Solar hot water providers recognise cheap solar PV as they shift to diverters
A new solar smart electric hot water system has hit the market in Australia, adding to a new wave of “solar hot water” technology that bypasses evacuated tubes and the like, and instead connects directly to rooftop solar, doubling as a cheap(er) alternative to home battery storage.
The new product, by long-time Australian industry player Solahart, is called PowerStore, and – like other solar diverters on the market – it monitors rooftop solar production, identifies when excess energy is available, then “diverts” it to heat water, rather than feeding it back into the grid.
As anyone following the industry would know, this service is nothing new – and has been offered by the likes of fellow Australian company Catch Power, Power Diverter, and Paladin, for a few years now.
These companies work with customers’ existing (or new) resistive element electric hot water tanks, an internet connection and a smart, small device installed in the switchboard. The smart version has cloud based software collecting data and weather forecasting.
SolaHart – as it says itself on its website – has pioneered solar water heating in Australia for over 60 years.
But times are changing, and so is technology.
Solar diverters – described to One Step by an industry insider as “the best thing to happen to solar hot water in 18 years” – have been chipping away at the traditional market, particularly as more and more Australian homes install rooftop solar.
SolaHart’s new offering in the space brings it up to speed on this. And – while nothing revolutionary – can perhaps, claim one first: a purpose-built solar smart hot water tank.
The company says the PowerStore tank includes temperature sensing throughout, and uses a two stage heating process to rapidly heat the top section of the tank first and improve hot water recovery.
It says the “unique, triple blade heating units” also allows for rapid changes in the amount of power used to match the available solar energy – such as when clouds pass or if there are changing electricity loads.
“Put simply, Solahart PowerStore is like a battery, in that it stores excess power – only it’s in the form of hot water,” says general manager, Stephen Cranch.
“Many households today fill their available roof space with panels to generate as much power as possible. However, these larger systems can produce more power than the household needs (especially during the weekdays), and this excess power is then fed back to the grid often for little financial return.
“(The PowerStore system) delivers hot water when you need it and uses your excess solar power to improve your solar investment.
“With a much lower up-front cost compared to a solar battery, it makes energy storage more affordable for Aussie families.”
Cranch offers the example of a family of four in Sydney that uses 25kWh of power a day.
“With a 5.2kW solar power system (this family) could export up to 50 per cent of its generation back to the electricity network.
“If they had replaced an electric water heater on off-peak tariff 2, the combined solar power and energy storage system could save this family up to $1,700 per year on their energy bills.”
Another Sydney family of five, this time living in Frenchs Forest, have installed a PowerStore, and combined with their 8.7kW solar system, are expected to save $3,500 on their annual power bill.
“The combination of Solahart PowerStore and solar panels will help householders enhance their solar investment,” says Cranch.
“It …helps reduce the amount of grid energy used to heat water, given that 25 per cent of your household energy is typically used for electric water heating.
“It also helps take pressure off the energy grid which is currently faced with a phenomenon called the ‘duck-curve’, where too much solar energy is being fed back to the grid during the day when demand is low,” he said.
PowerStore has a 10 year product warranty and a premium Class Y enamel coating allowing it to withstand high water temperatures and therefore store more solar energy.
Here’s a video you can watch about the technology:
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Sophie is editor of One Step Off The Grid and deputy editor of its sister site, Renew Economy. Sophie has been writing about clean energy for more than a decade.
It will work ok for those who have PV systems well over the size that’s needed normally. But as far as being better than evacuated tube solar water heating, unequivocally not!
The only problem i found with evacuated tube is that when the hot water tank is fully hot… which is quite often… it is doing nothing where as pv + heat pump will export to grid when hot water is full.
Even though your correct on that point, think about this, heat pumps require 1.2kw for the compressor to run, out of the whole PV array at least 2kw of PV needs to be dedicated just for it. Roof space needed is 10sqm, where an E.T. collector requires only 4.8sqm.
