accounting for snow & unavailability

[kamomeno68]

I started using PVsyst originally witth v5. At that time, I accounted for the increased losses due to snow by increasing soiling percentages in the winter months. I realize this method is not perfect, but it seemed like a reasonable option. In v6, however, there is the option of increasing unavailability in winter months to account for the increased lossed due to snow. Based on your experience, is either of these methods preferred over the other? Is there another way to best account for snow which remains on an array during sunlight hours?

Also, can you provide further explanation for how the "unavailability" section works, particularly the "unavailability periods"? For example, I chose an "unavailability period" = 2 days, and the "number of periods" = 4 periods. In the "unvailability periods" section, I can then choose starting date, starting time, and duration in hours for each "period". An example would be 1/21/1990, 9am, 12hrs. I assume these numbers are intended to represent simply fractional periods in a 365day/8760hr year, and not the actual hours chosen. For example, the pv system will not be producing for 12 hours on 1/21, so I'm a little confused how PVsyst would model this particular unavailability input.

Thank you!