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Renewable Energy: Flat panels -vs- Evacuated tube... ...the showdown...

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  1.  
    Simply put which is best for UK and why..?
    ...or perhaps in what circumstances is which better...

    - Cost
    - Appearance
    - Planet saving ability
    - Reliability
    - etc etc....

    ...pin your colours to the mast.. no fence sitting allowed....

    J :bigsmile:

    Only signed in forum members can vote! (admin)
  2.  
    Ignore Chinese gear for the moment and take a typical small FP (c£3k installed) against a small evac tube set-up (c£4k installed), other things (such as controllers and cyl) being equal. On a number of sunny but very cold winter days the lack of convection in a vacuum WILL mean the ETs perform better. In summer, too, they can perform better, but it becomes a bit academic then - is my water 60 deg or 75? Hmm, better have a HOT bath then (pause to stick skin back on). It comes down to whether you think the extra (undoubted) winter performance is worth +£1000. I don't. On the other hand, when a local discount scheme was offering ETs at only +£200 compared to FP I was advising everyone to snatch their hand off.

    That's my 2.5d-worth.

    Nick
    • CommentAuthortony
    • CommentTimeMar 6th 2008
     
    Tubes -- as they get you more in the colder months.
  4.  
    All things being equal, evacuated tubes for cool cloudy climates, a no brainer!
    • CommentAuthorskywalker
    • CommentTimeMar 7th 2008
     
    Evacuated tubes both for performance and maintenance.
    • CommentAuthorskywalker
    • CommentTimeMar 7th 2008
     
    Not sure you can ignore 'Chinese' tubes Nick, I think they make most of the 'European' ones now too!

    Plus at around £1000 for a 2X 20 tube array (£2000 with simple twin coil cylinder set up & all plumbing) fitted DIY; now available from a few suppliers. An absolute no brainer.

    S.
    • CommentAuthorMiked2714
    • CommentTimeMar 7th 2008
     
    Definitely evacuated tubes, at £570 for a rack of 30 tubes the total cost is all in the installation not the panel itself. I can see that flat panels may be needed for aesthetics in certain situations but that's all.
    Mike
    • CommentAuthorDantenz
    • CommentTimeMar 7th 2008
     
    Tubes if you want slightly better performance and don't mind the odd tube exploding or having to replace a failed tube every few years.

    Flat plate if you want a robust system that will never let you down and what does it matter if the performance is a bit lower - the energy is free.
    • CommentAuthorjon
    • CommentTimeMar 7th 2008
     
    How much area does an array of 2 by 20 cover?
    • CommentAuthorEd Davies
    • CommentTimeMar 7th 2008
     
    • CommentAuthorjon
    • CommentTimeMar 8th 2008 edited
     
    Thanks

    So, assuming the rack of 30 is £570, an array of 10 seems to be about 1.33 sqm making 30 about 4 sq m

    So the cost, pre4-installation, is about £150/sqm for the basic kit?

    A good price

    Does anyone know the real winter gathering rate for solar evacs in kWh per day?
    • CommentAuthorskywalker
    • CommentTimeMar 8th 2008
     
  13.  
    Evacuated tubes technology has always been the best in efficiency, and this was proven in a DTI side by side testing report in 2001.

    The technology has improved further with 'direct' evacuated solar tubes (no antifreeze).

    This gives the advantage of better performance and peace of mind but with no heat exchange required, this can free up your twin coil (when applicable) for other applications such as under floor heating/bio mass stoves etc.

    1. If you have a traditional ‘gravity feed’ system, with a southerly facing roof space, then you home is ideal.
    2. If you have a ‘vented’ thermal store with twin/solar coil, then your home is suitable too.
    3. If you have a Combi Boiler, then you will need to replace this at the end of it’s life for a condensing boiler with ‘vented’ tank.
    4. If you have a ‘high pressure’ system with gauges, then you will need to replace this with a ‘vented’ tank.

    You can learn more about this new solar technology at: http://www.heatmyhome.co.uk/water-heating-solar-panels.htm
    • CommentAuthortony
    • CommentTimeMar 8th 2008
     
    3 -- Not necessarily -- it is possible to have solar and a combi
    4 -- Not true either Solar can work unvented HW and unvented evac tubes
    • CommentAuthorjon
    • CommentTimeMar 8th 2008 edited
     
    Hi Skywalker

    I'm trying to get a sense of real output: For example as Keith is doing with PV: daily quantities of water say at 60 degrees C (from say ambient at 10): What quantity is produced: for example, one person mentions a bathload (which depends on the size of the bath)

    On the other hand, one of my cousins in Ireland reckons he gets 200 litres per sunny winter day of 65 degree water for his 4 metre evac array with outside temps of 10 degrees C: So, working that out, he's getting about 0.4 kWh/sqm/daylight hour as a 65C product: This is pretty good.. suspiciously good... is he exaggerating and merging a week of light use with one day of recording? He paid 3500 Euros for his system.
  16.  
    Gosh, me and me flat plates are starting to feel lonely! One thing I cannot argue about, which I didn't mention before, is ease of installation of ET cf FP. Absolute joy! The heaviest bit is the manifold! Compare that with one of the bigger, glazed, FP's.
  17.  
    Come on people don't let Nick be lonely... some one else out there must love FPs too...?

    What about planning...? Has anyone actually come across a planning situation where FPs were stipulated rather than ETs...? (Evacuated Tubes not Extra Terrestrials that is, the latter being harder to fix to the roof),

    Can't see it holding up well at appeal myself, but there I go applying logic to planning....

