Understanding Micro Grids

The jury is out on the definition of a micro grid

The definition of a micro grid changes depending on the project constraints in which it is used. The term gets thrown around with different context and a new definition almost every time I hear it. I’ve seen the differing points of view and it is about time for a consensus. We all need to be on the same page using the same terminology.

After Hurricane Sandy, we might be discussing a grid-tied system with large battery storage and smart electronics that can provide power during service outages. In developing countries, we might be discussing an off grid system with pay-as-you-go meters and less than 100 kilowatts of solar PV. On a university campus, we might be discussing combined heat and power for a group of buildings.

Technically these are all micro grids, but micro grids of different types. The best but most broad definition I have seen is from the Microgrid Institute:

A micro grid is a small energy system capable of balancing captive supply and demand resources to maintain stable service within a defined boundary.

Key Characteristics of a Micro Grid:

  1. Connecting to the traditional grid is optional.
  2. Resiliency, reliability, and sustainability are the core responsibilities.
  3. Backup for all system loads, not just the critical loads.
  4. Modern technology is needed to optimize energy production and usage.

According to the US Department of Energy:

A microgrid is a local energy grid with control capability, which means it can disconnect from the traditional grid and operate autonomously.

According to the Rocky Mountain Institute:

Micro grids are subsets of the greater grid and usually include their own generation (such as photovoltaics, wind turbines, and fuel cells), their own demand (lights, fans, televisions, computers, etc.) and often the ability to modulate it to match price and priority, and perhaps even storage capability (such as batteries or the distributed storage in electrified vehicles). What makes the micro grid unique is that it intelligently coordinates and balances all these technologies.

According to the Microgrid Institute:

A micro grid is a small energy system capable of balancing captive supply and demand resources to maintain stable service within a defined boundary. Micro grids are defined by their function, not their size. Micro grids combine various distributed energy resources (DER) to form a whole system that’s greater than its parts.

Most micro grids can be further described by one of five categories (as defined by Microgrid Institute):

  • Off-grid micro grids including islands, remote sites, and other micro grid systems not connected to a local utility network.
  • Campus micro grids that are fully interconnected with a local utility grid, but can also maintain some level of service in isolation from the grid, such as during a utility outage. Typical examples serve university and corporate campuses, prisons, and military bases.
  • Community micro grids that are integrated into utility networks. Such microgrids serve multiple customers or services within a community, generally to provide resilient power for vital community assets.
  • District Energy micro grids that provide electricity as well as thermal energy for heating (and cooling) of multiple facilities.
  • Nano grids comprised of the smallest discrete network units with the capability to operate independently. A nano grid can be defined as a single building or a single energy domain.

The most challenging part of our micro grid future is that it must be cheaper than the status quo.

There are some situations that micro grids will be implemented in an area for the first time, such as in developing countries; and other times, it will be introduced to replace the aging infrastructure and outdated equipment. The old generation will be butting heads with the new generation. SolarCity is proactively warning and preparing the utilities of the world with their Grid Engineering Solutions.

Read more from Joe O’Connor, author of Off Grid Solar: A handbook for Photovoltaics with Lead-Acid or Lithium-Ion batteries.

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