Right at this moment (1.40pm) my 9.3kw PV array is producing only 1,183 watts because it’s overcast, household load is 308 watts and the difference is putting charge into the battery, which is valuable! I certainly wouldn’t want a heat pump robing power. If it was cold enough, I could use some of that 875 watts excess to run an inverter split A/C to keep me warm!
My E.T. system has gained 3 degrees in an hour with water temp at 51, while using zero electricity.
Sure on sunny days the PV driven heat pump will work well, but it’s a trade off isn’t it and then one day the compressor will fail and that’s gonna hurt financially bigtime!
The Bosch Compress 3000, for example, only uses 600W for the heat pump. So you would still have 600W left even on an overcast day.
Sure, the heat pump is more complex technology than a simple resistive element, and will fail at some stage. The question is will it, because of it COP of 3 or whatever pay for itself before it fails?
So your saying you would risk bring in power from the grid just to heat water rather than use that power for other important loads like a/c?
On the other side of the coin the cop of 3 is only for ambient temperatures of 20c and above. On a cold overcast winters day cop will be reduced so will your PV output.
Imagine if you were off grid would you be happy to use the generator to just heat water, where if you had a properly sized E.T. solar you wouldn’t?
But I’m sure you won’t get the point!
Actually, I did some googling and found that the Sanden heat pump -which uses CO2 as a refrigerant- has still a COP of 3.2 at 10C. Where I live, day-time temperatures are never much below that, even in winter.
I also imagine that 99.9% of Australians do NOT live off-grid. So even if you had the rare day that is BOTH cold AND overcast (and usually it is one OR the other), you still need only 1kW or so to run your heat pump.
Many households have very low consumption during the day, say from 9am to 3pm. During that time a typical (these days) 5kW PV system would still put out somewhere between 500-1000W. So you would need to import some 500W, maybe for five or six hours, IF (!) you start the day with an empty (=cold) hot water tank. That will cost you about 1$ max, say, five times a year. Not a big “risk” in my opinion.
The main point why I would not install a solar hot water system these days is what Luke Sidewalker said above: With a solar hot water system that is sized to be sufficient on overcast days, you are wasting energy on most days (that or not overcast). I would rather have more PV panels on the roof, and feed the extra electricity into the grid, or charge a (future) battery, or even charge the (future) electric car.
A couple of big positives for this approach is the fact that all the plumbing is at ground level and the heating unit is not exposed to the elements. 2 or 3 kW of PV on the roof might take up more more area, but a fraction of the weight; you don’t have 300 kg of hot water on the roof. In fact I can see this being a good option whether you’re exporting solar to the grid or not – store that sunshine any way you can.
Solarhart has simply decided to adapt, rather than stay a dinosaur.
There is a better option, technically, and usually cost wise as well.
Heat pump hot water.
Run it midday when the sun is shining so it is powered from your solar panels. Unlike a standard resistive element heating unit where 1 kWhr of electricity gives you 1 kWhr of water heating, a heat pump will give you 3 to 5 kWhrs of heating from one kWhr of solar electricity. So you use your solar much more efficiently, may still be able to export some to the grid WHILE you are heating the water, and can still get all your hot water from solar for much more of the year.
I was thinking exactly the same thing. SolarHart’s concept already seems very out of date
Direct (resistive) heating of water is surely outdated when it so easy these days to get a air-to-water heat pumps. Some of them have control inputs to so you can automatically turn it on when you start feeding into the grid – maybe later in the morning. Some have simple timers, which probably works well enough in sunny Australia, since you just need 1kW or so to run your heat pump.
The new Fronius Primo inverters have a relay output you can use to control a load, like a heat pump or an air con system.
JWW I think it comes down to economics: panels at $500/kW are cheaper than RCHPs even at a COP of 3, and last much longer.
I agree – but I think a heat pump is probably more economical. The Sanden heat pump has a COP of 5.0, not 3.
Then it is a matter of roof space.
How much do you value your PV energy? 12cts/kWh?
My FiT is only 7c, so the value is even lower, and with a diverter you are less susceptible to overcast weather. My homemade diverter can turn down to about 10% without getting too hot, plenty far enough to avoid drawing grid on most overcast days.