    J
    • CommentAuthorEd Davies
    • CommentTimeMar 9th 2008
     
    "Has anyone actually come across a planning situation where FPs were stipulated rather than ETs...? "

    Yes, friend of mine doing an extension replacement (approx as large as the core house) half way up the Chiltern ridge overlooking the Oxford plain (I think it's an AONB - certainly looks nice) told me this afternoon that he was planning to use FPs. When I asked why not ETs he said for planning. I don't think he said specifically that ETs wouldn't be allowed but that with FPs looking more discrete he was fairly strongly advised that the whole thing had a better chance of going through. It has, they start building at the end of March, I think.
    • CommentAuthorJohan
    • CommentTimeMar 9th 2008
     
    Posted By: jonThanks

    So, assuming the rack of 30 is £570, an array of 10 seems to be about 1.33 sqm making 30 about 4 sq m

    So the cost, pre4-installation, is about £150/sqm for the basic kit?

    A good price

    You can get good quality European made FP for less then that per m2.

    I had a price for 6.6m2 of Schott ET panels at £5900, for that money I can buy 40m2 of FP. Which one will generate most heat in the winter?? Let's have a competion for best guess! :wink:

    Personally, I think it's too early to say ET are better then FP. ET's are not a proven design yet (commercially).

    FP's has been around for more then 30 years (comercially), and is a proven design. Many systems installed 25-30 years ago are still running as well as they did the day they were installed.

    How long has ET's been available? 10 year? I don't think that's long enough to say they are better then FP's. If in another 10 years the SAME tubes (no replacements!) are still running as good as they are today then you can start comparing them.
    • CommentAuthorjon
    • CommentTimeMar 10th 2008
     
    I can see advantages to both Johan

    But I haven' been able to get hold of any real performance data (particularly for winter: everyone wants to cite summer)) to date so comparison seems meaningless

    :sad:
    • CommentAuthorJohan
    • CommentTimeMar 10th 2008
     
    Posted By: jonI can see advantages to both Johan

    But I haven' been able to get hold of any real performance data (particularly for winter: everyone wants to cite summer)) to date so comparison seems meaningless

    :sad:" start="fileopen" height="15" alt=":sad:" ismap="false" hspace="0" loop="1" src="http://www.greenbuildingforum.co.uk/newforum/extensions/Vanillacons/smilies/standard/sad.gif" width="15" vspace="0" >
    Jon, I was just trying to give Nick some support for the FP's! :smile:

    The ET's are a great idea, but I think they need a few more years under the belt before saying they are superior to the FP's.

    There are reports comparing the two, but as I posted in the "Has anyone heard of the evacuated tubes disaster?" thread I haven't managed to find one in English...

    Here it is again: "I've attached a link to a report comparing FP to ET. Unfurtunately it's in Swedish (there is an Abstract in English though), but the most interesting part is the figures from page 42 to 49. http://www.sp.se/sv/units/energy/Documents/ETk/SP%20rapp%202002-20.pdf"

    Let me know if you want some bit translated and I'll do it (not the whole report though!).
  22.  
    What happens when the vacuum goes in an ET? Does it mist like a faulty DG unit, thus giving visual warning of failure? Do we know how long the vacuum lasts? If visual warning is not given (and received by the householder) then any or all can 'go'. Of course they won't stop working, but what you'd have is an uninsualed, small-absorber-area flat plate. Would a 30-year-old FP perform better than a vacuum-less vac tube set-up?
  23.  
    Heatmyhome said: ''The technology has improved further with 'direct' evacuated solar tubes (no antifreeze).'' What about limescale in hard water areas?
    • CommentAuthormark_s
    • CommentTimeMar 11th 2008
     
    I think it is visible - misting. There was a discussion about this on the navitron forum a while ago.
    • CommentAuthortony
    • CommentTimeMar 11th 2008
     
    The best evac tubes have tell tale metal oxide coatings at their bottoms which change colour when/if the vacuum goes.
    • CommentAuthorDantenz
    • CommentTimeMar 11th 2008
     
    Yes ET's visibly change colour when failed. I personally think you can get too wrapped here in what is marginal differences in performance between ET's and FP's. I re-itterate, the energy is free at the end of the day; what's all the fuss about. The extra output ET'S give during lower solar gain on cloudy and colder days amounts to very little averaged over the year.
  27.  
    Posted By: DantenzYes ET's visibly change colour when failed. I personally think you can get too wrapped here in what is marginal differences in performance between ET's and FP's. I re-itterate, the energy is free at the end of the day; what's all the fuss about. The extra output ET'S give during lower solar gain on cloudy and colder days amounts to very little averaged over the year.


    Please show how? Have you a link to some research?
  28.  
    I think the DTI research showed something like that, though I am now officially old and have no memory......
    • CommentAuthorEd Davies
    • CommentTimeMar 12th 2008
     
    "The extra output ET'S give during lower solar gain on cloudy and colder days amounts to very little averaged over the year. "

    Maximising the average over the year is fine for on-grid systems where you're just offsetting other energy sources. If, however, you want to use solar as a significant part of your energy input year-round then the most important thing is the output in the worst months. It would probably be worth accepting a reduced total for the year to get better performance in winter.
    • CommentAuthorjon
    • CommentTimeMar 12th 2008
     
    I agree with Ed. If I were comparing I would use a graduated factor for winter to summer to offset the advantages of heat gained during the Winter against Summer. But we appear to have no reliable data as yet for the relative seasonal performance of either type of system?

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