Home  5  Books  5  Magazines  5  News  5  GreenPro  5  HelpDesk  5  Your Cart  5  Register  5  Green Living Forum
Not signed in (Sign In to the Green Building Forum)
Welcome to new Forum Visitors
 Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications:: Apply now.




Renewable Energy: Evacuated flat plate solar thermal collectors

Bottom of Page

1 to 30 of 52

  1. <
  2. 1
  3. 2
  4. >
  1.  
    I'm looking at a new build in Wiltshire (UK) and considering the use of solar thermal heating. Unfortunately the orientation of the house means that the best we can get is roughly south-east facing.

    I've read many threads about flat plate vs evacuated tube, but still have some questions, particularly considering the Genersys evacuated plate collectors.

    The arguments seem to boil down to:

    Evacuated tubes work better when it is cold
    Evacuated tubes are always angled to the sun due to their cylindrical nature
    Evacuated tubes are relatively expensive compared to flat plates
    *Personally* I find ET's ugly (they'll be on the front of the house)....

    Flat plates have a larger surface area actually exposed to the sun
    Flat plates suffer some efficiency loss due to the incident angle of the sun
    Flat plates don't work well when it is cold

    So, it seems that evacuated flat plates, i.e. those supplied by Genersys, seem to be a good compromise. They are attractive (to me) and should still work effectively in colder weather. I haven't yet looked to see how they compare price wise. OK, I will need to oversize the array a little to cope with the angle of SE incidence, but this is probably OK (cost permitting).

    Has anyone else looked into these or have any direct experience of these panels? Do they work as well as ET's in cold weather?

    If anyone knows, how do the prices compare (generally) to ET's?

    Thanks very much,
    Mark.
    • CommentAuthortony
    • CommentTimeFeb 2nd 2009
     
    ET always and South East is no problem you still get what you get from the sun free. go for it.
    • CommentAuthorMarkK
    • CommentTimeFeb 2nd 2009
     
    whatever you choose, your potential supplier should offer you an estimate of annual performance based on SAP.

    That way, you can compare apples with oranges.

    If they don't, then they're asking you to "trust me ...i'm green and trustworthy"

    either way - you need to look a the total energy harvested for the year, not about what's going to give you the most heat on a spring day or the height of summer etc
    • CommentAuthorMarkBennett
    • CommentTimeFeb 2nd 2009 edited
     
    Posted By: tonyET always and South East is no problem you still get what you get from the sun free. go for it.


    Why always ET?

    In theory, wouldn't evacuated flat plate be better?
    • CommentAuthorMarkBennett
    • CommentTimeFeb 2nd 2009 edited
     
    Posted By: MarkK
    either way - you need to look a the total energy harvested for the year, not about what's going to give you the most heat on a spring day or the height of summer etc


    Well, yes and no.

    I'm not sure that relying on the total annual harvest as a measurement of effectiveness is correct. Huge amounts of capture during the three months of summer isn't so useful - we only use so much hot water in one day. Good amounts of capture spread over a longer duration is much better for us, which is why I think evacuated technology of some sort is preferable.

    Given that evacuated is a must, the evacuated flat plate are aesthetically more pleasing (to me) and as far as I can see could probably prove to be as effective as evacuated tubes.

    The only drawback appears to be a need to re-evacuate the panels every 5 years, which I don't think is necessary with tubes (although I've read a few threads on here about tubes failing in relatively short periods of time).

    Otherwise, I agree about getting quotes showing performance and cost for different systems, but I'm not quite that advanced on the plans yet so was trying to get a head start.
    • CommentAuthortony
    • CommentTimeFeb 2nd 2009
     
    there aint no such thing as an evacuated flat plate is there??
    • CommentAuthorMarkK
    • CommentTimeFeb 3rd 2009
     
    Posted By: MarkBennett
    Posted By: MarkK
    either way - you need to look a the total energy harvested for the year, not about what's going to give you the most heat on a spring day or the height of summer etc


    Well, yes and no.

    I'm not sure that relying on the total annual harvest as a measurement of effectiveness is correct. Huge amounts of capture during the three months of summer isn't so useful - we only use so much hot water in one day. Good amounts of capture spread over a longer duration is much better for us, which is why I think evacuated technology of some sort is preferable.

    Given that evacuated is a must, the evacuated flat plate are aesthetically more pleasing (to me) and as far as I can see could probably prove to be as effective as evacuated tubes.

    The only drawback appears to be a need to re-evacuate the panels every 5 years, which I don't think is necessary with tubes (although I've read a few threads on here about tubes failing in relatively short periods of time).

