Since the original, hyperbolic article is no longer linked, This post is to give some technical background on home electrical systems in the US for understanding of the underlying considerations of how secondary home power sources should operate. First two points of context:
1. The United States does not have a uniform electrical code, but instead has a document called the National Electrical Code (NEC) published regularly by the National Fire Protection Association (NFPA) as NFPA 70. The most current version of the code is from 2017. Looking inside out, the NEC stops at the main electrical service input to e.g. a house, and from that point a different code, called the NESC, takes over.
2. There are a wide range of variants of the NEC that are codified to force of law throughout the United States. And states/cities/municipalities can exempt and/or add to their preferred version. Here inside City of Atlanta boundary, for instance, we are on the 2014 version of the code. But even then there are different versions of the code in force at different locations in the multiplex.
---
With the caveats that not everything below is 100% uniform everywhere in the US, here is how wiring in US homes generally works. There's a few steps here, but it should all make sense:
A. There is a stepdown transformer with a "center tapped" secondary configuration. The end result of this is that homes are fed with two energized conductors ("hots") and a "grounded" conductor colloquially referred to as the "neutral." The two energized conductors are 240 Vrms apart, and each energized connector is 120 Vrms to the neutral (i.e. grounded conductor). Hold the idea that these three wires terminate on the incoming side of the main panel for items B, C, and D.
B. The wall outlet in a typical US house, colloquially called an "Edison" receptacle has three conductors. Those are an energized conductor (hot) the grounded conductor (neutral), and the "Equipment Grounding Conductor" (EGC). The latter is a green wire commonly referred to as "ground." Under normal conditions the EGC (ground) carries no current, because it is not a part of the electrical circuit between hot (energized) and neutral (grounded) connectors.
C. Now imagine that you have a wiring problem inside your table saw, and as a result the outer surface of that saw becomes energized. That surface is "bonded," i.e. conductively connected, to the EGC (ground). So if the surface has suddenly has a voltage on it, a large current then flows back through the EGC to the main panel. This is because the EGC is a low resistance path. This sudden surge in current causes the OCPD (i.e. "circuit breaker") to open. This disconnects the energized conductor (hot) feeding the table saw.
D. At the main panel, and only at the main panel, the EGC (ground) is connected (bonded) to the neutral (grounded conductor). This is so that the current from the EGC has a return path. In this case it goes equipment fault -> EGC -> EGC to neutral bond in main panel -> neutral coming into main panel from street -> center tap of secondary on the outside pole transformer. The winding of the utility pole secondary then completes the circuit with low resistance, insuring the OCPD (breaker) opens.
E. Note that neither the main panel "grounding/earthing," technically called the "grounding electrode conductor (GEC), nor any similar grounding/earthing (i.e. connection to physical earth) of the center tapped neutral at the utility pole play a role in the low impedance path for current that opens the circuit breaker. In fact, the earth is specifically excluded as a "ground fault current return" path by NEC 250.4(A)(5).
F. Any utility is concerned with essentially two things when it comes to secondary power at the house: 1)Feeding electricity back to the grid while their workers are making repairs/upgrades. 2)maintaining a singular low impedance "ground fault current return" path in the home at the main panel electrical service entrance.
G. Point F is why there are subtleties about what can be tied to the grid, and how the secondary "renewable generator" must behave in the event that it is exclusively providing power while the utilities' transformer is physically disconnected from the residence at the service entrance.
---
Beyond points F and G are lots of subtleties around sub panels, secondary current return paths, GFCIs, "floating neutral" generators, transfer switches, ground field impedances, etc. It is a surprisingly big topic, but I'm happy to try to answer specific questions.