Use the Solvent Excluded Surface dialog to generate Connolly surfaces. The surfaces can be generated with an internal algorithm which generates a point-cloud approximation or with the external msms program by M.F. Sanner.

To generate the surface simply press on the Generate button.

To remove the surface press on the Remove button which is enabled only after the surface has been generated.

Van der Waals surface can be generated by choosing a radius of zero.

Note: using a radius of 0.0 doesn't seem to work, use 0.001 instead if 0.0 does not produce the Van der Waals surface.

Molekel 5.1 or newer support mapping of electrostatic potential read from Gaussian .cube grid data; in case you load a molecule from .cube files you'll have the option to color-code Solvent Excluded Surfaces with values read from grid data, in this case a Map MEP(From Grid Data) label will appear close to the map MEP checkbox.