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For reasons of security and ohmic losses in the overhead lines, the public transport networks are usually divided into little islands of relatively modest dimensions (of the size of a suburb). The power needs are therefore highly variable: while a starting tramway can absorb 1 to 2 MW within a few seconds, during the rest of the time, only a small number of vehicles (or often no vehicle) have to be supplied. The only "load" which is to be satisfied will then be the "ribbon-consumption" of the vehicle's heating systems and other services specific to the network.

Due to the fact that the PV installation is unable to store energy, these very special characteristics require a preliminary and in-depth study of the on-site power demand, and its spread in time (power distribution analysis with a few-second sampling).

PVsyst is able to treat this case through the "Hourly probability distributions" load profile. We can assume that when averaging over a long period, an hourly probability profile should be statistically equivalent to few-seconds peaks with the same probability distribution.

With significant PV installations, the PV-array power sizing should keep the over-energy (PV energy which cannot be used by the load) at a reasonable level. This could be a serious limiting condition to the system size when the ribbon consumption is low.