Solar hot water panels going on my roof in 2013.
Two years ago, I ripped a perfectly functional solar thermal hot water system off my roof. It had been sitting there for a decade, dutifully heating about 70% of my water with the sun’s heat (the rest boosted by gas).
I removed it to use the precious north-facing roof space for something better — an array of high-efficiency REC solar panels.
Then, I removed the gas booster and swapped it for a Reclaim hot water heat pump. Why? With three EVs, I needed more cheap solar electricity, heat pump technology had improved to be quiet and reliable, and frankly, solar thermal hot water is on its way out.
Before: My roof with solar hot water and 6kW of Tindo panels (top)
After: 14kW of REC solar panels, Tindo relocated to E & S roof (bottom).
Solar Thermal Is Going Down The Drain
If you installed solar thermal hot water panels a decade ago, you probably felt pretty smug. It was the most efficient way to get hot water using the sun, and it made a big dent in your gas or electricity bills. But the economics have shifted dramatically.
A heat pump hot water system running on cheap solar electricity beats a solar thermal system in almost every way that matters. It’s 100% electric, easier to install and maintain, doesn’t dump hot water when it’s too sunny, can store solar energy to use at night, when powered by PV, or use off-peak grid electricity, and is cheaper to run. It also lets you use your roof space for the most valuable real estate in Australian energy: more solar PV.
Heat Pumps Versus Midnight Showers
But heat pumps aren’t perfect.
I live with three teenagers, who all enjoy 45-minute showers. Usually around midnight. If I want a hot shower in the morning, I need to boost the hot water in the wee hours. The bad news? I can’t do this directly with solar electricity. The good news? The heat pump is so efficient that my battery can effortlessly boost it with stored solar.
If I had no battery, I’d program it to boost between 1 a.m. and 5 a.m., when I get off-peak grid electricity.
Standing next to my Reclaim heat pump, waiting for my teenagers to finish up in the bathroom.
Turn On The Tap, Turn Off The Gas
The shift wasn’t just about hot water. That old gas booster was one of the last things tying me to a gas connection. Replacing it with a heat pump meant I could finally scrap the gas meter. I also had to replace the gas hob with induction. That turned out to be a huge upgrade in itself — cooking on gas after experiencing an induction hob is about as much fun as driving on diesel after owning an EV.
Solar Thermal Will Slowly Evaporate
Solar thermal hot water isn’t disappearing overnight. Some systems will keep running for decades. But new installations? They’ll keep shrinking. When PV was expensive, solar thermal made sense. But now? Heat pumps + PV have won the battle to give you a hot shower.
I’m so sure of this that I not only shut down the solar thermal on my roof, but also an entire website I’d built dedicated to this once-pioneering technology.
SolarQuotes today instead offers a growing body of advice on hot water heat pumps, including video explainers. As of last week, we now offer up to three quotes for heat pumps from verified installers.
I pulled my solar hot water panels off the roof for the same reason I don’t use a fax machine anymore1: technology has moved on. Fifteen years ago, both were essential technology. Today, they belong in a museum.
Phase Shift is a weekly opinion column from SolarQuotes founder Finn Peacock, in which he shares his views on all things home electrification.
Footnotes
- Fun fact: When I started SolarQuotes, I sent out many quote requests via fax! ↩
About Finn Peacock
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I hope 45 minute showers was an exaggeration, that’s ridiculous.
Does that water go down the drain or do you have grey water reclamation ?
About two years ago I had a similar decision to make. The relatively new (10 years old) gravity feed tank in the roofspace developed a leak.
The supplier made and sold me a new tank at a discount due to the known design fault. The plumber and his mate spent nearly a whole day installing the new tank, with lots of swearing.
All up about $2000 from memory. I boost it with an off grid array and occasionally off peak grid energy, so I should have free or very cheap water heating for 25 years, assuming this tank doesn’t develop a fault. I have everything crossed the collectors don’t start to leak.
Or in 2028 when the SA PFiT ends I might replace my roof and take your path. Assuming I am still above ground. 😉
Hi Rod,
Gravity fed copper hot water is great but it’s worth a pre-emptive element and thermostat change at ten years in my experience.
If I had solar hot water on my current (adequate) roofspace I wouldn’t be taking it off and dumping it. Even if my roofspace was at a premium I’d be weighing up the cost/benefit vs say 3 solar panels.
