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The Best Solar Hot Water System - Is It Available?

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Started 11 months ago by mick_queensland
Latest reply from Greg C

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mick_queensland
Member

Through months of research, taking many hours, I have finally decided that the ideal Solar Hot Water System is yet to be built and sold.
So, what does it look like? I hear you all say, ok, this is it.

It would consist of Evacuated Tubes with Heat Pipes, plugged into the bottom of a 318G Stainless Steel 315 litre Tank on the roof, with a 318G Stainless Steel Heat Exchanger inside the tank. The tank would have double the normal insulation thickness, approximately 100mm of the good stuff. The tank would have an expansion tank and would not be under pressure. It would have a booster element as an option.

Why do I think this is the best system?
Because there are no moving parts, no electric pumps, no temperature sensors, no valves (well not under any pressure anyway) no electronic controllers to set up or have fail, no water in the evacuated tubes, no water being wasted at all, the system will continue to work with a broken tube, almost no maintenance, nothing to break except the tubes.
It has the best of every system rolled into one and it should actually be the same price as the currently available systems!!!!!

Any opinions? Any suggestions for improvements? Has anyone seen one like this cause I want to buy it!!!

Cheers, Mick

Posted Saturday 18 Jun 2011 @ 12:47:12 am from IP #
swanning_it
Member

One addition, the boost shall be either gas or electric heat pump.

Posted Saturday 18 Jun 2011 @ 1:06:50 am from IP #
rockabye
Member

My original flat plate stainless tank solar hws made in Oz is still going strong after 20 years. Fits your description almost to a T. Electric boost was needed for a few days per year.

Posted Saturday 18 Jun 2011 @ 2:04:13 am from IP #
Lance
Key Master

These guys are importing all stainless open vented units that might be close, have asked them about how the tubes transfer heat, whether they have heat pipes or are flooded: http://www.ultimatesolar.com.au

Posted Saturday 18 Jun 2011 @ 2:11:21 am from IP #
mick_queensland
Member

Rockabye Flat plate collectors are as good as tubes except for being much heavier and if the glass breaks you have to have lots of help to replace the whole collector. With a tube, you just buy a cheap replacement (~$40) and slip it in, the system even keeps working while you do it, whereas the flat plate requires a system replacement, probably using a small crane. Otherwise I like the flat plate collectors. What make of SHWS is it that you have?

Lance, I have contacted a couple of the Ebay suppliers and the manufacturer in China. Yes, they do make heat pipe tube but they dont sell them on Ebay, well not that I have found yet anyway.

Cheers, Mick

Posted Saturday 18 Jun 2011 @ 3:21:50 pm from IP #
Gandini
Member

Mick_qld,

You say your "tank would have an expansion tank and would not be under pressure".

So how would the water get to the taps? Are you talking about a gravity fed system like the very low pressure tank-in-ceiling set ups which many people were glad to get rid of when mains pressure systems became available ?

Posted Sunday 19 Jun 2011 @ 1:45:39 am from IP #
gazmo88
Member

This not close ?

http://www.runonsun.com.au/www.runonsun.com.au/Passive_evacuated_tube_solar_hot_water..html

Not trien one myself mind.

Posted Sunday 19 Jun 2011 @ 3:09:25 am from IP #
Sunshine
Member

Whilst having the tank on the roof is a more simple system with less things to go wrong, they aren't suitable for alot of houses in older suburbs, if you have above ground power on your side of the street and if houses are on small narrow blocks like ours.
Crane is impossible in our situation, plus the old Qlder roof required strengthening as well, so split system with evac tubes was only way to go in my situation.

Posted Sunday 19 Jun 2011 @ 3:48:59 am from IP #
hamish05
Member

I agree totally mick_queensland. I would have installed that type (tank with ETs) if I had not removed internal walls, and been worried about the weight.

It would need to be in 2 models a/ for northern Australia, b/ for southern Australia. Difference being, the southern model would be fitted with more evacuated tubes.

BTW, I have just returned from 17 days in China. There are so many SHW systems with tanks and ETs on roofs its mind boggling, (very few plate mods). Don't know how well they work in the heavy smog which is chronic everywhere.

