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Housing - New Build: Solar panel location

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  1.  
    • CommentAuthorRex
    • CommentTimeMay 3rd 2009
     
    Hi there,

    We have the roof on the house now and am considering solar panels of DHW.

    Although probably undersized, I am considering two panels, one on each pitch to receive morning and afternoon sun. The problem is the roof pitches are more-or-less, south-east and north-west, with the se receiving the longest period of sun.

    Panels on the nw aspect would be able to feed the thermal store with a 4 or 5m vertical pipe drop, but the se aspect will need around 20m of pipe run. So I imagine heat loss from the se panel could be a factor.

    What do forum members recommend?

    Many thanks,

    Rex
  2.  
    One panel, appr 4m2 (depending on no's in hsehold) on SE side. I would forget NE.

    Insulate ridiculously well on the 20m run.
    •  
      CommentAuthornigel
    • CommentTimeMay 3rd 2009
     
    Nick is probably right but it does depend on the pitch of the roof.
    If pitch is steep then you might want to consider two panels or increasing the panel area.
  4.  
    I'd forget the side facing NW as well. ;)

    Maybe double the size of the SE panel instead.

    I wouldn't worry too much about the pipe run. Our one is really long too. The 22mm copper pipes are within that grey foam tube stuff you see in the DIY sheds and then the bundle of pipes is wrapped in glass fibre within a wooden box about eight inches square. It goes overhead from an outbuilding to the house.
    • CommentAuthortony
    • CommentTimeMay 3rd 2009
     
    I agree SE only and oversize.
    •  
      CommentAuthornigel
    • CommentTimeMay 3rd 2009 edited
     
    Posted By: biffvernon The 22mm copper pipes are within that grey foam tube stuff you see in the DIY sheds and then the bundle of pipes is wrapped in glass fibre within a wooden box about eight inches square. It goes overhead from an outbuilding to the house.


    I would avoid the grey insulation as it will melt when the solar panel is in stagnation and can get to 200c.
    Likewise soldered joints will melt.
    You need a high temperature epdm insulation as used on the preinsulated pipes that you can get.
  7.  
    Er, well, I rather suspect that my solar panel will not reach the temperatures at which solder melts.

    If it did the water would leak out so I guess that's failsafe!
    • CommentAuthorRex
    • CommentTimeMay 3rd 2009
     
    Thanks for the advice. From sunrise to about 14:30 is when the sun is on the SE roof; obviously at 14:30, it is not directly on it. Is there a chance of stagnation with two panels on this side?

    Also, I would use the recommended insulation, but the pipework will be within the rafters. We will have a warm roof with Warmcell insulation. Is this likely to cause any problems? Certainly should not be regarding insulation!

    Rex
    • CommentAuthortony
    • CommentTimeMay 3rd 2009
     
    If you can use evac tubes all the better and dont use 22 pipe 10 or 15 at the most.

    Biff, pressurised evac tube systems regularly get to 200C and are always fitted using compression fittings or brazed as solder does melt. :smile:

    Mine boiled in March several times
  10.  
    Boiling point tends to be a tad short of 200C in unpressurised systems. The trouble with evacuated tubes is they cost real folding money. I made my flat plate solar collector out of scrap alluminium sheeting from an old caravan. What's wrong with 22mm pipe, other than price?
    • CommentAuthortony
    • CommentTimeMay 3rd 2009
     
    too much water in it -- unless it is gravity system pipe losses are least the smaller the pipe
    • CommentAuthorJeff B
    • CommentTimeMay 3rd 2009
     
    We have 4 x 2 sq metres of FP collectors on a south-east facing roof. Today we had 9 hours of solar heating and 8 hours yesterday. At noon yesterday the collector was at 118C and the solar water temperature was 78C. The length of pipe is not an important factor in my experience. We have at least 20 metres, admittedly all indoors although all bar about 8 metres are in loft space. We also used 15 mm to reduce the volume of fluid. The insulation is mostly the black Armaflex variety. We typically get only a 1 degree drop in temperature over the 20 metres. We have a flow-back system so stagnation is not an issue.
    • CommentAuthorRex
    • CommentTimeMay 8th 2009
     
    Jeff,

    Thanks for your comments.

    Sound like that may be the way for me to go. I will look into my budget but was thinking of two panels on the SE side and may be one on the NW to benefit from the afternoon sun.

    Rex
    • CommentAuthorjaey
    • CommentTimeMay 14th 2009
     
    May I chip in on solar panel location? Our 106 agreement ( National Park ) stipulates solar panels to be erected in frames on the ground in a south facing field adjoining the new build. Actually in the same field where the GSHP collector pipes are buried. Having made a mess of that installation we would like to get this one right. Can anyone recommend such an installation system? Has anyone got such a system and if so how well does it work? We are in the Pennines. Thanks for any help. jaey.
    • CommentAuthorralphd
    • CommentTimeMay 15th 2009
     
    Posted By: nigel
    Posted By: biffvernonThe 22mm copper pipes are within that grey foam tube stuff you see in the DIY sheds and then the bundle of pipes is wrapped in glass fibre within a wooden box about eight inches square. It goes overhead from an outbuilding to the house.


