When it comes to efficiency, hot water heat pumps have long had the definitive edge over alternative technologies anywhere south of Brisbane. Our latest analysis further upgrades this advice: heat pumps today are the most efficient way to heat your hot water, no matter what area of Australia you live.
The Brisbane line once represented the supposed plan Australia had to abandon most of the country during World War Two, but in the energy efficiency world it represents a different line of defense entirely: north of Brisbane being the last area where there was at least some competition to hot water heat pumps.
Heat pumps are more efficient than conventional resistive electric hot water systems as they move heat rather than creating it, consuming way less energy.
However, efficiency comparisons with solar thermal hot water systems, which use roof-mounted flat plates or evacuated tubes to heat water directly using the sun, haven’t been quite so straightforward.
Our advice until now is that heat pumps were definitively the most efficient option south of Brisbane, due to lower ambient temperatures and sun hours. But our revised verdict is that solar thermal doesn’t keep up even in the north, especially if the heat pump is paired with solar panels.
At First Glance, Solar Thermal Still Has The Edge
SolarQuotes’ resident fact-checker Ronald Brakels says that surface-level analysis can give the impression that solar thermal hot water panels still have their noses in front:
“These days typical new panel efficiency is around 22%. Full sunlight is close is roughly 1,000W per square metre. So one square metre of 22% efficient solar panels will produce 220W of electric power under 1,000W of full sunlight. If we use the rule of thumb that a typical heat pump hot water system uses 1/3 as much as electricity as a conventional hot water system, that means it will provide 660W of heat energy to the water, making them 66% efficient,” he says. “Solar thermal hot water panels can transfer up to 80% of the energy in sunlight into heat into water, or 800W, so they beat heat pumps.”
A Deeper Dive Reveals Otherwise
Ronald warns that this isn’t the complete picture, however:
“But this is not a fair comparison! The solar thermal hot water efficiency figure is only for directly converting sunlight energy into water heat energy, while the heat pump figure includes losses such as heat loss from the cylinder overnight, which also apply to solar thermal. When put on an equal footing, the average heat pump comes out ahead.”
Another factor puts solar PV paired with heat pumps well in front, Ronald says:
“But the real killer for solar thermal hot water efficiency occurs when curtailment is considered. This is energy that isn’t used and which effectively goes to waste. In summer, a solar thermal hot water system can produce far more hot water than a household needs. This means much, or most, of the sunlight energy hitting the thermal collectors goes to waste. This can also happen on sunny days outside of summer, depending on hot water use. But with solar PV and a heat pump, if electricity isn’t required for heating water it can instead power the home, charge a battery, or be exported to the grid for others to use. While there are situations in which PV solar can be curtailed, they occur far less frequently than for solar thermal. Once this is factored in it ruins efficiency comparisons for solar thermal hot water, leaving PV solar + heat pumps the clear efficiency kings.”
Another Brisbane line remains in place however: zones 1 and 2 in the map above get a reduced hot water rebate, as hot regions typically have lower hot water use.
Does Solar Thermal Hot Water Retain Any Advantages?
These days, you’re not likely to save money by installing a solar thermal hot water system as opposed to large PV solar system and using a heat pump hot water system or a conventional electric hot water system on a timer.
Even if you don’t have solar PV you’re not likely to save money, as an electrically boosted solar thermal hot water system uses roughly the same amount of electricity as heat pump hot water. But there are a few advantages:
- If you don’t have solar PV with a battery that can provide backup power, solar thermal can keep your showers hot for as long as the grid is down, provided there’s adequate sunshine;
- Solar thermal is silent, while decent heat pumps emit noise from 37-55 decibels when in operation. That’s from quiet as a whisper up to a running microwave oven;
- Provided your roof can support the water tank, solar thermal hot water can save you the ground space a heat pump or conventional hot water system would otherwise require.
While they’re still not likely to save you money, if you’re in or north of Brisbane, they may come closer to paying for themselves because warmer temperatures and clearer winter skies means lower cost solar thermal flat plate collectors rather than pricier evacuated tubes can be used.
But In Most Cases, The Brisbane Line Is No More
These factors notwithstanding, hot water heat pumps generally are a better proposition for most Australians. SolarQuotes founder Finn Peacock has even ripped his perfectly functional solar thermal hot water system off his roof to create space for more solar panels, and added a hot water heat pump instead.