Posted Sunday 19 Jun 2011 @ 4:36:42 am from IP #
sun2steam
Member

Mick_q,
I think your system is a bit over-designed (=costly).
Having heat pipes between the tubes and the tank and a other stainless steel (why not copper?) heat exchanger is kind of double dipping and and adds unnecessary restrictions in heat flow to the system.

The system Lance refers to is most likely without heat pipes but with water filled glass tubes. This is the cheaper and more heat efficient solution. The only issue I can see with this system is a certain risk that in case of glass breakage the whole tank will spill out through the fracture, spill over the gutter and cut hurt somebody.

A general issue with tanks on the roof besides their wight is that the tanks have to be put horizontally which reduces possible stratification. Stratification is the layering of hot water over cold water which makes the hot water tank more efficient because hot water can be used 'to the last drop'.

And finally I would say that the direction of optimizing depends on what the goals are. If the goal is to build the 'best' hot water system in the world, Mike's system may come close. It the goals is to have the best compromise between cost, heat efficiency and CO2 reduction, the solution can be quite different. So for instance a bit of electrical boosting with cheap night time tariff does not cost much and will most likely financially outperform a gas booster.

Posted Sunday 19 Jun 2011 @ 11:00:45 am from IP #
mick_queensland
Member

Hi All,

yes, a lot of good points there. The system pointed out by gazmo88 is one that I already checked out with manufacturer. It has water filled tubes. I don't like water filled tubes for the reason that sun2steam pointed out. Other than that, the systems that are on offer currently have rather small tanks. I have considered using two systems in series.....

Sun2steam, I don't think it is over-designed, I think it is bullet proof, I guess I want a system over-engineered rather than built down to a price. Also, given the ridiculously high prices being quoted by current suppliers, I don't think it would be any more expensive.

I agree about the stratification issue, I have been mulling that over. One of my original specifications was that the tubes would plug into the bottom of the tank. Also, since it uses a heat exchanger, that would be positioned at the very top of the tank, the thermal flow in the tank liquid would be very calm and slow and would not be interrupted by cold water flowing through, so I suspect (feel) that it would work pretty well, and that there would be enough stratification to work in this situation.
Mikes system is far from the best.... sorry to disagree but it has way too many things to go wrong, it is overly complicated, and designed to under perform in Winter, which in my view is dumb.

Gandini, the tank would hold unpressurised, water heated by the tubes, with an expansion tank. The mains pressurised water would flow through the heat exchanger. There are several advantages to this, but the main two are that 1. water to be used in the house does not sit in your tank and therefore you do not need to heat a bunch of water up to kill rogue bacteria. 2. the tank will never go above 100°C since it is not under pressure.

I would estimate that the extra cost of Stainless Steel over any other material including copper would be negligible and the benefits outweigh any cost associated. Just me over engineering the system again sun2

Agreed on the option for number of tubes, in fact, a single tank system could be built with 40 ports, and you plug in any number of evacuated tubes you want, up to 40. You can effectively tailor heat gain to suit. Hey, not getting enough hot water, add a couple of tubes, the neighbours tree grown up and shading it a bit, add a couple of tubes, done in under an hour and for under $100.

So, far no-one has pointed to one of these available in Oz.

cheers, Mick

Posted Sunday 19 Jun 2011 @ 3:38:35 pm from IP #
sun2steam
Member

Mick,
have you added $50000 for a certification according to Australian Standards? Otherwise you will not get any government rebate or RECs.

Posted Sunday 19 Jun 2011 @ 9:14:03 pm from IP #
mick_queensland
Member

Hi Sun2
I havent added anything, I am looking for a manufacturer. So far, I dont think the current crop of solar hot water systems is as good as they could be. So, if $50,000 was amortised across all their sales, and if they only sold 50 systems, that would add an extra $1000. Hmmmm. Some of the "non-approved" systems are selling for under an approved system less the rebates....

Anyway, still hoping someone out there sells one similar to what I would like.

