Green Building Forum - Flat panels -vs- Evacuated tube... ...the showdown...

Flat panels -vs- Evacuated tube... ...the showdown...

Jeff B — Fri, 04 Jul 2008 18:36:02 +0100

Tony - I would very much like to borrow your book! How do I go about this? Thanks.

Jeff B.

Flat panels -vs- Evacuated tube... ...the showdown...

Ample — Sat, 05 Jul 2008 11:21:29 +0100

Hi Jeff
We fit these systems, we have about 40 systems running in the UK. with customer very happy with the results system cost about 8k, fitted 13K
But we need large roofing space minimum of 15Sqm.Plus if you got a swimming pool we can incorporate this as well with the same system.
Many thanks jeff.
Paul

Flat panels -vs- Evacuated tube... ...the showdown...

Jeff B — Sat, 05 Jul 2008 13:15:51 +0100

Ample - unfortunately that is well beyond my budget. I didn't realise you were an installer of solar heating systems; I thought you were a DIY-er who had built his own system and had a few tips to share! Thanks anyway.

Jeff B.

Flat panels -vs- Evacuated tube... ...the showdown...

Ample — Sat, 05 Jul 2008 15:02:44 +0100

Posted By: Jeff BAmple - unfortunately that is well beyond my budget. I didn't realise you were an installer of solar heating systems; I thought you were a DIY-er who had built his own system and had a few tips to share! Thanks anyway.

Jeff B.

jeff we are DIYer but specialists in solar

Flat panels -vs- Evacuated tube... ...the showdown...

rumi_ecobuilder — Thu, 08 Jan 2009 01:37:58 +0000

It has been an entertaining read looking at the discussions here. I am a pro solar installer and unlike many installers I install FPs, HPETs and CPCETs or put simply:
FP=Flat Plate,
HPET=Heat Pipe Evacuated Tubes
CPCET=Compound Parabolic Collector Evacuated Tubes (direct Flow)
Why do I install this variety? because I advisse my clients of the choice, advise them of the efficiency and then the decision is made according to the following constraints:

Personal informed choice of the client
Esthetic and planning constraints
Suitability to the structural constraints of the building

The most efficient, or to be more precise in terms powerful, of all these panels are the direct flow CPCETs. The reason for this is that the parabolic mirror exposes a greater area of the evacuated tube to solar radiation, up to 30% more.

The next most powerful are the HPETs and the least powerful are the FPs.

Accepting that cylinders, thermal stores, controllers and pumps can be regarded as pretty much the more basic part of the systems, getting the settings right takes a good deal of skill. controllers vary from make to make, I prefer the Steca controllers because of the high level of fucntionality and the fact that the factory has a very high environmental standard of manufacture.

Finally a note on efficiency, swimming pool systems, or systems where the object is simply to raise the water temperature a few degrees C above ambient are the most effiecient and can achieve efficiencies of 80-98%. Systems where the intention is to raise the temperature 50-60 degrees C above ambient can never be more that 20-40% efficient in northern Europe. However bearing this in mind, spending around Â£3,500- Â£7000 on a water heating system with a 10 year warranty which will need refilling every 5 years and will last at least 20-30 before needing a major overhaul and has no extra running costs, requires no fuel is very attractive. Finally any decent installation engineer can design a suitable system with any of the differnet collector types which will compensate for their relative inneficiencies

Flat panels -vs- Evacuated tube... ...the showdown...

Barry Johnston — Tue, 10 Mar 2009 16:21:07 +0000

I tend to agree with rumi in the previous post.

The ideal might be to give the customer a balanced picture of the hugely various concepts which pass for efficiency such as this marathon which ranges from component to global in its approach:

Collector stagnation temperature
N(o) (absorber) on its efficiency formula (which is what excites vaccy tube people)
N(o) (aperture) on its efficiency formula (which, being lower, has less sex in it)
to and from pipe dead leg volume
heat storage design and size / panel area
annual panel delivery
annual system delivery
annual fuel saved
annual energy saved
annual carbon saved
annual solar fraction of each bit
duration of any warranties for each bit
the labour warranty
key warranty exclusions
life expectancy
reliability
accreditation
maintenance frequency and costs
embodied carbon
operating energy parasitics
operating carbon clawback percentage
whole of life carbon and energy budgets
capital cost Â£
operating and maintenance cost Â£
whole of life cost Â£
and so on!