The first obvious solution is a 5 minute timer on the shower. Cold water often makes the unwise a lot smarter with a cold shock of reality. When recently hosting a distant young relative who ignored my requests for reasonable shower times, I didn’t go to the expense of a timer…. I just turned off the gas.
I suspect his parents will be very grateful if the lesson has stuck.
The poofteenth of power required to top up the temperature on my previous residence with solar (thermal) hot water was negligible. The $3 – $5K for installing a heat pump for hot water isn’t…. and how long is the warranty?
I must confess to a twisted giggle when I read this story while researching this response:
https://www.solarquotes.com.au/blog/are-heat-pumps-better/
I am however waiting for what seems to be a far too logical bit of domestic equipment to hit the market….
The irony of the modern home with it’s conflicting cooling (fridges, freezers, air temperature) and heating (hot water, air conditioning) results in having appliances wasting hot air and cold air at the same time.
Perhaps one day there will be heat exchangers that pump hot air to rooms, and cold air to fridges etc, or cold air to rooms and hot air to water heaters at the same time.
I do understand that the volume of air passing through a heat exchanger is far greater than the temperature difference between in and out…. but the devices do manage to heat hot water and cool rooms.
Ha
Considering all of the costs, including FIT lost and the relative longevity of the systems did you consider a simple storage HWS run from excess solar in stead of a heat pump system?
I understood heat pumps like AC systems could not just be switched on and off as excess solar is generated?
How will you control this system so it only uses excess solar production?
Hi Matthew,
I have seen a study (by SolarAnalytics?) where it’s been found that a heat pump running on a simple timer costs about $60/year. Moving to a solar controlled relay to switch the heat pump on when it’s sunny only improved things by $10/year, because they use so little electricity.
My last heat pump hot water bill was about $30 for the quarter. When i installed my PV system, Ithe installer originally had off-peak hooked up to it somehow, but for some reason, when my heat pump was installed, they connected it directly to the controlled load. Don’t know why they changed it, and when I called they wouldn’t change it back.
I was referring to continuing to use a storage HWS heated with a simple resistive element.
No moving parts and only possible consumable a sacrificial anode and maybe an element. I have a HWS in a place we now rent out that was installed in 1984. 20 years without doing a thing, not even the basic suggested service, is common with no moving parts.
So given the electricity is “free” as only from solar, except lost FIT that could be anything from 12 cents down to nothing, why not stick to a simple electric storage HWS?
Pink Batts strike again – Australia at risk of being being flooded by cheap, inefficient ‘faux’ hot water heat pumps.
https://switchedon.reneweconomy.com.au/content/australia-at-risk-of-being-being-flooded-by-cheap-inefficient-faux-hot-water-heat-pumps
Indeed something to be wary of: we have a summary of which systems are best here, and recommend using one of our verified installers if you do are considering a hot water heat pump.
For similar reason, I did not replace my solar thermal hot water system when it died eighteen months ago. Instead I went with a large standard electric boiler.
I didn’t go for a hot water heat pump because I am concerned about their longevity and reliability. I figured that I could spend the money saved on more solar electric panels instead. But then again, I don’t have teenage daughters.
Would you recommend stainless steel tanks rather than glass lined or vitreous enamel for increased life in heat pumps?
I also notice the brand you installed had a separate compressor. Does that improve efficiency?
In Bendigo as in many other areas in South Australia and Victoria we have had very little rain recently. As a result my solar panels are pretty dusty.
I am unable to reach the panels to clean them due to age. Is there any point in just giving then a clean with a garden hose from the ground.?
It is too expensive to get them professionally cleaned now that Victoria has approved a feed in tariff of $0.0004 per kilowatt.
Hello Brenton. Dust can certainly impact on the performance of your panels – and while the minimum FiT in Victoria has dropped, you might still get a better rate than that depending on your retailer. The main financial benefit of solar has long been self-consumption anyway, so it may well be worth hiring someone to clean them – just make sure they don’t use dishwashing detergent!
I live on a sheep property with dusty paddocks. Just for the heck of it, and having two separate systems on my north facing roof, I hosed off the dust from one set of panels. I reckon it made about 4% difference in production near midday. Unless you have a serious layer of dirt over the panels it hardly justifies the time and water to squirt them off, let alone pay someone to get on your roof.
