Flat solar roof? Probably a bad idea?

Discussion in 'Boat Design' started by Jeff in Boston, Feb 14, 2021.

  1. Jeff in Boston
    Joined: Sep 2020
    Posts: 92
    Likes: 10, Points: 8
    Location: Boston

    Jeff in Boston Junior Member

    I'm building a solar powered slow cruiser. I'm working on a design for the canopy. Large flat glass panels (though heavy) are 1/4 of the price of flexible panels per watt.

    The canopy will be about 8' x 10'. I was thinking an aluminum frame combined with FRP sheets with the solar panels on top. It would be much easier to make it flat with large panels, but I know houses with flat roofs always have puddling and leaking problems.

    I'm wondering if just the rocking of the boat or the fact that the trailer is unlikely to sit perfectly flat is enough to stop the problem? I would have some sort of lip around the edge to shed the drips.


    Thanks!
     
  2. portacruise
    Joined: Jun 2009
    Posts: 1,214
    Likes: 73, Points: 48, Legacy Rep: 218
    Location: USA

    portacruise Senior Member

    Snow and ice layers might affect power generation, overhead load, COG, Etc with a flat solar roof if you're doing anything during very cold periods. Also any possible self cleaning that might slide off could be diminished ( puddling and evaporation deposits). Hope this helps.
     
  3. Jeff in Boston
    Joined: Sep 2020
    Posts: 92
    Likes: 10, Points: 8
    Location: Boston

    Jeff in Boston Junior Member

    For winter it will stored under a peaked frame and cover to shed snow. For the self cleaning, I am fine using a hose and brush from time to time. I figure I will have to deal with seagull poop even if I have angled panels.
     
  4. fallguy
    Joined: Dec 2016
    Posts: 4,967
    Likes: 904, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    It might be best to spec the panels. 8x10 is not too size friendly to any panels I know.

    Most rooftops require lifting the panel off the roof for best performance. During the attachment, you can accomodate making the panels flat against a curved roof.
     
  5. Jeff in Boston
    Joined: Sep 2020
    Posts: 92
    Likes: 10, Points: 8
    Location: Boston

    Jeff in Boston Junior Member

    I'm looking at 80" x 40" panels. Three of them make 80" x 120". You make a good point about ventilating underneath to keep them cool.
     
  6. bajansailor
    Joined: Oct 2007
    Posts: 2,215
    Likes: 750, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    If you are able to put some camber (say 2" over 8') in to the aluminium roof beams, the roof will be stiffer / stronger, and will be more attractive.
    Re the FRP panels for the roof, will they be single skin, or cored with (eg) foam?
     
  7. Jeff in Boston
    Joined: Sep 2020
    Posts: 92
    Likes: 10, Points: 8
    Location: Boston

    Jeff in Boston Junior Member

    I was thinking single skin. I agree on the stronger, stiffer and more attractive. I'm thinking more and more that curved is the way to go.
     
    bajansailor likes this.
  8. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,208
    Likes: 970, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Doesn't have to be curved, a slight peak with 5 degrees max slope ? Panels to both sides of the peak, and your angle of incidence to sunlight still good.
     
  9. Will Gilmore
    Joined: Aug 2017
    Posts: 556
    Likes: 235, Points: 43
    Location: Littleton, nh

    Will Gilmore Senior Member

    Can't you design in a slight fore and aft slope? It shouldn't take much to shed water.
     
  10. portacruise
    Joined: Jun 2009
    Posts: 1,214
    Likes: 73, Points: 48, Legacy Rep: 218
    Location: USA

    portacruise Senior Member

    "For winter it will stored under a peaked frame and cover to shed snow."

    If the peaked frame is yet to be constructed, using sturdy transparent Greenhouse type panels (or some other scheme) that lets sunlight in would allow for some degree of solar generation during winter or even summer non-use storage periods. But that may be more trouble and expense than it is worth, for whatever gain is achieved- or if the power cannot easily be fed back into the grid? If this is a Leisure boat, some Leisure boats are only used a few times per year, as I understand it.

    What's the best canopy shape to minimize side wind loads for your particular Waters, might be another consideration.
     
    Last edited: Feb 15, 2021
  11. wet feet
    Joined: Nov 2004
    Posts: 729
    Likes: 128, Points: 43, Legacy Rep: 124
    Location: East Anglia,England

    wet feet Senior Member

    That would seem to be a practical solution.If the design of the boat would be compromised by doing so you might consider a faceted panel approximating a normal deck camber.
     
  12. Jeff in Boston
    Joined: Sep 2020
    Posts: 92
    Likes: 10, Points: 8
    Location: Boston

    Jeff in Boston Junior Member

    For fore and aft slope I'd worry about increase of wind resistance.

    Angled / faceted roof might work.

    I'm going to look more into the less expensive flexible panels. If I'm leaving the boat for a week a few glass panels on the cabin would top off the batteries, and I could cover less expensive flexible ones to increase their longevity.
     

  13. philSweet
    Joined: May 2008
    Posts: 2,466
    Likes: 270, Points: 83, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    The panels need to be self cleaning. You are better off with a 5 degree side slope and clean panels than with a flat dirty set. Five degrees is the minimum, a bit more is better. It you can spring for the distributed MPPT systems, that would be best. Then it doesn't matter if some panels are at different incident angles than others.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.