I’m a bit of an eco-geek, and trying to green up my lifestyle. I figured solar hot water was one of the best places to start, and this is the story of the journey so far. I now have a running system that generally works very well and I am happy with. I wasn’t an easy road however and hopefully others can learn from my mistakes.
There are several rebates available from both the Federal and some State governments (not Queensland). You can also sell the REC’s from certified systems. The Federal Gov rebate is currently for $1000.
A DIY system will get none of the above.
My house was fitted with an old instantaneous gas hot water system that had poor flow, awful temperature regulation and chewed too much gas, especially with the pilot light. I initially started considering all the cheapskate systems I could think of, whilst trying to achieve my ideal of solar booted with instantaneous gas when required. I like having lots of hot water and harvest my water from my roof. My council usage is almost nil, so I can waste as much as I like. The grey water from my shower irrigates my fruit trees, so long showers are just fine by me.
First idea was black poly pipe, or a DIY panel. The problem with poly is that it can’t handle both pressure and temperature. High temps are fine, high pressure is fine, but not both. Some very thick walled poly would probably cope, but with the weight, fittings and expense this wasn’t particularly practical. Poly also has a large surface area versus it’s collection surface. This means that it loses a lot of heat to the environment, limiting peak temperatures. The advantage of course is that as it’s cheap you can cover a huge are of roof. I know it can be made to work as many swimming pools are heated this way, plenty of farm cottages use the poly as both a heater and a tank, and I know how hot a simple garden hose can get water.
With poly you can get Low or High pressure rated pipe. Low pressure (low density pipe) is very cheap, and would collect and transfer heat very well due to the thin walls. It would only be able to run on an un-pressurised circuit (more on that later). The problem for me was I wanted my tank to be on the ground, not on the roof. With a two storey house this would result in a vacuum in the pipe from the weight of the water, and the pipe would likely collapse when hot due to it’s very thin walls. 7M (22ft) of head would be about 11PSI vacuum (yeah I know, wrong units, but it’s indicative).
High pressure poly is more expensive, doesn’t conduct heat as well due to the thick walls, and needs expensive fittings. I worked out the area I would need and it wasn’t particularly cheap.
The final killer was the lost radiated heat. Reading a number of efficiency articles, mostly relating to cookers, on the Internet, the heat lost without a glass cover was very significant. Vacuum insulation made a huge difference again. Toughened glass is expensive, and whilst I had some toughened glass doors, Brisbane is subject to hail, and I couldn’t see these lasting out that type of impact intact. I’m sure you could make it work, but it was too likely to be problematic for me.
The other types of DIY panel are simple box batch heaters, and home made copper collectors. The batch heaters are labour intensive to use, and the price of copper precludes making your own panel that way pretty quickly.
Then I saw that Australia had invented a more efficient solar hot water panel. Of course being Australia we had done nothing about capitalising on the invention, and now they were made in China. Beautiful, nice and cheap, just what I needed.
Vacuum tube panels range in price from $500 to $5000 depending on the source. The Australian brands were all at the “too expensive” end of the market for me, even though they are probably made in China too. I settled on a 15 x 1.8M tube panel from an importer in Sydney though eBay and had it shipped to Brisbane for $550. This was not entirely successful, and only 5 of the 15 glass tubes made the journey intact. Luckily most Chinese stuff are copies of something else, so they tend to be somewhat interchangeable. I dug around a lot until I found a local supplier with some spare tubes at the right price ($150 for 10)
I started with one 15 tube panel and a 250L tank. This was based on it being cheap, and I being cheap. I have since found that I use about 150L of hot water / day with my family of four five. A larger tank would be good for being able to last out several rainy days. The single 15 tube panel was adequate, but only just. Plenty of sun and it was fine, but after a few cloudy days the tank would only get just over lukewarm and cool off a bit more by the following morning. I have since found a table that says:
| People | Tank | 1.8M Tubes |
| 1-2 | 150 | 15 |
| 3-4 | 250 | 25 |
| 5-6 | 350 | 30 |
| 6+ | 400 | 30+ |
On the basis of this I installed an additional 15 tube panel (30 total) and have been very happy with the quantity and temperature of the water. I have not had the 250L tank approach boiling yet with 30 tubes, but regularly see 70C.
I considered putting the tank on the roof, but my house was built a little agriculturally and I didn’t trust the roof to handle 300kg+ sitting up there. I later regretted this decision and should have braced the roof and sourced a close coupled roof mounted system.
As the tank was going to be on the ground, I had to fight the natural circulation of the water. Normally the hot water moves up and the cold water down due to the difference in density. I wanted the hot water to come down from the panel and into my tank, and the cold water from the tank to go up. A pump was needed. I looked at the 12v options, and may still go that way yet, many of which use automotive derived parts. I had concerns about automotive pumps coping with residential duty cycles and pressures. Car cooling systems run at 14PSI, not 40-50psi. eBay again to the rescue got me a Hot Water Circulating pump that seemed fair quality and definitely heavy duty – $125. The fittings of course were some weird size, meaning more money later.
If you run a 12V pump then you can run it from a Solar Panel combined with a pump maximiser to get it started. This makes a lot of sense, as when the sun is shining, you want to be pumping. When the sun is not shining, there is no heat, and you don’t need to be pumping. I planned on putting in a Grid Feed solar system anyway, so figured that the solar power issue was near zero for me personally, and I wanted the heavier duty pump. To run the 240v pump however you need a controller. You can build one yourself, but I cheated and bought a Chinese solar pump controller for $150. It had the advantage of also controlling the heater based on a combination of time and temperature. The power rating of the controller was sufficient to run the pump,but to avoid overload the 3.6KW booster element needed a secondary relay which I paid $23 for.