May be if I had the space where to put this massive Heat pump, I would be sold on it but for now I am keeping my Solar Hot water. It is tidier and everything what you said about the heat pump – using solar during the day, boosting with battery at night after the kids have showers , is valid for the Solar Hot water…and I have an electric booster switch, no gas one!
I’ve been the recipient of solar quotes weekly updates for quite a while now, and look forward to reading them. Many insights and advice, all to my advantage, not to mention informative, interesting reading.
We replaced our 180w X 16 panel system mid last year as well as our solar HWS, with a heat pump. Now have 6.6kw system in place and awaiting an affordable battery. (Both pensioners).
Thanks for your articles.
Hi Finn. Nicely written article, thanks. Jowever, if you have 3 teenagers all taking 45min showers, you need to address that. Waste of precious water, environmentally disastrous.
I could not believe that you would tolerate that while obviously an advocate for renewable energy sources.
Cheers
Everyone likes a hot shower. But if 45 minutes is real and not poetic license then I find the amount of water used offensive.
Fresh clean potable water is not a resource that should be flushed down a drain.
I do like the take on PV + heat pump plus battery.
Hi Nick,
One of my best mates has a teenage daughter with a water use problem… they do exist sadly.
I am a self funded retiree and own my own home. I have a 3.2 kw solar system and despite the installation in 2009, the system is still performing very well with 19 kw generated in the Summer months. I also have a solar hot water system on the roof and is a Rheem- approaching 25 years old but with regular maintenance, still working fine. In fact since installation I have always been able to switch of boost on the first day of September and leave it off until the first day of March. This effectively provides me with 6 months free heating of water. Live in SA and am the only occupant of my home. My energy bills are very manageable with the dearest bill in the April to July quarter. The question I have is: replace hot water system with another solar package as all plumbing is there or a heat pump? The solar unit is mounted on the ground with collectors on a North facing roof. I don’t have an EV and do not intend to purchase one. I am not interested in a battery either as it would take years to get the installation price back. What is your advice when the hot water system eventually fails? Thanking you for your time. Regards
If your solar hot water is still working fine, then keep it!
If it fails, if the price isn’t horrible, replace it with another one.
Your own words tell the answer! 6 months a year of free hot water, with a minimal roof footprint.
Agree.
You are most unlikely to get 25 years out of a heat pump
Already bought a spare tank for the day our 30 year old, 315 litre tank leaks .
Dave I suggest you keep the Solar thermal. My Rheem system was installed in 1981 (44 yrs) but was connected to soft water. It outlasted me as I sold the house.
we are a pensioner couple and have a 1.5kv solar system facing east installed 10 years ago and still working good. Solar hot water panels installed 11 years ago facing west with the tank on the ground, there is a switch in the meter box i can turn it on or off and have never run out of hot water. very rare to have a big bill.
Hi Ian,
It’s worthwhile occasionally verifying that your solar hot water is working.
Slide the insulation back on the pipes that go up to the solar collectors. The one at the bottom may be tepid or warm, however the one at the top should be warmer, too hot to touch preferably.
While the lights might be on and the motor may be humming oftentimes the impeller gets jammed and so it’s worth feeling the temperature of split HW systems.
Ha ha ha!
Sorry mate…. I’m guessing you must have a lot of spare cash to do what you’ve done?
First up?
Solar Vacuum Tube Arrays at 85% efficiency versus PV Arrays at optimum 23% efficiency at present for domestic panels….
Go figure?
My math says you need 3 times the area for PV to match Solar Tubes? Mine use NO electric backup for my province!
Makes No sense!
Yes. Heat Pump Water Heating is quarter the cost of resistive electric elements, but up to 10 times the installed cost, depending where you are!
PV’s at only 23% efficiency are looking around 10 years to return investment, where some installers are reporting 30-40% failure in that time!
As an Electrician, unless you have inordinate sums of Free Money, the numbers dont stack up, not even for EV Charging due to Must Have Powerwall battery system as well!
My house is 254m². Only quarter is facing the correct direction for optimum PV generation…..
Current efficiency giving 150-200w/m², or 10-12kw during peak sun…… and probably 60kwh MAX for a full summer clear sky day in my New Zealand area at best.
On top of this is then your Power Wall to store for your EV night charging…..
Again, at present efficiency, very few ‘Ordinary’ wage earners will find this a convincing or ‘affordable’ saving……
BUT!