Cheers, Mick

Posted Sunday 19 Jun 2011 @ 9:42:58 pm from IP #
Ueee
Member

Just thought i would throw my 2 cents worth in. As a courier i see lots of houses here in Canberra, and i always keep on the lookout for hot water and pv systems-just to see what direction they face etc. The steepest systems i see are tilted at about 45deg. This would still provide plenty of boiling water in summer but will under perform in winter. The optimum pv angle here is about 45deg but i believe that hot water panels would work better in winter and still have enough summer gain at 60deg or even more- our sun is 30deg at midday in winter-so the average shortest day angle is less than this. Hence i am making flat plate collectors and am going to try them on our NW wall above the windows(gable end of house). This should still provide enough summer gain, plenty of winter gain and some frost protection as the collectors will be under 400mm deep eaves. My Sister just moved into a new house with an appricus system at about 20deg tilt, facing north. I was amazed to see on a warm (15deg), sunny day last week that the collector temp didn't get over 65deg. There could be something wrong with the system, but it seems to provide just enough hot water for them. My small scale testing with vertical flat plates, not double glazed, facing NW shows i can get the collector to over 70deg in less than 20 minuets. Are all the installers missing something here? Or do they put standing systems up further in the too hard basket? It also amazes me to see both PV and hot water systems directly south of large gum trees and other shading-i suppose some installers will do anything to make money. Ok, rant over, good luck mick

Posted Sunday 19 Jun 2011 @ 11:52:16 pm from IP #
gazmo88
Member

mick_queensland said:

"system pointed out by gazmo88 is one that I already checked out with manufacturer. It has water filled tubes. I don't like water filled tubes for the reason that sun2steam pointed out. Other than that, the systems that are on offer currently have rather small tanks. I have considered using two systems in series....."

But this page here seems to indicate that this is not the case:

http://www.runonsun.com.au/www.runonsun.com.au/Overview_and_schematics..html

Somewhere else it shows a couple of them seriesed up.

Lies, damn lies and web pages .... I know

To me this looks about as agricultural as you could get, (i.e. few moving parts, repairable with a large hammer, and ugly as sin) but in life I tend to be a big fan of simple.

I am very keen to hear of something more appropriate though.

Posted Monday 20 Jun 2011 @ 2:11:58 am from IP #
Johnnojack
Member

Ueee I agree most systems need to be tilted up higher for better winter gain, there was an article in Renew mag. saying just that. Problem is a proper stand needs to be installed to hold the tank and it adds a few hundred bucks and makes it look unacceptably ugly to some. If you look at the pictures in the ads for solar HW you never see any pipework. I worked for a solar HWS installer for a while and there were complaints about the ugliness of the pipework, (did they think you could have no pipes?)
A stand makes it even worse. Even with the no tank on the roof models if the panels are tilted up it exposes a big length of the hot pipe which when flat is fairly minimal.
My panels are 30deg and yes they boil in summer and at the moment don't do much.
Solution - steeper roof pitches? reflectors?

Posted Monday 20 Jun 2011 @ 4:14:35 am from IP #
Ueee
Member

Firstly i must apologize to any conscientious installers reading my last post, i know not all of you are just in it for a quick buck.
Johnnojack, imagine that, you need pipes for a HWS?? Come on surely in this day and age of wireless everything, Bluetooth, hands free, remote control etc, surely we could have "Pipefree" solar hot water? I can understand some people's worries about the look of 30 tubes standing at 60deg on there roof, but surely if the financial benefit (everyone speaks that language) was pointed out, wouldn't most people come round to the idea? My father is an example of it, after complaining he had to boost the system a few times in winter (Hills, true north, no shade at all) i told him he should get the tubes stood up at a higher angle, i was amazed to hear him say that they didn't want to stand their 30 tubes up more cause of the look- instead he had bought the 30 tubes and a 300l (for 2 people) tank to make up for the winter loss!!

As much as i love the idea of "the perfect system" it really depends on your location and personal preferences. I decided on the DIY systeme because i can change, enlarge, or even completely remodel the system if i need to, plus i like a good challenge! I know this is really not a viable option for everyone, but after reading about all the problems people have with purchased systems, the misleading internet information as outlined by gazmo88 and just general confusing and often contradicting information about solar how water systems, I thought i'd give it a try.

Just imagine if every house in australia had solar hot water. Would we still need a carbon tax?

