15 minute resolution modelling

[Rapha123]

With more accurate sources of solar irradiation data with higher temporal resolution, PVsyst would be considered more accurate if 15 minute temporal resolution modelling was possible. There are several papers out there such as by Sandia explaning the much greater accuracy of using 15 minute resolution data compared to hourly data. I assume this would not be too much of an ask and as computers are more powerful nowadays, the time for simulation should not be too much of an issue.

Thanks,

Rapha

[André Mermoud]

I'm not sure that for the usual use of PVsyst, i.e. long-term forecast of PV yield, we gain much accuracy with sub-hourly simulations.

The first reason is that with grid-connected systems, the global system's behaviour is very linear with the irradiance.

The only differences in yield may come with non-linear effects, the main one being the operation in over-power conditions.

Any other effect (including the shading effects) will be averaged over long periods, so that the final result will be very close.

Now Meteo data in sub-hourly values are very scarce: they usually only concern on-site measurements or research projects. This restricts the use of sub-hourly simulation to the close analysis of measured data.

Probably the articles mentioning a better accuracy essentially concern these cases (i.e. the "instantaneous" accuracy).

Passing to sub-hourly values is not just a question of memory or calculation time.

Implementing simulation in sub-hourly values in PVsyst is not a straightforward task. Many fundamental options and organizations in the program are based on the hourly steps choice. Passing to sub-houly values would imply to completely review the "physical" variables organization in the program (which is not simple), the tables, data storage, data presentation, etc... This would represent many hundreds of working hours, and we have other priorities in the pèresent time.

[Oguzhan]

Dear Andre Mermoud,

As this is my first post for this forum, first I would like to thank you for creating this forum to answer the questions of the users and make it available for the users to discuss the problems that they face with PVsyst.

I am a senior electrical-electronics engineering student in Middle East Technical University (in Turkey) and I have been conducting a research about the effect of time resolution of collected irradiance data on the results of simulation programs. I have used evalation mode of PVsyst for past 1 month and I believe this is the correct forum topic to write my suggestion as Rapha had already suggested a similar suggestion.

There are two very valuable articles (you can easily access them) about this topic:

1. Inverter Sizing of Grid-Connected Photovoltaic Systems in the Light of Local Solar Resource Distribution Characteristics and Temperature (written Bruno Burger & Ricardo Rüther)

2. Why Hourly Averaged Measurement Data is Insufficient to Model PV System Performance Accurately (written by Steve Ransom & Peter Funtan)

In the light of these articles, I have observed that hourly averaged data cannot sense the instantaous irradiance peaks which are over 1000W/m2. It may seem unimportant but in the first article it is experimentally observed that those instantaneous irradiance peaks which are more than 1000W/m2 form 5% of total irradiance in Freiburg corresponding to 16% of total energy and 9% of total irradiance in Florianopolis corresponding to 23% of total energy.

I can understand that PVsyst operates with hourly steps and it requires a challenging work to change this system to sub-hourly steps but this hourly step calculations mislead the investors in inverter selection. People are not aware that irradiance levels which are more than 1000W/m2 do exist and they happen instantanously (without increasing the temperature of PV panels) so they are able to contribute a lot to the energy yield. However, as the people are not aware of this situation, they are inclined to choose undersized inverters. These undersized inverters cannot operate with high power inputs which happen at these irradiance peaks so they cannot track MPP properly (operating point shifts towards higher voltages as you already explained in FAQ). As a result energy yield is decreased due to the wrong inverter selection.

Another disadvantage of hourly averaged data is that in underestimates the advantage of broad DC input voltage property in inverters. In simulation results, we cannot see the effect of sudden irradiance drops in cloudy weathers with hourly averaged data. But we are aware that sudden irradiance drops can cause sudden voltage drops in PV arrays and these voltage drops prevent the inverters whose minimum input voltage is too high from operating. Here, inverters which have wide broad DC input option has a great advantage but a random investor cannot observe this situation according to the simulation results.

As a result, I believe we CANNOT neglect the advantages of better time resolution irradiance data. My sincere suggestion for PVsyst is to put an effort in this topic and enhance the program so that it can operate with minutely averaged irradiance data.

I am looking forward to get a response from you in this topic.

Thanks a lot,

Best Wishes

Oğuzhan