The tank came from the local newspaper – $125 for a 250L Rheem that was 4 years old. The guy I think had been smarter than me, collected the Government rebates and had a system professionally installed. It cost him a few more dollars than I was planning on spending, but he had I believe far less headaches. The tank was labelled “Solar Convertible”, but I think Rheem may be deluding themselves here. I have since seen other tanks that would be far easier to convert. Look for additional ports near the top and bottom of the tank, it will make life much easier. The tank was an enamelled steel pressure cylinder.
Now roughly speaking, in Australia tanks come in two varieties. Pressurised and Heat Exchange. In most tanks, the water in the tank is the water that comes out of your shower. They are very simple with a pipe leading into the bottom of the tank, and a pipe leading. out. There is a heater in the bottom with a thermostat attached, and a safety relief valve somewhere that will open if the pressure or temperature gets too high. These tanks stratify well, keeping cold water near the bottom and hot near the top. You’ll know very suddenly when all the host water is used up. The heating element and / or the solar pumping also breaks up the stratification, meaning your tank may indicate cooler whilst it heats, as it mixes. Expect big differences in temperature between top and bottom.
The other variety is commonly a Sachs – the Saxon Copperflow. In this system the tank is better thought of as a bucket of hot water that is not under pressure. There is a coil of copper pipe that leads in and out that is connected to your cold and hot water system. There are several differences with this type of system. The water in the tank must be topped up occasionally from the valve on the side. They are supposed to work automatically but don’t seem to particularly well. As the tank is not pressurised, you can circulate the water through low pressure solar heatiing pipes without them bursting, an interesting idea. The circulating pump is also not running with a pressurised circuit, making it a much simpler device. The un-pressurised copper tank is supposed to have a much longer life than a pressurised enamelled steel tank. These systems don’t statify, so tend to cool down gradually as you use them up. Temperature measurements are easier on these tanks.
Finally, hot water systems are supposed to heat up to above 60C every 24hrs to stop nasty things growing in them. A tank that keeps the heat reservoir seperate from the water that goes through your taps would be less subject to bacterial issues, especially in the event of it not heating to full temperature.
Last but not least was the plumbing. This is the bit that hurt the most. I managed to get it all at trade price through mate from Reece plumbing, but there was still $500 worth of pipe, insulation and fittings. Keep in mind that the more fittings you need, the more expensive it will be. In many houses today they are running PEX (Cross Linked Polyethylene) pipe, a grey plastic pipe that is rated for mains pressure hot water up to 90c. It’s cheaper than copper, and far easier to fit, all the connections are push on or crimp on. On a split solar system you need to connect the tank to the panels, and you MUST use copper pipe for this. The water in this circuit will exceed well over 100C and will cause plastic pipe failures. I believe my panels have hit over 160c when the circulating pump stops. More on that later.
The fitup is pictured below.
| Solar controller and relay in a weatherproof box. I had to put a sunshield on the box as it was getting to hot with direct sun. |  |
| The display / control panel for the controller is supposed to go inside the house. My block walls make routing the plug too difficult, so it lives in a $10 waterproof letterbox. |  |
| One of the sensors for the solar controller. They work very poorly. Although accurate when tested, they don’t get a good pickup from the tank so give a false lower reading. I have tried thermal paste etc. Newer models screw into the tank water fittings, a much better idea. I’m going to try and convert mine. The sensors are thermistors, not thermocouples. |
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| The collector panels have a port where you can insert the panel sensor. It’s in a copper tube and gets a good reading. The long run of wire to the roof, despite being heavy gauge upsets the calibration somewhat. I silver taped all the insulation to protect it from the sun, but the tape isn’t lasting. I’ll find some better tape one day. You can see the distortion from soldering the copper. It’s a long story explained below. |
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| My first panel 1/2 installed. I hooked up all the plumbing first as I didn’t want it overheating. They are supposed to be ok run dry but I was cautious. Water pipes were not taped at this stage.My roof faces north at about 27 degrees. |  |
| The ten replacement tubes were slightly longer. I had to improvise their mounts somewhat.Thank you to Rod at SolarOz for helping me here. |  |
| First panel fully installed – 15 tubes at 1.8m long. |  |
| I decided I wasn’t getting enough hot water and bought another panel from another guy. $550 for a 15 tube model. |  |
| The new panel didn’t have “feet” making screwing it down a bugger. I should have made some up but was in a hurry. Make sure yours come with feet. |  |
| Not sure if I trust this plastic clip to last 10-15 years. |  |
| 250L Tank + plumbing. Controller not fitted in this pic. I ran the circulating pipes in insulation then in PVC pipe to conceal and protect the insulation from the sun. Use talcum power to make it easier to thread it through. |
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| The roof penetration. This is Sikaflex, not silicon, so it will last. Ideally I should use a Decktite but the roof is only shallow pitch and I wanted minimal interference for drainage. The penetration is through the eave so a leak is not significant. You can see the sensor wires coming up as well. 50mm PCV is Internal Diameter. Drill the hole to 58mm external. |
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| The eBay pump. It has 3 settings with different power and flow rates. Low is fine for both running and priming the loop. The first one had a fault that gave me some stress. It was replaced under warranty. It has no mounts so I had to fabricate some. These pumps are designed for this and similar jobs, so should last a long time. They are very heavy and heat tolerant. |
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| This is my home made 5 way adapter. Simple in theory, not so simple in practice. The valve and other thingy came with the HWS. I have no idea what the bulgy thing in the pipe is. |
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| Picture of home made 5 way adapter that screws into the base of the HWS. Hot water from panel on LHS. Water to panel and cold water in on the T pieces. I had to bend my tube to make it fit. These are a bugger for leaks due to the number of fittings. Use PLENTY of tape. |
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Now for the install.
I of course had a plumber do all this as doing your own plumbing is illegal. All stories below are his, not mine. That would be naughty.
