Re: energyplus PV

[David Bradley <bradley@xxxxxxxxxxxx>]

Brent,
  I had thought that the E+ folks dumped that PV work in favor of a
different model many moons ago... glad to hear that it is still kicking
around though.

> The first issue is an easy one.  The Energy+.idd data dictionary
> includes default values and I think maybe the following are mixed
> up.
>  
> GENERATOR:PV:EQUIVALENT ONE-DIODE,
> < snipped >>
>  
>    N15, \field Temperature Coef. of Isc
>          \default -0.079
>          \type real
>          \units A/K
>    N16, \field Temperature Coef. of Voc
>          \default 0.02
>          \type real
>          \units V/K
>  
> I think the values may be switched.  Could it be that the 0.02 value
> is the default temp coef and -0.079 value is for the voltage coef. 
> This seems more in line with the I/O ref and various catalog data I have
> seen.

yep, I think you are correct about that.

> The
> second issue seems to be a tricky numerical problem that is causing the
> model to crash.  It seems to depend on the number of cells in series
> and if this gets too high the model has numerical problems.  For
> example, the input below crashes E+, but if I reduce the number of cells
> in series (within the module) from 112 to 104 it runs.  Maybe modern
> PV modules have more cells and higher voltages and pack more power than
> the model?s numerics can handle?  Have you seeing anything similar
> going on with TRNSYS implementation?  

I plugged in your data and I get a similar problem. I am not sure what
you are specifying for cell temperature - I just stuck it at the
reference condition cell temperature for the time being. The TRNSYS
developers have largely abandoned that equivalent circuit model of a PV
array in favor of one that was more recently developed at the Solar Lab.
Apparently some work that David King did at Sandia showed some problems
with the equivalent circuit model - I did not follow the details
particularly closely. I will see what I can do about tracking down the
numerical instability in the model (Type180) that is implemented in E+ -
it may be a little while, however, as I have to be out of town for a few
days and then am teaching a training course. I'll let you know what I
find.

Cheers,
 David

 

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