Material Insights · Understanding the Material World

Distribution grids, mini-grids and interconnectors: How it works

From substation to meter, and solar mini-grids where wires end

What this tab covers How the energy actually moves, step by step: the science that makes it work and the engineering that makes it practical.

Distribution networks take power from high-voltage substations and deliver it at falling voltages along local lines to every meter. Mini-grids do the same job for a village or site with their own generation, and interconnectors join national grids so they can trade and back each other up.

Step by step

  1. Primary substationTransformers take power from the transmission grid and lower it to medium voltage, for example the 20 kV used across most of France's distribution network.
  2. Medium-voltage feedersOverhead lines or underground cables carry power through towns and countryside, with switchgear that can isolate faulty sections.
  3. Distribution transformerA pole-mounted or ground-mounted transformer near the street lowers the voltage again to the low voltage used by homes and shops.
  4. Service line and meterA short cable connects each building; a meter, increasingly smart or prepaid, records use for billing.
  5. Mini-grid alternativeWhere the main grid does not reach, a local solar-battery plant with diesel backup feeds its own small network serving a few hundred customers.
  6. InterconnectorAt borders, AC lines or HVDC links join national systems so surplus or cheaper power can flow where it is needed.

The science

Heat lost equals current squared times resistance, so voltage is kept as high as practical for as long as possible and lowered only near the customer. Low-voltage circuits carry high currents, so losses per kilometre are relatively high in this last stage. Transformers work only on AC, one reason distribution is AC. In a solar mini-grid, panels make DC, batteries store DC, and inverters convert it to AC for the local network.

The engineering

Distribution is the largest part of the grid by length: Enedis in France alone runs about 1.4 million km of lines. Networks are mostly radial (branching like a tree) so faults can be isolated, increasingly with automated switches, sensors and remote control. Third-generation mini-grids are privately run solar-hybrid systems with prepaid smart meters and remote monitoring, often designed to connect to the main grid later.

Key numbers

Enedis distribution network, France About 1.4 million km15 Mini-grids installed worldwide (about 2021) 21,557 in 131 countries and territories, serving over 48 million people7 Typical third-generation mini-grid 50 to 100 kWp solar, 200 to 500 kWh batteries, 200 to 800 customers7 European cross-border exchange capacity 116 GW in 202410 People without electricity About 750 million, about 80% in sub-Saharan Africa19

Sources

  1. Mini Grids for Half a Billion People: Market Outlook and Handbook for Decision Makers (2022 edition) World Bank ESMAP, 2022
  2. Money on the line: scaling electricity interconnection for Europe's energy future Ember, 2025
  3. Enedis and ABB partner on SF6-free switchgear Enlit World, 2025
  4. Building the Future Transmission Grid: Executive summary IEA, 2025