For the tank base he put it on large pavers and some sand and concrete mix. The cold inlet and hot outlet I just tapped into the existing pipes and soldered them in. A valve was fitted on both the inlet and outlet to allow me to keep using the existing gas hot water if I needed to and to work on the system.
The solar loop pipes were put in insulation then threaded with some twin wire into a length of 50mm PVC pipe. Talcum powder makes this much easier, but it’s still awkward and needs 2 people. This got screwed to the wall and inserted through a 58mm hole in the roof.
Next he made up the 5 way adapter as per the pics above. I have since found tanks with spare ports at the top and bottom, this may be a better solution. My tank has a curved bottom inside, so he had to bend the pipe to allow it to insert more than 50mm. This does restrict it somewhat. I have no idea how Rheem claims these tanks to be solar convertible, it’s far too difficult. You could do it with T pieces on the inlet and outlet ports, but this risks not mixing the water from the panel with the water in the tank and possibly drawing very varied temperatures into your hot water lines. A bad idea.
The downside with top and bottom ports is siphoning. At night the warm water will tend to flow upstream to the panels and lose heat. If you have top and bottom ports, you’ll need to install a low pressure non return valve inline. A brass flapper check valve might do the job, but may not close if installed vertically. YMMV. Anecdotally (internet forums) many people report problems with these non return valves.
I recommend you assemble the frame for the solar panel on the ground to sort out any problems. Mine could be mounted several ways and it’s far easier to make changes before you are on the roof. Also test fit a tube for practice. Once up there the frame from was screwed to the roof battens with roofing screws and some silicon underneath to stop weeping into the holes. The panel didn’t come with plumbing fittings and used a weird size pipe. I couldn’t match it so had to silver solder on some standard 3/4 pipe. This is a very difficult job as there is no length available and it’s very easy to melt the plastic and insulation. Lesson: Make sure your panel pipe is a known size, or comes with fittings.
Make sure that any compression fittings you use near your panel use Copper olives. I found out several weeks later that Nylon olives melt when they get too hot and won’t cope with a panel. Instant leak and water loss. They are rated for hot water to 85C, not for solar loops with boiling water. They will be fine until the panel is not getting water circulating, at which point the water will boil and the temperature continue to climb. I would hazard a guess that mine got to over 160c when the pump was switched off. Water at 65PSIA (Atmosphere + mains pressure) boils at 147C, a pretty high temperature for plastic to cope with. Your circulating loop may get that hot.
My second panel came with the correct size copper fittings, but it had no feet, as pictured above, making mountind a bugger.
Your fittings and pump can now be connected. Plenty of tape = 10+ turns on all the threads will stop most of the leaks. Mine was a bugger for leaks, he hates BSP fittings. The threads are supposed to taper making them seal as they close up, but manufacturing tolerances between vendors insures there are gaps and sometimes teflon tape just isn’t up to the task. Compression fitting with olives should only be done up gently. Once pressure is applied then start to tighten them till they stop leaking. He found this to be far more reliable then tightening them first. If you over-tighten they deform the pipe and won’t seal whatever you do. Fun fun fun.
You can now fill, bleed and pressurise your system and check for leaks. As the loop to the roof will be full of air, if there is a leak, it may take some time to show up. You can run the pump to push the water up and air out.
Once all the water is connected you can insert the vacuum tubes into the panel. The ends need to be coated in thermal paste, so don’t leave them in the sun or you won’t be able to touch them. They are very tight into the rubber seals. A spray bottle of soapy water makes this very easy. The plastic end caps can be a bugger and aren’t particularly well designed on any of the panels I have seen. Luckily the retention is done mostly by the top, the plastic doesn’t do much.
I ran my pump initially off a simple timer switch until I had time to fit the controller. This works well enough, but does waste some power and isn’t most efficient. On a day with no sun you end up circulating hot water into a cold panel. Luckily the vacuum tube type panel used here wastes almost no heat and may still be warm in this situation.
The first pump I had was faulty. It would run just fine until the circuit was pressurised, at which stage it would stall. They are designed such that the bearings are supposed to have water on both sides to balance the pressure, this one would push onto it’s bearings and stall. A replacement pump rectified the problem. I would recommend not unscrewing the silver cover cap on the pump unless you have to. The area underneath is pressurised by the circuit and can be problematic to re-seal. The pump will stall with this cap off.
When I installed the controller I put it into a weatherproof box with the control panel. This became tedious as whenever I wanted to check or change anything I had to unscrew the cover. It’s too difficult for me to core drill my wall to put the display inside, so I put it into a cheap letterbox that is waterproof. The controller is not waterproof. My controller can switch up to 2KW, but the element in the hot water system is 3.6KW. A heavy duty relay resolved the heater issue.
When you program the controller read the manual, it’s a little complex. What I have found is that the controller will stop the circulating pump once the tank reaches it’s “set” temperature. As this is the same “set” temperature used for the heater, I wanted it quite low. This stopped the pump one day, boiling the panels and melting the nylon fittings. Now it’s set to the max of 75C. I think it’s a bit silly that they don’t let the tank get over 75C from solar, but I have checked different brands and they all seem the same. The pump runs when the temperature difference between the panel and the tank is a set amount. This works fine as well as the sensors get a reliable pickup. The short sensors I have a dodgy at best and don?t read the tank temperature well to all. This can cause the pump to run into the evening and some heat to be wasted. Make sure your pickups actually go into the water of the tank, not just the surface of the steel inside.
I have set my tank thermostat (the one built into the Rheem) to minimum. This means that if I do need to boost, I use the minimum power required. The controller may keep trying to keep heating, but the tank will turn itself off at the temperature i have set. Technically this should be over 60c for health reasons.
