RE: [GBlist] Roof angle for active solar?

["Ralph Bicknese" <ralph.bicknese@christnerinc.com>]

Bob:

Sorry for the confusion. I hope this explanation is clearer.

To maximize collection on any surface year round the best tilt angle is
equal to the local latitude.  That applies to photovoltaics as well as
domestic water heating (or to cooking an egg on a piece of solar heated
sheet metal).

To optimize for space heating in winter, a tilt angle of latitude plus 15
degrees is preferred.  This would apply to collection with an active solar
space-heating panel or to south facing glass in a building.  However, for
passive solar space heating uses, that tilt is usually not easy to shade.
Vertical glass for passive solar collection works quite well with little
penalty for not having optimal tilt.

For domestic water heating some people prefer to increase the tilt greater
than the latitude to boost winter performance.  The theory is that in the
summer the ambient temperature is much higher and losses through the panels
and piping are much less than in winter.  At most locations the summer
sunlight is also more intense than in winter.  So to balance summer and
winter gains one can increase the tilt 10 to 15 degrees beyond latitude.  It
depends in part on your local summer and winter ambient temperatures and on
your summer and winter intensities of sunlight.  Is there a local solar
installer you could ask?  The best solutions are often local ones.

Cheers,
Ralph Bicknese

-----Original Message-----
From: Robert Jordan [mailto:rwjordan@charter.net]
Sent: Thursday, December 27, 2001 2:56 PM
To: Ralph Bicknese
Subject: Re: [GBlist] Roof angle for active solar?

Ralph,
Thanks for answering.  I am a little confused though.  You say "The best
angle for year round solar collection is equal to your latitude or 40.5
degrees.  The best angle for water heating is considered to be equal to your
latitude plus 15 degrees."
 Are you making a distinction between DHW and generic solar collection or
just that it is more difficult to collect heat in the winter, so optimize
for the winter and get a bit less in the summer?


> The answer to your shading question is quite a bit more complicated .
 I understand the dependency on window size.  Do you know of anything
written on optimizing overhangs due to the condition that the longest day
occurs a month and a half before the hottest day?
Thanks
Bob Jordan
>
> -----Original Message-----
> From: Robert Jordan [mailto:rwjordan@charter.net]
> Sent: Thursday, December 27, 2001 11:39 AM
> To: greenbuilding@crest.org
> Subject: [GBlist] Roof angle for active solar?
>
> I am designing a house West of Boston, Latitude approximately 40.5
degrees,
> that I hope to some day have passive solar on.  The rear of the house
faces
> directly true south.  The house will be well insulated and tight.  I
gather
> that DHW is viable.  Is it worth trying to collect enough hot water to
> satisfy at least part of the heat load?  I also hope to have a masonry
> heater.  Further down the road is PV.  I would like to design the roof at
a
> pitch such that the panels can lie flat on the roof.  Can anyone offer
> advice as to the best roof pitch for this program?
> Thanks in advance,
> Bob Jordan
>
>
>
>
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______________________________________________________________________
This greenbuilding dialogue is sponsored by REPP/CREST, creator of
Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
Environmental Building News and GreenSpec http://www.BuildingGreen.com
______________________________________________________________________