# Forum Home Renovation Plumbing  Solar Hot Water vs Heat Pump

## mattwilliams78

I live in an area with no mains gas. I was thinking of replacing my existing electric system with either a new electric boosted, solar hot water system (split system - don't want tanks on my roof) or a reverse cycle heat pump system (i.e. Dux Airoheat). Rebates are similar for both so it just comes down to installation costs and preference. 
Does anyone have any advice on which to go for?

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## woodbe

Go Solar if you can, but beware of badly situated or shaded roof. Be aware that a difficult install due to roof height or access will easily add years to the payback. Whatever you do, put the boost onto offpeak power as it will still be supplying a significant amount of your hot water. See if you can fit a switch to it and turn it off completely during the hotter months. 
Personally, we went with offpeak heatpump (Siddons) due to a badly situated and very high roof. It has slashed our hotwater power bill by 75%. 
Michael

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## Smurf

If you are in an area that is affected by frost then the heat pump will be less hassle. No glycol, drain valves and so on to go wrong and with a 70%+ power saving it would be hard to beat with solar in cooler climates anyway. 
I'd look more seriously at solar only if you didn't have mains power or lived in a more tropical climate where you won't need to worry about frost.

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## Bloss

> If you are in an area that is affected by frost then the heat pump will be less hassle. No glycol, drain valves and so on to go wrong and with a 70%+ power saving it would be hard to beat with solar in cooler climates anyway. 
> I'd look more seriously at solar only if you didn't have mains power or lived in a more tropical climate where you won't need to worry about frost.

  None of these issues now apply to solar. The coolness of the climate is not the issue - the amount of sunlight is - so for example Canberra in winter sill has about 5.5hrs of sunlight. Sydney  has around the same number of hours - cloud cover reduces it compared to Canberra. Evacuated tube solar is the go. Good point about boosting too - although IMO better not to use off-peak, but to have manual switch inside the house.  But having said that heatpumps will give good service and savings too. 
Although solar needs some electricity to move water around it is a tiny amount. Energy costs will continue to rise so the return on investment period for solar will reduce over the life of the system and increasingly so  - the bills for the heatpump will increase as electricity prices increase (and they will - IMO dramatically) over that time.

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## woodbe

The point about having switchable offpeak boost is that south of Queensland, boost will be required for a significant part of the year, and paying day rate for that boost will become quite expensive, especially with escalating energy costs. 
Also, don't forget that our largest demand for hot water is during the winter months, when solar is performing at it's worst. $$$  :Frown:  
In southern climes, a heatpump HWS on offpeak will probably cost less to run per year than a solar system with day rate boost.

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## mattwilliams78

I've been digging around and I found a few people complaining about noise with the heat pump (being a bad neighbour, causing disputes) and also about expensive maintenance on the heat pump if it all goes wrong i.e. you need to call out a fridgie and a plumber, extra costs. Has anyone come across that? 
I haven't done the calcs but I was chatting with people at work and we agreed that it was pretty hard to beat the cost effectiveness of an off-peak hot water system. To be honest my main motivation is to get mains pressure on the hot water, followed by reduced CO2 emissions at no extra cost followed by reduced bills (my bill is already pretty low - only about $60 a month for two of us, can't see how I would save much more than $15 or $20 a month.) 
I won't have any problems with frost - coastal Sydney. And if all goes to plan I am considering reroofing in 3 or 4 years so the panels may have to move temporarily.

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## Bloss

> The point about having switchable offpeak boost is that south of Queensland, boost will be required for a significant part of the year, and paying day rate for that boost will become quite expensive, especially with escalating energy costs. 
> Also, don't forget that our largest demand for hot water is during the winter months, when solar is performing at it's worst. $$$ .

