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Will the real microgrid please stand up? (What is a microgrid and why should I care?)

by Marilyn Walker, Ph.D. on October 29, 2012

This is the second post in the HOMER Energy Microgrid Learning Series, designed to help the layperson understand what microgrids are and why they will soon be a household word. Microgrids are independent energy systems that provide grid backup or off-grid power. A slightly more technical definition is a local power network that uses distributed energy resources and manages local energy supply and demand.

To start with the very basic, the two key pieces to the word are “micro” (small) and “grid” (an interconnecting system of links). Microgrid is a fairly new word coined by the power industry to refer to small power systems that have some of the same characteristics of the greater power grid.

So, a microgrid is a special case of a power grid. In order to be a power grid, the following must be present:

  1. At least one way to generate electricity. This can be a diesel generator, a wind turbine, solar photovoltaic panels, or something else. Because this is a grid, i.e., it is interconnected, there can be more than one form of generation.
  2. If there is more than one form of generation, then some type of control is needed so that the parts work well together.
  3. A way to distribute the electricity where and when it is needed.
  4. A means to deal with excess generation – what happens when more electricity is generated than is needed? This is often some kind of storage, such as a battery.
  5. There needs to be one or more electric loads, i.e., consumers of the electricity. These are generally called “loads” or “load” in industry jargon.

So – the key pieces are generation, control, distribution, storage, and load, linked together in a network. There can be multiple generation sources, multiple storage mechanisms, and multiple loads – the grid makes that possible. But there is generally only one point of control. This diagram shows a microgrid that has multiple generation sources serving one load (a single building):

 

A microgrid combining renewable resources (solar and wind) with a diesel generator, a battery, and controls. (Image courtesy ZBBEnergy.com, modified from original.)

 

The “micro” part of the equation means simply that it is “smaller than the utility-scale grid”. It could be anything from a single building to an island or isolated village of substantial size. In future entries we’ll talk more about how size impacts what is or is not a microgrid.

There has been considerable “debate” about what should or should not be called a microgrid, and it is this variability that we will cover in the rest of this series. There is no single size or configuration for microgrids – they can range over many orders of magnitude in size. They can be simple or complex. They can be attached to a power grid or completely independent from it.

In order to understand why microgrids are so important and what problems they solve, it’s necessary to understand how the power grid works. So that is our next entry – a quick primer on how the grid works.

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