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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.
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Renewable Energy: Energy for DHW.

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  1.  
    • CommentAuthorMrT
    • CommentTimeDec 12th 2007 edited
     
    For hot water I currently have electric shower, plus an 8.5 kw direct feed water heater, kind of like an electric shower feeding the kitchen tap. We are trying to work out if we should go for a new indirect cylinder connected to a back boiler on a wood burning stove and maybe a flat solar panel feeding another coil on the cylinder. The stove could also supply a couple of radiators in currently unheated and occasionally cold rooms.

    The only roof elevation I have available is orientated at ESE, the pitch is about 30 degrees, hardy optimal.
    Would I get any benefit from a solar panel on such a roof.

    Would it better to continue to use what we currently have, with cold rooms. or go for the back boiler/ solar combo and back it up with a immersion. I use solid fuel for space heating so already have the logs.

    I want to avoid gas as we are unconnected at the moment but can see the a gas boiler maybe moree efficient.
    •  
      CommentAuthornigel
    • CommentTimeDec 12th 2007
     
    At a low angle of 30 degrees you get over 90% of the maximum yield if it is facing east so yours should be fine.
    • CommentAuthorskywalker
    • CommentTimeDec 12th 2007
     
    Hello MrT

    I would take the time to look at your whole system. If you are going for solar take a look at heat stores. DPS are well thought of (http://www.heatweb.com/) but there are other manufacturers. The benefit of these is that you can run a shower at mains pressure, run your heating system and connect solar and have them heated by many different heat sources. They are not cheap but as you are likely to have to do a lot of plumbing anyway worth considering and would allow you to ditch (sorry recycle) your current electric heaters.

    There are concerns over the type of solar collector you use. Recieved wisdom is that evacuated tubes are more efficient at our latitude than flat plates. However there are concerns as to the reliability of evacuated tubes. Unfortunately much of the debate is led by manufacturers/retailers so it is difficult to get to the bottom of it currently. There is a recent thread starting on this.

    S.
    • CommentAuthorskywalker
    • CommentTimeDec 12th 2007
     
    I have some different figures to nigel (which may be wrong but are from the green building bible/navitron)

    With an easterly aspect quoted figures suggest that you will get around 80% of the heat you would get with a full southerly aspect. Angle of mounting advice varies but is usually at the same angle of your latitude (around 50 - 60deg for most of the UK) or latitiude + 10deg depending on who you chose to guide you. In practice collectors work at quite a wide range of angles but I do not know enough to be able to tell you how much difference mounting at 30deg will make. In any case you should be able to mitigate for this by having a larger collector. There is also the option of an east west system (two panels mounted on different roof surfaces) but if you have only one elevation pointing in something like the right direction this may not be an option.

    .
  5.  
    You don't have to put a solar panel on the roof. If you have good solar access (i.e. no trees or buildings over shadowing) on the south side of the house, you could build a pergola attached to the house with the panel orientated sue south at the optimum angle situated on top of it.

    This would probably be an easier installation than on the roof and hence might be cheaper (or safer if DIY). If the panel is below the cylinder you could set the system up to thermosyphon doing away with the need for pumps. Might also provide some shade in mid-summer.
    •  
      CommentAuthorOlly
    • CommentTimeDec 12th 2007
     
    According to the solar sundial lookup table that I have on an old spreadsheet of mine, you'll still get 90% of optimum output at ESE with a 30 degree incline, interestingly this is the same as for a panel mounted on a horizontal plane. However I think my table is for PV systems, solar hot water panels may perform differently.

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