 in a year I would have to divert 5,479 kilowatt-hours.

      My parents, who have tariff 31 in Queensland, used 232 kilowatt-hours over the last quarter which was mostly in winter. Even if they used that much in summer as well it would only come to 928 kilowatt-hours. While there are definitely families that use far more than this, it is definitely not typical.

  5. I would suggest including the Fronius inverter that has a threshold relay. Ok sure it’s not really a “diverter” as such but claims to do exactly the same job. ie heat hot water using excess solar electricity that would oterwise have been fed in to the grid.
    As i understand it you set the relay to operate when feed in/excess solar energy reaches the desired level. Its not clear to me if the relay can work with off peak or controlled load where feed in (excess) has not reached the set point on a particular day.

  6. Hello, this comment is not related to power diverters, as interesting as they are.
    Couldn’t figure out how to write to you directly, so leaving a comment here. Just wondering if you have had a look at Suntenants in Sydney. As a landlord wanting to install pv on the rental, this is an interesting approach. Just wondering what your view is – particularly if considering installing a larger system intended to export most of it output.

    Love your writing style. Adding amusement to an otherwise dry subject!

    • Ronald Brakels says:

      Hello Paul.

      I haven’t looked into SunTenants, but I have written about Matter which sells rooftop solar electricity to tenants:

      Looking at the SunTenants site I am afraid there is not enough information there for me to understand what they do. Since they haven’t given me enough information to form an opinion I’ll ignore them for now. But if you uncover interesting information, please don’t hesitate to inform me.

  7. A suggested small correction – in the above article, is

    Single Phase or 3 Phase: Most homes have single phase power, but an increasing number have 3 phase. If your home has a large ducted air conditioner that serves multiple rooms there is a good chance you have 3 phase power.

    I suggest that the text
    ” If your home has a large ducted air conditioner”
    be corrected, by inserting the word ” refrigerative”, so becoming
    ” If your home has a large ducted refrigerative air conditioner”.

    Reason – we have a large ducted evaporative air conditioner, which does not require three phase electricity supply, and so our house has single phase electricity supply.

  8. Erik Christiansen says:

    Ronald, if the surplus power is fed to a resistive heating element, then it’s no big deal for it to switch in and out as clouds go over, but if there’s a heat pump in between, then there’s the same “starting the compressor on load” problem as with an air conditioner. So I can’t help wondering if any of the (AC output) diverters have a cycle timer to set a minimum off time after cutting out.

    I figure that with a system with battery, I’d be able to bridge a cloud or two with battery power, and the lower heat pump consumption will be much less of an issue.

    • Ronald Brakels says:

      Yep, devices that provide threshold power have various timers that can be set, generally including minimum operating time, delay before turning on after the threshold is reached, and delay in turning off after surplus solar electricity falls below the threshold amount.

  9. David Pearson says:

    I’m in Melbourne. My background is IT technical, and I’m retired. I installed a 4.8 kw system in Feb based on information such as you are providing. The reality is that the actual does not reflect the reality. In summer the system does generate a reasonable output, but in winter, unshaded, and facing north, the output is minimal. Had I known the reality, I would never have gone solar. I have a two rate smart meter, monitored by a Pipit500 so that I can read the meter remotely.
    Until a month ago my rate was around 32c peak and 22c Offpeak (Ausnet). The best discount I could get was 38% on usage. If I elected to use the feed in tariff which was 5.8c per kWh, my discount would have dropped to around 14%. You don’t need to be too bright to figure that applying for a FIT would result in an increase in cost, not a saving.
    Given the cost of installation, added to which the removal of some trees, and the nightmare of having Goodwee fiddling with the inverter setting to stop the unit thinking the grid voltage was at least 280v, the basic system as described was misleading. In terms of diverting power to an offpeak HWS, these theoretical essays of yours are fantasy.
    They certainly do not apply as a realistic investment in Melbourne. As someone now retired, who has spent a lifetime project managing large electronic installations, I suggest the complexity and cost of getting an experienced professional to install and maintain any of the diverters for a normal user is far from the picture you are painting.
    Great for early adopters who philosophically feel they are saving the planet, but until solar costs reduce in cost and installation complexity, the cost/benefit ratio does not stack up. As someone who managed and architected projects up to several hundreds of millions of dollars, I am aware that many things are technically possible, but the reality is that for most people implementing your suggested solutions would not only be non-viable, but turn into a nightmare due to the difficulties of finding knowledgeable qualified technical implementation and support.
    The major issue, I have found, in practice, is that the electricity wholesalers, actively discourage solar by restricting the size of units, and paying 5.8c kWh which they then sell at 44c per kWh to your neighbour.

    • Ronald Brakels says:

      Hello David.

      Sorry to hear your solar system isn’t performing well. In Melbourne in June, which is the worst month for solar, a 4.8 kilowatt north facing system should be producing an average of around 11 kilowatt-hours a day. If it was significantly less than this you may want to contact your installer and let them know it hasn’t been operating as it should.