Then to name which collectors or systems tend to be best at each one.

The to ask the consumer to prioritise this list.

Then to congratulate the customer on their choice, whatever it is, provided that it is not to abandon solar at all.

In the less than ideal world, we spend more time explaining explain the benefits of our technology, as most solar hot water suppliers do. You can probably guess what would be are given that I run a solar innovation business!

Regards, Barry

Flat panels -vs- Evacuated tube... ...the showdown...

Peter C — Tue, 24 Mar 2009 01:46:30 +0000

Hi,

I also agree with informing the consumer of the options available, even better I have the systems set up so they can see them working.

Some want a cheap starter system others want real value, sad thing is many buy the cheap system thinking or believing they are getting the best value for money.

Flat panels -vs- Evacuated tube... ...the showdown...

brig001 — Tue, 24 Mar 2009 08:39:37 +0000

Hi, has anyone got any experience of these? http://oxfordrenewables.co.uk/solarfocus-cpc
Planning to DIY something similar as it seems a nice way of concentrating the sun in a low profile package.
They call it CPC (Compound Parabolic Reflector), but it looks more semi-circle to me. I came to the conclusion that a semi-circle (or maybe a third...) would give good collection without tracking as long as the pipe had a fin to pick up on the plane focus.

Flat panels -vs- Evacuated tube... ...the showdown...

MarkK — Tue, 24 Mar 2009 13:15:22 +0000

this debate should be killed off. It's so counterproductive. It used to educate, now it just confuses.

fp or et? who cares? it's horses for courses and if you use an accredditted supplier who produces a price and an estimate based on SAP, then guess what.... you CAN compare apples with oranges.

SAP may not be perfect but it takes the whole myriad of complex variables involved in the manufacture of the collector, the orientation, the amount of energy required, and reduces it very nicely in the same way for each collector to a simple amount of kWh per year.

so you have price, performance and aesthetic. Simple, informed decision without any of this (much of it quasi) engineering speak and hobby horse ranting.

OMG..i'm ranting too

Flat panels -vs- Evacuated tube... ...the showdown...

James Norton — Mon, 29 Jun 2009 12:12:03 +0100

...Mark,

Killing threads off seems a bit harsh, you will recall the thread wad started on the basis of what are the pros and cons...

ie which horses for which courses...?

J

(100 yeah! )

Flat panels -vs- Evacuated tube... ...the showdown...

James Norton — Fri, 16 Oct 2009 13:34:04 +0100

So any one disagree with Evac tubes for best marginal condition / stretching the season option?

Also within ETs in terms of Â£s per output over say 20 years do the Navitrons and the cheap replacement tubes still have it or is it worth spending a bit more for that extra efficiency or reliability...?

J

Flat panels -vs- Evacuated tube... ...the showdown...

joe90 — Fri, 16 Oct 2009 18:15:31 +0100

anyone care to answer brig001 above, I like this design and would like to hear from anyone with an opinion or hard facts on this product.

Flat panels -vs- Evacuated tube... ...the showdown...

Tuna — Fri, 16 Oct 2009 20:54:52 +0100

Posted By: James Norton
Also within ETs in terms of Â£s per output over say 20 years do the Navitrons and the cheap replacement tubes still have it or is it worth spending a bit more for that extra efficiency or reliability...?

J

If you're talking about Â£'s per output, anecdotal evidence is that FP's will win simply because their lifespan is much extended beyond that of ETs. I've read suggesions that 40 years is possible for an FP panel, whereas ETs are viewed as reliable if they last half as long.

Flat panels -vs- Evacuated tube... ...the showdown...

brig001 — Sat, 17 Oct 2009 07:30:50 +0100

Hi joe90, still no info on that actual product, but I have managed to DIY one. Unfortunately, I found out that the panel is the only one part, the plumbing etc takes time too, consequently, I have run out of time this year. I have put a pre-heat tank in the loft, all connected to the DHW circuit, so I "just" need to mount the panel and connect it all up. When I get some figures, I'll post them here.