For more, read our guides on solar-powered hot water options and our deep-dive into hot water heat pumps.
About Max Opray
RSS - Posts
While heat pumps are efficient they are not in my view the most cost effective All those moving parts just to heat hot water. Hot water diverter using excess solar works great for me and many others. Simple and low cost especially with low price of exports.
Can’t generate it without some capital cost.
Dearer to generate it than not use it in the first place
The extra capital is a few hundred dollars of a diverter and an extra panel or two. That’s far less than the capital of the heat pump. If I’m running on 3c — or even 8c — marginal electricity what do I care about efficiency?
The advice here is usually to get as much solar as you can afford and which will fit on your roof. Anyone living in a single family house will have ample power to use, water heating will hardly make a dent.
The biggest problem with energy hungry water heating, and the best argument for efficient water heating, is what time you use the water. Many of us shower before the sun is up, so whatever technology we want it well insulated and set to as high a temperature as possible so it can still deliver 50 degree water to the taps 12 hours since last light. I don’t think I have seen heat pump systems that can heat to more than 70 degrees. I have seen resistive water heaters that can be set to 90.
You are exactly right my green catch diverter is magnificent !!
In July 2028, I have some hard decisions to make.
To upgrade our solar PV which will require a new roof, or not. The decision is more complicated by our off-grid solar PV boosted, solar thermal, thermosyphon gravity feed hot water system.
This setup means we seldom boost from the grid. This year so far, 20.7 kWh. Some years, zero. In Adelaide.
The local manufacturer of these tanks has retired and good luck finding a plumber with experience in thermosyphon setups. A heat pump would also mean a lot of new plumbing.
What is missing from this comparison is a critical analysis of cost, reliability, long term lifespan and an important alternative option – Solar PV +resistive storage hot water.
I am assessing options for my new home. I already have 9.2kw solar but will double it and add a good size battery this FY taking advantage of the generous battery rebates.
If you have excess solar, this option can make sense if combined with timed switching and reasonable storage size, combined with good siting/insulation to reduce heat loss – particularly in colder climates (though not an issue where I am).
The cost of purchase of the resistive system is a lot lower, the reliability is widely regarded as much better for good brands and maintenance costs are very low. Also, no noise issues or other day to day issues. Lifespan will probably be longer too.
Why is this option not considered particularly in a place Solar Quotes where readers will tend to be more informed? It seems the best option for me.
This article was about hot water system efficiency, and in particular how our advice around solar thermal is changing: resistive isn’t competitive on this measure, which we note at the top. Resistive has other benefits as you say, we’ve compared them with heat pumps here.
Having owned two heat pumps, I wouldn’t consider them again. Water quality is rarely mentioned yet it’s a huge factor from a reliability perspective.
It also has an effect on the warranty.
Ideally you’d run them on rainwater.
Hey Paul water quality with a wrap around tank heat exchanger is not an issue and basically anything you can drink is fine.
If you bought a number of nasty machines I hear your pain and we see dead ones everyday.
iStore has had ….2 tank failures after 10 years and well north of 30,000 out there.
Solar thermal systems (which we sell too) are much harder on the parts as they have to deal with 100deg water temps everyday and frosts in winter , that wreaks havoc and they fail. OHS risks of roof installations not mentioned but someone falls off a roof in your business – that’s the end of your business and the cost of making this activity safe is very very high.
As for storage tanks electric. Vs heatpump they are the same tanks.
Hey Ka
The first was a Dux and the second was a Rheem 325i. Very expensive.
Whilst the tanks may be the same, it was the circulation pumps that failed in mine.
The Rheem had a compressor failure at the same time, so it was convenient to blame the failure of the compressor on the circulation pump seizing due to poor water quality. God knows where the logic of the failed compressor and water quality come into it.
They said I should have installed a water softener before installing a heat pump, so, I sarcastically reminded him that at no stage during the sale process, was water quality mentioned.
Whilst we were arguing about logic and warranty and me (potentially) without hot water for over a month, I bought a resistive HWS which I still have. I have replaced the element once, so water quality?
Both units only lasted just over two years.
