How Microgrids and DERs Can Maximize Sustainability and Resilience in Industrial and Commercial Facilities

Distributed energy resources (DERs) like solar energy, wind energy, combined heat and power (CHP), battery energy storage systems (BESS), and even conventional generators can be significant contributors to improvements in sustainability and resilience in commercial and industrial facilities, especially when combined into a microgrid using an automated control system to intelligently coordinate and manage energy generation, flow, storage and consumption.

To maximize microgrid environmental and economic benefits, the controller must balance the operation and integration of DERs in real time, manage smart loads like lighting, heating ventilation, and air conditioning (HVAC) systems, electric vehicle (EV) charging and information technology installations, use historic demand information to project future load profiles, provide safe and efficient connections to the utility grid and provide support for demand response functions with real-time energy pricing data.

This article reviews the elements that comprise a microgrid, looks at microgrid architectures, presents an overview of IEEE 1547, which establishes requirements for interconnection of DERs, and IEEE 2030 that provides a comprehensive technical process for describing the functions of a microgrid controller, then considers how microgrid controllers can enhance sustainability, resilience, and economic benefits, and closes with a brief overview of cyber security concerns for microgrids.

What does it take to make a microgrid?

Microgrids are diverse in their implementations and components. To discuss how microgrids and DERs can maximize sustainability and resilience, it’s best to start with a definition and a few examples of microgrid components and architectures. The U.S. Department of Energy (DOE) defines a microgrid as “a group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that act as a single controllable entity with respect to the grid. A microgrid can connect and disconnect from the grid to enable it to operate in grid-connected and island-mode.”

While the definition of a microgrid is straightforward, there’s a range of microgrid categories, operating modes, and possible subsystems to choose from when building a microgrid, and realizing a microgrid’s maximum sustainability and resilience involves numerous architectural and operational choices. Automation is an important consideration. Examples of automated subsystems include (Figure 1):

• Generation within the microgrid, including a diverse range of DERs and CHP
• Power distribution networks
• BESS
• Loads like HVAC systems and machines and motors in industrial facilities
• Managing electric vehicle charging and vehicle-to-grid (V2G) connections
• Microgrid controllers and switchgear
• Interconnects to the utility grid for grid-connected installations

Figure 1: Microgrids can include various DERs, CHP, and loads. (Image source: Schneider Electric)

Microgrid categories

Microgrids can be categorized by whether they are off-grid or grid-connected:

Off-grid facility-led is the most common category. Use cases include remote areas not served by the commercial utility grid, like mines, industrial sites, mountain homes, and military bases.

Off-grid community-led are also found in remote locations. Use cases include remote villages, islands, and communities. While facility-led microgrids are controlled by a single entity, community-led microgrids must cater to the needs of a group of users. They can require more complex command and control systems.

Grid-connected facilities have a single owner and are used to improve reliability in areas where the main grid is unreliable, and power is necessary, or in cases where there are economic incentives for sheddable loads and other services from the microgrid owner. Use cases can include hospitals, data centers, continuous process manufacturing plants, and other high-availability buildings.

Grid-connected communities have multiple energy users and producers connected to the main grid and managed as a single entity. Use cases include business or university campuses, villages, and small cities. These can have a diversity of energy users, producers, and storage facilities and can be the most complex to control.

Sometimes microgrids are islands

In addition to discussing the components of a microgrid, the DOE definition refers to microgrid operation in “both grid-connected and island-mode”. The definitions of those modes are straightforward, but implementation is more complex and is addressed in some IEEE standards.

IEEE 1547-2018, Standard for Interconnecting Distributed Resources with Electric Power Systems, details technical requirements for the interconnection and interoperability of DERs with the power grid. IEEE 1547 is an evolving standard. Earlier versions of IEEE 1547 were designed for low DER penetration levels and did not consider the potential aggregate regional impact of DERs on the bulk power system. IEEE 1547-2018 added stricter requirements regarding voltage and frequency regulation and ride-through capability to help the reliability of the transmission system. More recently, the 1547a-2020 amendment was added to accommodate abnormal operating performance.