    I would avoid the grey insulation as it will melt when the solar panel is in stagnation and can get to 200c.
    Likewise soldered joints will melt.
    You need a high temperature epdm insulation as used on the preinsulated pipes that you can get.


    Then go with flat plate instead of evacuated tube so you don't have to deal with the high stagnation temps.

    -Ralph
    • CommentAuthorralphd
    • CommentTimeMay 15th 2009
     
    Posted By: Jeff BWe have 4 x 2 sq metres of FP collectors on a south-east facing roof. Today we had 9 hours of solar heating and 8 hours yesterday. At noon yesterday the collector was at 118C and the solar water temperature was 78C. The length of pipe is not an important factor in my experience. We have at least 20 metres, admittedly all indoors although all bar about 8 metres are in loft space. We also used 15 mm to reduce the volume of fluid. The insulation is mostly the black Armaflex variety. We typically get only a 1 degree drop in temperature over the 20 metres. We have a flow-back system so stagnation is not an issue.

    Hi Jeff,

    What's the height from your collectors to your tank? I like drainback systems but above 20' of head a standard circulator pump won't work.

    -Ralph
    • CommentAuthormaureen55
    • CommentTimeMay 18th 2009
     
    What is your roof pitch? This is just as important an aspect of maximising the solar panel potential as aspect. We followed the advice on http://www.biorock-uk.com/solar_powered_pump.html page and our PV solar powered pumps worked all winter without a hitch. They are facing SSE at an angle of around 65 degrees and power dirty water pumps. Our roof has a very shallow pitch of about 35 degrees, so we have had to fix them to a garage wall on a frame as the solar panel manufacturer told us that they would be very inefficient when used on the roof at that angle. We originally placed them on a stable wall, but forgot about the shade from the adjacent tree in the summer - another important point to be born in mind.
    • CommentAuthorbiffvernon
    • CommentTimeMay 18th 2009
     
    Angle of pitch is not something to worry over much about. If you've already got a sloping roof, then that's the right pitch for you. Ideally you want the panel to be at right angles to the incident sunshine. Annoyingly, the Sun moves (relatively). In the winter you want a steeper angle than in the summer. In the evening you want a steeper pitch than at noon. Best to just go with the slope you've got and double the area you first thought of.
    • CommentAuthorJeff B
    • CommentTimeMay 18th 2009
     
    ralphd: do you mean the height of the solar collectors above the drainback tank or the height above the thermal store?

    maureen55: the roof angle is about 45 degrees, and the panels face SE. Regarding your point about trees. There are a row of ash trees growing in our neighbour's garden, right at the boundary. Currently they pose no threat at all to our solar collectors (in terms of shading) but I would imagine in the not too distant future they may grow tall enough to start shading them. I wonder where I would stand - would I have the right to ask that they be trimmed back to a sensible height so that they do not affect my solar collectors? I get on well with the current neighbour so I don't think it would be an issue, but I'm wondering if she sold up......? BTW I have taken plenty of photographs as evidence!
    • CommentAuthorDantenz
    • CommentTimeMay 18th 2009
     
    There is no mention here of the size of hot water cylinder, yes if it's a 180 L then 2 panels would make a good contribution however, if it's a 300 L then I would go for 3 panels or 6m2. Especially with the extended pipe runs. Heat loss from long pipe runs is not so much the problem as this can be insulated against, it's the fluid volume that's the killer. Increased fluid volume is not so much a problem when there are high levels of irradiation as the fluid is able to be quickly heated and energy can then be delivered to the cylinder fairly quickly. However, with lower levels of irradiation much of the gathered energy can simply be absorbed into the fluid rather than delivered to the cylinder.
    • CommentAuthorJeff B
    • CommentTimeMay 19th 2009
     
    Dantenz - I'm not sure if your comment is directed to me or not, but I can say that we have 8 sq. metres of solar collectors and a 300 litre thermal store.

    Jeff B.
    • CommentAuthorralphd
    • CommentTimeMay 19th 2009
     
    Posted By: Jeff Bralphd: do you mean the height of the solar collectors above the drainback tank or the height above the thermal store?

    The height above the drainback tank (i.e. the head your pump is working against).

    -Ralph
    • CommentAuthorJeff B
    • CommentTimeMay 19th 2009
     
    Ralphd - the drainback tank is about 2 metres below the upper connections on the solar collectors. The drainback tank is located in the attic space.

    Jeff B.

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