From memory the Rheem was nearly 6k, so A) I’d never knowingly buy a Rheem product and B) Extremely unlikely to ever buy a heat pump HWS again.
Hi Paul,
You’ve sadly been victim to poor heat pumps and it’s likely the plumber has been sworn off them too.
I’ve spoken to one of the manufacturers who when pressed admitted they rushed to market with bad designs & then tried to bullshit contractors & customers alike. They’ve poisoned the market for a decade or more.
Water quality is what brings solar thermal split systems undone as well. The pump might hum but unless you feel the pipes on a sunny day you won’t know it’s failed because the booster element covers for it.
Better idea is that many heat pumps now use a tank wrapped with refrigerant coil, they don’t circulate water at all because the tank is heated with a blanket so to speak.
Hopefully they have all learnt a lesson.
I totally agree with you Patrick. I much prefer a few extra solar panels and a resistive water heater. They are silent, cheap, simple and long-lasting. Most importantly, every plumber in the world knows how to fix one. Heat pumps involve electrical circuitry, plumbing and complex reverse-air-conditioning systems. If something goes wrong you might need a plumber, an electrician and an air-conditioning expert to fix it.
I’d be very interested in a cost comparison with resistive vs heat pump over a forty -year period using primarily solar power. In my experience you’re lucky to get 10 years out of a heat pump and I’ve seen plenty of resistive tanks that have lasted forty years with only an element swap out.
Hi Andy,
I totally agree with you, right up until I don’t have enough energy to charge my EV in winter 😉
Heat pumps should be as reliable as an old beer fridge but we’ll have to see what pans out as the best.
Sadly proper copper is hard to come by now, even old mate Bill is winding up his local manufacturing.
You might try Wilson in Melbourne though?
Wilson just released a new split heatpump and it’s one of the best things to hit the market with stainless everything and high output power.
I expect it will be something close to $7k
Ohhh that sounds good Karl,
Will they add it to a copper cylinder though? 😉
I have a gas powered rennai infinity hot water system. How do I calculate if buying a heat pump system is better (cost wise)? I have 15kw of solar pv paired to a 50kw Sigen BESS.
The key is whether doing so allows you to disconnect from gas entirely, saving you the supply charge we have some analysis on average savings per city from quitting gas, but it won’t be specific to your circumstances.
How much gas do you use?
MJ / kWh
3.6:1
Heatpump will use 1100kWh to do the same job as 18,000MJ instant gas.
Typical 4 person house
Or 300kWh standing and 200kWh /person / year
Typically I’d tell you a 50kWh battery is way too big for a 15kW inverter and you’d struggle to use that much battery.or have enough array to charge it if you could
Depending on location a heatpump needs 1000W compressor heating power per person in the house to provide good performance, longevity and be able to reheat in a 4hr window in winter when the sun is out or cheap energy is available.
I got this 50kWh battery for less than the value of the rebates on your 50kWh battery it drives itself down the road too. only complaint is I didn’t have one when I was her age.
Tesla Model 3 Review: Great Car, Ridiculous Claimed Range https://share.google/G6LNtmLH55L7ZCkix
I feel there is another issue: Roof mounted solar thermal systems are far more expensive to install. In the last few years, I replaced a hail damaged roof. My old Solar Edwards Stainless system was flushed, moved & re-installed because it would have been difficult to install a heat pump. I used new//s/h panels because my old panels were u/s.
I am now contemplating building a small PassivHaus (Passive House), that will use a heat pump, but I will hot feed a resistance HWS for the Kitchen/bathroom due to line length. The small HWS will be heated from PV via timeswitch & contactor. In effect I will only be heating the small amount of cold water until the HW comes thru. Probably a 50Lor 80L system.
Passivhaus is really really expensive in a world where bulk PV and a thermal battery (house and water) can be heated during the day in our mild climate almost regardless how much leaks back out.
6star house for us 43sq
We heat only 11-2pm flat out OVO free period
House uses 30kWh to heat spaces and hot water wash dishes etc only problem for winter is the EVs that use more in winter too and they are another 40kWh a day.
If there is plenty of sun we will keep heating
27kW on the roof. 15kWh battery is overkill despite using 75kWh a day.
