Trace ST problems [RE-wrenches]

[Eric Smiley]

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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