Trace ST problems [RE-wrenches]

[Michael Welch, Home Power]

John - You have incorrectly posted the operating temperature of the ST as 0 to 45 Degrees Celsius. It is actually -39 to 45 Degrees Celsius. Please refer to ST data sheets stating Rev A 09/00 in the bottom left corner for accurate information.

 From Pagan MacKay, pagan.mackay at traceengineering.com and posted at her request by Michael.

jberdner at sma-america.com wrote at 01:11 PM 02/22/2001 -0800:
   
>Travis / Carl:
>
>Sounds like more smoke and mirrors to me.
>
> From the MPPT perspective I really don't think thin films are all that
>different than crystalline .
>Most thin films have a lower fill factor, i.e.
>  softer knee on the IV curve.
>If you draw the power curve for a module using the IV curve data you see a
>hump that peaks out near the knee of the IV curve.
>For thin films the hump is typically broader so they are less sensitive to
>changes in operating voltage.
>Usually this means that thin films are easier to track than crystalline
>since they are less sensitive to variations in operating voltage.
>
>The main issue with thin films is the higher Voc to Vmp ratio.
>The original genesis of the ST was for EPV modules as part of SMUD's PV
>program.
>Unfortunately, the MPPT window is too narrow to work with most thin film.
>With the MPPT window being only 52 to 85 it is very difficult to find an
>array configuration that it will power track year round.
>You really need an DC input voltage MPPT window of 2 to 1 or more to track
>year round in most locations.
>
>Most module companies will supply you with the temperature coefficients for
>voltage, current, and power if you ask.
>Ideally you want to design the system so that the inverter can track the
>array all the time.
>There are simulation programs out there that will give you the Max power
>voltage but you can "back of the envelope it" pretty close by using the
>coefficients and the ambient temperature plus 20 C for cell temperature.
>
>Another problem with the ST and thin films is the maximum UL allowed voltage
>of 120 Vdc.
>This is another reason why you can only use it with 4 crystalline modules in
>series.
>This means the ST will violate the UL Listing if you hook up two EPV modules
>in series (or five crystalline module) if the temperature falls below
>freezing.
>The rumor is that SMUD is none too happy about that.
>
>An then there is the ambient specification of 0 to 45 C -
>Hmmm, where can I use it where the temperature never is hotter than 45 or
>lower than 0 => indoors only!
>And then there is the fan that comes on at 150 to 200 Watts and stays on
>(NOT a UL requirement by the way)
>I heard from an installer yesterday that had a call back to move the
>inverter because it vibrated the wall so badly that the people couldn't
>stand it.

   
Michael Welch
   
------------------------
"Society is like a stew. If you don't keep it stirred up, you get a lot of scum on top."

			Edward Abbey
         
Michael Welch, michael.welch at homepower.com www.homepower.com
      Associate Editor, Home Power magazine
      Office Coordinator, Redwood Alliance
      (Not HP mag's #s) 707-822-7884 fax: 707-822-3481
      

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