Mistakes – need a bigger garage, bigger laundry. All 4 beds with WIR and ENS should have ditched upstairs living area in favour of bigger bedrooms as kids aren’t moving out and more likely boyfriends and girlfriends moving in. Oh and more power points in the kitchen
Passivhaus would have been another $500k on the house we built
We generate 28,000kwh and use 22,000kWh
So I’d argue better than passivhaus as it can pay for the emissions it took to build
Agreed solar thermal HWS are now ineffective because of curtailed heating potential. But regular REHWS hooked up to active timers/contactors that work with a home’s solar system are really solar HWS too but with no curtailment issues and practically cost nothing to run if running on solar power. Other advantages of REHWS are: simplicity, ability to customise electric elements to suit solar power availability, can have dual elements for very quick recovery, noise free, no ventilation requirements, can be installed indoors and are inexpensive.
They don’t work in Vic for 4 months of the year because you need 15kW panels on the roof to make enough hot water and a free energy plan that runs it flat out 3hrs is providing
3x 3.6kW – tank standing loss of hot water
= Less than 20mins shower time.
They suck slightly less as the cold water temp gets higher as you go further north but the energy saved will drive an electric car 15-20,000kms a year so if you are electrifying, simply don’t have spare and hence paying for the electrons and when you have to buy 3x more of them it isn’t viable.
Nor is cost of solar and battery economically viable vs simply using 70% less energy to heat water in the first place
Bear in mind that the resistive element HWS does not require a battery as well, as they run directly from the pv. Those without a battery benefit from buying less grid power in early morning and afternoon if they put the money saved buying the cheaper resistive HWS into more panels, and they load shift to heat the water at times when surplus sunshine (and lack of other uses like when the electric car is with the boss at work) would mean curtailment by SAPN. We must never confuse energy efficiency with cost effectiveness or practicality, otherwise we would live in esky style houses and no windows but have LED lighting both day and night , because that is the most energy efficient housing.
Great article, but I think the comparison is not pragmatic. The heat pump option is more efficient per m2 of sunlight collected (which I think is your point and a good bit of knowledge), but the rooftop HWS comes with its own solar collectors, so sunlight energy collected is greater.
What I mean is, people are typically not choosing between an extra 2kW of panels on their roof (plus a heat pump HWS) versus a rooftop HWS. For most, they already have a solar system installed or designed and the decision is whether to add a rooftop HWS or a heat pump.
Anecdotally, in Brisbane we have a rooftop solar HWS and a smart circuit to both measure the electricity used by the booster, and to only provide electricity in certain circumstances (to help with the curtailment issue you mentioned). Last year we used around 100kWh total on hot water for the year (1.8kW booster for around 50hrs).
Compared to 2-3,000kWh for heat pump, or about 2kW of extra panels based on my 2024 total generation.
Efficiency is just one measure in which heat pumps have overtaken thermal systems: our recommendation is that they also beat them on install costs and running costs. But thermal hot water systems are great and there’s little need to replace an existing one that’s working well (unless you are very keen to maximise rooftop PV).
Thanks Max. I’m not sure I agree with you, from a systems perspective. For clarity, in agreement with your article, I agree I’d be better off with a heat pump HWS and say 15kW panels on a 12kW inverter, compared to a rooftop HWS with 13kW of panels on a 10kW inverter. Because heat pumps are more efficient and energy collected that isn’t needed for hot water can be used elsewhere. And rooftop space and cost is similar.
But, I’d argue that if you already have a solar system and you need to replace your HWS (and you can’t be convinced to install another solar system to maximise roof coverage) adding a rooftop HWS will be a better option, from a system perspective, than adding a heat pump HWS.
Even more so if you restrict the rooftop HWS from using electricity whenever it wants. The lack of smarts in rooftop HWS is another topic that I hope gets attention soon. If it’s morning and the outlook is full sun, you don’t need the booster!
Heatpump in your location is 900kWh a year for 4 people
Nothing like 2-3000kWh
Ok, awesome, thanks. The sources I used said it would be higher for my location and behaviour. Regardless, that’s still 10x the electricity compared to what I’m using now. It’s also worth noting we used zero kWh for hot water (not grid nor our self generated solar- the booster never turned on) in the first two years we had the rooftop HWS, but we’ve gotten used to longer winter showers and baths in the last couple of years so the booster has been flicking on more regularly.