The controller can also set when you want to boost. I set it for the end of the day. My logic is that if by 4PM the tank is not up to temperature, then it should boost for 2 hours to get it warm enough, or until the thermostat on the tank cuts out. The controller thermostat is set to 75c for the reasons discussed above with the pump. That’s why I use the tank thermostat for cutout.
I normally keep the boosting disabled as there is a function on the controller to lock it out. I have only needed to boost three times so far when the panel was too small, or when the controller has played up.
| Costs | |
| Tank | $125 |
| Panel 1 | $500 |
| Replacement Tubes | $150 |
| Panel 2 | $550 |
| Pump | $125 |
| Replacement Pump Shipping | $15 |
| Controller | $150 |
| Replacement Cont Shipping | $15 |
| Relay | $32 |
| Plumbing | $500 |
| Pad for Tank | $50 |
| Wiring | $75 |
| Box for Controller | $75 |
| Total | $2362 |
Key lessons
- Get a big enough tank and enough tubes the first time
- Pumps / Sensors / Controllers / Electrics are problematic
- Plumbing is expensive. Copper plumbing is very expensive
- Don’t trust couriers
- Leaks happen
- Have an understanding family if you DIY
- Understand the gov’t rebates well
- Nylon olives will melt and leak
- Chinese build quality is not ideal, but is good for the price
- Chinese fitting sizes may be non standard
If I was doing this again I would NOT do a ground mounted tank. If you had a roof mounted tank it would circulate naturally. You could run PEX piping, much cheaper and simpler than copper. The loop wouldn’t be needed, saving $500 of fittings, a pump, a pump controller, sensors and wiring. Natural circulation is a far better idea. The downside is that you need a horizontal tank and these are much harder to come by. There are some Chinese ones coming in now I believe. The other option if you don’t care about aesthetics is to mount a normal tank somewhere on your roof with the panels lower than it.
I think I could have saved $500 or more and a heap of problems with a roof mounted tank.
A new gas system would have cost me about $1000 and gas was about $150/qtr. This would have probably dropped to $100/qtr. That means that it will still pay itself off, especially if I don’t have to boost.
I am currently still using the tempering valve that was fitted to the house. Technically a solar system needs a solar compatible tempering valve fitted to cope with the temperature. A tempering valve normally is onyl designed for water up to 85C. Water at 65PSIA (Absolute – atmosphere + 50PSI mains pressure) boils at 147C, not 100C, meaning that water leaving the system could boil at the taps or cause instant burns. The tank is designed to release water if the temperature exceeds 99C or the pressure gets too high, this is through the safety valve. A solar compatible tempering valve is about $350 vs $125 for a normal one.
You also have to decide what part of your house you want tempered. I like water up to 70C for my washing up tap, shaving and washing machine. The shower and bath should only be 48C. The maximum you can set on a tempering valve is 50C, meaning if you want the hot water to be hotter, it has to be untempered and may reach boiling. There is no simple answer I have found for this problem. Here are some details on Hot Water Safety
My system was installed about Sept ’07, but I’m still debugging a few things.
Update (31/08/08)
The solar controller (pump / heater controller) has given me heps of problems so far. I have now removed it and am using a home built one. This has it’s own issues, we’ll see how it goes. Contact me if you need more info.
Update (30/06/10)
The homemade controller is going strong. I dont control the booster with the solar controller or a timeclock anymore, but have put it on off-peak power instead. That way it’s only on at night. This combination seems to work well. It means the realy is no longer needed.
The alternate would be instantaneous gas boosting.
Useful Links
Interesting article. I looked at solar heating 30 years ago, but never finished the project. Just for the sake of intest here was my plan. Collector and tank were roof mounted and at atmospheric pressure, thermo syphon powered. Collector was to be 2 sheets of copper (2 ex hot water systems of the day) with washers between them and spot welded together withe the ends soldered into a copper feeder pipe at top and bottom, all painted black and under glass. The receiver tank had coiled copper inside (again the hot water system of the day) which was pressurised. Cold in – hot out. All up it would have been a cheap, fairly inefficient system, but the hot water from the roof was to go into the electric off peak system so that the electricity usage would have been minimal. Just a thought. Had young kids then so I could not be without hot water.
Hi Paul,
An excellent article.
I had to smile towards the end, that plumber of yours has just the same writing style as yourself.
Last year I applied a bit of lateral thinking to a friends solar hot water problem. I used the same plumber as you did I think.
She lives in a block of strata titled units and her large Beasley system was leaking somewhere in the guts. The copper was covered with the moulded insulation and plastic so there was no way of even finding the leak without wrecking it anyway.
She had quotes from two plumbers to replace it, around $2500, even with the government discount. Her body corporate did not want to fix it. (They will eventually have to replace the lot, they are all the same age).
I asked my friend if she was on good terms with her immediate neighbour, another owner occupier. She was. Here’s where the lateral thinking came in, literally lateral.
On the roof, the plumber cut a tee into the neighbour’s outlet pipe (hot) and with one 8M length of 12mm copper was able to reach my friend’s equivalent pipe. A cut and the leaky system was disconnected, an elbow fitted and both units are now using the one solar heater. They are both single people using a heater that would provide for a family of four. The inlet stop cock was closed and the old system is still sitting there there waiting to be replaced.
Problem not solved, just deferred indefinitely for a cost of about $120.00.
Cheers
Bill
Our local green plumber is about to install diesel furnace-to-solar HWS conversion for our HWS & slab hydronics.
Components: 2 x 18 tube Sunplus vac tube system, heat exchanger in the slow combustion heater flu, 1,000l tank with 3 coils, 2 gas instantaneous boilers (1 small for light demands, one heavy – washing, spa – we have a 5 bedroom house).
Rough estimate below $17,000, less rebates. As its not a conversion from gas or elec, we may not fit the bureaucratic criteria for rebates.
