PV generation tools

ladybug-tools
1

Hi all,

I’ve been comparing the legacy PV generation tools (based on PVWatts1) with the more recent version using EnergyPlus. It yields quite a few differences.

I was wondering what EnergyPlus module it uses to calculate the PV production. What’s the engine behind it?
Also, is there a way to get more detailed output such as cell temperature and radiation, like you can with the legacy version?

2

Have you read:

The simple model in EnergyPlus is very simple, and will not give very accurate results. A better model is Sandia Photovoltaic Performance Model, that is accessible as weøø. Then there is a complex model, but that needs a lot of extra data.

As I understand the LBT implementation, it does not take in enough data for the complex model. So I would think it is the simple one or perhaps the Sandia one, but I haven’t checked the code.

3

That’s what we are wondering. Is it the Simple, the One-Diode or the Sandia model that’s used in LBT?
If it’s the simple model, I’d rather keep using the Legacy PV Watts module, but worry that at some point it will no longer work properly.

4

I see now that there is also a PV Watts model in EnergyPlus:

There is also a PVWatts generator which abstracts away specifying PV modules and array properties for a simpler input structure.

And it seems that this is the one addressed in LBT:

comments = (
            'PV generator name', 'PVWatts version', 'DC system capacity {W}',
            'module type', 'array type', 'system losses', 'array geometry type',
            'tilt angle {deg}', 'azimuth angle {deg}', 'surface name',
            'ground coverage ratio')

https://www.ladybug.tools/honeybee-energy/docs/_modules/honeybee_energy/generator/pv.html#PVProperties.to_idf

Why don’t you do a comparison of a couple of scenarios, and report here?

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5

I have another question. The latest version only gives results for DC-power and AC_power, it no longer gives radiance results, nor any results for cell temperature. Normally, the PV watts does calculate those things. Is there a way to change the script to include those outputs?

6

With @tvanbesien we modified a little bit the script to add the radiance and the cel temp. here it is GenLoads+Cel_T+POA.zip (8.6 KB)

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