Posted Monday 20 Jun 2011 @ 8:56:27 am from IP #
Ueee
Member

Oh, and as for reflectors, surely if a system on a stand is too ugly, then a giant mirror on the roof will be too? Reflectors are a great idea (just think of large scale solar arrays-the type that heat salt/water to drive turbines-not sure what there called) but i think too many urban councils would ban there use due to unwanted reflections etc. If i lived in a rural area with some space i'd love to see what gains could be made with reflectors both for PV and hot water.

Posted Monday 20 Jun 2011 @ 9:08:46 am from IP #
gazmo88
Member

Ueee said:

"Just imagine if every house in australia had solar hot water. Would we still need a carbon tax?"

Switching off Facebook and twitter would probably save enough electricity to do that !

As to your other points I am reminded that " the best is often the enemy of the good"

In so many areas of life you pay 90 % of the cost for the last 10 % performance

Your father's installation seem to be a good example.

One day we might aspire to the perfect solution, in the meantime my approach will be to attempt the "90%" solution ...... Compatible with whatever improvements I can see coming .... unless Mick_Queensland manages to find the 100% solution before I start

Oh and I doubt the council where I will be building will be big fans of mirrors on roofs. Their planning rules mandate dark colored roofs. Stupid stupid stupid ..... Gaaaaargh

Posted Monday 20 Jun 2011 @ 1:00:29 pm from IP #
mick_queensland
Member

Hi All,

firstly, let me clear up the runonsun website and the equipment that is sold there. Yes, they have heat pipe Evacuated Tubes, so the site does not lie. I am in contact with that supplier even now. They are approved and do garner RECs/STCs which may be good if you are looking for that. They do have stainless tanks. They are mains pressurised tanks, and they are close to but not 300lt in size. So, as you see, this system comes close to my ideal. On the same website http://www.runonsun.com.au/www.runonsun.com.au/Evacuated_Tubes.html you can see they also supply water filled evacuated tubes, so you get to choose which type of tube you want. I hope Andrew is appreciating all this promo here, it was not my intention to promote any one system, I am merely ensuring that his website is not misrepresented on this forum.

As for mirrors, I considered this when SWMBO was not impressed by the "ugly big thing on the roof" The WAF (Wife Acceptance Factor) was low for such an angled stand and tank on the roof. However, she has evolved now, up to a point where I get to choose whatever I think will ensure we dont pay for hot water any more. The WAF is now high. In case you were wondering about the WAF of a reflector system, I was going to do a stealth installation and see how long before she noticed it, hehehe. By the way, it does not need to be mirror finished.

I also agree that you should choose a system that suits your own situation and that one system does not fit all. I am still looking Gazmo!

Mick

Posted Tuesday 21 Jun 2011 @ 1:06:46 am from IP #
gazmo88
Member

Mich said:

"I am still looking Gazmo!"

This is great news for me as I reckon you will get there before I need mine

I hope.

Thanks for clearing up the website thing, I had spoken to Andrew once or twice on the phone and he sounded like a nice guy. Not bought anything from him so of course that should not be read as an endorsement (or otherwise) of his products.

I also looked at the Ultimate Solar website and there is a remarkable similarity between their stuff and the Runonsun stuff. Maybe they source stuff from the same Chinese factory. Stuff looked OK as well.

TLA translation: around here its DPP - Domestic Planning Permission

Posted Tuesday 21 Jun 2011 @ 7:45:49 am from IP #
Gandini
Member

Mick,

Interesting info about Run On Sun. Their ET plus roof mounted tank system seems to be a newcomer and I'll be interested to see how it goes.

It ticks most of your boxes but would you want to mount it at the optimum angle for winter performance i.e. about latitude plus 20 - 25 degrees?

Looks don't really matter to me and I guess anything can be made structurally solid and stable but I have some reservations about a horizontal tank up in the air on a frame above tubes angled at 50 to 60 degrees.

Of course in a rural area or on a large block in suburbia you would probably be able to mount it at ground level provided it was not shaded.

And how does the use of a heat exchanger affect efficiency (small drop or ?) and would insulation on the pipes into and out of the tank be able to resists freezing in winter?