Feeding all the house hydronics is prob too unrealistic, but experience will tel. 5 hydronic zones, heavily insulated, solid brick home. We’re on a farm on tank water, 250,000 litres in conc tanks, so water quantity is not an issue with 1100mm rainfall/yr. For simplicity, we’ll use 240v hydronic pumps & extra pipe insulation to shift the water uphill from the wood-fired heater as we’re on 3 slabs – we have a PV system to counter it. Wood from storm damage on the farm.
This replaces a ’70’s large diesel boiler, costing $6.30/day for hot water only, for 2 people, not using the hydronics at all! Diesel is farm-delivered, adding 5c/l.
Looking forward to checking its performance. Might write it up for the ATA’s website.
A very interesting read. I am considering doing something very similar. My property is low set so I hope that will help a bit. Your experiences will help many to minimise the technical problems of solar installation. It is hard to find such good information. You have done well
Unless all our governments start thinking about making “alternatives” affordable through rebates and zero purchase taxes they will never meet the CO2 reductions they pretend to care about. Global mass production of solar water heating and installation without purchase tax *minus* rebates makes sense. Until they do this only the middle classes and wealthy will bother with solar. Improving supply efficency is far too slow.
Hi Paul, Nice DIY solar hot water article! It certainly highlights the greater technical challenges of hot water storage on the ground requiring a pump and sensors etc. A roof top tank able to work with passive thermosiphon is definitely much easier.
I’ve found working with low pressure gravity feed rather than mains pressure enables the use of low pressure poly and the ability to build a very cheap system. There is a catch with low pressure systems though and that is the internal house plumbing should use a larger pipe size to deliver similar flows at lower pressure. Your readers might appreciate a look at my home-built solar hot water system at: http://www.littlegreenguide.com/build-solar-hot-water-system.htm
Just a quick comment on your plumber… I find it really irritating that we are by law, forced to employ “qualified” tradespeople for relatively basic tasks. It’s a symptom of “nanny” governments, effectively telling us we’re not capable of making informed assessment and decisions ourselves. It’s a very negative style of governance.
Hi Paul,
I had an evacuated tube solar hot water system installed 12 months ago to replace An old flat plate Beasley system from 1980. My system uses the same controller as you installed originally & I have had nothing but problems from day 1. It was installed “professionally” & I have had the installer back numerous times over the last 12 months. The system doesn’t seem to heat the water over about 35c max & I am wondering whether I have a problem with the controller. I have burnt my bridges with the installer who insists that the system will only heat the water to lukewarm. I know from my old Beasley system that that is just not right. So I.m wondering if you could tell me where you obtained the controller as I would like to get a spec sheet & a display for my system.
Cheers
Greg
Paul
I’am not an ecogeek but I appreciate your meanderings and especially like the emphasis on cheap. I am doing research on a hot water setup for my new house which was a carpenters workshop before, cut a long story short lack of cash means my total hot water consists of an 80 litre mains pressure tank with a 1.9kw immersion heater. Now I thought that using another 80 litre tank (80 euros a pop), stripping the insulation off, dumping it in a enamel bath (70 euros each), put a lid on the bath, insulate to the max, park it outside then using thomasons corrugated solar panels at atmospheric, just run tap water through a cental heating pump to the roof across the collectors down again to the bath with the mains pressure tank in it (heater element removed and bunged). Tee the pressurised tank into the existing hot water system and voila! (maybe need a shutoff valve for the old tank)
Paul,
Very interesting. I’m very happy with my setup which is similar to yours. Even during winter I seldom use the electric boost; but that depends on how cool you can tolerate the water. It is always hot enough for showering; it’s dishwashing where I sometimes add a jug of boiling water rather than run the electric boost. My system uses 24 tubes and is also a Chinese eBay unit. Fortunately mine came with the adaptors to connect to 1/2″ copper tubing, but yes what’s on there is a weird size.
The controller works well, but as you found necessary, I added a relay to switch the element. My tank temperature sensor is actually immersed in the water being a 1/2″ BSP fitting.
I notice no mention of a non return valve to prevent reverse thermosyphon at night. This was a real problem before I installed it. The system would lose most of the accumulated heat overnight, dissipating it into the cool night sky.
The other key factor is insulation. Thick foam insulation instead of the green stuff I used first makes a big difference. I wrapped the foam insulation in aluminium tape I got from Jaycar. It seems to weather very well.
Curious that you felt the need to add another lot of tubes…I’ve been tempted to try this myself as it would give a greater reserve on cloudy days. Tank is 125L stainless steel which is just adequate for 1-2 people and is ok but after one cloudy day it starts to run out.
Hi Paul,
Nice work. 25 years ago, I built a drainback (DB) solar hot water system for my home. It uses 2 pumps – pump 1 for the solar loop and pump 2 to circulate the potable water between the 120 gallon (about 450 liter) storage tank and the heat exchanger coils in the DB tank. When collecting heat, the pump 1 pumps water from the DB tank to the collectors and back down with solar heat, and pump 2 transfers that heat to the storage tank via the DB / storage loop. When the sun goes down, both pumps stop and the collector water drains into the DB tank, so there is no water in the collectors to freeze. Problems:
1. The glass on the central collector broke mysteriously and was replaced.
2. The op amp in the controller had to be replaced.
3. The start capacitor for one of the pumps failed and was replaced.
Without antifreeze, there is no required maintenance except I should oil the pumps. It’s been problem-free for the past 10 years or so.
Mine, too was a DIY – I did get some tax benefits courtesy of Jimmy Carter.
