Below are some of the most frequent questions we are asked by our customers. We hope you find the answer you seek but if not please fill out the form below and we will be in touch with you and also add the question and answer to this list.
How does solar hot water work?
Solar Hot Water is actually a pretty simple technology. Imagine if you go out into the garden in the Summer and you pick up your hose pipe, and you turn it on, and you say wow that’s hot, that’s how simple the technology is.
So basically the infrared spectrum of the sun, heats up water that’s in an efficient solar collector and the heated water is transferred to the tank either through thermosiphon, where the tank is above the solar collector or through a pump which is controlled by a solar controller, which tells the pump when to switch on and off.
While a hosepipe will do all the work for you in the summer, you need a solar collector because you need to get some winter gain and to get through those days when the sun doesn’t shine.
What are the differences between Solar Hot Water and Solar Power?
Fundamentally these are two quite different technologies, the Solar Hot Water system harvests the infrared spectrum of the sun, the heat spectrum of the sun, whereas PV or Solar Power Systems are a much more complex technolgy that harvests the light spectrum of the sun.
The Solar Power System leans more towards the ultraviolet spectrum, but generally the whole of the light spectrum and takes the irradiance of the sun, which acts on the contaminants within a silicon chip. This creates positive and negative ions that create direct current (DC) that then gets converted into our 240V (AC) by an Inverter.
So, as you can see Solar Power is much more complex in terms of the differences in the technology.
Does Solar Hot Water make more sense than Solar Power?
The equation has recently changed with the feed in tariff for Solar Power System’s now only 8 cents for every kW hour you produce from your panels, over and above what you use. As you pay at least 26 cents for every kW/h you use, it only really makes sense to have a system that will cover your daytime usage, primarily during the time the hours when the sun is highest in the sky.
To produce an excess you would have to have a very large roof to justify producing enough electricity to cover the cost of your night time usage.
Hot Water generally according to Sustainablty Victoria represents up to 28% of a households energy usage, and here is Southern Victora, with a gas booster you can save 75% of that with a good effcient system that is properly sized and with an electrically boosted system you can save 60%.
So it definitely makes more sense to get a Solar Hot Water System in the current environment with the pathetic feed in tariff (FIT) of 8 cents, but really both of these technologies will pay for themselves, and they are two of just seven things you can buy in your lifetime that will actually pay for themselves.
What’s the right sized Solar Hot Water System for my home?
In a Solar Hot Water Heater, you are looking for enough hot water being heated free from the sun, to see you through a few days of cloud and rain, so, big is beautiful.
If you have a large body of water being heated by an appropriate amount of solar collector then you can use the water for your household one day, and then if you have a bit of rain the following day, you have a large enough tank with residual hot water which means you are not going to be using as much gas or electricity to boost it, and that means it’s a more efficient system and that also generally means you get a better rebate.
So, by going to a big system, bigger than what you would normally have, then you are actually getting a bigger bang for your dollar.
Where should I site my solar hot water system in my home?
The first priority is siting the solar hot water tank as close as is possible to your kitchen and bathroom /s. In some homes this is difficult because as a result of poor planning the bathrooms are at opposite ends of the home. Remember that the bathrooms it where the largest volume of hot water is used and that the kitchen is where the greatest frequency of use is.
If you use hot water in your clothes washing then the siting in relation to the laundry would seem to be another consideration – but in reality it should not feature in the decision making about where to site your solar tank as all the water will go into the washing machine (no water wastage) and the machine won’t mind waiting for the hot water to come down the pipe.
If you are using gas to boost your hot water in the winter then the continuous flow gas booster (used in most systems) should be installed right next to the solar tank (or even mounted on the tank if that is appropriate) as the closer the gas booster is to the solar pre-heated water the sooner the gas will switch off and so the savings in gas start then.
If you separate the solar tank and gas booster then the gas will fire up to heat the cold water sitting in the pipe between the tank and the booster everytime you open a tap and the solar pre-heated water will “die” in the pipes when you switch the tap off which will have the effect of reducing the overall efficiency / savings.
Sometimes it makes sense to have a roof mounted solar tank in circumstances where the bathrooms are on opposite sides of the house, as the solar tank then is in a more central position in the house.