If I won the money, yes, I would install a system exactly as you suggest, purely because ‘bang for buck’ is no issue when you’re spending “Free Money”.
I’d be interested to know if energy-wise solar-electric+heat-pump really beats solar thermal, or if it’s mainly the flexibility and simplicity of going pure solar electric that wins out.
In theory solar thermal’s direct transfer of solar heat into the water should be way more efficient than inefficiently converting it to electricity to heat the water with. I get that heat pumps don’t heat with electricity, they collect and concentrate ambient heat into the water, but heat pumps have efficiency losses and limitations too (do they include electric heating for a boost when needed?).
I feel like some kind of integrated solar thermal heat pump would be even better, where the heat pump can collect not just ambient but also solar heat, requiring a reduced solar footprint compared to pure solar thermal, but with significantly boosted heat collection compared to a pure heat-pump.
I guess in the end it depends on your overall heat vs electric requirements. Why waste a whole panel on solar thermal if a solar electric panel in its place can generate as much or more of the electricity needed to generate all the heat you need with a heat pump?
Good point Donovan,
I think in some cases it’s just about added complexity for diminishing returns.
Hi, living in the inner city there’s often no room down the side of the property or courtyard for a heat pump, which is the case for us, so we’re stuck with instantaneous gas at the moment.
I’d appreciate an article about resolving the space issue.
For example, what are the pros and cons of about roof mounted horizontally mounted heat pump tanks? I’ve only found one online to date; not sure what that says about them!
Hi Ryan,
I’ve seen a Solahart close coupled tank mounted inside a roof space but it needed a custom stainless drip tray installed, it was a great job but needed a good budget and good installer.
You could use a copper tank inside the roof, but again it would need an innovative plumber to add a (Reclaim/Panasonc?) heat pump unit.
We’ll look into an article soon I expect.
An informative and interesting video.
I had a heat pump about 10 years ago. (Rheem MP 325), but never again. Their service and warranty was abysmal.)
The unit was in a holiday home which was used for 6 weeks every year. It only lasted about 2 years and there were issues (apparently) with the water quality. (We are on mains water in the Eyre Peninsular)
Funnily, this “issue” was never raised when I made the very expensive purchase or I never would have spent $6,000 on it.
This leads me onto my current concern with heat pumps. Recent inquiries have led to the better manufacturers advising not to install one, because of the water quality in our area. Whilst I like their candor, I’m a little disappointed that the technology hasn’t somehow managed to negate the effects of poor water quality. I’m even more disappointed that we are paying for poor quality water.
Hi Paul,
10 years ago Rheem heat pumps were rubbish (as they later acknowledged quietly to the industry) and sadly they’ve poisoned a generation of customers and contractors.
I’m not qualified to advise but you may find a whole house water filter is a good investment.
A heat pump that circulates water through the compressor unit (like Reclaim) probably won’t like hard water, however a unit that wraps the existing tank with the refrigerant heating coil is really no different to a conventional mains pressure tank, so that might help you.
Hey Anthony, I purchased a water softener and after checking the resistive HWS tank, there is little calcium compared to without the softener.
I’m still reluctant to get another heat pump until the water supplier, somehow gives us better quality water. (So pretty much never.)
Given that most people are buying water from the government, it seems counterproductive that the government is subsidising heat pumps, knowing that they will fail if you feed them the poor quality water that they are supplying. (SA Govt for example)
For me at the moment I guess the economics are, that it’s cheaper to replace a resistive HWS than a heatpump (this is of course provided that you have enough solar generation to run the resistive HWS as I do)
Perhaps when I feed the HWS my rain water, it will be time to revisit the heatpumps.
In one recent newsletter, it was commented that solar hot water is superior to solar panels and heat pump hot water from Brisbane north. But a day or two later, another newsletter recommended the latter with no qualification on location. Which is it?
Hi Andrew,
I think the answer is that Finn has written a story about his household in Adelaide without expanding to the rest of the country.
North of Brisvegas the ambient water temp is warm and the days are sunny, so solar thermal hot water costs least to run.
However the expense to install it can be high. I’ve installed a lot of Solahart close coupled (tank on the roof) units and always liked them. If you have the plumbing in place then I wouldn’t hesitate to replace a close coupled unit with another of the same.
