How Microgrids Work? - Types and Examples
Microgrid equipment at the National Wind Technology Center in Colorado. | Photo courtesy of the National Renewable Energy Lab.
What is a Microgrid?
A microgrid is a local energy grid with control capability, which means it can disconnect from the traditional grid and operate autonomously.
How does a Microgrid Work?
To understand how a microgrid works, you first have to understand how the grid works.
The grid connects homes, businesses and other buildings to central power sources, which allow us to use appliances, heating/cooling systems and electronics. But this interconnectedness means that when part of the grid needs to be repaired, everyone is affected.
This is where a microgrid can help. A microgrid generally operates while connected to the grid, but importantly, it can break off and operate on its own using local energy generation in times of crisis like storms or power outages, or for other reasons.
A microgrid can be powered by distributed generators, batteries, and/or renewable resources like solar panels. Depending on how it’s fueled and how its requirements are managed, a microgrid might run indefinitely.
How does a Microgrid Connect to the Grid?
A microgrid connects to the grid at a point of common coupling that maintains voltage at the same level as the main grid unless there is some sort of problem on the grid or other reason to disconnect. A switch can separate the microgrid from the main grid automatically or manually, and it then functions as an island.
Why would a Community choose to Connect to Microgrids?
A microgrid not only provides backup for the grid in case of emergencies, but can also be used to cut costs, or connect to a local resource that is too small or unreliable for traditional grid use. A microgrid allows communities to be more energy independent and, in some cases, more environmentally friendly.
How Much can a Microgrid Power?
A microgrid comes in a variety of designs and sizes. A microgrid can power a single facility like the Santa Rita Jail microgrid in Dublin, California. Or a microgrid can power a larger area. For example, in Fort Collins, Colorado, a microgrid is part of a larger goal to create an entire district that produces the same amount of energy it consumes.
What are the Different Types of Microgrids?
Two key types of microgrids can be distinguished, and two other related types of power systems apply very similar technology.
- Customer microgrids or true microgrids (µgrids) are self-governed, and usually downstream of a single point of common coupling (PCC). Many of the most well known demonstrations are of this type. They are particularly easy to imagine because they fit neatly into our current technology and regulatory structure. Just as a traditional customer has considerable leeway in the operation of the power system on its side of the meter, so the restrictions on the nature of a µgrid are relatively loose. For this reason, one would expect much of the early deployment of microgrid technology to be of this type.
- Utility or community microgrids or milligrids (mgrids) involve a segment of the regulated grid. There are also existing well known examples. While technically, they not be different from µgrids, they are fundamentally different from a regulatory and business model perspective, primarily because they incorporate traditional utility infrastructure. The corollary of this feature is that utility regulation comes much more significantly into play. In other words, any mgrid must comply with existing utility codes or accommodation must be made in the code.
- Virtual microgrids (vgrids) cover DER at multiple sites but are coordinated such that they can be presented to the grid as a single controlled entity. Very few demonstrations of vgrids exist, but they have been proposed in the literature. Note that to be consistent with the definition above, the system must be able to operate as a controlled island or coordinated multiple islands.
- Remote power systems (rgrids) are obviously not able to operate grid-connected, isolated power systems involve similar technology and are closely related. So close that from a research point of view, they are commonly described as microgrids.
Examples of Microgrids
Microgrid projects have been undergoing a boom for the last past years after proving their value in critical situations.
This page will present state-of-the-art examples of projects accomplished or still under construction. As we will be updating this page frequently, please feel free to come check it out regularly.
Here are some of the most interesting examples of Mirogrids our in the wild:
New York University
New York University (NYU), one of the largest universities in the United States, has produced power on site since the 1960s and installed a large oil-fired cogeneration plant in 1980. At the end of that facility’s useful service life, NYU made a transition away from oil-fired technology towards a modern natural-gas fired combined heat and power facility, with eyes towards microgrid capabilities, better reliability, and a better control of their energy expenditures.
The upfront capital cost of the upgrade was significant at $126 million. However, tax-exempt bonds arranged through the Dormitory Authority of the State of New York and through NYU tuition and fees helped to provide low-cost financing sources.
The CHP system has an output capacity of 13.4 MW (twice as much as the old plant’s capacity) and has been fully operational since 2011. It supplies electricity to 22 buildings and heat to 37 buildings across campus. The microgrid consists of two 5.5 MW gas turbines for producing electricity coupled with heat recovery steam generators and a 2.4 MW steam turbine. The NYU microgrid is connected to Con Edison distribution grid and purchases electricity when demand is superior to the on-site generating capacity.
