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Renewable Energy: Solar Panel Brise Soleil

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  1.  
    Good morning everyone.

    I'm looking for thoughts on mounting solar panels directly on a house wall, or building a supporting "porch".We don't have any *really* suitable roofs for PV in our new house, so I'm wondering about a solar brise soleil made of PV solar panels along across our garage and front door - about 8-9m run.

    The only one I have seen was in the episode of Grand Designs called Stealth House, here:
    http://tinyurl.com/brisesoleil

    This is our southern facade. It is a reasonably well specified recent (2009) conversion of a 1940s bungalow, reduced to 3 outside walls and rebuilt inside. Unfortunately that row of lime trees along our eastern boundary are TPO'd.
    http://tinyurl.com/ferdinandfacade

    I quite like the idea of having it 12 feet off the ground rather than 25, for installation, maintenance and for the convenient jet washing of pigeon poo. The electric meters are in the garage, so cabling etc will be simple.

    Does anyone have any experience of doing anything similar, or thoughts on the idea?

    Thanks in advance.

    Ferdinand
    • CommentAuthorSprocket
    • CommentTimeApr 22nd 2013
     
    Hmmm.... are those trees likely to be a problem?
    •  
      CommentAuthorjoe90
    • CommentTimeApr 22nd 2013
     
    Only before midday!!!!! (if its true south facing)
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 22nd 2013
     
    Micro Inverters may help, costly mind.
    You will almost certainly need to get some structural calculations done, though there are MCS companies that would not care.

    On a more flippant note, would you not save more money and energy by changing the cars!
  5.  
    That 4x4 is the previous occupant. I have a slightly derogatory term for unneccessary 4x4s that rhymes with plankatank, and would get me banned.

    @joe90 - it is very close to true south. They are mainly limes, so it is a little less of a problem in autumn-spring, but .. my .. the leaves in summer.

    So, yes - needs careful thought, but it would do quite a bit for us, and (being pragmatic) solar panels are not *that* much more than a simple rain shelter. Just to stick something as simple as polycarb sheets up there would cost a fair bit; more for something that looked acceptable.

    Ferdinand
    • CommentAuthortony
    • CommentTimeApr 22nd 2013
     
    Probably need planning
    • CommentAuthorpmusgrove
    • CommentTimeApr 22nd 2013
     
    PV as Brise Soleil work well but getting a regular MCS fitting company to put them on is difficult. We have just put up a line producing 10kWp above windows on the 2nd floor of a building in Bristol and the suppliers thought up every reason why it couldn't be done due to wind loading. It will cost as there do not seem to be fittings that can be bought off the shelf to use PV as brise soleil.
    • CommentAuthorRobinB
    • CommentTimeApr 22nd 2013 edited
     
    Posted By: ferdinand2000They are mainly limes,

    Aren't lime trees the ones that make everything below them sticky in spring? And whilst I'm being a bit negative most solar panels and associated wiring and fixings look a bit tatty underneath, would need care to look "proper".
  9.  
    @tony Yes - I'm expecting to need planning.

    @pmusgrave.

    Ease of construction/cleaning and less wind are 2 reasons why I like to be at Gnd/1st level not 2nd - no scaffold tower etc. So it looks as though it needs careful calcs and/or a support frame - which might just be as simple as two steel beams and cornet posts. Such a structure might hide the gubbins.

    @RobinB. Yes - limes drop honeydew on cars, though I'm not sure whether these are small-leaved limes (which I think are much better for town trees) or large-leaved or common limes (which I think are bad). I won't know until later how bad this is. I can clean easily using a jetwash though.

    What that all says is to take a little time and talk to a few local installers, as ever.

    Ferdinand
  10.  
    Hmmm. There' a piccie of a construction detail on the Underhill House project blog:

    http://www.aipassivhaus.com/blg-august10_7_3885157519.jpg

    They used individual frames bolted to the wall and a pair of beams, which looks custom. That framing is similar to the hinge-side frame inside a stable door or heavy garden gate.

    Hmm. I'm thinking about the steel framework from walkway canopy systems, from suppliers such as Halfem, either with a post or two, or cantilevered.

    It looks a pricey thing to do even economically, though whether that is more than installation and maintenance on a roof is another question.

    Ferdinand
    • CommentAuthorpmusgrove
    • CommentTimeApr 23rd 2013
     
    The post above link shows the frame. Alloy is best otherwise unless you are very careful you will get galvanic corrosion. Why they have left big spaces between the panels escapes me.
    • CommentAuthorseascape
    • CommentTimeApr 23rd 2013
     
    To let some sunlight through?
    •  
      CommentAuthorjoe90
    • CommentTimeApr 23rd 2013
     
    I really like this idea and it could look quite good if done correctly and serve dual purposes. I think the wind loading would be greater than the weight of the panels (no idea how heavy PV panels are??) Steel, ally or timber according to taste and any structural engineer could design for you. I confess I dont like the look of a lot of panels on a roof but this could be a good alternative, it may even catch on.
  14.  
    > Why they have left big spaces between the panels escapes me.

    If you count there are 16.

    So it's probably to keep within the 40p or whatever it was top rate FIT tariff, assuming there was a breakpoint at 4kw in 2010-11.

    I think the aim here was to prevent shadow overheating the room through south facing windows, so the rainproofing was less important.

    >(no idea how heavy PV panels are??)

    I believe it is around 15-20kg for a 1mx1.6m in general, but I've never picked one up, so I'm open to correction.