However split system solar thermal with a pump isn’t as reliable and if you get frosts, they waste a lot of energy pumping hot water through the panel at 2am.
We live in Brisbane in a three-level freestanding townhouse, so installing anything on the roof is expensive. We put on 10 kW of solar PV panels a couple of years ago (thanks, SolarQuotes) but kept our gas HWS. We have had a BEV for a year now and the time has come to change out the gas hotplate and HWS, and maybe add a battery. And it is probably also time to add more solar PV panels. So advice on the HWS would be appreciated. Thanks.
Hi Andrew,
You can get installer quotes for heat pumps through solarquotes now.
Click “I’m ready” then enter your postcode and you’ll find the button on the right
Finn, I continue to love your work & also that you are helping keep Australia populated with 3 kids! Such HW upgrading makes complete sense for your home.
5 people, or the usual (?) 4.4 peeps per family, doesn’t really help this single retired gent from understanding how to really see inside what it’s worth spending my dosh on, when considering all of what any new panel-array/AirCon/battery/EV charging system here ‘should’ be including.
When fitting a new pv system, when could it just be better to use a timer for the resistive HW unit or perhaps just fit a smaller element inside? Returns vs outlays are the toughest to determine, given that ‘no-one’ seems to write about single person pv systems.
There’s no real sign of when Australia will actually allow V2L/G or H to be used whilst grid connected. When could it be worth disconnecting from the grid if one were considering using a CHAdeMO EV or hybrid to connect the car’s battery to the home system, even using DC?
As we seemed to see when you watched that Sigenergy installation, can I just flick a switch to disconnect from the grid when the car is connected and get FiTs the rest of the time?
Hi David,
You raise a lot of good points so we might have to get our man Ronald to do a study on very low consumption. It’s a hobby we should all celebrate.
Large solar PV systems and small elements on a timer are the cheap and cheerful way for sure.
Just heat the water in the daytime with solar energy. If the hot water runs out at midnight, hard cheddar.
I’d have thought a 1-time manual override would be available, to soften that cheddar with some grid if needed?
When I re-roofed abt 8 years ago (hail damage), we drained & cleaned the 400L tank (Edwards Solar HWS) & fitted s/h collector panels because originals were U/S. In my case the PV is on the shed (15+Kw), so the HWS was not a problem. Also, if moved, I would need to re-plumb the system.
My preference now for HWS is to use Resistive HWS, running off a time switch. The advantage is that one can have more than 1 HWS, so keeping the pipe runs short. An extra 1-2Kw of panels will approx cover the HW usage of a family. (10-12 Kw max needed per day). Important to use a contactor to switch the 3.6Kw load, not the relay contacts in a timeswitch.
Public hasn’t quite caught up yet.
Page 10
https://www.energycouncil.com.au/media/bytccxig/australian-energy-council-solar-report-q2-2023.pdf
Will soon be moving into a home with a solar thermal water heater (rooftop collectors, ground mount tank) but no solar PV. No idea of the water heater system’s condition but I will at least check the tank’s anode when we get there. It is electrically boosted, on a controlled load I think. New place is not far from where we are now.
In our current home we’ve been using a variable power solar PV diverter for several years and that’s been the best option for us.
Heat pumps makes little $ sense given water heating with resistive element costs us less than $40/year to run (we only consume ~5 kWh/day to heat water, it’s northern NSW and we have 11 kW of PV + 2 hours free grid energy every day).
In the new place if/when the solar thermal fails we could just put in a much cheaper and highly reliable resistive element stainless steel water heater, move the water heater circuit off controlled load and set it for 12-2PM and it would cost nothing to run, be an easy replacement and it will last a very long time.
The main issue with the new place is the pool heating is also solar thermal and takes up all the prime roof real estate. Fortunately there is a large shed roof I’m eyeing off for installing as much PV as I can.
Hi Alex,
They make heat pumps for swimming pools too.
Easiest way to diagnose split system solar is to feel the pipes. When the pump is running one will be significantly warmer.
Bear in mind the little magnetically coupled pumps will hum quite happily if they are pumping well or if the impeller is jammed. You can’t tell by ear.
Thanks Anthony, yes aware of heat pumps for pool heating and will be learning about the existing system.
Heat pump for pool would be the longer term plan, it could even be taken off-grid as I suspect we’ll have some tight limits on how much grid-tied PV we can install. But for now converting a known working system is not in our budget (the former owner sold and installed solar thermal pool heating systems). Current system provides a 10 month swim season.
