What is the difference between +Web and Power Line Communication level (bars)?

For Envoys with an LCD Display

A "+ Web" displayed in the Envoy indicates that the Envoy is online and communicating with the Enlighten servers. The number of bars displayed is unrelated to the strength of the Internet connection between the Envoy and Enlighten. (Note that the newer Envoy-S and IQ Envoy models do not use an LCD display.)

Instead, the number of bars displayed on the Envoy LCD display indicates that the signal strength of the communication between the Envoy and the Microinverters. The Envoy and Microinverters communicate over the AC power lines in the home. Power line communications is separate from Internet communications.

For more information, view the Envoy Installation and Operation Manual (LCD Envoy).