    My alternative location (or for the other 8 panels) would be on the roof of a putative new shed/workshop along the northern boundary behind the house, but that is 15m from the house and would need more electrical gubbins plus holes in the ground. Also you can see the size of the gable from the initial photos - it is *high*.

    I'd expect the most cost-effective support to be made by a local joiner or off the shelf canopy system, but I can't see it costing much less than £1000-£1500, and perhaps more. I think I would need to build what amounts to a veranda and use the panels as the roof.

    Ferdinand
    • CommentAuthorSeret
    • CommentTimeApr 24th 2013
     
    Posted By: joe90any structural engineer could design for you.


    Definitely, any undergrad engineer could knock the sums off on the back of a fag packet. Keep it simple and your local light engineering shop could fabricate for you in a jiffy. As folks have said, the only problem might be convincing your MCS installer that it's kosher. Hardly rocket science though. I'd work backwards and start by asking installers if they've done it before and what would be enough to satisfy them.
    • CommentAuthorpmusgrove
    • CommentTimeApr 24th 2013
     
    The calcs for the mass loading (don't forget snow) are easy but the wind loading is a little more difficult and it is the wind that is the critical factor. If the BCO/ MCS is going to be a stickler you need to consider this carefully as wind does funny things around buildings! Just over-engineer it and check it once a week after it is up for any signs of stress and you should be OK.
    •  
      CommentAuthordjh
    • CommentTimeApr 24th 2013
     
    Posted By: pmusgroveThe calcs for the mass loading (don't forget snow) are easy but the wind loading is a little more difficult and it is the wind that is the critical factor. If the BCO/ MCS is going to be a stickler you need to consider this carefully as wind does funny things around buildings!

    Assume that the wind is going to blow at the panel as though it was a wing. Work out the maximum lift developed by a flat plate airfoil at the optimum angle of attack. I suppose the local airflow might be significantly greater than the measured windspeed as well, if you're unlucky.

    I'd hope structural engineers have handy tables to look up the results given standard assumptions.
    • CommentAuthorSeret
    • CommentTimeApr 24th 2013
     
    I'd be inclined to go the other way and design it assuming the maximum wind was going to act perpendicular to the panel (ie: max drag). That'd probably never happen in real life, but that's sort of the point of overengineering.

    In a simple case like this I don't think you'd need to worry about fancy stuff like resonance, it's small enough you could just model it as rigid. Just imagine the wind will catch it from the worst possible angle, chuck in your fudge factors for urban environment, gusts, etc and you're laughing.
    •  
      CommentAuthordjh
    • CommentTimeApr 24th 2013
     
    Posted By: SeretI'd be inclined to go the other way and design it assuming the maximum wind was going to act perpendicular to the panel (ie: max drag). That'd probably never happen in real life, but that's sort of the point of overengineering.

    No, that's the point. Lift forces can be significantly greater than drag.
    • CommentAuthorSeret
    • CommentTimeApr 24th 2013 edited
     
    Really? For a flat panel not mounted on a roof? Didn't know that.
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 24th 2013
     
    Countered by the 20 kg weight though.
    • CommentAuthorSeret
    • CommentTimeApr 24th 2013
     
    Posted By: SteamyTeaCountered by the 20 kg weight though.


    Sure, but you'd still need to account for all the magnitude and direction of all the forces, even if they cancel out.
    • CommentAuthorEd Davies
    • CommentTimeApr 24th 2013
     
    Posted By: SteamyTeaCountered by the 20 kg weight though.
    Lift isn't necessarily upwards, just perpendicular to the relative airflow.
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 24th 2013
     
    True.
    • CommentAuthorpmusgrove
    • CommentTimeApr 25th 2013
     
    My calcs showed that lift certainly is the worst case especially when the panels are close to the top of a ridge roof as the panels act like a foresail on a yacht. Consider how one of those can drag a heavy boat through the water (or try and hold the sheet without a winch) and it becomes apparent how strong lift can be!
    • CommentAuthorSeret
    • CommentTimeApr 25th 2013
     
    Posted By: pmusgroveMy calcs showed that lift certainly is the worst case especially when the panels are close to the top of a ridge roof


    What formula are you using? Is it even valid to model a panel on a brise soleil the same as one fixed to a roof?
    • CommentAuthorpmusgrove
    • CommentTimeApr 25th 2013
     
    Went back to first principles from structures and aerodynamics days at Uni and lifted mean wind speeds from Building Regs. Will look for the notes and post them if found but have no PI insurance! And no the effect of a wall behind a brise soleil is not the same as a ridge on a roof. The Schuco rules state that the top of the panels should be 0.5m (I think) from the ridge so that site is worth a visit too.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 25th 2013
     
    Posted By: pmusgroveConsider how one of those can drag a heavy boat through the water (or try and hold the sheet without a winch) and it becomes apparent how strong lift can be!
    And that's also the order of magnitude of wind (let alone internal buoyancy even when there's no wind) that acts on a building to create airchange, even thro tiny hairlines and pinholes. People don't generally get it, what forces airtighting efforts are up against.
    •  
      CommentAuthordjh
    • CommentTimeApr 25th 2013
     
    Posted By: pmusgrovemean wind speeds

    For a real design you would need peak speeds, of course, (sailing rule of thumb is add 50% to mean speed) and add something to allow for eddies around the building. I think there's often accelerated flow over the top of a roof, for example.
  30.  
    Thanks all for this.

    If I proceed ... resurgam.

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