Aside from not having solar PV, the home has no heating or cooling system either. The local climate means it’s likely not needed all that much but it will be needed at times and so heat pumps for reverse cycle aircon will also be going in. That’s a whole ‘nother research project!
Hi Alex,
Try https://m.facebook.com/groups/MyEfficientElectricHome/
Maybe it’s just me. One of my cars is now 57 years old, my Home Theatre speakers are 51 year old Janszen electrostatics, and I hate throwing good stuff that still works (or that can be easily and cheaply fixed) away.
Energy wise, we put a solar thermal HWS on back in 2007 – wow, that is 18 years ago! In 2009, we spent a lot of money on a “HUGE” 1 kW solar panel system. We now have two 6.6 kWh PV systems – one north facing, one east/west facing, to maximize daily solar usage – and battery backup.
Our solar thermal HWS sprang a leak about a year ago (it had a stainless steel tank, but it split at a weld – disappointing, but it made it to 18 years). Time for a replacement – do we go heat pump, plain resistive, or another solar thermal? We decided to go with another solar thermal. Our house and garage roof is already maxed out with solar panels, so it was unlikely we would use the space occupied by the solar thermal heat exchange panels for more PV. Being in Adelaide, we get lots of sun, so the HWS does not need any grid electricity from around October to April, and then in the other months, it’s back to a mix of solar heating and cheap Controlled Load boosting. The next time we do any electrical upgrades (which will probably be before the end of autumn), we will probably swap the HWS boosting over to daytime via a timer, where either our existing solar or the cheap 10 AM to 3 PM electricity rates will be used to boost the HWS in winter.
The solar thermal HWS is simple and cheap to run. A heat pump – not simple, and I believe still prone to failure and expensive repairs or replacement. I suspect solar thermal HWS will be economically comparable or better than heat pump HWS in SA for a while to come. Whether people choose it or not – that’s another matter.
Good points David.
Perhaps see if you can get a hot water circuit controlled by your solar inverter or a CatchControl device.
Our solar thermal was installed in 1995. ( so 30 years old this June) Still going strong. 300 litre tank in the roof with electric pump to boost pressure. Free hot water from mid October to early April. Bought another tank 5 years ago before manufacture Gramal closed down. Still wrapped up under my decking.
No heat pump is going to last 30 plus years.
My average hot water cost was .51 cents a day last year.
Good on ya. Heat pump is clever/efficient use of C.O.P. science and sort of negates the inefficiencies of any PV source involved hey.
Keeping it simpler for me is my DIY H.W.S. >
The old incontinent solar thermal HWS panels started having pipe leaks. I decommisioned it, improved the (remote) 180L tank insulation, screwed in a 48v element (modified to 96v), installed a 240v thermostat, put 6 x 250W used grid tie panels on the roof in 2 strings of 3, made a Solid State Relay thermo switching circuit to operate from 12v via the thermostat, adjusted that to 95c and installed a thermo mixer on the output as in this article above to make it safe at the hot water taps. No teenagers 🙂 just 2 of us, we are careful and lasts for 5 rainy days.
About the removal of solar hot water, did you consider using an instant electric hot water system ?
I purchased a house which had one already installed. I liked that you never run out of hot water (except in a grid outage) and you only pay to hear the water you actually use, you are not heating a tank every day regardless of use. However it does draw a lot of power when used ( seems to average pulling 9kw )
I like it even better now we have solar and a battery, having a PW3 means its discharge rate matches the IHWs draw rate.
We have not lived in the house over winter so as the days get shorter we will see the hot water usage in the evening and morning drain the PW and need to import from the grid.
Hi Mark,
I would be hesitant to run an instant electric hot water with a PW3 because it’s pretty hard work for an inverter & battery.
Wracking it with a 9kW load for the duration of a shower won’t do the battery much good.
Interesting to know it seems to cope without derating itself after some time..?
An interesting factoid about solar+heat pump:
20% efficient panels x 5:1 COP = the same amount of energy goes into your water as hits your panels. Always bemuses me that the panels aren’t the heat exchanger, in that this would be a kind of back-to-the-future-II kind of sequel to this article.
I did this 5 years ago, when Finn was pumping for solar thermal. The reason was 10 years of no more gas connection = capital cost of a HPHW system (well, capital premium over a gas heater anyways).
