A grid, in essence, is any combination of power sources, end customers, different wires to connect it together, and centralized controls to make it all work.
Typically a grid is made up of the following components:
- Generation sources (fossil fuels, nuclear, solar, wind, etc)
- High-voltage transmission lines to carry power long distances
- Distribution lines to reach individual customers
- Substations that integrate the transmission and distribution networks
A grid can be subdivided into smaller operating regions, whether that be for individual utility territories, multi-state competitive marketplaces, or other independent networks. Grids are also oftentimes layered — an individual utility grid that is also part of a regional market — and are typically linked together into larger interoperable systems.
In the continental US, we subdivide the entire network into three distinct grids — the Eastern Interconnection, the Western Interconnection, and the independent Texas Interconnection. Each of these grids operate independently of each other with limited sharing of power between them.
A ‘minigrid’ is a term used to quantify the size and scale of a grid, but otherwise has the same components described above, except most likely does not have any transmission lines used to move power long-distance since it has a smaller footprint. Minigrids typically stand alone and operate independently, but they can also be linked together into a network of minigrids similar to the US network of three ‘full-size’ grids.
There are often minor discrepancies between the particulars of these definitions between international groups and individual countries’ own terminology. These differences stem from how these different grids are deployed and the priorities and perspective of the organization’s making the designation.
The UN Framework Convention on Climate Change defines a minigrid as an independent network with a power rating below 15 MW (roughly 3,000 US homes), but that is not a hard and fast metric by any means. The more inclusive US definition of a minigrid is similar, but is not limited to being fully independent from other networks.
Minigrids are most often deployed to serve isolated or rural communities, remote industrial operations like mining, or small island populations where connecting to a larger grid is either technically impractical or too cost-prohibitive.
With this foundation of understanding in hand we can describe some of the other common types of grids, which are mostly defined in relation to this centralized grid concept.