Bri.

Flat panels -vs- Evacuated tube... ...the showdown...

solarfriend — Sat, 17 Oct 2009 14:19:37 +0100

Had my system running for 13.5 months now. Itâ€™s a ( Solartwin F/P type copy ), and has worked faultlessly so far. Because of changing gas supplier and gas prices going up and down it is going to be difficult to calculate the savings made. I must be saving though because for the last 4/5 months we have used very little gas. Keeping up the diary is a bit of a pain, but when I stopped it I got a flood of emails to keep it going so I will continue for a while.

Two things to consider.

By using a certain website they promise a Â£35.00 cashback. I am waiting for my check. Then I will look at switching again. Donâ€™t know how often you can do this, but it has to be taken into account.

What if I suddenly die? You have to think about this. The websaver 2 account that I now have with B/G will be too complicated for my wife.
( usernames/passwords/taking your own readings etc ) So next time I switch I will go back to the old quarterly paper bill.

What about the system? Who will operate it? My system is quite simple to isolate if I am not around. Just close two valves. I have labelled these and shown them how to close them. Then pay the window cleaner Â£50/Â£100 to remove the panel. This would not be possible with a complicated E/T setup. I study this whole thing all the time and can see no advantages to the E/T type systems. Only snag with F/P systems at the moment is a reliable supply of pumps. http://www.solarfriend.co.uk

Flat panels -vs- Evacuated tube... ...the showdown...

amber — Tue, 20 Oct 2009 13:03:38 +0100

When it comes to vacuum tube systems, naturally some are better designed than others. The LaZer2 from SolarUK.com is one of those which has done away with the glass to metal seal on the collectors (which have the potential to fail). It comes with a 25 year warranty. The great thing about renewable products like this is that you are effectively buying 25 years of energy in one go. With gas and electricity prices set for further hikes, as a result of the unstable global market highlighted in the recent Ofgem report into the UK's energy supplies, a solar hot water system is looking increasingly cost effective.

Flat panels -vs- Evacuated tube... ...the showdown...

Tuna — Tue, 20 Oct 2009 13:43:22 +0100

'amber', should you perhaps declare that you work for SolarUK?

Flat panels -vs- Evacuated tube... ...the showdown...

joe90 — Tue, 20 Oct 2009 20:50:38 +0100

My main concern over ET systems was the failure of the vacuum (I have had a lot of double glazed panels fail recently) but with a 25year guarentee on the tubes I will look long and hard at the SolarUK system.

Flat panels -vs- Evacuated tube... ...the showdown...

solarfriend — Tue, 20 Oct 2009 21:38:46 +0100

Can you imagine taking something back for a refund that you bought in 1985. Just after the Falklands war.

Flat panels -vs- Evacuated tube... ...the showdown...

wookey — Wed, 21 Oct 2009 00:52:46 +0100

All the cheapo chinese 47mm and 58mm tube panels have done away with the glass/metal seal too. So no advantage there (only the 70mm tubes have the metal/glass seal).

Solarfriend - you say you see no advantage in ET systems, and describe them as 'complicated'. There is no complexity difference between ET and FP setups. Both can be very simple. And I still haven't seen anyone selling FP panels in the UK that are cheaper than than the eco-nomical ET panels. So SFAICT looks are the only reason to choose FP. And limited roof space is the only reason to choose any of the expensive non-chinese ETs.

Flat panels -vs- Evacuated tube... ...the showdown...

solarfriend — Wed, 21 Oct 2009 09:05:14 +0100

I would say ET systems are more complicated than the ( rubber tube flat panel, original cylinder, 12 volt pump, small P/V and tubing ) that is needed for a Solartwin type copy system such as mine. For an ET type system I would need. The evacuated tubes, a new twin coil cylinder, an expantion tank, considerable plumbing, antifreeze and a mains powered pump/controller. My system is giving me all the hot water I need ( as long as the sun is out ) and has used zero electricity in 13 months. With just the one mechanical part ( the pump ) that may need attention in the future.
If I were thinking of buying a system with a 25 year guarantee I would haggle a bit. How about 50 0r 75 years.