There are other advantages in a roof mounted tank (see close-coupled / thermosiphon systems), but because of the need to keep the tank and gas booster close together the roof mounted tank makes best sense in an electrically booster Solar HWS, except where there is a flat roof, in which case, the gas booster can be mounted on the back of the mounting frame.
Note: There are regulations that relate to access to gas boosters that vary around Australia and you should check with your installing plumber about how to resolve these issues. Sometimes a ground level on / off gas cock is sufficient and other circumstances may require having permanent roof access stairs to meet the regulations.
Where should I place my solar collectors?
Your North facing roof is the place to put your solar collectors. Sometimes this is not possible because you may have filled it with PV (solar electricity) panels or you don’t have a North facing roof available.
The West roof becomes the next best choice – and it is not as bad a choice as people imagine as most solar hot water systems will deliver all the hot water you need in the summer months so winter is the time when you need to maximise the havesting of the Sun’s heat and in many parts of Australia we have overcast or cloudy mornings which dissipate by mid to late morning and it is normally only a short wait before the Sun falls on the West facing solar collectors.
With evacuated tubes it is possible to use a frame to side-pitch the solar collectors on the West facing roof to point North. Here the frame is attached to the roof so that the manifold at the top is parallel to the roof not to the ground. Evacuated tubes have gaps between each tube for the wind to pass through but flat plate collectors present a 2 or 4 square metre “sail” to the wind and side pitching this style of solar collector is not wise (nor is it allowed by regulation).
The further South of the Tropic of Capricorn (23.5 degrees South, roughly Rockhampton in the East and Cape Farquhar in the West) you are: the further North from East and West the Sun rises and sets in the winter and the further South it rises and sets in the summer.
The Winter Solstice (shortest day 22 June) is the date to check if your roof has any shading issues.
What angle should I put my solar collectors on?
Laying the solar collector flat on the roof is the easiest (cheapest) option. Most Australian roofs are 26 degrees and this angle is acceptable.
In the case of flat, or near flat roofs, a pitching frame is necessary. In the case of flat plate collectors the angle is prescribed by regulation depending on the wind zone in which you live.
With evacuated tubes because windage is not an issue, you are able to set the angle of the collector on the frame at a steeper angle. Popular wisdom says that you should set the frame at the angle of your latitude plus 5 degrees but you can go steeper if you wish, this allows you to “spill” some summer over-efficiency and get some additional winter gain. Aesthetics will play a part in your decision.
What are the differences between flat plate and evacuated tube collectors?
Flat plate collectors are 2m x 1m generally, as described they are covered by a flat glass plate and are the traditional solar collector and they work fine.
The evacuated tube is a more modern solar collector, and it s one that the Australians invented 30 years ago at the University of NSW. The evacuated tube is essentially a 2m long test tube, with another test tube inside and the air has been evacuated from between the two layers of glass. This means that the suns rays travel through a vacuum and so when the heat is collected on a heat collection surface nothing escapes because their is a vacuum between it and the outside atmosphere.
One of the fundamental differences between the flat plate collector and evacuated tube collector is that the evacuated tube presents a curved surface to the sky, so the suns rays come in on the perpendicular from early morning to late evening, whereas the flat plate collector has a higher degree of reflectivity as it has a flat surface to the sky. So the evacuated tube has a passive solar tracking system, and the flat plate collector has some high reflectivity.
Having said that their are also high peformance flat plate collectors with slightly prismatic undersides to the glass that reduce the amount of reflection.
A flat plate collector or a hosepipe will do all the work for you in the summer, the only gain you get from an evacuated tube is in the Winter and it’s probably marginal, but there is no doubt in my mind, that the evacuated tube is more efficient.
Why Boost Your Solar Hot Water?
The temperature of your hot water will need to be raised to 70 degrees in the case of gas boosted solar hot water and 60 degrees in the case of electrically boosted. This is to meet regulations that exist to kill bacteria in water.
Given that most people shower in 40 degree water, many users of solar hot water dice with Legionella and turn their boosters off (gas ignition at the power point in the case of continuous flow gas boosting and at the circuit board in the case of electric boosting) in the summer months, during which time the temperatures in the solar tank very often exceed this minimum just from The Sun’s heat.
