How is average power per hour calcualted?

[Steve_NO]

We are using PVsyst for simulation and compare the results with the real data. We see that energy values per hour are not the same, often the e.g. peak is moved +1 or +2 hours (yes, we already took away summer/winter time). Among other theories why that is so, we would like to know how PVsyst calculates the average of the hourly production.

1. Is there a calculation for values within an hour, or does PVsyst take all the values for 1:00pm from the sources (e.g. radiation at 1:00 from meteonorm) and calculate a value, assuming this will be the average of the coming hour?

2. Does PVsyst calculate values within the hour, and then generates an average of that? And here it would be interesting how this is done. I made an example (see figure):

• all the values of that hour are put to the begin of the hour
• all the values of that hour are put to the end of the hour (i.e. the begin of next hour)
• the values for 1:00pm are taken +/-30min around that hour
• something else 😀

 

Thanks, Steve

[Linda Thoren]

In general, the denomination of a given time interval in PVsyst is always defined as the beginning of this interval. This is valid for hourly, daily or monthly values. For meteo data, the time stamp is the time interval over which the irradiance measurement (or any other value) is averaged. For example, the time stamp 11:00 corresponds to measurements averaged between 11:00 and 12:00.

When using irradiance models, the solar geometry should be calculated for an "average" of the time interval. PVsyst uses the middle of this time interval  (in the previous example 11:30). 

Different weather data providers have their own definition of the timestamp and thus will be adapted to match the one in PVsyst.
 

[Steve_NO]

Thank you. Now we have to wait for the answer of the inverter company 🙂