Flat panels -vs- Evacuated tube... ...the showdown...

crusoe — Wed, 21 Oct 2009 11:30:08 +0100

Hmm, may be a bit strong to kill the debate MarkK, but I do understand how you feel. The GBF (F appears to stand for Fantasy to me sometimes!) is a microcosm, but reflects the larger world outside - and not everybody - especially the experts (vested interest?) - agree there either. Some common sense is being injected in these latter comments, which is welcome in a confusing and often technical debate.

Some interesting points are being made for and against on both sides. Excepting perhaps Thermomax, who I understand (not first-hand, but from a colleague who has fitted much of their gear) have had their own issues, the ET tube market is not by any means mature. Nor stable, or profitable, when big players like Schott and Vaillant drop off their perch. Nor as reliable as I would wish were I asked to make the investment. It is developing. As is FP technology, albeit more slowly. But when a FP system like Filsol - a very simple, modular (read 'easily replaceable') stainless steel sheet collector, can have a proven life of 30 years + AND perform better (DTI report) than not one, but several ET systems, we are into what appears to me to be a rather misdirected debate.

I have fitted alternative energy systems since 1978, starting with WB stoves and diversifying into varying shades of green since. And solar is a definite part of that mix. So I am an installer - and I integrate technologies. Hence my perspective is different from a customer, a solar provider, or even a designer, any or all of whom are entitled to diagree with me...and who may be right.

My tuppence worth: If I have learned two things which may be relevant in this debate, they would be these:

Firstly: In this debate, and hence your purchase decision, try and ignore lengthy warranties, even underwritten ones. They confuse the issue and cause us to suspend critical judgement with the presumption that the product must be good when it has a bigger warranty. Witness the automotive industry - cheaper-built cars with hugely better warranties than demonstrably better ones.

A good name for quality, longevity and back-up is worth a lot more to me than a prolonged warranty. Why? Well, we saw this in the '80s when, due to unexpected problems with stainless applications, a lot of WB chimney systems fell apart. One, a reputable firm with a great product for the time, had a 25 year warranty - I still have the paperwork - but with the problems, the firm had folded more quickly than the paper its warranties were printed on. 'Underwritten' I hear you cry....? No. The ongoing financial crisis - predicted and fulfilled by Drs Leeb et al - has shown that there is a worldwide financial instability which can leave very little untouched. When sacrosanct fiscal depositories like pension funds in big PLCs can be raided, what hope guarantee depositories in faceless backstreet insurers.

Secondly: I fit what the customer is comfortable with, bearing in mind all the caveats in previous posts. I would advise people to get past the FP vs ET vs whatever-unproven-technology-may-come-along debate and focus instead on HOW we are using what we already have. We are straining down the gnat but gulping down the camel when we are not even using what we have to its full potential. Anybody who fits a system - FP or ET - which is designed to stagnate is fitting a system which is not even half green.

Why? Because it is wasting potential energy. Energy which could be reducing our gas/oil/even log consumption. According to the Met Office, (and ignoring 2008!) we usually get get 30-40 days where solar will work well in the shoulder seasons down here. We have had an exceptional late summer and autumn (I 'hail' from Cornwall btw) which has already exceeded that quota, and the systems I have fitted over the past few years - ET or FP - which are storing that 'excess' solar energy instead of allowing it to fritter away in stagnation - have been able to dump that heat in the cool evenings into the house for space heating - UFH or rads.

Do your own figures, work out your own payback, but if your two panels have heated the DHW and can be re-directed to pre-heat the CH in a Thermal Battery (my term, as it re-charges slowly, but call it what you like, Thermal Store is often used), you will be cutting years off your payback (I feel another debate coming on....)
Now think what five or six panels could do to your ongoing fuel bills - and yes, your property value, as, like it or not, homes which are cheap to run and comfortably warm are going to rise fast in value against bigger, colder mausoleums.

A few people on this forum have already done this - Johan I remember for one. So I submit my point and shall call it the Stirling Moss Principle - it is less important what you drive than how you drive it.

Regards from Sunny Cornwall!!

Crusoe

Flat panels -vs- Evacuated tube... ...the showdown...

Johan — Wed, 21 Oct 2009 18:07:34 +0100

Thanks Crouse, my system work very well indeed!

