Paul's esoteric meanderings

  

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.
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.
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.
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.
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.
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.
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.

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

1. Get a big enough tank and enough tubes the first time
2. Pumps / Sensors / Controllers / Electrics are problematic
3. Plumbing is expensive. Copper plumbing is very expensive
4. Don’t trust couriers
5. Leaks happen
6. Have an understanding family if you DIY
7. Understand the gov’t rebates well
8. Nylon olives will melt and leak
9. Chinese build quality is not ideal, but is good for the price
10. 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

http://www.voltscommissar.net/K4/kernkraft.htm

I ordered a vacuum tube based solar hot water collector from a company in Sydney for freight to Brisbane. I used Smartsend to get it here as they specialize in eBay type stuff, and this was an eBay type thing. Allied Pickfords delivered the tinkling box of broken glass apologetically to my door.

The pictures below tell the story of how well couriers treat products labeled in 10 places “Glass, Fragile, This Way Up”

Of the 15 tubes, 5 made it intact.

I have a video of breaking these into the rubbish bin and they are pretty tough. Made from borosilicate glass they take some smashing. Looking at the box the courier has either dropped them on their end or crushed the end, as the tubes busted through the polystyrene and the cardboard. Lesson learnt, don’t trust these to a courier. A number of phone calls to other suppliers in Brisbane confirmed a high loss rate with couriers, and most will no longer use them.

Luckily for me I found (too late) a Gold Coast supplier who could supply replacement tubes, and who was $150 for spares vs the commonly quoted $500 for 10 tubes. Thank you very much Rod from SolarOz.

I’ll post pics of the system when it is fully installed and operational.