[RE-wrenches] Tube solar collectors

[Darryl Thayer]

HI Joel 
I have done ev tube and flat plat, I am amazed that the flat plate is almost as good to better than the ev tube.  

As to PV it is true that the output goes as the angle, (cosine function) but if you have a wavey surface it is very slightly better than a flat surface.  the cosine effect is there for the entire array, and the modern modules with antireflective coating compensate for much of the reflected energy.  So I doubt that the tubes are any better.  
Daryl 

--- On Sun, 7/19/09, Michael Welch <michael.welch at re-wrenches.org> wrote:

> From: Michael Welch <michael.welch at re-wrenches.org>
> Subject: Re: [RE-wrenches] Tube solar collectors
> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
> Date: Sunday, July 19, 2009, 12:27 PM
> Hi Joel. No experience here, but I
> did talk to one of their installers (I think it was Carlisle
> Energy Services) at Intersol last week, displaying one of
> the modules with its mounting system. Some additional info
> to consider:
> 
> E-T thermal collectors do have a "flat plate" in each tube,
> so angle of incidence is still critical.
> 
> Solyndra's have wrap-around PV materials inside their
> tubes, so E-W angle of incidence stays the same throughout
> the day.
> 
> They recommend reflective (like white) roof coating which
> picks up more bounced sunlight from the bottom side.
> 
> But it seems to me the main advantage is that they do not
> require roof penetrations or even ballast, making them a
> potentially quicker and cheaper install. The claim is that
> wind underneath will not lift them, and if wind load
> requirements are higher than normal (not sure where they
> draw the lines), merely putting skirting around the outside
> edge of the array keeps the wind out from underneath the
> modules.
> 
> All that said, I also look forward to hearing about field
> experience and performance.
> 
> Joel  Davidson wrote at 07:15 PM 7/18/2009:
>  
> >Wrenches,
> >
> >Solyndra claims that their tube collectors "perform
> optimally when mounted horizontally and packed closely
> together, thereby covering significantly more of the
> available roof area and producing more electricity per
> rooftop on an annual basis than a conventional panel
> installation." See http://www.solyndra.com/Products/Greater-Rooftop-Coverage
> >
> >It is my understanding that a solar thermal or PV tube
> or flat plate collector's performance is based on the angle
> of incidence and that curved collector performance decreases
> as the angle of incidence moves away from perpendicular.
> >
> >Does anyone have any field experience with solar
> thermal evacuated tube collectors or Solyndra PV to show
> that tubes perform better than flat plate collectors?
> >
> >Joel Davidson 
> 
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