After getting the system working properly at the beginning of June (plumber didn't fill it properly first time around so too much air in the solar loop = POOR efficiency!) I've had 4 continues months with 100% solar hot water and the little bit of heating on cold nights that is required every now and then. I guess next year I can probably count in May as well as it tends to be dry and sunny, making for 5 months which is pretty good. Admittely living in East Anglia probably helps as we get a fair bit of sunshine here.

I worked out a payback in the region 7-10 years on the basis there are no changes in the gas price, etc. I supect the way things are going I'll probaly be nearer to 7 years then 10...

wookey, I know you're a big fan of the Navitron, Eco-nomical ET's because they are well priced. However, you can get higher effeciency FP's for less then either of those two from more then one supplier in the UK.

I have 8m2 of FP and 750l of storage for those wondering...

Flat panels -vs- Evacuated tube... ...the showdown...

joe90 — Wed, 21 Oct 2009 18:33:20 +0100

crusoe,

Thanks for a balanced, sensible, contribution.

(P.S. missed you)

Flat panels -vs- Evacuated tube... ...the showdown...

James Norton — Wed, 21 Oct 2009 22:04:58 +0100

Posted By: Johanknow you're a big fan of the Navitron, Eco-nomical ET's because they are well priced. However, you can get higher effeciency FP's for less then either of those two from more then one supplier in the UK.

...where for eg...?

J

Flat panels -vs- Evacuated tube... ...the showdown...

tony — Wed, 21 Oct 2009 23:15:55 +0100

not possible

Flat panels -vs- Evacuated tube... ...the showdown...

crusoe — Mon, 26 Oct 2009 09:22:30 +0000

Johan. You still there? Comments on FPs v Navi ETs interesting. Were you going to come back with more info? Can't hold my breath much longer...

Crusoe

Flat panels -vs- Evacuated tube... ...the showdown...

Johan — Mon, 26 Oct 2009 09:37:55 +0000

Wasn't sure I was allowed to post links to suppliers here. It might sound like I'm promoting them! Anyway, here you go:

http://www.solexenergy.co.uk/ (they don't have the panels on their website, but I know they are shifting their old stock atm so there is true bargins to be had. Good location for you crusoe I think, no?)

http://www.earthwindfire.co.uk/ (I don't know their current pricing, but these are the ones I have and I paid a fair bit less then the ET's cost)

I have no connections to either of them, and I don't think there is anything wrong with ET's! You need to consider all parameters when you choose the panels for your system.

Flat panels -vs- Evacuated tube... ...the showdown...

crusoe — Mon, 26 Oct 2009 19:01:10 +0000

No, Cornwall is miles from anywhere :) Dorset, where's that?

As someone said earlier, it's horses for courses (am I still allowed to mention things equine...?)

Johan, I may not make the same choice of panel as you or anybody else - that's personal choice - but you are using yours to their full potential, which I applaud. I just wish UKSolarAuthorityPLC, whoever it is that decides the agenda to train Joe Plumber, would take note.

Still, leaves a big chunk of the market to those of us who buck that trend. I do find it a big educational ask - and time-consuming - telling an average eco-confused customer what their options are!

Crusoe

Flat panels -vs- Evacuated tube... ...the showdown...

simonm — Wed, 14 Apr 2010 13:40:33 +0100

If you are going for these tubes be careful to select the right ones. there are two types.

Tubes which are connected (bonded) as a single unit to the copper fluid outlet. This eventually cracks due to constant expansion and contraction, the vacuum is lost and the efficeincy of the tube plummets.

Better to consider the all glass tube that fits around the copper collector, there is effectively nothing to go wrong and this type of tube can be guaranteed for many many years. An example can be seen on the www.solaruk.com website (Amber mentioned this above) though I am sure many other suppliers also use it.

With regard to price, on my own website I have managed to work up a bit of a price comparison, this is now about a year out of date but I'm sure still relevant. It shows 4 of the main suppliers, all about Â£4,000 for typical installation.

http://www.solarkent.co.uk/solar-water-heating/comparison.asp

I'm sure the introduction of the Renewable Heat Incentive is going to change all the costs etc. Don't ask why and how, its just that free money always does.