Trace ST problems [RE-wrenches]

[Bill Brooks]

Eric,

Remember that EPV modules have a very poor fill factor and therefore are not
far off the max power point with a few volts. However, I have seen EPV
modules operating at much lower than 39 Volts (try 34 Volts). A good rule of
thumb is to not believe manufacturers specifications--that goes for modules
and inverters.

The MPPT window of an inverter is based on the line voltage. The low end of
the voltage range is always suspect from the manufacturer. If the line
voltage is 124Volts (3%high) the low end of the MPPT window just went up 3%
(that would be about 44 Volts on the Sun-Tie). Now we have a 10 Volt
differential--Very significant power loss.

Bill.


> -----Original Message-----
> From: Eric Smiley [mailto:Eric_Smiley at bcit.ca]
> Sent: Monday, March 05, 2001 3:20 PM
> To: RE-wrenches at topica.com
> Subject: Re: Trace ST problems [RE-wrenches]
>
>
> John's post caused a stir here as we are planning on using the ST in the
> near future.
> Fortunately the ST has a larger MPPT window (42-85 Vdc) than John stated.
>
> >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.
>
> On paper, it looks like the standard EPV module would be a poor
> choice for the ST.
> I was very surprised that Trace had done field testing with EPV
> modules and they worked at voltages as low as 40 Volts!
>
> http://www.gridtie.com/support/technicalbriefs/tn3/index.html
>
> I have specs for a standard 40 Watt EPV module and a letter from Alan
> Delahoy which gives the voltage temperature coefficient as -0.28%/
> degree C.
> Vmp = 44.8 volts
> Voc = 62.2 volts
>
> At a module temp of -20 C.
> Vmp = 44.8 x 1.126 = 50.4 volts
> Voc = 62.2 x 1.126 = 70.0 volts
>
> At a module temp of +70 C
> Vmp = 44.8 x 0.874 = 39.2 volts|
> Voc = 54.4 volts
>
> In other words the SunTie shouldn't work very well with these particular
> modules at high temperatures.
> We weren't planning on using EPV modules anyways, but perhaps Trace
> would like to comment on how they got such exemplary results at such low
> voltages?
>
> I have also done the above calculation for four nominal 12 V
> crystalline modules and Solarex Millenia modules.
> They fall within the MPPT window at the above module temperatures.
>
> ----------------------------------------------------------------------
> Eric Smiley
> Project Leader - BCIT Technology Centre
> Photovoltaic Energy Applied Research Lab (PEARL) - BCIT
> ph: (604)432-8657 www.bcit.ca/~tc/pearl/index.htm
>
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____________________________________________________________
T O P I C A  -- Learn More. Surf Less. 
Newsletters, Tips and Discussions on Topics You Choose.
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