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Renewable Energy: Roof mounted PV winds load calcs for Outer Hebrides

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1 to 17 of 17

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    Hi ,
    Anyone looked into design details for roof mounted PV in the Outer Hebrides
    Wind speed from national chart are >28-29m/s

    Roofing in the area generally involves fully sarked rafters with OSB and all tiles nailed

    I was looking into fitting a GSE inroof system ,just wonder about its suitability , I'll contact manufacturer/supplier
    but was just wonder if anyone had any site experience in that area.
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      CommentAuthorSteamyTea
    • CommentTimeJan 4th 2018
     
    I would think from a structural viewpoint that a roof integrated system is treated the same as an on roof system.
    The loads are probably less i.e. no tiles, so less weight and the wind loadings similar.

    If an MCS installed system, then it needs an SE to sign if off anyway (I think).
    • CommentAuthorjamesingram
    • CommentTimeJan 4th 2018 edited
     
    uplift is my main concern, its in zone 5 which isnt on most the pv framing supplier loading charts.
    Ive spoken to supplier and theyve suggest its ok with additonal fixings
  4.  
    its going on a SIPs roof which further concerns me as i wont have a nice big rafter to screw into
  5.  
    Ooh err! Well that'll be some whacking great big cold-bridging studs all the way trough the SIP to a steel bearer on the inside, then...?
  6.  
    nick , yes was worrying about that , or perhaps glued and screwed batons to strengthen the structure. Certainly worth get a structural engineer to look into it
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      CommentAuthorSteamyTea
    • CommentTimeJan 4th 2018
     
    I think we had someone on here that sold SIP roof panels.
    When I question them about fitting PV, he rather dismissed the issue away.
    I think local strengthening is probably needed. There is snow load to worry about.
    • CommentAuthorTimSmall
    • CommentTimeJan 4th 2018
     
    I did the wind calcs for my PV, which is near the South coast. The site has reasonably high wind loading being near the top of a hill which faces a SW-facing valley, and about 2 miles from the coast.

    With the GSE panels, you can use extra brackets if necessary (e.g. 3 or more per side instead of two). You may also want to go for bigger fixings than theirs (I did, although the GSE ones are probably OK, I think the UKNA for screw fixings is conservative, and GSE's are based on pull-out tests), and/or something to increase the depth which the thread is embedded in the timber.

    Being a lean-to extension, the worst-case snow loadings were pretty fearsome (a snow drift against the house, a couple of metres deep), and I switched my battens for decking to support the max snow load in some places.

    The other half of my panels are more conventional frame mount ones on a flat roof, and some newly (at that time - I think I purchased a copy for about £25) published research on uplift factors for framed PV modules was very useful and produced a more practical design vs. applying the bare Eurocodes.

    You can get software to produce a directional site wind analysis (doing so manually is pretty tedious) based on your map location, which I'd recommend.
  9.  
    Sorry to be boring on this as it could be an interesting debate - but go with what the manufacturer/supplier says and get some insurance.
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    Tim , Peter thanks for thoughts , yes I'll be doing what im told by the experts :-)
    • CommentAuthorvalasay
    • CommentTimeJan 8th 2018
     
    For what its worth I live on the west side of Lewis and have wondered about solar panels since I cant afford a wind turbine otherwise that would be the clear choice given the wind speeds here.
    I'm very nervous about the wind load since its only a few years since the wind gauge broke after recording winds in excess of 136 mph! The important thing is local knowledge because there are houses only a mile and a half away that are completely sheltered and would have no difficulty with wind loading and can grow trees and shrubs...
    The option I would consider would be ground mounting but do think too about the risk of them acting like sails without the sides and back being protected in some way.
    The other little thought is about maintenance. Its not always easy to get willing tradesmen to do the trickier jobs and ground mounting might make maintenance easier too.
    I have no knowledge of anything practical but these are my thoughts from experience of being exposed to the wind.
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      CommentAuthordjh
    • CommentTimeJan 8th 2018
     
    Posted By: valasayThe option I would consider would be ground mounting but do think too about the risk of them acting like sails without the sides and back being protected in some way.

    I wonder if there's any market for moulded backs to stick on the underside of panels, giving them an aerofoil shape so they develop downwards lift instead of trying to pull away?
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      CommentAuthorSteamyTea
    • CommentTimeJan 9th 2018 edited
     
    Been told, but never looked, that the modules on the Cornwall County Council building have an aerofoil to stop them lifting.
    I know who fitted them.
    • CommentAuthorTimSmall
    • CommentTimeJan 9th 2018
     
    valasay - Out of interest, did you look at the smaller DC wind turbines like the 5kW Britwind? I was wondering what they'd come in at vs. a similar sized (in terms of annual output) PV system? You could of course make the argument that the wind energy is more "useful" since more of it's output comes when your (and the rest of the country's) demand is higher...
    • CommentAuthorjamesingram
    • CommentTimeJan 13th 2018 edited
     
    Valasay , I discussed ground mounted with the client, which to me seemed at a lower risk of wind damage.
    Its a new build on north west coast (SIP structure) so needs some mircogeneration as part of planning , I'm not sure but presumed planning might want it 'on/in' the house to qualify perhaps not, and additionally planning would be required for a ground mounted system as well.
    the roof finish is metal sheets, which the client says is common up there so really a PV panel will have no more up lift than a large sheet , that doesnt mean both wont be rippped of when the wind gets going.
    A small Wind genny would certainly be a better suited generator for the location.
  16.  
    £30k ish is the only price I can find for 5kW Britwind (all in) googling about , but these figures dont seem that up to date
    • CommentAuthorRex
    • CommentTimeJan 20th 2018
     
    I'm sure there are issues with using local roof tile styles, but have you considered NuLok tiles (http://www.nulokroofing.com/uk/). They look like slate and are firmly held down on both the lower and upper edge so thee is no chance of the tile lifting.

    Furthermore, if you want to replace one tile it is a very simple operation. They also supply PV tiles that fit onto the roof with the same system. All flush with no edges to allow the wind to get under.

    And no , I don't work for them but have them on my roof and am a very happy bunny!

    Rex

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