Boosting your Solar Hot Water with gas
Almost all gas boosted solar hot water heaters use a continuous flow (sometimes called an Instantaneous Gas water heater). These are wall mounted units (although they are often seen mounted on the back of pitching frames where solar hot water systems are placed on flat roofs). The beauty of this method of boosting is that the gas switches off as soon as the solar pre-heated water gets to them in the summer and as soon as you turn off the tap in the winter – so you only heat the amount of water that you use and no more.
It is important to order the correct type of gas booster. There are two types of gas available: Natural gas this is town gas that is piped to your property from the street via a gas meter often found at a front corner of the house. LPG (Liquid Petroleum Gas) is bottled gas which needs to be used if mains gas supply is not available in your area. The two different gasses require different gas jets and the units are not interchangeable.
These are high megajoule (Mj/h)units (20 litre per minute [lpm] gas burners require 160 Mj/j 26 lpm units require 200 Mj/h and 32 lpm units require 250 mj/h) that use a large amount of gas for a short period as they heat cold water as it passes through a heat exchanger. This means that if you are replacing an existing gas storage heater you will almost certainly need to up-grade the size of your gas supply pipe and probably back to the gas meter (or bottle in the case of LPG). The cost of this upgrade will depend on the size of pipe required which in turn is dependent on the distance between the gas booster and the gas meter, but for an easy calculating you can allow $50 per meter for the copper and the labour to lay it.
Continuous flow gas water heaters require the tap / shower to be fully turned on as the gas will switch off (for safety reasons) if there is a flow of less than 6 litres per minute. In the spring and autumn, when the water temperature in the solar storage tank is at about the temperature that the gas booster is set to boost to (70 degrees) then the gas burner sometimes switches on and off causing a temperature fluctuation.
To avoid these two issues and to avoid an expensive gas pipe up-grade, some people use their existing gas storage heaters as the solar booster. This saves the cost of a new continuous flow gas booster, the gas pipe up-grade and the additional cost of plumbing a new booster. However, this means that they will not qualify for a rebate as there are only a few solar hot water systems that have registered pre-heaters for rebate.
Boosting Solar Hot Water with Electricity
An electrically boosted solar hot water heater is substantially less expensive that a gas boosted solar HWS as there is no need to purchase a separate continuous flow water heater or the additional plumbing labour to fit it.
Most solar hot water systems come with a choice of Mid or Bottom mounted electric elements and these are usually connected to off-peak power when available. Because the mid element only heats the top half of the tank your electricity costs are going to be lower – it is more efficient and therefore attracts a larger solar hot water rebate (STCs).
In a 400 litre solar tank, a mid element will heat the top 200 litres of water at night which is plenty for a household of up to four people (allowing a generous 50 litres per day per person of hot water). If there are more people in the home then a bottom element is advised. Solar hot water systems are ideally large enough to store enough hot water to last a few days as this will allow for some days of cloud and rain without the need to boost, making for a more efficient system with lower boosting costs.
It is possible to use an existing electric HWS and retrofit some solar collectors and a solar controller and pump. We can supply you with a 4 way valve that will transform the cold water inlet to the tank into a solar flow and solar return (where the solar heated water is returned to higher up in the tank via a pipe) as well as the cold water inlet. The controller sensor is then placed against the internal tank (usually near the element for ease of access). This is only a worthwhile financial proposition if you have at least 6 years life left in your existing tank as you will sacrifice the possibility of a solar hot water rebate (STCs).
Some solar hot water systems offer a choice of element size. It will take the same amount of electricity to heat a given amount of water so the element size only determines how long that process takes, and in most cases where the boosting occurs at night, this may not be urgent. If however you have a Mid element and are prepared to be interactive with your solar hot water system to maximise the solar gain by switching the element off as much as possible, you will want to recover the heat quickly with a larger element. Other considerations may be existing cabling in the house, and if you are off grid you will want a small element which you would connect directly to your generator rather than to your batteries.
If you have off peak power available then you probably would not require a timer to control when the boosting occurs. If you don’t have off peak power available then you will need to consider your household’s use of hot water for showers to adjust the time of boosting If you have solar electricity panels you may want to use the electricity that you generate and you would set the timer for the last few hours of sunshine in winter (summer will not require much, if any, boosting if you purchase an efficient and correctly size solar HWS).