Good luck with your system. – Rich
Hi Paul. Thank you for publishing your experience for the benefit of others, like myself, who are interested in doing a similar installation. You mention about Rheem’s “solar convertible” tanks not being very adaptable for conversion, and that some other tanks with extra outlets being better for this purpose. I have noticed that even a relatively new (2-3 years old) Rheem “solar convertible” tank does not have on the outside skin the inlet and outlet ports for connection to the solar panel. Are the ports on the inner tank wall? I haven’t been able to get any information about that from Rheem’s website. What brand of tanks do you know of that have the extra ports built-in? Do you know whether it is practically feasible to convert a standart gas hot water tank into a solar storage tank? All Rheem’s solar convertible tanks are electrically boosted.
Chris
Hi Paul
Thanks for a great article – very informative and detailed.
You mention that if you were doing a system again, you would have a roof mount tank, with natural circulation.
But would this mean that you couldn’t use evacuated tubes ?
Because I can’t see how thermosyphon natural circulation, could work with those tubes, that are closed at the bottom.
Wouldn’t you have to use a flat plate collector ?
regards John
Water doesn’t flow though the tubes. The bulb at the top of each tube gets hot from heat carried up through the heat pipe. In a thermosiphon system the bulb goes either directly into a tank, or to an inclined circulating manifold.
There are also sytems that have water in the tubes, but they tend to be only gravity feed.
Thanks Paul, I see now.
If you were doing it again as a thermosyphon & evacuated tubes with heat pipes, would you still have a pressurised tank, or gravity feed.
Being an engineer I used to be at all times a bit curious why the pump was obligatory, since a law of thermodynamics states that heat always flows toward cold. Theoretically, the mix valves beneath the sinks must operate without the pump. Nicely, in the future I unplugged the timer to see what would happen. You understand what? The taps produced hot water just as quick without the pump running! Now we leave the pump off all of the time. My advice is to save lots of yourselves cash and simply purchase the undersink valve kits (about $50 every). The pump can at all times be added later should you discover it’s still necessary. Perhaps some water programs require the pump. Hope this helps!
Hi Paul
I’m just at the beginning stages with my Solar unit experience (Copper Pipes unit in a glass covered aluminum window frame purchase from Trademe imported from Germany) I have just got the solar panel on the roof which was a mission by itself, ended up getting a hiab crane on a truck to lift it to the second story roof. The difference in the pipe size in the solar collector really got me, you couldn’t go get a joiner from the plumbing supply, cause nothing fitted it, maybe imperial or automotive pipe, however finally solve it with a joiner and a socket from my socket set. Found the right size socket and smacked it in half way into the joiner with a hammer, then soldered it to the pipe coming out of the solar panel and crox nut the end to fit the new copper piping. It’s going to be interesting the power saving i get. I currently have a power bill for $258.00 NZ dollars, I will post the new power bill after i have competed the installation. Thanks
I have recently put similar system (20 tubs x 1500mm) on our roof (Postcode 4650). Although the last week has been overcast and raining at times we have not seen high temps. Good enough for a shower but washing up not the hottest. 50c is highest but mostly 40c. Its not quite clear on the photos what size copper pipe runs from manifold to tank and tank to manifold. I am only using 13mm to do both and think maybe I need larger diameter piping. Only reudce at pump and the four or five way inlet to tank.
All 12 volts with pump and differential controller powered by 20w panel.
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Forgot to add website
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Hi. All
I am a newbie to this. I have just purchased 3 S/H flat panels. My intent is to run a ground based tank with an instant gas HWS. I understand about the need for a pump (perhaps someone can suggest a source for this and a controller) But what I don’t get is how these systems deal with overtemp conditions. As stated the panels can get to +180c. I want to set tank temp to around 70c so the pump will stop at 70c. How then is the panel saved from thermal runaway ?. If it boils at whatever temp will there be a vapor lock that the pump can’t clear when it turns on again ? Can the temp of the panel get so high it will damage it”self ?.
I hope I have explained my query well enough. I will appreciate very much if some of you more experienced people can set me straight.
Hi Paul
Back for an update, however it’s now getting into winter “frosts” more money. I have the system working and going really well although it did rain for about 7 days after I installed it, which got a bit frustrating.
Yesterday 28th May a solar controller arrived a my door from Trademe $177.00 this will turn the system into an automatic water heating machine. I’ve got it all running just have to get the sensor up to the panel later today as the ceiling cavity gets up to 57 degrees. Another great heat source which i have tapped into already.
Although the panel is copper pipe with glass it still reaches 67-70 degrees which is perfect as the cylinder has a glass liner inside and I’m told that the temperature isn’t to exceed 74 degrees or the glass/enamel liner will break. Not good for a hot water cylinder.
(Steven above) yes I use 20mm copper pipe and only 12 mm at the retro fitting
I meant to let you know the latest power bill which is $208.00 a saving of $50.00 dollars although it is now winter and a normal power bill in winter is $330.00 dollars so that’s $92 dollars so I fell I can now afford a relay for when the sun don’t shine.
Better go and check the controller cheers Hamish
what has happened in this article is the same as i have done and the same reasoning and problem progression i have a 30 tube system non pressurized with roof mounted tank that is boosted with a flow sensing pump that matches mains pressure ……i have it connected to a wood fire also ….. very clever people
i imported tubes and manifolds from china and gained a new skill of freight forwarding and customs broker etc i mounted my tank a 215 liter on its side in the roof cavity and have a float tank feeding from mains to make it safe to boil with out exploding as a tap is opened the pump kicks in and i get great flow and only use power if i use water …i live at orange nsw and it is marginal for effective solar water heating but the wetback on the houses wood fire has the same thermal convection conected to the roof tank and if its cold we have the fire on and a by product is hot water and no electricity or gas and no extra wood now i am scared about hail and will consider a cage to protect my precious tubes
How Long is the set up guaranteed to last. I live out in Colorado and with the winter snow and Summer hail storms I am wondering if I spend the money will I get the return I am looking for. Great Build though I really enjoyed reading it.