Seems that I’m going to remain one of the “odd ones out” in relation to this.
I’ve chosen to buy a brand new evacuated tube solar hot water heating solution from Run On Sun Australia. The design works for the additions and alterations on my original 1960 built Adelaide Hills home (Belair) specifically caters for it.
My split system (tank indoors in a services room) I’d argue is completely different to the close-coupled flat plate system that you’ve described. I would never buy one of them.
I’ve got no shortage of good quality roof space for solar PV… also by design.
Let’s catch up in 20 years time and compare systems and the total electricity consumption numbers (mine has mid-tank electric element boost)
If roof space is an issue, sure you can’t beat pv panels, but if you have the roof space, both is a great way to go, then your hot water is not pulling power from the grid or zapping batteries at night.
Hi Mark,
Using batteries to heat water really is a fools errand, you’ve got that right.
I did the same thing a couple of years ago. Also ripped off my perfectly functional pool heating. Needed the roof real estate for PV panels.
Hi Kris,
As installers we hated pool heating because it was usually wasting the best available space on the roof just to warm some water.
Many people now use heat pumps to warm the pool & then with PV solar they can power other things when the water is warm or it’s not swimming season.
Question
Im interested in installing underground copper pipes for our new heat pump. We live at 950m near Canberra and experience long cold winters. Can you tell me the pros and cons. From what I understand the efficiency of the system depends on the difference in temp between the source (ground) and the desired temp.
Although written about personal experience, the author has inferred that his experience must apply in all other situations (ie solar thermal belongs in a museum). If you are 100% off-grid as I am, solar thermal with gas boost remains a reasonable option for diversification of energy inputs. You either use a petrol powered generator to charge a battery to boost your heat pump or you use LPG to boost your solar thermal. We are currently doing the latter but we need to replace our hot water system and will carefully consider the best option moving forward.
I also scrapped the gas meter with a Reclaim hot water unit. An amazing piece of equipment, you hardly know it’s there.
Interested in solar water heating/ heat pumps for new house.
You may be right with your Heatpump and Solar electricity vs solar hot water and gas.
There is big difference in staying along the coast and staying in the country side. Specially if you are on an off grit solar system.
I can see in your circumstances this makes perfect sense, but I wouldn’t necessarily advocate it for everyone, living everywhere.
I live in Canada, and I want to plan a system for my new home I plan to build, and I want to build a system that works all year round, including -40°c winters. The days are very short, so you’re not getting much PV input, and what you do get, you’ll use through the middle of the day when you time your big appliances to come on.
I’m thinking of building a system of Solar PV and solar thermal, where much of the solar thermal heat is deposited under the house, below the frost line, in a form of thermal battery, so none of the summer excess heat goes to waste. A 2nd set of lines will use this enhanced geothermal heat, and liquid to liquid heat pump technology, to ensure I have plenty of hot water for both heating the home (underfloor) and DHW. By using vacuum tube solar thermal tubes, they can continue to work, albeit at a reduced rate, through the winter too, and this will greatly reduce the load resting on the PV shoulders.
No system is perfect, but I think this should work pretty well for where I live.
Elsewhere at Solarquotes there is advice about solar diverters that, I think, makes the point that resistive element HWS are good for this because they can use small (voltage) amount of excess solar whereas heat pumps can only use full voltage.
Anyway I ordered a dual element replacement HWS so that, in future, I can look at the diverter option. The main element is on a controlled load circuit. But there is a spanner in the works… the electrician explained that, under the latest standards, dual element HWS must have a common neutral line and so second element would have to be part of the controlled load circuit – the explanation being that plumbers who switch off one circuit to work on the tank could be zapped by the second circuit.
Does this make sense?
Hi Michael,
All the neutral wires are bonded to the same bar in the switchboard in any case.
Dual element units have always routinely been wired with lower element connected to off peak/controlled load as well as day tariff on the top element.
If you put an isolating switch next to the hot water tank, both active supplies can be ganged together through the same mechanism.
One switch will make the plumbers safe.
I’m just doing the opposite of what you did.
I recently installed a 1500L tank and bought very cheap second hand solar vacuum tubes.
My reasoning goes like this: Solar panels have an efficiency of ~20% compared to a vacuum tube system (with back reflectors) of say ~80%.
