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According to the U.S. Department of Energy,1 a microgrid is a group of interconnected loads and distributed energy resources (DER) 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 either grid-connected or island mode. Additionally, the microgrid’s operational controls need to be fully coordinated when connected to the main power grid or while islanded, requiring additional equipment, communications and control applications. Installing only a backup diesel genset at a premise is not technically considered a microgrid. However, significant opportunities exist to deploy DERs integrated to the grid while not technically comprising a microgrid.
There are three main types of microgrids: remote, grid-connected and networked.2
Also known as off-grid microgrids, they are physically isolated from the utility grid and operate in island mode at all times due to the lack of available and affordable transmission or distribution (T&D) infrastructure nearby. For these remote scenarios, renewables, such as wind and solar, typically provide a more economic and environmentally sustainable DER solution for the microgrid operator. Additionally, many remote microgrids are considering battery energy storage systems for backup power in lieu of conventional generators.
These microgrids have a physical connection to the utility grid via a switching mechanism at the point of common coupling (PCC), but they also can disconnect into island mode and reconnect back to the main grid as needed. In grid-connected scenarios, a microgrid that is effectively integrated with the utility service provider can provide grid services (e.g., frequency and voltage regulation, real and reactive power support, demand response, etc.) to help address potential capacity, power quality and reliability, and voltage issues on the utility grid.
In islanded scenarios, local voltage and frequency controls are required within the microgrid and can be provided by energy storage (e.g., battery, flywheel) or a synchronous generator (e.g., CHP, natural gas, fuel cell diesel). Due to its ability to perform multiple functions for grid services and emergency backup power, battery energy storage systems have been gaining popularity for microgrids that need to operate in both grid-connected and island modes. When serving a relatively small geographic area, grid-connected microgrids demonstrate economic viability for educational campuses, medical complexes, public safety, military bases, agricultural farms, commercial buildings and industrial facilities.
These systems, also known as nested microgrids,3 consist of several separate DERs and/or microgrids connected to the same utility grid circuit segment and serve a wide geographic area. Networked microgrids are typically managed and optimized by a supervisory control system to operate and coordinate each grid-connected or island mode at different tiers of hierarchy along the utility grid circuit segment. Community microgrids, smart cities and new utility adaptive protection schemes (e.g., closed-loop self-healing) are examples of networked microgrids.
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1 https://microgridknowledge.com/nested-microgrid/
2 https://www.energy.gov/sites/prod/files/2018/12/f58/remote-microgrids-dan-ton.pdf
3 https://microgridknowledge.com/nested-microgrid/
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This article was written by Dr. Stuart Laval.
Dr. Laval is a member of Duke Energy’s Emerging Technology Office, where he leads the development of grid-edge operational technologies and pioneering utility interoperability standards. He currently serves as the co-chairman of the Open Field Message Bus (OpenFMB) task forces at the UCA International Users Group (UCAIug) and North American Energy Standards Board (NAESB). Dr. Laval has more than 15 years of experience in the development of over 30 technology solutions in electric utility power systems, telecommunications and power electronics. He holds a bachelor’s degree and master’s degree in electrical engineering and computer science from MIT, an MBA from Rollins College, and a Ph.D. in industrial engineering from the University of Central Florida.
6 Things to Know Before Your Microgrid Installation
Microgrids are an excellent way to ensure your facility or campus never loses power, even when your main grid is down. After you reach out to a microgrid installer, they can help you develop a personalized microgrid solution designed to generate power for you and reduce your dependence on your local utility grid. If you’re considering setting up a microgrid at your business, campus, or facility, take a moment to learn more about some of the six most important things to know about microgrid installation.
While a somewhat misunderstood term, a microgrid system refers to a decentralized power plant that can work autonomously to generate energy on-site or in conjunction with an existing electric grid. Microgrids contain one or more types of distributed energy resources that produce power. For example, a microgrid may feature wind turbines, backup generators, fuel cells, and/or solar panels. These distributed energy resources are managed via control systems and cutting-edge monitoring systems, and many recent microgrids feature batteries for energy storage.
Typically, microgrids are used by industrial parks, government buildings, military installations, data centers, retail businesses, campuses, and medical facilities to generate and store energy. Since these decentralized power plants can work independently of an existing power grid, they allow organizations to deliver important services even when a centralized power grid is down. With an independent microgrid, organizations can rest easy knowing they’ll still have energy despite the status of their local energy grid.
Unfortunately, there’s often some confusion about what a microgrid actually is. Due to this confusion, it’s important to know what they aren’t to ensure you don’t invest in a system that turns out not to be a microgrid. After all, you probably won’t want to install a system that turns out to not provide continuous power when your main grid is down.
For example, even though microgrids often use solar energy, stand-alone solar and storage systems are not microgrids, as they don’t ensure you have electricity all day and night. During a power outage, a microgrid’s controller can disconnect the microgrid from the main grid to make sure you have power until the outage is over. With just a single solar energy system, there’s no guarantee you’ll have power throughout the entire outage.
Virtual power plants (VPPs) and distributed energy resources management systems (DERMS) are also commonly confused with microgrids. While VPPs can use several distributed energy resources like microgrids, they’re designed to solely provide a main grid with power. Additionally, DERMS are similar to microgrids because they manage distributed energy resources. However, a DERMS refers to a software platform designed to view and manage distributed energy resources, and it won’t provide power during an outage or cut itself off from a main grid.
Unlike simple backup power systems, microgrids feature bumpless backup power. With bumpless backup power, your microgrid’s controller can switch from manual mode to automatic mode or vice versa without disrupting your processes. During a bumpless transfer, your controller’s output will stay the same while switching to its automatic or manual mode, preventing process issues and damage to actuators.
One of the major advantages of microgrids is that they can integrate several different distributed energy sources. For instance, a microgrid can draw power from wind turbines, solar panels, diesel-powered generators, batteries, and the main utility power grid. These multiple energy sources allow microgrids to provide power even when one energy source is down.
Typically, basic microgrids will contain a natural gas or diesel generator for energy creation but won’t feature a renewable energy source. In contrast, advanced microgrids usually integrate diesel or natural gas generators with one or more renewable energy sources. Since microgrids can connect to a utility power grid or separate themselves from it, they can also supply your facility with power from your local grid when it’s operational.
If you’re worried a newly installed microgrid might not meet your future energy demands, you’ll be happy to know that a microgrid can scale with your needs. While you might start with generators and a solar power source, microgrid installers can add new distributed energy resources to your grid to provide more power once you need it.
People often think microgrids will be too expensive to install and maintain. However, they can be quite cost-effective, as some states offer incentives for organizations that install microgrids, and you can usually find many financing options. Additionally, if you need more load capacity than your existing utility infrastructure can provide, installing a microgrid is often much less expensive than upgrading your utility infrastructure.
Some microgrid companies also offer energy-as-a-service plans that require minimal to no upfront expenses. Instead of owning the grid yourself, the microgrid company will own and charge you per kWh, meaning you’ll still have your backup energy source without the higher costs of owning a microgrid yourself.
While you might think microgrids are only beneficial in emergencies, they could potentially save you money in electricity costs. Since microgrids can be customized to your particular facility, they can maximize your organization’s energy efficiency and keep monthly energy costs lower.
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