Hello
I have a 300L stainless solar thermal which was installed in 2009. I have not replaced the element or the temperature controller. It is on a timer set up. In the last twelve months I have use 2251 kwhs of power, and the new rate for off peak hot water is $0.20735 with gst included, so that comes in at about $467.00 for the year to have hot water available 24 hours a day.
I do use hot water for a number of clothes washes each week.
I understand heat pumps have a shorter life than solar thermal, which could make heat pumps more expensive over the life of hot water systems, than solar thermal. Replacing the solar thermal is not going to be cheap, so when it comes to that, I will be considering my life expectancy, since another solar thermal will probably out live me.
Hello
Just a note to say the temperature setting on the thermostat is 60/65 degree Celsius to try and prolong the life of the hot water system, but in summer the sun heats it higher than 65 degrees Celsius
Neil a heatpump would use less energy than that annually.
In fact that much energy is double what a heatpump uses.
Its enough energy to run a heatpump for 8 people (two heatpumps recommended for 8 people).
My understanding is
– That heat pumps can not use small amounts of solar energy, like a resistive hot water system can using the right sort of diverter. they need the full whack to run.
– Most electrical authorities (if not all) will not allow you to connect a hot water system to both off peak power and your solar, so if you dont generate enough power to heat your water, you are paying full grid price.
– A battery may nullify both of these issues
These factors combined mean you really need to make sure you have excess power available in winter to either directly run, (or to top up the battery), before dropping the hammer on a heat pump if you have solar. Otherwise if you have to buy power in winter, buying off peak hot water power is likely the cheapest power you will be able to buy, but that might mean paying for that off peak power for your heat pump for 9 or 10 months when you dont need it.
So the heat pump might be cheaper to run, working out how to power it might be tricker.
Max, I’m trying to understand the advantage of heat pumps but your drawing confuses me. In bold you show inputs and outputs in kW, but beneath these you describe them as ‘Energy’ (which I think is probably fundamentally appropriate). If so, did you maybe confuse the units, meaning in bold you should rather have had them as kWh, not kW?
Hi EM,
A heat pump is both a kind of solar hot water service and a magic pudding.
You harvest heat from the air and “pump” it into the water in the tank, but the machinery that runs the pump is quite efficient compared to just taking cold water and pouring electricity into it via an element like your toaster has.
If you use 1kW to turn the compressor, and keep that rate of work up for an hour, you will have added 1kWh to your power bill.
If the heat pump has a Coefficient of Performance of 3:1, you’ll end up putting 3kW of heat into the water for every 1kW of electricity used.
So electrically the heat pump uses 4.3 apms of current at 230V, whereas 3kW element by comparison would use 13 amps of current at 230V.
The diagram should perhaps be simplified so that 2kW comes from the air (ignoring losses)
You’re short
Even rubbish heatpumps get COP4 of water heating into the water.
An iStore gets COP4.82 at 20deg average heating a whole tank from 15-60degC
It gets COP4 down at 7 deg and it doesn’t get much colder than that during the day anywhere in Australia and up at 32deg ambient is COP6 and gets >5kW heating power.
I work for iStore
Cheers Karl,
I think the image is going to get a workover for simplicity.
Thanks for feedback all, image removed
Karl: – “An iStore gets COP4.82 at 20deg average heating a whole tank from 15-60degC”
CoP depends on a number of factors including primarily the refrigerant used & the ambient air temperature.
For example, per the test report published by Washington State University in association with Bonneville Power Administration, titled Laboratory Assessment of Sanden GAU Heat Pump Water Heater, dated 18 Sep 2013, for the laboratory assessment of the Sanden model # GAU-A45HPA heat pump water heater (HPWH), Table 3 included:
Outside Air Temperature _ CoP _ Output Capacity _ Input Power
17 ºF ( -8.3 ºC) _ _ _ _ _ _ 2.1 _ _ _ _ 4.0 kW _ _ _ _ 1.9 kW
35 ºF ( 1.7 ºC) _ _ _ _ _ _ 2.75 _ _ _ _3.6 kW _ _ _ _ 1.3 kW
50 ºF (10.0 ºC) _ _ _ _ _ _ 3.7 _ _ _ _ 4.0 kW _ _ _ _ 1.1 kW
67 ºF (19.4 ºC) _ _ _ _ _ _ 4.2 _ _ _ _ 4.1 kW _ _ _ _ 0.97 kW
95 ºF (35.0 ºC) _ _ _ _ _ _ 5.0 _ _ _ _ 4.6 kW _ _ _ _ 0.93 kW
Lithgow reached -7.2 ºC on 20 Jul 2025.