Firstly, a HP & PV only makes sense if you already have the HP. Solahart’s shit offering will set you back $4.5k without any PV for the price.
Secondly, if you don’t have either, an evacuated tube SHW is about the same price and will effectively cost nothing to run year round if correctly sized. You can then use PV more effectively like powering A/C.
I think its dreaming to think an etshs can be operated in Canberra year round without any cost.
Ha, I live in Maitland NSW and we have on average 240 full sunny days pa, while Canberra averages 246. For 18months prior to June, I didn’t use even one watt to heat water.
Correctly sized ETSHW can do that! If it isn’t sized spot on and budget is a consideration for a lot of people, a smaller collector is used, it won’t be quite as good, but who is going to bitch about spending $10- 20 p.a. boosting?
E.T. performance has nothing to do with ambient temperature JFYI!
Why do I need a Solarhart PowerStore when I can achieve the the same with my Dux electric HWS?
Well you don’t!
See my post above.
Yes. I would also be interested in finding out why you wouldn’t just get a large Dux electronic heater. Just need to be a bit clever how you control it??
If you have enough PV & an twin element electric tank already, I have cost a effective solution for $ 2,500 plus installation. If anyone is interested call me on 0411 729 336.
I kind of like the simplicity of the standard electric element system connected to PV with a timer for the middle of the day.
It makes no sense to install rooftop solar HWS, given it is largely wasted space in the summer when much of the collected energy goes to waste, unlike PV.
We find that a heat pump (Sanden), operating between 9 and 3 on a timer to maximise the daytime warmth and solar PV works really well. (disconnected off-peak/ controlled load)
I wish the govt, or some other independent body would do life cycle costing for each of the hot water and PV options.
I note the article referred to controlled load 2. Most people without solar hot water are on control load 1 where the tariff is less than the best FIT. In this scenario the are better off selling their excess to the grid.
Good idea. I’ve oversized my PV considerably for most days, so usually have plenty extra to divert and, since off-grid, would otherwise toss the extra. Now, does anyone know of a good off-grid diverter or am I stuck with home brew solutions?
I looked at http://mk2pvrouter.co.uk/1701.html
from the UK, but have not gone further yet
Ok the SOLAR CONSTANT – or the agreed averaged amount of solar power hitting the earth surface, from sunrise in the east, to sunset in the west and the north and south poles and the super intense equitorial sunshine at midday…. Everyone said cut the crap and call it an averaged of 1000W of solar energy per square meter. A simple coil of 3/4″ or 19mm poly pipe of about 2 meters in diameter, gives an area of (2 x 2 x 0.78 “The Hanson constant” ) of a bit over 3 meters squared, and from the time decent sun hits it, it’s putting out 500W and it peaks at maybe 4000W and then it wanes later in the day..
Now if we use an indirect heat exchanger or a pipe carrying the HOT solar heated water through the bottom of the electric hot water tank at low pressure, by thermosyphoning, where the hot water rises and the cold water sinks….
If you work this out – and I have not timed this in a long time, OK and I will round things up or down more to illustrate the point, rather than being “more” technically correct…
Assuming that 1000W will heat 1 liter of water from 20*C to 60*C in 2 minutes. That is health and hygiene water temperatures, and I have a hot water tank of say 200 litres, well if we average the suns heat input to around 1000W for 10 hours a day, then 10 hours = 600 minutes — divided by 2 minute lots — = I can harvest enough heat to heat 300 litres of water from 20*C to 60*C……
So for those of us in the southern hemisphere….. i.e. Straya.
What some REALLY clever person figured out was that rather than having your panels ALL facing north (hypothetical maximum sun harvesting position) – with MY modifications – IF you had say 30% of your panels facing north east, and 30% of them facing north west and 30% of them facing west, you would be doing MOST of your harvesting during the times of the peak loads….
A simple double glass covered and insulated poly pipe coil – with some brains and a low pressure pipe side and a water to water heat exchanger in your high pressure side…
The thin walled poly pipes last a LONG time – 20 – 30 + years…