Posted Tuesday 21 Jun 2011 @ 7:47:49 am from IP #
mick_queensland
Member

Hi guys,

I found this web page a while ago and I think everyone here will find it useful.
http://www.macslab.com/optsolar.html
The page gives accurate formulae for calculating solar panel tilt angles and gives examples, graphs and explains the method behind the formulae. For solar hot water I would tilt for maximum winter production which gives a fairly even production throughout the year, and it seems like it would be even enough to cover your all year hot water requirement without boost of course.

Using a properly tilted panel your summer production will only be just a little lower than your winter production, and you will over-produce slightly in autumn and spring. Gee, isnt that the results we want! more in winter compared to summer....
The winter angle formula is (Latitude° x 0.89) + 24° = tilt from horizontal°
Many thanks to Charles R Landau for the formula and his informative webpage.

Only problem is getting a frame that tilts to the correct angle. Might have to either modify existing or construct it myself. The other thing you need to consider with a system that has a tank on the top of the frame, is to ensure you dont overbalance the whole thing with too steep an angle.

Cheers, Mick

Posted Wednesday 22 Jun 2011 @ 1:10:16 am from IP #
hamish05
Member

Good simple info mick_queensland. For me at 37.46 deg, (Melb) it means that I require my collector to be at 57 deg.

At the moment however I am at approx 23 deg (roof) plus low angle frame 12deg. That only makes 35deg, which is a long way short of the recommended angle. This probably accounts for the reason I use so much electricity boosting in winter. All-though, wouldn't matter what angle it was at, when every day we have heavy cloud this time of year.

It's probably not an easy one for me to to rectify at the moment either, unfortunately.

Posted Wednesday 22 Jun 2011 @ 2:38:13 am from IP #
Maat
Member

Hi~~~~,
We live on the Gold Coast (Qld)and are in the process of gathering information and getting quotes for a new solar hot water system. Our present one is a flat panel type well over 20 years old and NOT effective in winter, even on a sunny day like today. When we bought the house 7 years ago we found that we often ran out of hot water in winter so contacted the manufacturer for help. We were told that the system "...worked on the surrounding air temperature and so we should leave the electric boost on ALL through winter."
This didn't seem to be an economical or sensible way to heat water so we are now considering the evacuated tube system (with the tank on the ground) as a replacement.
Thank-you, mick-Queensland, for the information on how to calculate the panel angle. We will make sure that this is one question we ask those companies from whom we obtain quotes.

Posted Wednesday 22 Jun 2011 @ 4:40:46 am from IP #
amun-ra
Member

hamish 05 just see your local dealer or installer and get three 30 deg frame legs to replace the 12 deg that would get you in the ball park of ideal you may need to extend some copper but only a meter or so would be easy and not to expensive

Posted Wednesday 22 Jun 2011 @ 5:51:33 am from IP #
hamish05
Member

Yep amun_ra. I've been looking at the frame schematic since my last post and can see it's not going to be a very difficult mod to do or have done.

As I said b4, it will just have to wait awhile, unfortunately. Its good however to at least now know the optimum angle for best winter performance.

Posted Wednesday 22 Jun 2011 @ 6:05:59 am from IP #
amun-ra
Member

hamish05 the frame for the system you have has been designed to be modified to suit a range of tilt angles and situations they can be modified but the labour cost for a plumber onsite is quite high so standard tilt angles are normally used

Posted Wednesday 22 Jun 2011 @ 6:19:38 am from IP #
kesa32
Member

l agree with Hamish, down south here we don't get much sun in winter , and like him ours is at about 34 degree tilt , and not doing much on days like today .....it was that dark and grey our 4.8 KW solar pumped out a grand total of 3 KWs for the day
In all honesty l reckon here in Victoria , with a fullsized family this time of the year , you'd need a 60 tube system tilted ideally to get no boosting at all of a night time

Posted Wednesday 22 Jun 2011 @ 8:00:36 am from IP #
hamish05
Member

kesa32, yes days like today, and there are heaps of them this time of year, test your faith in SHW and PV.

For comparison, my 3kW PV only produced 2.2kWh today. The lowest daily generation since instillation. My SHW collector only managed 9 pump a-rounds for the whole day.

Even standing it up another 20 deg wouldn't have made much difference. Guess we will have to "electric boost" again tonight.

Posted Wednesday 22 Jun 2011 @ 9:21:46 am from IP #

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