I have just purchaesd an 18 evacuated tube system with gas boost. My thoughts and comments are; Why do we have to by law pay supposedly professional people to do a job they clearly have insufficient understanding about and lack the professionalism their trades require. Most seem happy to take the money and run. I have had to fix plumbing leaks, fault find a failed pump, fault find a low circulating flow in the circuit, design the system to perform due to insufficient tubes on initial supply, properly insulate copper pipework, lift wiring off sharp edged strapping, replace damaged tiles I was not told about.
A comment on previous posts, you should have a steam trap on the outlet of your panels to remove air and steam if it forms when sthe panels tagnant. Also helps with bleeding air out during initial filling. Due to town water pressure water will have to get somewhere around 150 degrees before it boils, with a steam trap it will vent. If your system water pressure is higher the boiling point is higher
Normally one should use 13mm copper as if you use too larger size copper and using a pump controller you will be trying to move too much water and it will sit in the pipes too long before reaching the tank and so efficiency falls off.
Hi Paul
It’s now the 22nd of October 2011 and starting to just warm up. I have since purchase a rely ($57.00), so that the solar controller turns the water cylinder on if the required tempture hasn’t been reached. Now It works by itself. It gets up to 54-60 degrees most day which is fine for showing etc.
I have received another power account dated the 14th of September so it’s been a month since the rely has been in operation.
Been a bit naughty and used the dryer for every load of washing, that shoots the power usage up, however in saying that the account has dropped to $173.28
the account before this was $233.43 so that’s a $60.00 drop
We have a deep freeze, Fridge freezer with eskmo in the back making ice, heated towel rail, and a 2 group commercial coffee machine plumbed in, which boiles every 10 seconds and a 27′ Imac which is on all the time. Our heating we use gas which isn’t used much.
Hope this helps your readers in getting there solar water going on there roofs.
The next job might me a gridtie and a solar panel then the power company will be writing me cheques. Nice.
Hi Ken
The solar controller will operate everything that you are worried about.
You can ajust the setting so it won’t pump 180 degree water into your cylinder.
Also when freezing in winter the controller will start the pump up at 4 degrees and raise the temp in the solar panel to 8 degrees stopping freezing the pipes.
The boiling in the pipes you will need a pressure release value most plumping supplies have them, the price in NZ is $70.00 dollars. This is fitted at the top of the hot outlet pipe on the solar panel, you will need a T join. this is what it looks like link below:
http://img.alibaba.com/wsphoto/v0/443352414_1/Pressure-release-valve-Pressure-relief-valve-safety-valve-DN15mm-G1-2-.jpg
The pump, don’t buy a cheep one. They are loud, get bloody hot, and mine smelt electrial hot. I purchased a very quite from trademe. Ebay have then too as well as solar controllers.
http://www.trademe.co.nz/Building-renovation/Plumbing-gas/Water-cylinders-heaters/photos/a-415224944/p-184458170.htm
All the best
Changed my black box controller for a solar controller that shows whats going on http://www.ebay.com.au/itm/CONTROLLER-SOLAR-WATER-HEATER-water-proof-240V-Australia-Newzealand-/330646928720?pt=AU_HotWaterSystems&hash=item4cfc17bd50 It also controls my gas boost and automates it turning off when >62C so no gas wastage. Gas bill in spring is 30 to 60 cents a day now.
Have a grundfos pump which is good, adding another 6 parabolic mirror tubes to make 24 to give sufficient heat. You always should have a water expansion valve on the cold water inlet, this allows water to expand rather than the hot water relief valve going and dumping hot water.
If you get a panel air/steam vent make sure its rated for 200C as some are rated at only 120C and this is not enough.
Hi Paul, I searched to see if it is common that solar hot water systems boil over as my new commercial system did today. It was a day with the temperature reaching 34 degrees in Perth. An overflow / pressure relief
Pipe was installed over a small patch of garden beside three house slab.
It discharged 6 buckets of water at 90 degrees!!
The overflow arrangement needs to be changed, but above all three panel needs to be made less efficient! Has anybody organised something like a Venetian blind over their collector?
With poly you can get Low or High pressure rated pipe. Low pressure (low density pipe) is very cheap, and would collect and transfer heat very well due to the thin walls.
I now have 24 parabolic mirror tubes ( equivelent to 30 standard tubes) in 315 litre tank. On 3-4 days in a row I can have stagnation in the panels when the pump shuts down at 80C. Do you have a cold water expansion valve at the cold water inlet after the NRV. This should expand and allow cold water to discharge when the water in the system expands. If you only have a hot water pressure/temperature valve then its not enough and if they lift it can dump near the whole tank of hot water.
I made up a wooden frame with heavy black plastic over it and fitted it to one (6 tube) panel. This derates the system enough in summer to not boil over. It means I have to fit and remove once a year but better than the water loss and also burning people.
Thinking about an automated system that covers one panel when >75C
if its your cold water expansion valve dumping the hot water then your whole tank is at near 100C. Suprised that the relief valve has not lifted yet. What size tank do you have and how many people in the house. maybe overrated for your circumstances?
Paul.
Did you ever get the thermocouple fittings to relocate your termistors? I made up a system you might like to use. You buy a brass T piece a male/male for the pipe end and male male for the tank outlet and a fitting that will take 15mm copper pipe and is meant to slide the pipe through the fitting. I soldered the copper pipe into this fitting with its end squashed and soldered. This gave me a thermocouple pocket into the outlet pipe. It works well when there is flow from the tank. My system has a commercial one at the pump outlet but I cannot find out where to buy them from. That pocket goes further into the tank fitting thus showing the tank water temp better.