Boosting Solar Hot Water with Wood Fire
In most parts of Australia The Sun will give you more than enough hot water from a correctly sized solar hot water system through all of the Summer and large parts of Spring and Autumn.
Even in the Winter The Sun will give you a large rise in water temperature from the cold water base but it probably won’t get the temperature to meet the minimum regulation temperature so you will need to boost the temperature of the solar pre-heated water.
The time of year you need to boost coincides with the time of year that you need to heat your house and if you choose to do that using a slow combustion wood fire, you have the option of buying a fire that is capable of having a water jacket (also known as a wetback or boiler) in the fire box.
This can be linked to your mains /pump pressure solar hot water system via a heat exchanger that will keep the water jacket open and vented and safe.
How Does a Heat Pump Work?
Heat pumps work like a reverse refrigerator by using the differential between the ambient air temperature and the refrigerant in the heat pump, which is at low temperatures. When this heat is absorbed into the refrigerant it evaporates and becomes a gas which is then compressed to superheat it – this high temperature is then transferred to the water via a heat exchanger.
Unlike the refrigerator, which gives off heat after it has cooled the contents of the fridge, a heat pump gives off cold air so it is important to site the heat pump in an area with good air circulation otherwise it will be sucking in cold air instead of ambient temperature air. This would force it to work a lot harder and use more electricity. The ideal siting is against a North or West facing wall where there is good air circulation. The warmer your climate the more efficient will be your heat pump – having said that, heat pumps will still work in sub-zero conditions.
The differences between a heat pump and a solar hot water heater are as follows:
Heat pumps have a number of moving parts – a fan, pump and compressor as compared to a thermosiphon solar hot water heater which has none, or a ground mounted tank which has a pump.
A heat pump uses electricity all year round, whereas an electrically boosted thermosiphon system only uses electricity to boost in the winter and on cloudy days at other times or days of high hot water demand. Additionally, a ground tank solar hot water system uses small amounts of electricity to run the solar pump and controller.
Most heat pumps do not have anything on the roof which means they are much easier and cheaper to install.
Heat pumps produce some noise – some more than others. If this noise is during the night it may be noticeable.
WHEN IS A HEAT PUMP THE MORE APPROPRIATE CHOICE
When you do not have a North facing roof
Or you have a North facing roof at the front of your home in an area with a heritage overlay
Or your North facing roof is covered in shade
Or you have PV panels on your roof that only earn a small feed-in tariff – so you have excess “very low cost” electricity during the day.
IF YOU HAVE PHOTOVOLTAIC (PV) SOLAR ELECTRICITY AT YOUR HOME
If you have a recently installed a PV array for making solar electricity and are only receiving 8 – 10 cents per kW/h, it makes a lot of sense to use a heat pump to heat your water, using a timer to turn on the heat pump between say 11 am and 3 pm when the ambient air temperature is highest and when your PV system is at maximum production.
How much will I save going to solar hot water?
For an electric system… on average it is going to be a 60% saving on the hot water heating component of your bill and that’s going to be based on a mid element tank, which means it is installed at the halfway point between the top and bottom of the tank, so it will only heat the top half of the tank. With a 315L tank, you are looking at roughly heating 160 Litres on the off-peak power above 60 degrees, so in the winter, you’re only going to heat the top half of the tank which means that you’re not going to need to spend as much to heat up the full 320 Litres.
On a gas boosted system it’s going to be closer to a 75% saving on average on the hot water heating component of your bill, as this is going through a continuous flow otherwise known as an instantaneous gas heater, and that’s one that will only heat the water when necessary and only the water you use, so when you turn the tap off, the gas turns off.
Is an instantaneous hot water heater as efficient as solar hot water?
No, clearly that is not the case as with an instantaneous gas heater (otherwise known as a gas booster) all of your hot water is being heated by gas. It is a very efficient way of doing it, however if the water your feeding into the gas booster is being pre-heated by the sun to 70-80 degrees in summer then your not going to be using any gas.