    Otherwise, I agree about getting quotes showing performance and cost for different systems, but I'm not quite that advanced on the plans yet so was trying to get a head start.


    yep good point - that's why the solar fraction is important. As a rule of thumb, 60% of your annual DHW requirement covered by solar should mean that you will not be creating surplus energy in the good months.

    If you're set on well insulated flat plates, have a look at shuco's double glazed collectors; its heat loss coeeficient is 30% better than most other flat plate collectors and it's zero loss coefficient is marginally better than a thermomax tube.

    2.51m2 of aperture area per collector compared to roughly double the price for just over 3m2 for thermomax.
  8.  
    Posted By: tonythere aint no such thing as an evacuated flat plate is there??


    Only from one supplier so far (hope this doesn't count as advertising - it's not intended to be).
    http://www.genersys-solar.com/world-first-solar-panels.asp
    • CommentAuthorMiked2714
    • CommentTimeFeb 3rd 2009
     
    I think the issue with the Genersys plates is that they have a monopoly. I'm not sure if they allow a DIY option but they are unlikely to make it financially worthwhile.

    A couple of other comments:
    "Evacuated tubes are relatively expensive compared to flat plates"
    This is no longer correct.

    "(although I've read a few threads on here about tubes failing in relatively short periods of time)"
    This related to a particular issue with a particular manufacturer's flow though evacuated tubes. I'm not aware of it applying to any heat pipe ET's

    I think it all boils down to whether you want a supply and fit package (go for Genersys) or whether you are willing to save money (and increase area) by procuring the kit yourself and either DIY'ing or getting a plumber you trust to do the job. As its new build you should not have any additional scaffolding costs which is a major cost of retrofit package deals.
    • CommentAuthorTuna
    • CommentTimeFeb 3rd 2009
     
    I'm not so sure that the stated advantage of ET over FP is as great as claimed. The available energy during the winter months is so dramatically lower that I can't help but wonder if the efficiency of solar panels is irrelevant? Even if you can place your tubes to minimise self-shading due to low winter sun, the difference with very little solar input amounts to pennies. It might be more significant in regions where the external temperature stays lower for longer, but for most of the UK we live in relatively benign conditions.

    During the winter period, the vast majority of heat is going to need to come from another source, so why worry about minor heat loss if FPs have other characteristics that are of benefit?

    As for the Genersys plates - the seal is between a number of materials of different types, exposed to all weather conditions and having to cope with combinations of heating and cooling on a daily cycle. Whilst they provide for 're-evacuation', I would expect that once the seal goes (and it will), the panels would be unable to hold a vacuum for more than a couple of days. I could well be wrong, but the point of tubes is that the seal is as small as possible and has the minimal amount of different materials (or just glass in the case of 'thermos' style tubes). Even then, tubes do loose their vacuum so these panels will have to pull off a major feat.
    • CommentAuthorMiked2714
    • CommentTimeFeb 3rd 2009
     
    Tuna: Depends on how you define winter. If its December and January then I agree with you. But in early / late winter and in spring and autumn there is very useful solar energy that can provide all your DHW on a bright or sunny day. Whether in these conditions there is a practical and significant difference between FP and ET output I can't answer.
  12.  
    Posted By: TunaAs for the Genersys plates - the seal is between a number of materials of different types, exposed to all weather conditions and having to cope with combinations of heating and cooling on a daily cycle. Whilst they provide for 're-evacuation', I would expect that once the seal goes (and it will), the panels would be unable to hold a vacuum for more than a couple of days. I could well be wrong, but the point of tubes is that the seal is as small as possible and has the minimal amount of different materials (or just glass in the case of 'thermos' style tubes). Even then, tubes do loose their vacuum so these panels will have to pull off a major feat.


    Well, they offer a 20 year warranty, so either they're very confident of the longevity of the seals, or they don't expect to be around long enough to have to pay out many claims. They seem to be a pretty big company, so I hope it's the former.
  13.  
    One other advantage of flat plate collectors is that many can form part of the fabric of the roof and save the cost of tiles etc. Not a big deal in a retro-fit, but for a new build it helps reduce the investment.
    • CommentAuthorralphd
    • CommentTimeFeb 3rd 2009
     
    Evacuated tubes will frost up more than flat plate. The glass surface on a flat plate will warm up quicker when the sun comes out and melt the frost.

    I'm also concerned about the robustness of evacuated glass tubes; I've hauled a 3m^2 flat plate collector up onto my roof and there is a lot of flexing and bumping involved.