  Well  practical experience in Canberra and region, some of the coldest area in the country says no it isn't - unless you do not use the solar and boost sensibly. Many people are surprised because they use off-peak or day rate boost and no change to use patterns and get lower savings (sometimes none) when moving to solar. The system needs to be designed to suit - that means choose optimal panel placement direction to north, angle, no shade etc, the largest tank you can afford or get (and upgrade the insulation on all tanks of whatever type!), and that use-habit change - mainly showering in the mornings not later afternoon or night. The best will have a switch inside for the boost and a timer - so that you can set when any boost comes on - manually if you do need it, but in the hours you know are best for your installation location and usage patterns, and by its thermostat at those times. 
Demand for hot water is actually higher in summer months when people take more showers (usually the highest use) and often longer ones. No-one should be washing with hot water nowadays and most dishwashers use an internal element heater even if you don't want them to. Sure the solar produces more hot water when there are less hours of sunlight, unarguably, but with commonsense and good design that can have little impact - less in Sydney too as the water rise temperature is quite a bit lower.   

> In southern climes, a heatpump HWS on offpeak will probably cost less to run per year than a solar system with day rate boost.

  That is not my personal experience or that of many other I know in the ACT region. My comment was mostly about making assumptions on costs _now_ - the capital cost and running costs need to be over say 6-8 years (to be conservative) and IMO energy costs will rise dramatically over that time (and calculations need to account for the cost of the money although that is reduced now). 
Even on small usage the percentage savings in Sydney would be around 60-80%, but without knowing more detail of how much is HW vs stove, lighting etc hard to quantify by us. A $60 bill is very low so the numbers make it harder to get a reasonable return on investment. But your reason include mains pressure - either will give you that (the pump I referred to for roof top solar only circulates the water to and from the panels - the water to your outlets is at mains pressure. 
On environmental grounds solar is still more efficient overall - the electricity you use comes at <25% in Australia ie: the energy used to produce it vs energy at your house. The heat pump itself is very efficient (a COP of 3 to 5 for units in Oz residences), but does not counter the earlier losses in production and distribution of the power. But 'reducing CO2 at no extra cost'  :Confused:  One way or another we are all going to be paying extra costs to meet greenhouse gases and our wasteful uses of fossil fuels and that will increase rapidly over the next several years - solar will shield you form much of that. 
Noise is nothing like A/C, but there is a compressor and condenser and if the neighbour has close windows etc that can be an issue with a  heat pump - not usually though. Effectively no noise with a solar though and none with off-peak. Moving evacuated tube solar to re-roof is a snap, but the frame a little harder, and pipework would need a plumber if you could not work around it (often you can). 
Summary IMO - Lifetime investment lowest cost and best ROI to meet all your issues is evacuated or flat plate solar - (300-400l tank). Next is heatpump, but electricity costs will continue to increase and at an accelerating rate  - forecasts are always problematic, but I'd bet heaps on that one being right. If you are looking at cash now and how much to run over the next year or three then a standard off-peak (as you have no gas) will be cheaper by far. You'll get a little greenhouse reduction, mains pressure and lower capital cost - but over the life of the system you will pay dearly for that choice. Of course you might move and then the off-peak is the buyer's problem!  :Smilie:  
Funny how complex a simple decision can get eh!

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## mattwilliams78

Appreciate all your comments Bloss, I agree with what you're saying (though I'm not sure about the payback of the evacuated tubes - they seem to me to be more of a cool climate issue and that on my 350deg (NNW) facing roof I'm hoping/guessing that I will get enough off a flatplate) 
To explain my CO2 reduction at no extra cost - in very simple terms. Say my existing off peak system uses 10kWh of heat overnight - about 70c worth on off peak rates. I switch to solar but I still need 5kWh of boosting (conservative 50% saving in energy/greenhouse) but those 5kWh during the day will cost me 14c each or 70c overall. Therefore I have halved my CO2 at no extra cost. Since my bill is only $60 a month I am guessing that any increases/decreases will be no more than +/-10/month. Some providers charge you that for Green Power anyway. 
I'm thinking solar will be the way to go. Through my employer I'm hoping to get a discount on a Rinnai Beasley/Sunmaster flatplate system so I'll let you know how the plumber quotes go.

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## mattwilliams78

sorry, rereading your comment "CO2 savings at no extra cost" I mean operational cost. I'm willing to lose the installation cost in rebates, "K Rudd stimulation" and getting myself reliable new mains pressure hot water.

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## Uncle Bob

I wonder how the reliability is for heatpump systems too. Being mechanical with moving parts brings extra failure modes.