Take a good heat-pump with a scop of 4 and you need about the same (solar) surface to heat your water.
The difference kicks in at higher temperatures say at water temperatures above 30°C (sorry for the Fahrenheit guys) where the (s)cop of the heat-pump hits rock bottom whereas the vacuum tubes still shine (pun intended).
A little online calculator reveals that heating 1500L of water from 30 to 90°C needs an energy equivalent of ~100kWh.
I can store the hot water for many days, as the tank is well insulated. If I wanted to store this energy in form of electricity (Which I could use in turn to heat the water via resistive heating where the Ccop is ~1)to get from 30-90° I’d need a battery of 100kWh – which really isn’t cheap.
To finish the story: I’m installing the solar pipes in my garden, along a long and already existing wall. When spring comes and I need less heat to heat my home I’m gradually covering the solar tubes with solar panels using a dedicated attachment mechanism. This protects the pipes from overheating and produces cheap energy at the same time.
Of course this only works because my installation is easily accessible.
I will keep my on roof tank solar thermal and replace with same for engineering simplicity, super long life (around double heat pump), silent operation, near zero running costs and grid down/off grid capability.
Each to his own!
I cannot seeho replacing a solar thermal makes sense. In Sydney I have a solar thermal. Close coupled system that is now. 25 years old and still with now issues. My mother in laws solar close coupled is now almost 40 years d an still working both with controlled load electric boost.. Whilst you may save a small amount in electricity over a few years then what is the life span of a electronially controlled compresor based system. The close coupled flat plate has no moving parts or electronics and can last many years longer. Your compressor system may well have a life of say 10 years so any electricity saving will be well and truly counteracted by the replacement costs of the compressor based system. This is before we even get to the embodied energy in the manufacture, transport and installation that will probably be done 3 or 4 times as often for compressor systems as compared to flat plate systems.
I moved to Northern NSW in October last year, and the house came with a 4yo Solahart close coupled system. Grid power has been turned off the whole time!
My last house in Brisbane had 6.6kWh of panels with a 5kWh inverter, and a switch so the electric HWS only came on in the middle of the day…worked well with generally free HW…unless it was a hot day and I needed AC too.
I really like the Solarhart and won’t be removing it anytime soon…even if it needs boosting in winter (only time will tell). The house has a 10yo old 5kWh cheap Chinese inverter that can peak at 3.5kWh in the middle of the day. I still have plenty of roof space when it dies, but reckon I’ll keep the Solarhart anyway.
Hi Mark,
There’s a good reason these things haven’t changed much for the last 45 years, though I do wish they’d offer an evacuated glass tube collector.
Hi, I’m confused, in SA a single phase home with solar is limited to 5K most new systems add panels to the maximum allowed by the inverter.
How does adding panels to the system for running a heat pump work surely it would overload the inverter when the heat pump isn’t heating.
Our 20 year old Edwards is still working as its on rainwater, I’d probably replace it with the same if it fails.
Rgds Stewart
Hi Stewart,
We have a few articles on oversizing if you want to click here for more.
SA will allow 10kW of solar inverter capacity per phase for generation, plus another 10kW for battery inverter capacity. (but a hybrid counts toward both totals and you have a site limit of 30kVa)
Solar is limited by manufacturer spec so theoretically if you had six Sungrow 5kW units on a 3 phase property with batteries; it would be impractical but you could have 72kW of solar without needing secondary network protection.
So far I’ve seen three 10kW units and 60kW of solar actually deployed.
Anthony, so – hypothetically in SA on a single phase, if someone were to have (A) an existing 6.6 kW panels with a 5 kW inverter (no battery), and (B) an existing AC coupled battery with a 5 kW inverter (no panels), they could add (C) a new hybrid system consisting of 6.6 kW of panels and 5 kW hybrid inverter with a battery and not exceed the limit?
(A) + (C) is 10kW of solar inverters and (B) + (C) is 10 kW of battery inverters. Have I understood you correctly?
Hi David,
I think you’ll get away with that, however making it all equipment compliant with Flexible exports may be a stumbling block. They offer no grandfathering of old gear sadly, but CatchPower and Switchdin may be able to help with technical solutions.
Speak directly to SAPN for confirmation.
https://www.sapowernetworks.com.au/connections/connect-solar-and-ev-chargers/small-embedded-generation/technical-standards-and-useful-links/