Impacts of external shading in EnergyPlus are set using the Solar Distribution input field of the Building object. You would want to set this to "FullExterior" at a bare minimum to account for how external shading surfaces affect solar gains on other surfaces, but there are other options to account for beam radiation distributed on internal surfaces and external reflections as well. If this field is set to "MinimalShadowing" EnergyPlus will calculate the incident solar radiation on the PV surface correctly, but then assume that the building surface behind will also receive the same amount of incident solar radiation.

In OpenStudio, you can change this input field under the Simulation Settings tab, then expanding the Simulation Control area. Reference the screen shot below.

To model the electricity generation of the PV array, you can look at Unmet Hours posts HERE and HERE

OpenStudio does now directly support OpenStudio in the SketchUp plugin using the "Add Photovoltaics" user script under "Add or Alter Model Elements".

OpenStudio lets you assign PV to base or shading surfaces. Currently if you want to model it as detached PV vs. building integrated you can use an offset shading surface. If you don't mind writing an EnergyPlus measure you can also model it as a vented cavity. That will more accurately model the interaction between the PV and the building roof, vs, just shading it.

Here is the before image with the user script dialog displayed. Before you call the script select the surfaces you want to apply it to.

Here is the after image. A texture is used to identify where PV is associated with surfaces.

The standard reporting measure will display a power generation table when PV is used in the model.