LONDON — For nearly a century, wealthy countries have relied on just one model of power distribution: sending electricity over huge transmission grids from big generating plants to customers in their homes, offices and factories.

That may be starting to change. Renewable-energy technologies like solar and wind power, which in many countries have begun to shake up the mix of energy sources, are now also challenging the traditional distribution system.

Advocates of a decentralized approach, known as distributed generation or distributed energy, envision a day when grids will no longer be one-way systems.

Thousands of small generators, including rooftop solar panels and facilities that extract energy from garbage or sewage, could feed into the system, replacing or complementing big coal, nuclear or natural gas plants, they say.