Depending on your circumstances I reckon heat pumps are a con job. I replaced the 3.6kw element in our 319ltr Dux resistive HWS with a 1.8kw element and then plugged it into a a regular PowerPoint via a wifi controlled timer switch. I set it to come on at 11.30am each day and off at 2.30pm. As there is only two of us, this is adequate time to fully reheat. The entire project cost me $70 and I my hot water is now 100% heated using self consumed solar. On a cloudy day, to avoid using grid power, I’ll simply switch the system off and back on when the sun comes out again as it stores enough hot water for 3 days. And if we get a really bad run of weather the Controlled Load circuit has been connected to a dedicated outlet that I can simply switch to if needed. Free hot water for $70 as opposed to $3000 for a heat pump hws? It’s a no brainer.
A – illegal to do what you are doing re mixing your energy supply to controlled load and an outlet.
B) with that much energy input you have an extremely low hot water demand
Average use is 200l / day
The way it is set up is completely legal. Circuits are totally independent and not mixed. And yes, a couple of quick showers a day is pretty much all we use.
I also suspect it is illegal. My sparkie told me recently the rule is that you can only plug into a GPO an appliance that was originally supplied by the manufacturer with a flex lead and a plug ie idiot-proof. If it hasn’t got a lead and plug then it needs to be wired in by a qualified electrician. But maybe you are a qualified electrician so it’s all good?
Yes, I’m qualified. All good.
A resistive with a solar only hard to beat now I’m only getting 1 cent fit !! Heat pumps cost twice as much last half as long are noisier and water isn’t as hot,doesn’t matter if they’re more efficient it costs a arm and a leg to get a electrician for repairs !!
You don’t have Aircon or a fridge?
Surely not heating your house with a fan heater or oil heater?
Sure they work harder for longer but
Decent heatpumps with STCs don’t cost twice as much or last half as long and yes they do save those costs over their life.
Even its as simple as your grandkids not having to strip that CO2 back out of the air.
As it stands it’s something that’s cheap and easy to do. Saves bucket loads more emissions and costs for a typical family than home batteries do and costs a fraction of what a home battery does.
A heatpump will need a starting capacitor in its life and will live a long and happy life if sized appropriately for the household >1000W compressor heating power per person in the house = decent longevity.
Buy a cheap shitter with half that power that needs to run twice as long each day and wonder why it didn’t last…?? Yeah nah just needs to be built for the job
I work for a heatpump manufacturer -a decade in going great
Eek! Anthony, you are burning my eyes! 🙂
Heat = Energy, units in Joules, but kWh is fine, kW isn’t a measure of heat.
Hi Glen,
Cheers for the correction.
I understand where you’re coming from but without having a back and forth conversation it can be difficult to get a handle on exactly what people understand. Even a phone conversation sometimes leaves you having to cover the same ground 3 times to get a clear explanation across.
Adding some typos never helps but the footnotes in this explainer might.
The take home message for the average footbaw fan is that heat pumps are grabbing “free heat” from the air.
It’s clear that heat pumps are neat tech, but longevity/reliability is still a great concern for many and the industry only has itself to blame for selling crappy low quality product for years. They are still doing it.
The trust deficit with HPWHs is large.
Solar thermal WHs at least have a long track record of long lived systems.
HP brands considered good quality are ridiculously expensive and is a significant barrier for many.
My plumber wanted ~$8k to replace our solar thermal system with a quality HPWH. Cheaper brands exist but they have not been around long enough and come with very short warranties. They won’t install them, have had too many issues.
If these things are so good then why don’t the warranties back that up?
I’m not looking forward to the day our solar thermal system finally dies. And it will die because the former owner did not perform routine maintenance, anode removal no longer possible without tank damage. Just hoping we squeeze another 2-3 years out of it.
Mate look at heating power
An iStore has the same grunt as a fancy one and it doesn’t cost the earth.