Forgot to add that the vitreous enamel tanks described above do not break above 75C but develop fine hairline cracks in the enamel. This lets the water reach the steel liner. If you have your tank internal anode working ok and not eaten away by minerals, the tank will still last a long time, however if the sacrificial anode is eaten away and not replaced (check 4 yearly) then the tank can develop holes. I think the issue is really the enamel outside temperature compared to inside temperature. if there is a high diff then the enamel cracks. I have an Aquamax tank and they say keep the temperature to less than 75C for this reason.
Hi Paul,
We’ve finally reached summer and the sunshine is doing its job, heating up the solar panel up to 92 degrees at times. I’ve turned the hot water cylinder off for the last 4- 5 weeks and the power account has dropped to $147.00 I finally fell as it’s all worth it. It runs automatically with the odd tweek now & then.
*I feel that taking the time to crox the copper pipe & use hemp & graphite instead of tape is well worth it. You won’t have leaks.
Thanks Peter that is good to know. 🙂
Hi Paul
New power account for the summer has arrived now down to $143.00 finally I’m happy, considering it really wasn’t much of a summer.
Hope everyone gets these type of results or even better.
Solar power maybe next.
Cheers Hamish Curtis.
Hi folks …
I have a tube kit and saxon hw cylinder as Paul mentions, but not the solar one… Anybody familaiar with these will know that the cold in is combined, there is no lower in socket.. So I am wondering if anybody has ideas how to convert it to solar
Saxon is difficult without modifying the tank. I would consider swapping tanks unless you like brazing. It’s not a pressure vessel which helps a bit.
Me2,
Try the website Runsonsun. he has a special fitting that will allow you to attach cold water and also the return from the solar panel as well. If you provide me with an email address I can send you the article I have on it also if you want. you also need to put in a non return valve to prevent reverse flow at night or put in an anti syphon bend in the pipework as well.
Just looking at one fitting he has it allows cold water in to the tank, cold water to the panel and hot water from the panel.
Anyway if you go to the site and email him he can send you the info that might help
Hi Mate, I am writing from the Gold Coast Australia. We have had a lot of bushfires lately and I’ve only just been able to connect to the web. Thanks for the great post. It helped me a lot with my university social studies assignment 🙂
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Regards
Andrew
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Hello Paul
Will the solar panel works like a treat and has been for the last two years and has been a huge energy saving over that time.
I have gone one further than that and am now designing & manufacturing Drip fed Waste oil Heaters for the local New Zealand customers, The customers normally purchase complete built unit with wetbacks for heating homes with hotwater either for radiators, hotwater cylinders or spar and hot tubs and swimming pools.
I burns waste oil from car or truck engines cleanly giving of free heat. These heaters can easy reach 600 Plus degrees fahrenheit.
I hope I have you interested because people from the rest of the world purchase plans on how to build their own heater. The website is below please check it out. http://dripfedwasteoilheating.webs.com
Plans sell for $20.00 NZ dollars only.
Fantastic DIY thanks Paul! Thorough instructions, lots of pics and great advice. Might have to have a go at building one for ourselves. Cheers, Joe
Thanks for the great article. I’ve installed one of the Chinese-designed thermosyphon systems, which is performing really well so far. I’ve written some docs that can be found here:
http://guesstimatedapproximations.blogspot.com.au/2014/11/water-at-my-house-part-2-hot-water.html
http://guesstimatedapproximations.blogspot.com/2014/10/solar-hot-water.html
I really like the system, particularly its simplicity and the fact that the water that comes out the tap is instantaneously heated by the heat stored in the HWS tank.
Cheers,
Hi
I am habitual DIY jill of all trades who just cant help playing with plumbing and anything else I’m not supposed to do because it’s illegal or not building code specific, but of course I use the same plumber as Paul. I have just finished building a cottage made from about 5 tonnes of recycled junk. It’s a very pretty cottage- stand alone solar powered, homemade composting toilet, slow combustion wood stove, gravity feed water, solar hot water connected to the wetback in the stove. The solar hot water system is a Chinese open vented close coupled 120L stainless steel tank evacuated tube system I purchased in a community buy scheme from a company near Toowoomba – Polygreen Solar. I paid $550 for the 12 tube system which is perfectly suited for the situation. It also works exceptionally well without the need for controllers etc. The tank sits on it’s frame on the roof peak at a height of about 5.5 m. The cold feed goes into a small gravity fed tank with a float valve inside it, attached to the top of the main storage tank. This is supplied from a 2000 gallon tank that sits on a 6m steel tower next to the cottage. On sunny days the water boils by about 11 am and on cloudy days it reaches warm temps that are ok for a shower but not great if you are cold sensitive like me. My solution is to connect it to the wetback in the IXL slow combustion stove so that on cool cloudy days it is boosted by the heat in the firebox. It’s only a small system and two people easily use 120L of hot water. With a wetback in the loop there is minimal chance of running out of hot water while you heat the house, cook a meal and dry your boots. I have the hot pipe in the loop connected to the bottom spigot of the hot water storage tank on the roof and the ‘cold’ feed connected via the cold supply at the upper end to the gravity feed tank with a non-return valve in the cold supply line to prevent the hot water circulating through the loop going backwards. I also have ball valves in suitable places so I can shut off parts of the system for easy maintenance eg to replace the wetback when I discovered it was leaking. It meant the house plumbing still functioned because I could isolate the wetback from the rest of the plumbing. Steam pressure is vented through the solar hot water tank via the open vent in the gravity feed tank and drops from a small copper pipe I’ve extended onto the roof so that the water goes back into the rainwater supply tanks on the ground. It works with the Edwards flat panel collector and tank I have connected to a Rayburn wood stove down here at the homestead and it is well and truly proving itself at the cottage. Now (with the friendly plumber) I’ve just installed a similar larger system on a friend’s house. Yeah we built the house too, with a builder, of course.