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## woodbe

Bloss, No argument that solar is preferable if the situation suits. We disagree on the peak/offpeak power connection, and that is a small difference that could be changed down the track. 
Heatpumps are pretty reliable. Well, as reliable as any other modern refrigeration unit. We chose the Siddons because of it's slightly higher efficiency, lack of a defrost heater element, and use of a standard split system outboard unit that can be serviced using standard parts. Being a split system, the heated water tank can be placed in a protected area away from wind and rain if desired. As far as noise is concerned, it is very quiet we never hear it run, but then again, I wouldn't park it outside someone's bedroom window either... 
We have in mind that if the power price escalates to make the few kw that the heatpump uses expensive, it will make a very efficient boost system for our future solar panels high up on the roof. 
Regarding FlatPlate and Evac Tubes, apart from the efficiency, also consider hail damage. Evac Tubes being less prone to this. 
woodbe.

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## Smurf

From a resource use perspective, it's ridiculous to be running any storage water heater on a continuous electricity supply unless there really is no other means of you getting hot water.  
The entire notion is absurd when you think about all the energy transformations and losses it involves. Building power stations and transmission lines which burn fuel to heat water to produce steam to turn a turbine to generate power to heat water which is stored, with losses, for use at an off-peak time. Truly ridiculous when you think about it. At least with off-peak we don't have the inefficient plants running and transmission losses are lower - it's still not an efficient process but at least it's better than running at peak times. 
As for heat pump versus solar, the simplest way to look at it is which will use less electricity? Assuming use of the same tariff for the booster or to run the heat pump, If the solar is saving 50% then you'll be better off with a heat pump which saves 70%. But if the solar will save you 80% then that's a better option.  
For me here in Tassie, it would be hard to get a 70% saving with solar. Typical figures are more like 50% for most systems. That makes a heat pump a more attractive option in this climate. Obvioulsy it's different if you live somewhere hot, in which case solar would be the better choice. 
As for the Summer versus Winter usage argument, I can confirm from electricity industry data that Winter hot water loads are substantially higher than Summer hot water loads. From memory the increase is in the order of 30% so it's not trivial. These figures are for households in Tasmania (almost all of which have electric hot water) and may differ in other states (though Victoria would likely be pretty much the same).

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## Smurf

> To explain my CO2 reduction at no extra cost - in very simple terms. Say my existing off peak system uses 10kWh of heat overnight - about 70c worth on off peak rates. I switch to solar but I still need 5kWh of boosting (conservative 50% saving in energy/greenhouse) but those 5kWh during the day will cost me 14c each or 70c overall. Therefore I have halved my CO2 at no extra cost.

  Don't forget that power generation during high demand times is less fuel efficient at the margin. Also losses will be higher at that time too. Also the energy and emissions associated with building more power stations, transmission lines etc to meet greater peak demands which do not exist at all if you go off-peak. Also the greater variation in system load reduces the practicality of using renewable (instead of fossil fuel) generation sources in the overall supply. 
I'd only go for a boost on the continuous tariff if you can make sure it's only used at off-peak times. The idea of running it at, say, 7pm in Winter makes for a rather polluting boost. I'd personally just go off-peak.

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## woodbe

There is a discussion on envirotalk of these issues, with interesting conclusions regarding electricity use in non-ideal solar latitudes as well as the merits of Evacuated tubes and flat plate (and other stuff):  Evac Tube discussion 
woodbe.

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## Bloss

> I wonder how the reliability is for heatpump systems too. Being mechanical with moving parts brings extra failure modes.

  They are very reliable - but more to go wrong than solar - have similar warranty periods. 
As to peak vs off-peak most energy providers will not allow day rate boost - just switched off-peak (with daytime and night time periods) - still worth having your own over-ride. 
The other thing with evac tubes is they can be added and subtracted by the moderately competent homeowner that really wants control of energy use. Costs have come down massively on them too - and will keep doing so. Sydney is less a concern - in Canberra I am looking at doing hydronic heating using the evac solar, but in Oz a bit early yet. I don't mind leading edge, but not bleeding edge . . .