  10. Hey David, Please don’t denegrate the great work that Ronald is doing – its really hard finding all the different makes & models suitable for your requirement & Ronald is conveying a needed message to those not only in the know but the uneducated (on this subject) as to reasonable paths to follow if they wish to use solar energy as a power source.
    On the subject of water that is hot enough to shower, I/we (2 of) here in Port Macquarie have the greatest system (In my mind).
    It is a 30 tube SHWS, 250l 3.6kW, SR208C SHWS controller (with its timers & temp control), a (home made – is controlled by SR208C, controls pump, gives me a display of export/import power, 6.4kW PV(in reality about 4-5), can control >5kW (24kW triac))
    I need only to boost a few days a year, so I have ridded the meter box of the CL1 meter & relay.
    I reckon I am going to save-wait for it about $150 per year not much in the scheme of things but I know the energy is not coming from anywhere but the sun. Cost me about $300 installed (me-tech & sparky mate)
    Ronald – Love your blog.

  11. Greg Webber says:

    You could also look into the Solic 200. Available in Australia for $399 uninstalled. Looks like it has great possibilites as a very good price

  12. Hi,
    I have decided that a solar diverter is the best way to go for me as I currently export to the grid most of my solar energy (even when I set Dishwasher and washing machine on timer delay).
    So this article is great. Keep up the good work.
    One question that hasent really been spoken about is the advantages/disadvantages of the control method (phase angle, burst etc) Is one better than the other for efficiency, energy calculations, electrical noise?
    Also, do all diverters send whatever they can to the element whenever they can. For example, is it ok to just send 200W to a 3.6KW element?
    It also seems that only one product allows you to monitor operations from a website, but that product seems very expensive.

  13. I had an Immersun installed for two years up until today when it literally went bang and lost all its magic smoke. No chance of a warranty claim or even help so I’ve googled and found this helpful article. I just did my sums – I’m south of Sydney on an Origin plan that includes a 18% discount on usage, so my effective cost with discount per kW/h for Off peak power is 9.43 cents.

    I get a 9 cent feed in tariff, so my saving is only .43 cents or an approximate saving of around $9 per year based on my usage.

    Based on a $9 saving, it will take too long to recoup my costs for any diverter … now I’m kicking myself for forking out $1k two years ago for the Immersun as the UK company that bought them out doesn’t want to help, other than sell me a new one.

    My take-away from this is that even if the company offers a 5 year warranty, it’s no use if the company has gone out of business or has phoenixed.

  14. Hi,

    Great article. Your comment that “Australian family of 4 only uses around 1,500 kilowatt-hours a year for heating water.” is probably too low. It’s more like 4000Kw per year based on personal experience.

    • Ronald Brakels says:


      There is a lot of variation between different parts of the country and households, so I think the figure I used is roughly correct. But if I come across solid evidence the number I used is too low I will update the article.

      • I have to concur with Brad… 1500kWh is a low number for hot water heating.

        Based on the following assumptions:-
        Cold water in at 20C
        Final hot water at 65C
        Delta is 45C

        Water heating specific 4.18

        1kWh = 3.6MJ

        So, 1500kWh = 5400MJ

        Energy required to heat water = 4.18 * 45 * Mass of water (in grams).

        Working backwards, Mass of water = Energy / (4.18 *45) / 365
        to get daily water used in total

        = 78652 grams
        = 78 litres/day

        4 people = 19 litres of straight hot water at 65C per person per day
        Dliute with cold water to 50% brings to roughly 38 litres.

        Mains water flow at 10L/min for a decent rain shower (none of that water saving devices rubbish as it takes longer to rinse out soap/shampoo).
        Brings us to a 4 min shower/per person/per day. Wow, that is really penny pinching it!

        Nah, the real world is about 10 mins in the shower. For some people, they even take 20 mins. In summer, cooler showers usually prevail and in winter – hotter showers, so, on average, the whole year balances out in hot water usage per day.

        So, for 10mins = 100 litres water used, 50% hot/cold brings us 50Litres of hot water, which is 50,000 grams.

        Back to the energy formula brings us:-
        Energy used = 50000 * 4.18 * 45 * 365
        = 3432 MJ per person per year
        Family of 4 = 13728 MJ required to heat water from 20C to 65C.

        In kWh terms, this translates to about 3813 kWH (assuming 100% efficiency), so essentially the 4000kWh is pretty close to the mark that Brad says.

        Now, this only applies for bathing purposes only. Let’s not forget that there’s dishwashing (mine is connected to hot water directly, so the dishwasher does not heat the water using peak rates!), then there’s clothes washing. A warm water wash is way better than cold water wash. Detergents work better at warm water wash, which means less harsh chemicals are required in the cold wash which means it’s better for the environment.

        Which is why Solar Hot Water and Heat Pumps are essential if one wants to reduce the amount of energy required to heat water!!!! Heating water is an energy intensive process. Most people don’t realise this. It’s just fortunate that if we have off-peak rates to offset the energy costs for heating water. Imagine if we didn’t have off-peak rates? People would be compelled to find the most economical way to heat water. Firstly and obviously – using the sun to do most of the work. Using excess PV energy diverted to heat water is one of the best way to do it, since off peak rates are now between 12c and 35c per kWH. FiT is around 12c (in NSW). So, unless your off-peak rate matches FiT, then best to use your excess PV electricity to divert to hot water system.

        The physics don’t lie……

  15. Chris O'Neill says:

    “But the lower temperature set point should be at least 60 degrees to control the growth of Legionella”

    According to the cited :

    “At 50 °C (122 °F) – 90% die in 80–124 minutes, depending on strain (Decimal reduction time (D) = 80–124 minutes)”

    i.e, at 50 °C there won’t be growth of Legionella numbers but decay so unless your cold water supply has a problem with Legionella, you won’t have a problem with Legionella in your hot water.

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