POA in PVWatts v5 single timestep

I am using the "pvwattsv5_1ts" module to calculate array AC output for several consecutive hours. In the example file that comes with the SDK (using "pvwattsv1_1ts"), it says that the POA input is "from previous time step".

It's not clear to me why this is needed or how the POA is used as an input. Partly, I want to make sure that I'm not overriding the POA calculated from beam and diffuse components in my weather file. If that's not what it's doing, how should I initialize the POA value for the very first hour of my simulation?

Hello,

The POA and cell temperature variables are "inout" variables. As inputs, they are passed to the cell temperature model as starting values for the algorithm. As outputs they are the POA calculated from the beam and diffuse inputs, and the cell temperature resulting from the cell temperature model. So you are not overriding the calculated POA or cell temperature outputs.

For the first time step of the simulation, the POA and cell temp variables are the initial conditions of the module at the beginning of the year (the values are probably not too important). For subsequent calls to the pvwatts5_1ts module, the values should be set to the last calculated values from the previous time step because the module temperature model in PVWatts accounts for transient heating/cooling of modules.

Best regards,
Paul.