consideration for cloud conditions

[sairam]

Sir,

in India almost 4 months of monsoon season is without sunlight.

Is this condition is already simulated/included in PVsyst for Annual Yield calculation ? or we have to manually deduct the generation for those 4 months?

Regards,

Sairam

[Bruno Wittmer]

The meteorological data, which is at the input of the simulation, accounts already for cloudy conditions.

The solar irradiance arriving at ground, splits up into the direct (beam) component, which is only strong if there are no clouds, and the diffuse component, which is always there at daytime and usually increases in the presence of clouds.

Therefore, to get a useful simulation result, you have to make sure to use reliable meteorological data for your input, that reflects the meteorological conditions at the site of your PV installation.

The default meteorological data source in PVsyst is Meteonorm, which provides reasonable values for any spot on the globe.

You can also choose other meteo data sources as explained in the Tutorial and Online Help. In this case make sure to validate the data quality.

[sairam]

Please find attached file,

please advise if the radiation data is correct for the month from June to September.

location - santej - near Ahmedabad city, Gujarat, India

Latitude - 23 deg 8 min - N

Longitude - 72 deg 26 min - E

Altitude - 52 Meter

Time Zone - 5

[sairam]

what is the standard value for radiation kwh/m2.day for such cloudy monsoon season ?

[Bruno Wittmer]

The values in your picture correspopnd to the NASA-SSE data for Santej.

Meteonorm, which is the PVsyst default, gives slightly higher values for the Global horizontal irradiance and slightly less for the diffuse, which means that it has less clouds.

I recommend to make a simulation with both inputs, to get an impression of the impact this difference has on the result.

[Tobias]

Dear all,

I would like to ask a new question here because it also is about consideration of cloudy conditions. I hope this is ok.

In my understanding, Meteonorm data consists of monthly irradiation values that are converted to hourly values by "some algorithm". This is perfect for estimating the yearly yield. However, in some locations for example in Chile it would be helpful to also have a more realistic characteristic. Some locations in Chile are always cloudy in the morning and after noon time there are clear sky conditions. I have attached an example of such a daily profile.

Is there any way to take this characteristic into consideration when generating hourly values? Especially in this spot almost every day looks like the attached image. So I would like to simulate different azimuths. Since the sun does not shine so much in the morning it might be a good idea to direct the modules more to the north-west. Also for selling the energy at the spot market, it is interesting to have an idea about the hourly distribution of the energy.

I know, it is possible to purchase hourly climate data but maybe there is a way to generate this characteristic synthetically. Anyone an Idea?

I hope I could make my point clear.

Thank you for your help!

Kind regards

Tobias

Cloudy Day in Chile

[André Mermoud]

The synthetic generation is a statistical model, based on the real measured data of dozens of sites.

The elaboration of such a model is very complex, and it required very sophisticated checks.

It is not possible to modify it, by addin such "fuzzy" conditions. The only way for your evaluation is to use really measured hourly values.