So what we would suggest to do is look at your gas bill, and find out a way of working out how much of that is dedicated to hot water, not heating or cooking, cooking is generally a very small proportion of the bill but heating can be a very substantial part. So if you look at your summer gas bill then that’s going to give you a rough idea, but it’s actually going to be a bit understated as the water coming out of the tap is much cooler in winter so the system will need to work a bit harder.
If you have an instantaneous hot water system, try and work out what your gas bill is using the above method and know that with a properly sized system you can save 75% of that, because the sun is going to do all of the work in the summer (many customers switch their gas boosters off in the summer so that it doesn’t come on at all) during daylight saving months, and then in the winter months the water temperature in the solar tank will be anywhere from 25-30 degrees depending on the weather and so that’s already a really good start, which is obviously still going to save you gas.
Gas prices are going to continue to go up, so it makes an awful lot of sense to put in a solar pre-heater to the gas booster while there are still rebates, the Government subsidises solar hot water systems by around $1,000.00
How long would you expect a solar hot water system to last?
All of the brands we sell are good ones, but there are varying types of materials used. A stainless steel tank can last a very long time, generally speaking it will last twice as long as a vitreous enamel tank. Now they are substantially more expensive because most of the stainless steel tanks available here in Australia are made here in Australia of this very expensive material.
Sometimes a stainless steel system can cost as much as $1400 more than a vitreous enamel one, but the vitreous enamel will on average last about 10 years and a stainless steel will last at least twice as long as that.
There are certain techniques that experienced plumbers can use whilst installing systems to make systems last a whole lot longer, by reducing the stresses and strains of pressure during stagnation during the summer months as well as other devices available to assist here.
So, how long will a solar hot water system last, the tank will last at least 10 years, most of the evacuated tubes have got 15 year warranties on them, however it is a very hard question to answer fully because of the many varying qualities of water. For example in Southern Victoria and Melbourne they have very good quality water so they would get a little bit longer life out of their solar hot water heaters.
Is there a particular brand that is better than others?
As with most things, it’s more about horses for courses, so it’s more to do with the situation you’re setting your solar hot water system up in.
So this will depend to a large extent as to whether or not you have a north facing roof, what angle that roof is, if you have a flat roof, whether you have room to put the tank on the ground, whether you want to connect it to a wood fire… there are so many permeatations, so we recommend firstly looking through the questions and answers on this site so that you are able to better work out the ideal solution to overcome the challenges in your building.
What are the main issues that can arise with solar hot water?
Almost all of the problems that we have seen occur with solar hot water systems in the past are poor installation ones, but generally these days plumbers are very good and know solar hot water better than ever.
One of the main problems that we encounter is people having high expectations of long runs, so if you have a solar collector on one end of the house and the tank right on the other end then their are going to be heat losses. It’s still worth doing because you’re still going to be saving money but obviously in such circumstances where heat losses are encountered it pays to reduce this with some really good insulation.
The most reliable type of system would have to be the close coupled thermo-siphon type as there is nothing that can really go wrong with no moving parts, so assuming it has been installed correctly, then you will find there are hardly any problems at all with those systems.
The sort of things that we have seen happen with ground tank based systems are that the pumps die, once again largely because they have not been installed properly. Also as ground tank systems require pumps they also need a solar controller to tell it when to switch on and off, and as these contain electronics they can sometimes go wrong.
In general the industry is now very mature and the pumps and solar controllers being used across the market are now of a very high quality whereas sometimes in the past they may have tried to use cheaper versions to save money, however this was found to be counterproductive.
Does solar hot water require a specialised plumber to install it?
All plumbers have the capability of putting in a solar hot water system, these systems are just a solar collector on the roof, tank on the ground and connected to a gas booster or an electric element for boosting. Once mounted to the roof, connecting it all up is just a matter of joining pipes, so provided the plumber is capable of reading instructions and many of these instructions come in picture form, then yes any plumber is capable of doing it.
What can a customer do if they have a problem with their solar hot water system?
They should go back to the plumber who installed their system first and foremost and have them come and rectify the problem, and hopefully those plumbers will learn from their mistakes. If the plumber finds that the manufacturer is at fault, meaning the replacement parts are covered by warranty then you can find your manufacturers contact details here (add link)
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