PVsyst inverter

[mikofski]

mimic pvsyst
I would like to mimic pvsyst so as to be bankable

a pvsyst inverter
Inverter model: efficiency says:

Set of 3 efficiency profiles: this is a more accurate definition: we define an efficiency profile as above for 3 different input voltages. At each step, the simulation will perform a quadratic interpolation between these 3 curves, as function of the real input voltage.

Sandia grid inverter model
Any idea how the Sandia inverter model compares?

Other pvsyst inverters
There are 4 options single curve, Euro per weighted efficiency, etc..

See also grid inverter-efficiency curve

[cwhanse]

I agree, pvlib.inverter.pvsyst would be a good addition. In the case of PVsyst option 3, input consisting of three efficiency curves at 3 input voltages, these data are typical for an inverter datasheet. Perhaps we can start there, since I don't know how PVsyst builds the curves from CEC efficiency and threshold power (option 4).

The Sandia inverter model assumes that the efficiency curves evolve linearly as the input DC voltage changes; as @Peque has pointed out, a given device might not follow that linear behavior. An interpolation would be more general.

[Peque]

Would it be interesting to support reading .ond files directly from pvlib? For what I know, it is a non-standard and not documented format used by PVSyst to import/export module data, so probably no... 😂 but maybe I am wrong (?).

[btaute]

The ability to read in .OND files (inverters) and .PAN files (modules) would be a big help for people trying to transition to pvlib from PVSyst.

[cwhanse]

I think @frivollier has shared some tools to read OND and PAN files. I would support adding capabilities to pvlib, either directly or by importing from @frivollier 's project if there's intention to maintain that project.

[mikofski]

CanadianSolar CASSYS is another source of code to parse and model inverters:

• inverters.cs
• DatabaseImportModule.vba - even includes reading Delphi-native real48 datatypes from the binary OND files.

[frivollier]

Despite some good intentions I won’t be maintaining or updating this project to read PAN files but I could help anyone that want to take it over. Fred

On Tue, Jul 14, 2020 at 3:15 PM Cliff Hansen ***@***.***> wrote: I think @frivollier <https://github.com/frivollier> has shared some tools <https://github.com/frivollier/pvsyst_tools> to read OND and PAN files. I would support adding capabilities to pvlib, either directly or by importing from @frivollier <https://github.com/frivollier> 's project if there's intention to maintain that project. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1002 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AALHKPXBNGXK6JPUQJ5CFGTR3SVGZANCNFSM4OZDEGPA> .

-- Frederic

[kandersolar]

In #1199 (comment) @cwhanse said:

That would be a nice addition to pvlib. But, to my knowledge the inverter model in Pvsyst is not fully documented. The Pvsyst license prohibits reverse engineering the software. Without reference to complete and open documentation, I don't think we can add inverter.pvsyst and claim that it's the model in Pvsyst.

Just curious, is that still the case? Do we expect to ever be able to address this feature request?

[cwhanse]

Just curious, is that still the case?

AFAIK, yes.

[mikofski]

Should we just close this issue? AFAIK pvsyst just interpolates between the curves to get the efficiency. I don't know how it compares to Sandia grid inverter model, but I think it can't be bad to have a function that just does that. I also think the ability to read PAN and OND files would be very helpful. And measurements from the CEC solar equipment lists too while we're at it.

def interp_inverter_eff(eff_curves, pdc_timeseries, vdc_timeseries, voltages, method="quadratic"):
    """
    interpolate inverter efficiency given 3 voltages

    Parameters
    ----------
    eff_curves : numpy.ndarray or pandas.DataFrame
        table of efficiencies with indices or first column as the DC power monotonically
        increasing and each consecutive column at a different monotonically increasing
        voltage corresponding to the ``voltages`` parameter
    pdc_timeseries : numpy.ndarray, pandas.Series, or pandas.DataFrame
    vdc_timeseries : numpy.ndarray, pandas.Series, or pandas.DataFrame 
    voltages : numeric
        a sequence or scalar of the corresponding nominal voltages, must be
        monotonically increasing and length must be same as columns in ``eff_curves``
    method : str
        how to interpolate the efficiency if given 3 voltages

    returns
    -------
    efficiency : numpy.ndarray or pandas.Series
    """
    eff_curves = pd.DataFrame(eff_curves, index_col=0)
    f = scipy.interpolate.interp1d(x=eff_curves.index, y=eff_curves)
    eff = f(pdc_timeseries)
    try:
        num_volts = len(voltages)
    except TypeError: 
        num_volts = 1
    else:
        if num_volts > 1:
            g = scipy.interpolate.interp1d(x=voltages, y=eff.T, kind=method)
            eff = g(vdc_timeseries)

    return eff

[cwhanse]

OK with me to close, or to keep the issue open. It would be nice to have the Pvsyst inverter model in pvlib, the real blocker is the lack of documentation.

[mikofski]

I'm not sure if the above function works, as you say, there's no docs - which according to the pvlib ethos means it doesn't go in - soo... how about a gallery example or we start a contrib folder?

[cwhanse]

The interpolation is simple enough that I'm ok adding it with the docstring being the reference, if you are persuaded that there's demand for it. It would fill a gap between the Sandia/adriesse models (which require fitting) and the PVWatts model (a single parameter), in that this interpolation could work from the data in the CEC listing or from digitized datasheet curves.

[adriesse]

Does anyone else see the irony here? The opening line is:

I would like to mimic pvsyst so as to be bankable

And:

It would be nice to have the Pvsyst inverter model in pvlib, the real blocker is the lack of documentation.

Please let the banks know!

[adriesse]

If you have some data and are tempted to use interpolation, I suggest you also give the fitting routine for the ADR inverter model a try. It is located here.

This model is well-documented, and being based on the summation of physically explained losses it is pretty much constrained to produce physically correct efficiency curves. If there is enough demand I can move it to pvlib.

[adriesse]

Maybe we could join forces and publish a paper with a title like "Bankability assessment of inverter simulation models" in a publication that bankers read.