Microgrids

Microgrids have the ability to control and shape the amount of load it is drawing from the grid. With a higher number of distributed energy resources (DERs), there are certain voltage and power characteristics that must be maintained. Microgrids offer the ability to regulate these quantities as well as reduce or offset the amount of load presented to the supplying utility. These capabilities result in microgrids being able to support the utility during periods of heavy strain on the grid.

A key benefit of microgrids is that everything is local. There is no requirement to build out expensive transmission lines. The addition of localized energy generation to meet any incremental needs does not require any capacity upgrades to transmission feeders. This can be tremendously beneficial for growing communities. 

Microgrids in rural or remote locations are especially lucrative. By carefully designing the amount of local generation through the use of wind, solar, geothermal, or other alternatives, and coupled with adequately sized energy storage, one is often able to electrify rural communities with a reliable energy supply. 

The deployment of microgrids has a positive impact on the local workforce and the creation of jobs. Skillsets to operate and maintain a microgrid may lead to further job opportunities and the availability of energy, in turn, spurs economic growth.

Microgrids can be designed and operated to maximize the use of renewable resources. Their overall greenhouse gas emissions and other pollutants can be low while offering efficient, sustainable, and reliable energy. 

Substantial investment is needed to design, configure, and implement a microgrid solution. One must assess current energy needs as well as plan and anticipate for the growth in demand. Feasibility of adding local generation and/or storage must be considered and connectivity of the various distributed resources must also be planned. These considerations may increase the initial upfront costs for a microgrid deployment.

Communities that are considering microgrids often do not have the technical knowhow and must rely on external expertise to help them design and operate these systems. Over time, communities may develop the necessary skillsets to own and operate their microgrids. 

The regulatory frameworks for microgrids are only emerging. Mechanisms to regulate microgrids are nascent. Tariff structures, interconnection process, ownership regimes, ancillary services to the grid, among many other considerations are currently underdefined. These lead to complicated scenarios ownership and operating scenarios

Microgrids offer a lot of flexibility; however, depending on how a microgrid is designed, adding more energy resources, such as more generation, storage, or loads can become cumbersome. Sometimes, the amount of growth needs in a deployment can be underestimated resulting in a choice of components that may not scale up very well.

A systems-scale analysis is usually undertaken to cover microgrid performance expectations and an engineering design establishes its stability and dynamic characteristics. The nature and diversity of existing components such as existing PVs, batteries, electric vehicles, water heaters, heating and air conditioning equipment, and lighting and their times of use are understood. Any existing generation assets such as diesel generators and photovoltaic solar arrays are cataloged.

Various modeling tools are used to run through scenarios and a design that meets the needs of the community is developed. This design may include the addition of additional components within the microgrid. 

A community may have various existing legacy devices that still have not reached their end-of-life. Many such devices can be retrofitted to become ’smart’ and participate in the control mechanisms of the microgrid deployment.

Control strategies in microgrids play a vital role in ensuring its smooth operation. There may be various configurations for these controls such as hierarchical, distributed, or hybrid control strategies. The control system also interfaces with the utility grid at one or more points of common coupling (PCC). The controller typically serves as the arbiter to meet energy (or price) optimization goals, scheduling of the activation of various devices in its control, and gracefully degrading the level of service when conditions are suboptimal. The controller hardware is also responsible for switching seamlessly between modes of operation, such as when it gets disconnected from the grid and when it reconnects. 

Because of the nature of distributed energy resources with a microgrid, there may be an increased need for development and implementation of protection modes for fault conditions. While the field of protection has been studied and well understood for power systems, some of their specific applications for microgrids are being actively researched.

It is apparent that the size, number of devices, the total energy generated or served, and the variety of devices add to the level of complexity of a microgrid. Their configuration and coordination using controls can also become complex. The S&C Electric Company presents the following chart to appreciate increasing levels of microgrid complexity.

A microgrid designed for an individual customer (e.g., a data center) connected to a central utility system for enhanced service quality and resiliency. Microgrid assets would be located “behind” the utility meter. Such microgrids can be owned and operated by the customer, utility (i.e., under a fee-for-service arrangement), or a third party microgrid developer, or some combination thereof.

A microgrid serving a single- or multi-owner contiguous set of facilities (i.e., a campus) typically behind-the-meter of a utility grid. These systems may serve customer load on a full-time basis and/or be designed to provide back-up islanding services. Department of Defense bases, universities and airports are common sites for campus-level microgrids. Utilities may or may not be involved in campus-level microgrid operation beyond the point of common coupling.

A microgrid that serves one or more customers designed specifically to provide uninterrupted service to critical infrastructure and vitally important community assets. Government- or ratepayer-funded investments in these microgrids are common due to the social values associated with maintaining critical services during power outages.

A fully operational microgrid, sometimes referred to as a mini-grid, serving an electrically isolated community without connection to a larger electricity grid. Remote microgrids are a “one-stop shop” for all services, from provision of energy to maintaining stability and power quality. These are already common for service to islands and geographically remote/rural settings.

A microgrid serving energy to two or more different properties nested within the service territory of a utility. Community microgrids can operate independently from the grid but are otherwise connected to the utility network through a point of common coupling (PCC). They are a means to increase local energy independence and resilience.

A type of community microgrid operating a feeder segment or substation balancing area to provide non-wires alternative services as a primary use, while simultaneously offering partial or full resiliency services to customers during utility grid outages.

Feeder segments or substations configured to be islandable microgrid hubs with all hardware installed except generation. Portable generators are staged at islanding point by truck, rail, boat or helicopter, and configured to plug into feeder segment or substation microgrid hubs when needed. Temporary microgrids are a resilience-only application (i.e., no value stacking opportunities) but do provide flexibility for where microgrids can be quickly deployed and is thus a form of “flexible resilience.”

A prospective future microgrid application in which sub-service-territory balancing areas, substations, feeder segments, or transformers act as clustered and nested microgrids, maximizing reliability and resilience among them. Most likely, this use case would consist of a series of community microgrids that also provide NWA characteristics in order to justify their investment.

Utilities sometimes receive special regulatory approval to build-own-operate microgrids because of their novel and unique nature for the jurisdiction and the need to foster learning in the utility and regulatory environment. Realistically, a utility pilot will attempt to pursue one of the above use cases.