IEEE 2030.74 describes the functions of a microgrid controller in terms of two steady state (SS) operating modes and four types of transitions (T) (Figure 2):

• SS1, steady state grid-connected mode, has the microgrid connected to the utility grid. The controller can use the components in the microgrid to provide services like peak shaving, frequency regulation, reactive power support, and ramp management to the grid.
• SS2, stable island or “islanding” mode is when the microgrid is disconnected from the utility grid and is operating in isolation. The controller is required to balance the loads and microgrid generation and energy storage services to maintain stable microgrid operation.
• T1, refers to a planned transition from grid connected to steady state island mode. Even when the utility grid is available, there may be economic or operational incentives to switch to island mode. In addition, this mode can support testing of microgrid operation.
• T2, is an unplanned transition from grid connected to steady state island mode. This is analogous to the operation of an uninterruptible power supply in a data center and is often used when the main grid fails. The microgrid seamlessly disconnects and operates as an independent power network.
• T3, refers to steady-state island reconnection to the utility grid. This is a complex technical procedure with a ‘grid-forming’ generator on the microgrid sensing the frequency and phase angle of the grid power and exactly matching the microgrid with the main grid before reconnecting.
• T4, is a black start into steady-state island mode. In this case, the microgrid has gone down and must be isolated from the utility grid and restarted in island mode. This situation could occur because of an unexpected outage that the microgrid controller cannot handle using a T2 stable transition, or it might be necessary if the island does not have sufficient generation or energy storage reserve to continue to supply all the loads and must shut down all nonessential loads before bringing the generator online. In addition, any BESS on the microgrid must be at least partially recharged before being reconnected.

Figure 2: IEEE 2030.74 requires microgrid controllers to accommodate two steady-state conditions and four types of transitions between those states. (Image source: National Rural Electric Cooperative Association)

Implementing microgrids

There are almost as many combinations of DERs and loads as microgrids, but automated controllers and switchgear are common elements. In large microgrids like the one illustrated in Figure 1 above, they are often separated into a centralized control room, distributed switchgear for DERs and loads, and for grid-connected designs, a substation that serves as the switchgear between the microgrid and the utility grid.

Microgrid controllers need information, and to maximize resilience and sustainability, they need to be quick. The controllers use a network of sensors to monitor the functioning of the DERs and loads in real-time. For grid-connected microgrids, the controller also monitors the status of the local utility grid. Should any anomaly occur, the controller responds in milliseconds and sends a command to the associated DER, load, or switchgear.

Switchgear sizes range from a few kW to multi-MW and need to respond to controller demands in a few milliseconds or risk a serious fault condition. Some switchgear feature smart circuit breakers that operate autonomously to provide an additional layer of protection.

For smaller installations, the controller and switchgear can be combined into a single piece of equipment, sometimes referred to as an energy control center (ECC). ECCs are available pre-wired, assembled, and factory tested. ECCs simplify and speed up the installation of microgrids and can manage multiple energy sources, including grid power and DERs with prioritized loads. For example, Schneider Electric offers the ECC 1600 / 2500 line of ECCs for building-scale microgrids (Figure 3). Some features of the ECC 1600 / 2500 line include:

• Configurable to order with power ratings from 100 to 750 kW and can be optimized for existing or new buildings
• Works with multiple DERs like PV, BESS, wind, gas, and diesel generators
• Controller enables resilience during outages, including using PV with an anchor resource such as a standby generator or BESS
• Automated intelligent metering gives insights into power quality, energy usage, and DER production
• Switchgear with a 1,600 to 2,500 A power distribution bus
• Cloud-based analytics to maximize resilience and return from investment from DERs

Figure 3: ECCs combine the microgrid controller (left) and switchgear (right) into a single piece of equipment. (Image source: Schneider Electric)

Safe and secure energy

Cyber security is an important aspect of energy security and resilience. The International Energy Agency (IEA) defines energy security as “the uninterrupted availability of energy sources at an affordable price”. Microgrids can significantly contribute to ensuring low-cost, secure, and resilient energy supplies.

Communication is an essential element of microgrids. This means communication to the cloud, and possibly with the local utility grid, to optimize performance. In addition, the various DERs and loads that comprise a typical microgrid come from different manufacturers and employ heterogeneous communication protocols and technologies. Internet connectivity and wireless technologies like Wi-Fi are found in almost all microgrids and can be essential for maximum benefits. They also support ancillary functions like gathering weather forecasts and real-time fuel and energy prices.

Ensuring cyber-security is complex. In addition to secure hardware, policies, procedures, and people are required to address cyber vulnerabilities that can enable attackers to access sensitive networks and data and even manipulate control software resulting in damaged microgrid operation. Terrorists are only one concern; there are also competitors or unscrupulous employees to consider. Operator errors can occur, networks can have unknown loopholes due to outdated software, and so on (Figure 4). Cyber security can’t be an afterthought. It must be designed into all aspects of microgrid hardware, software, and processes from the beginning to be effective.

Figure 4: Vulnerabilities from people, processes, and holes in physical security can present microgrid attack vectors. (Image source: Schneider Electric)

Summary

Microgrids integrate numerous DERs and loads into a single system to maximize energy sustainability and resilience. Several microgrid architectures can be used to support specific energy and connectivity needs. The increasing number of microgrids and the growing penetration of DERs has resulted in an evolution in the IEEE 1547 interconnection standard and is driving an increased focus on microgrid cyber security.