Solar resource data sets come at different temporal resolutions – monthly and hourly. PVsyst and other solar energy modeling software allow you to model hourly data based on a monthly input. Is this good enough?
For tracking plants, this approach may have too much uncertainty to even use in the early prospecting stages of project development. Vaisala did a study where we used PVsyst to compare the P50 energy results from using hourly TMY data to results from using monthly averages. The same underlying data set was used and the only difference in the projects was the temporal resolution.
The news was good for fixed PV. The energy differences between the models was less than 1% and the maximum difference was around 2%. That is a deviation that is acceptable at early project stages, although in later development stages you will want to reduce the uncertainty.
The place where the difference really shows up is in tracking plants. For tracking plants, the average difference was 2% and the maximum difference was over 7%. This is enough to make or a break a project; thus, we recommend hourly data in these cases at all project phases.
What if you didn't have to choose between keeping a tight schedule, accuracy of the resource data, and the cost to acquire it? With Vaisala's Solar Time Series Tools you can get access to highly accurate resource data within hours and for as low as $50 a time series for hourly data.
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