Yet, unlike before, the NYU microgrid is now able to island from the distribution grid. This has been successfully tested during Hurricane Sandy when the NYU microgrid successfully islanded from the local distribution grid and continued to provide reliable power to much of the NYU campus.
The modernization of the plant has presented impressive results both economically and environmentally and has proven its benefits. NYU has evaluated savings on total energy costs to be $5 to $8 million per year. The new facility has drastically reduced NYU’s local emissions with an estimated 68% decrease in EPA criteria pollutants (NOx, SO2, and CO emissions) and 23% decrease in greenhouse gas emissions. This has been a great step towards the commitment that the university made to the City of New York to decrease its greenhouse gas emissions by 30%.
Borrego Springs
The project’s partners include Lockheed Martin, IBM, Advanced Energy Storage, Horizon Energy, Oracle, Motorola, Pacific Northwest National Laboratories, and University of California San Diego. The U.S. DOE supported the project with $7.5 million of federal funding, with additional funding coming from SDG&E ($4.1 million), CEC ($2.8 million), and other partners ($0.8 million).
The community is a somewhat isolated area fed only by a single sub-transmission line. Islanding of the entire substation area is being demonstrated for reliability reasons as well as a potential alternative to building additional transmission capacity. Prior to the microgrid project launch, the community already had many rooftop solar PV systems installed. SDG&E is exploring the possibilities of price driven demand response, via interaction with in-home storage, electric vehicles, and smart appliances using the areas installed smart meters and home area network devices.
The total microgrid installed capacity will be about 4 MW, with the main technologies being two 1.8 MW diesel generators, a large 500 kW/1500 kWh battery at the substation (which will be instrumental in achieving peak load reduction), three smaller 50 kWh batteries, six 4 kW/8 kWh home energy storage units, about 700 kW of rooftop solar PV, and 125 residential home area network systems.
In terms of control systems, the project incorporates supervisory control and data acquisition (SCADA) on all circuit breakers and capacitor banks, Feeder Automation System Technologies (FAST), outage management systems, and price driven load management at the customer level.
SDG&E will be conducting a detailed cost-benefit analysis of the project, using a methodology developed by the Electric Power Research Institute for the DOE’s use in evaluating smart grid projects. The benefits are typically classified into four categories: economic, reliability and power quality, environmental, and security and safety. If the project (or portions of it) proves to be cost effective, then SDG&E will likely seek out future microgrid projects.
Fort Collins
The main goals are to develop and demonstrate a coordinated and integrated system of mixed distributed resources for the City of Fort Collins,reduce peak loads by 20%-30% on two distribution feeders, increase the penetration of renewables, and deliver improved efficiency and reliability to the grid and resource asset owners.
The microgrid project involves multiple customers including the New Belgium Brewery, InteGrid laboratory, City of Fort Collins facilities, Larimer County facilities, and Colorado State University main campus facilities as well as a variety of distributed energy generation technologies. It has received $6.3 million in funding from the U.S. Department of Energy and $4.7 million from the various industry partners, including Eaton, Advanced Energy, and Brendle.
Technologies in the project include solar PV, CHP, microturbines, fuel cells, plug-in hybrid electric vehicles, thermal storage, load shedding, and demand side management. The combined distributed generation and load shedding capabilities is 5 MW spread across five customer locations. The larger FortZED project represents about 10-15% of Fort Collins Utilities’s entire distribution system, with a peak load of 45.6 MW across 7,257 customers.
There will be a total of 345 kW of solar PV, as well as 700 kW of combined heat and power, 60 kW of microturbines, and 5 kW of fuel cells.
The brewery in particular can produce over half of the power it consumes, when its own distributed generation facilities (790 kW biogas power, 200 kW solar PV) are running at peak power. Additionally, the various facilities have diesel-based backup generators totaling 2,720 kW in capacity, which are typically used for emergency power.
Demand response will occur through various heating, cooling, and ventilation rescheduling using existing Johnson Controls and Trane building automation systems.
Overall, the project is considered to be very innovative for a small municipally-owned utility and will offer interesting lessons for other milligrids under development.
What other Resources are there?
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To learn more about what the Energy Department is doing to research microgrids, you can visit the Office of Electricity’s https://www.energy.gov/oe/microgrid-portfolio-activities.
Sources:
The article was recreated from the resources that no longer exist (are online):
Energy.gov – “How Microgrids Work?”
Grid International Group – “Types Of Microgrids”, “Examples Of Microgrids”, “New York University Microgrid”, “Fort Collins Microgrid”, “Borrego Springs Microgrid”
