13.6: Microgrid Technology
- Page ID
- 41980
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A microgrid is a collection of generation resources, loads, and other DER that presents itself to the grid as a single controllable entity in order to (1) provide ancillary services to the grid in support of grid operations and (2) separate from the grid in the event of a grid outage and operate in an islanded mode. As shown in Figure 13.6.1, the normal operation of the microgrid is “grid-connected.” In this mode, the grid provides power when microgrid generation resources are unable to alone support the load. In this mode, the microgrid is also able to provide resources to the grid, these are called ancillary services. These ancillary services include local load and generation management wherein the microgrid can shed or add loads and can reduce or increase generation in response to signals from the utility or ISO when the grid itself is experiencing a local deficit in generation resources (for example, no wind to drive wind generators, or no sun to drive solar generators) or a local excess in generation (for example, generation from renewable resources that exceeds existing loads). Overall, microgrids reduce the impacts associated with intermittent and flexible resources on the grid.
Microgrids also increase the reliability and resiliency of the community served by the microgrid and the community adjacent to, but outside, the microgrid. In the case of a grid outage, the microgrid can seamlessly disconnect and remain in operation and maintain the microgrid community with electricity. While some loads may have to be shed to match the load to the microgrid generation resources, loads critical to the operation and safety of the microgrid community can be retained intact. An islanded microgrid can provide services such as shelter and food to the adjacent community. In principle, an islanded microgrid can provide electricity to grocery stores, fire stations, gasoline stations, and hospitals in the adjacent community and can assist the utility in restarting the grid.
The potential of microgrids is driving the evolution of microgrid controllers to communicate with loads, generation resources, and other DER (for example, energy storage systems) and thereby (1) optimize the grid-connected microgrid performance, (2) provide ancillary services, (3) support engagement in the electricity markets, (4) manage seamless islanding and reconnection, and (5) provide emergency services to communities adjacent to the microgrid.* In addition, the microgrid controller must communicate in the future with the utility, ISO, and other microgrids to provide (or buy) the services outlined.
A nanogrid (Figure 13.6.2) is a controllable grid within a microgrid, typically a smart building (equipped with a building management system, for example) that is capable of providing ancillary services to the microgrid and separating from the microgrid (retaining building critical loads in service) in case of a microgrid outage, and of managing DER, lighting, and plug-in loads within the nanogrid.
As the population of microgrids increases and the technology evolves, other possibilities emerge, including the following:
- Microgrids could become part of the hydrogen economy, not only utilizing hydrogen for generation and fueling FCEVs, but also generating hydrogen for use within the microgrid and potential export from the microgrid (Figure 13.6.3).
- Microgrids could operate at a frequency different from the grid, connecting to the grid through a power electronics connection, thereby eliminating the need to synchronize with the grid.
Nanogrids also have the potential to transform the manner by which electricity is distributed in a building. In addition to alternating current (AC), electricity can be distributed as direct current (DC), serving directly DC loads (such as computers, servers, and LED lighting). Since evolving distributed generators produce DC (for example, fuel cells, photovoltaic panels), the inversion of DC to AC and the rectification of AC to DC and the consequent losses of up to 20% can be avoided, as discussed in Section 13.1.
*Emergency services refers to services provided during a natural disaster or other unforeseen occurrences. These services include energizing critical loads such as hospitals, shelters, and other critical facilities, as well as providing mobility to the community through providing electricity to PEVs and hydrogen to fuel cell vehicles.