When it fails the change and savings will buy you another.
Get some penetrating oil on that anode twice a week, and hit it before summer
get the replacement teed up now just in case.
Will cost less to run and maintain than the SHW and it’s on the ground
iStore do not have a large enough tank. And are you really advocating for tech that requires early replacement? Buy cheap, buy twice (or thrice)?
What a waste of materials and the environmental cost of manufacturing, installation and disposal of an item not expected to last a decade, when we have water heating tech which will last multiple decades.
Completely agree that heat pumps are the most efficient. But in country NSW where the day time temperatures are quite low, there doesn’t seem to be much heat to extract out of the air. My home air con heat exchanger spends a lot of its Winter running time doing multiple de-icing cycles. Using the panels on the roof to run a hot water heating element on Winter’s days seems faster and more effective. Agreed, it’s not as efficient, but Winter is a quarter of the year and having something that is less effective at heating water in Winter bothers me.
Using a battery to heat water is like running it on peak rate power – nuts!
Heatpumps are such a small load they are no longer worth managing.
4kWh a day vs 16kWh a day for a typical 4 person load.
Can heat the tank in peak solar production times is an essential service so done before peak rate times kick in at 3pm has them running in the warmest parts of the day.
Get one with at least 1000W compressor heating power per person in the house for it to meet those daytime goals.
We put 6kWh into our heatpumps a day with 4 people. COP4 gives me 24kWh worth of water heating.
I would need to find another 18kWh of energy every day for 4 months.
June and July my solar yield is 1.3kWh/kWp installed hence I’d need another 14kW on the roof.
I don’t have space for that, nor do I have spare grid connection capacity even with 40Ax3phase.
Cars to charge, house to heat, really cold, home battery to charge water to heat = can use well north of my connection capacity even when there is only 1 car on
Hi Karl,…I understand you are passionate and have some very good arguments made,…and I 100% agree with you on the energy efficiency aspect,…. but i do not agree with the cost effective position in most cases.
If we can find a way to heat our water without damaging the environment and in a cost effective manner then all is good.
Clearly if we have no available space for PV then it will be better to buy an economical Heat pump, or if we use all our best roof space already to run the house and electric cars etc,
Consider the winter when we lack opportunity for good PV production due to short days and cloud cover,…. we can also economically cover our south facing roofs with panels,… and on the worst solar days the power from them is just the same as those facing north at steep angles,…the added advantage is that we have sunshine on those south facing panels later and earlier in the summer to help with the air conditioning too!
If heat pumps were cheap to install we would!
Sorry that previous reply went in the wrong place.
Heatpump looses 25% of its heating power in winter sure no worries
Needs 100% more energy to heat than in summer = takes longer.
Takes longer for an element too.
Summer heating 20-40 to have a shower
Winter heating 10-50 as all the losses are higher and the cold water is cold!
Most heatpumps will get COP3-4 in temps 5deg
So still using substantially less energy than gas or an element and you have more chance of being able to generate it yourself vs me having to knock down some more trees to build wind turbines or spend $$$$ to put them off shore.
Those with a Fronius inverter and a tank with a resistive element may find it to be a cheaper alternative to heat pumps and I would recommend that for new builds. A new tank is only about $1,000 installed (150 l only) and demand a minimal 1,800W element as there will be more days with less sun.
Heat pumps will be dearer, perhaps noisy and definitely with moving parts.
Agree totally. In the interests of being a bit self reliant, Resistive are very easy to maintain. I mentioned earlier that I have had two heat pumps and never again. The reliability needs to improve dramatically. Getting trades people to come out to a regional area with the correct parts and same day is impossible.
At least with a resistive, you can get a new element and TP valves from your nearest hardware store.
Most people seem to only consider efficiency, but it doesn’t matter how efficient HP are when they are broken down and you don’t have hot water.
Solar thermal HWS here, years old but going strong. It won’t last forever, so when it dies the plan is to replace its panels on the roof with 7-8 more PV solar panels plus a simple resistive HWS. While heat pump HWS might technically be “more efficient”, they are far more expensive, noisier (an issue in densely populated parts of Sydney), more complex to run and repair, less reliable, and have a shorter lifespan.
Exactly and it costs a arm and a leg to get a electrician to come !!