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## Smurf

> As to peak vs off-peak most energy providers will not allow day rate boost - just switched off-peak (with daytime and night time periods) - still worth having your own over-ride.

  There's a good reason for them not allowing day rate boosting. If we all did that then, well, let's just say we'll no longer have to worry about air-conditioners overloading the system since we'll have far more regular overloads and blackouts due to heating water. 
Winter evenings are a very high demand time as it is (they are the absolute peak in some areas) and that's when people would likely turn the boosters on. If this became more than a few consumers here and there, if it actually became common to have solar HWS with day rate boosting, then we're going to have to build a lot more power stations to run them all. And they will be low efficiency open cycle power stations due to the intermittend usage which somewhat defeats the environmental purpose of it all in my opinion. 
There are some solar systems around which are fully automated and boost with off-peak. That's far more practical if we're going to have them in every house. 
I'm not against solar, actually I've always liked that idea long before the CO2 issue was mainstream. But the idea that we have even half of the houses in Australia each having a 3kW booster that they can switch on whenever they like seriously worries me. Odds are rather a lot will get switched on when people get home from work in Winter and find that the sun hasn't been shining during the day. That's the same time they're switching on the heater, oven, TV, lights etc. We don't have enough power stations for too many people to do that, the system is pretty stretched at that time as it is.

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## GraemeCook

My analysis is slightly different from the above. 
In very broad terms, solar hot water heaters basically produce about twice as much heat as you need in summer and half as much in winter, averaging about 75% year round.  This means that you pay for about a quarter of the energy produced. 
Heat pump water heaters generally have a coefficient of performance, COP, of between 3 - 3.5.   This means that you pay for about 30% of the energy produced. 
Thus there is not a major variation in the annual costs of heat pump versus solar hot water.  
With the available subsidies there is not much difference in the installed capital costs of solar or heat pump water heaters.   See www.orer.gov.au for specific details. 
Additionally, heat pumps are much more complex than solar systems.   Servicing costs and possibly a longer life expectancy tips the choice in favour of solar, but not by much. 
If the siting for solar panels is sub-optimal - eg shading from trees or other buildings - then go heat pump. 
Finally, if you have a European type house heating/cooling system using a heat pump where the domestic hot water can be an accessory to that house heating heat pump, then that heat pump addition is an easy winner. 
Cheers 
Graeme

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## Smurf

> My analysis is slightly different from the above. 
> In very broad terms, solar hot water heaters basically produce about twice as much heat as you need in summer and half as much in winter, averaging about 75% year round. This means that you pay for about a quarter of the energy produced. 
> Heat pump water heaters generally have a coefficient of performance, COP, of between 3 - 3.5. This means that you pay for about 30% of the energy produced. 
> Thus there is not a major variation in the annual costs of heat pump versus solar hot water.  
> With the available subsidies there is not much difference in the installed capital costs of solar or heat pump water heaters. See www.orer.gov.au for specific details. 
> Additionally, heat pumps are much more complex than solar systems. Servicing costs and possibly a longer life expectancy tips the choice in favour of solar, but not by much.

  Seems like a reasonable analysis to me. What location is it based on?  
As for the maintenance, I'm actually thinking the opposite after hearing various horror stories with solar panels rusting out in just a few years. In contrast, the refrigeration system in a heat pump is proven technology that ought to last as long as the tank (in theory at least).

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## woodbe

> Seems like a reasonable analysis to me. What location is it based on?  
> As for the maintenance, I'm actually thinking the opposite after hearing various horror stories with solar panels rusting out in just a few years. In contrast, the refrigeration system in a heat pump is proven technology that ought to last as long as the tank (in theory at least).

  Ours is a stainless tank, the heat transfer to the tank from the heatpump is by conduction from outside the tank (It's wrapped and bonded between the tank and the insulation) I'm actually expecting the refrigeration unit to die first, (10-20 years) but being separate units we should be able to pick up some efficiency improvements that occur between now and then. 
woodbe.