    In many cases I think unglazed flat plate is the best; here in Canada it's half the cost of glazed. You just can't use it for most of the winter (when there is not much sun anyway).
    http://www.thermo-dynamics.com/products.html

    In my case I still went with glazed because I got a government subsidy. The unglazed collectors aren't CSA rated but the G32 panels are.
    http://ralphdoncaster.googlepages.com/solar
    • CommentAuthorMiked2714
    • CommentTimeFeb 4th 2009
     
    Posted By: ralphdEvacuated tubes will frost up more than flat plate. The glass surface on a flat plate will warm up quicker when the sun comes out and melt the frost.

    That's just symptomatic of the heat loss you get from flat plates. In the UK frost on ET's doesn't seem to affect their output anyway. Perhaps with heavier frosts in Canada its more of an issue.
  16.  
    Why are you considering the installation of solar heating?

    A typical domestic installation (4 m2) in the UK has a payback of 50 years if the displaced fuel is gas/oil, which far outweighs the life of the product.
  17.  
    That should say in excess of 50 years
    • CommentAuthortony
    • CommentTimeFeb 4th 2009
     
    What about if you look at it as an investment? Then you get a decent return on capital employed and reduce reliance on fossil fuels.

    even borrowing the money makes far better sense now than at any time during the past 50 years.



    What is the payback time on a house? or a computer?
  19.  
    The embodied energy far exceeds the energy produced by solar thermal in the lifetime of the product which is less than 20 years. The glycol needs changing at least every 5 years. I dont know the embodied energy in glycol, but I'm attempting to find out.

    Payback is not only money but also the amount of CO2 genuinely saved through the life cycle. Which ever one you choose, money or total CO2, its an impossible payback.
    • CommentAuthorralphd
    • CommentTimeFeb 5th 2009
     
    Posted By: ecoenergyniWhy are you considering the installation of solar heating?

    A typical domestic installation (4 m2) in the UK has a payback of 50 years if the displaced fuel is gas/oil, which far outweighs the life of the product.


    My 3m^2 installation has a total cost of under CAD1200. Payback counting a 5% cost of money is under 10yrs.
    Payback counting gov't subsidy of is 1-2yrs.

    http://ralphdoncaster.googlepages.com/solar

    -Ralph
    • CommentAuthorjon
    • CommentTimeFeb 5th 2009
     
    "The embodied energy far exceeds the energy produced by solar thermal in the lifetime of the product which is less than 20 years."

    How do you know this ecoenergyni?
  22.  
    Took the time to work it all out.

    Took a typical collector apart, weighed the components, calculated embodied energy.

    Added the copper for pipes, wire, valves etc....

    Pay back moneywise should be the true cost not including subsidies. Otherwise, if you were given a system, the payback would be zero years.

    The only advantage at the moment I can realy see for solar thermal is to give brownie points for SAP and the like.

    As for financial payback, its impossible. 4m2 installed in UK price typical £4000. Produces approx 1200 kWh/annum. Using gas as the displaced fuel at 6p/ kWh = £72/annum saved ( assuming you can utilise all the hot water in the summer ). 4000/72 = 55 years.
    • CommentAuthorralphd
    • CommentTimeFeb 5th 2009
     
    Posted By: ecoenergyniT
    As for financial payback, its impossible. 4m2 installed in UK price typical £4000.


    So I've done the impossible by installing a 3m^2 system for CAD1200.
    Hmmm... my next impossible task will be world peace. :bigsmile:
  24.  
    What the insolation value at your location?
    • CommentAuthorjon
    • CommentTimeFeb 5th 2009
     
    "Took the time to work it all out.
    Took a typical collector apart, weighed the components, calculated embodied energy."

    Where did you get your embodied energy figures from?

    I too have done this calculation and come to a remarkably different conclusion.
  26.  
    BRE
    • CommentAuthorralphd
    • CommentTimeFeb 5th 2009
     
    Posted By: ecoenergyniWhat the insolation value at your location?

    I'm near Halifax, NS.
    https://glfc.cfsnet.nfis.org/mapserver/pv/index_e.php

    -Ralph
  28.  
    Thats around 46 north? Should imagine insolation about same as UK at approx 950 kW/m2/annum.
    • CommentAuthorjon
    • CommentTimeFeb 5th 2009
     
    BRE?

    Which BRE documents show embodied energy? The best research I know of is from Bath. Which documernt from BRE did you use?
    • CommentAuthorralphd
    • CommentTimeFeb 5th 2009
     
    Posted By: ecoenergyniThats around 46 north? Should imagine insolation about same as UK at approx 950 kW/m2/annum.

    Close; 45 degrees.
    Follow the link I posted; it's insolation maps for Canada.

    -Ralph

1 to 30 of 52

  1. <
  2. 1
  3. 2
  4. >
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press