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## Bloss

> There's a good reason for them not allowing day rate boosting. If we all did that then, well, let's just say we'll no longer have to worry about air-conditioners overloading the system since we'll have far more regular overloads and blackouts due to heating water. 
> Winter evenings are a very high demand time as it is (they are the absolute peak in some areas) and that's when people would likely turn the boosters on. If this became more than a few consumers here and there, if it actually became common to have solar HWS with day rate boosting, then we're going to have to build a lot more power stations to run them all. And they will be low efficiency open cycle power stations due to the intermittend usage which somewhat defeats the environmental purpose of it all in my opinion. 
> There are some solar systems around which are fully automated and boost with off-peak. That's far more practical if we're going to have them in every house. 
> I'm not against solar, actually I've always liked that idea long before the CO2 issue was mainstream. But the idea that we have even half of the houses in Australia each having a 3kW booster that they can switch on whenever they like seriously worries me. Odds are rather a lot will get switched on when people get home from work in Winter and find that the sun hasn't been shining during the day. That's the same time they're switching on the heater, oven, TV, lights etc. We don't have enough power stations for too many people to do that, the system is pretty stretched at that time as it is.

  If you read my other posts you will see that I am well aware of those issues and have written much about them. I was saying that day-rate is not allowed and not suggesting it would be good for it to be, just that for solar users that would be most convenient. My main point was that you should still get a switch on the off-peak too - so you can control the boost within the off-peak hours not just have it at the whim of the thermostat and the energy providers timer. You can always switch off at the board, but it's more convenient to do in the house - I have them mostly installed in the kitchen.

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## Smurf

> If you read my other posts you will see that I am well aware of those issues and have written much about them. I was saying that day-rate is not allowed and not suggesting it would be good for it to be, just that for solar users that would be most convenient. My main point was that you should still get a switch on the off-peak too - so you can control the boost within the off-peak hours not just have it at the whim of the thermostat and the energy providers timer. You can always switch off at the board, but it's more convenient to do in the house - I have them mostly installed in the kitchen.

  No worries.  :Smilie:  
I was just going by your "better not to use off-peak, but to have manual switch inside the house" comment and taking that to mean a switch installed and connected to 24 hour supply. That idea just rang a few alarm bells but it's all good, just a misunderstanding.  :Smilie:

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## mattwilliams78

OK - I got the prices back from Rinnai through work and they're pretty good. The difference between the sunmaster and the beasley is somewhere between $600 and $1000 and all I can see different is the tank construction. Both systems are 315L and both have 2 Enduro panels. But the Beasley is a stainless tank and appears to have some kind of inlet arrangement that encourages stratification whereas the sunmaster is an vitreous enameled steel tank and has a sacrificial anode. It looks like it might be a standard tank rather than a dedicated solar tank. The warranty on the Beasley tank is 10years but only 5 years on the sunmaster. 
There also is some cost difference between panels but I can't see what for - the BE18801732 vs the R18801740? 
What do you think guys, is it worth the extra? what kind of maintenance costs are there on an anode needing replacing? how often?

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## Bloss

Just me - I'd go stainless. 
And Smurf - I could've phrased that earlier post better eh!  :Smilie:

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## Smurf

> what kind of maintenance costs are there on an anode needing replacing? how often?

  The anode itself costs $40 - $50. At least they did when I last bought one in 2007. 
Legally you shouldn't DIY but it's a simple job as long as there's space (nearly equal to the height of the tank) directly above the tank in order to get it out. (That would be to the side if it's a horizontally mounted solar tank since the anode will still be screwed into one end). The anode is simply screwed into the top of the tank but is not flexible so needs to go straight in and out, hence the need for space above (or beside) the tank. 
If there is not sufficient space, you would need to drain the tank (after disconnecting the pipes) and move it in order to change the anode. That's a lot of hassle and most wouldn't bother. 
Anode life depends on water quality. Manufacturers generally recommend inspection and replacement (if necessary) every 5 years. I'd be checking it a bit earlier if you live somewhere with harsh water. 
As for the tank life, my parents have a mains pressure vitreous enamel electric tank that was installed in 1978. So far so good but obviously it's going to fail someday. I have one that is dated 1994, it's quite rusty inside but I flushed it out and put a new anode in when I bought the place in late 2007 and so far it has been OK. But then I know of others who have had them fail after as little as 7 years. All of those are electric tanks not solar however.

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