Microgrids are providing exciting opportunities for electrical contractors. The microgrid was conceived to provide a reliable energy supply to remote geographical locations where it is not economical to extend traditional electric utilities. While intended for use in developing countries, microgrids also are finding applications in urban areas of developed ones.
Properly designed, installed and maintained microgrids can increase energy supply efficiency, reliability and sustainability. ECs installing on-site distributed generation (DG) should be familiar with microgrids because the next step in the evolution of DG energy systems requires the integration of multiple, small-scale DG energy production sources that have diverse operating characteristics into a cohesive and reliable energy supply system.
What is a microgrid?
A microgrid is a localized power system that provides a safe, economical energy supply to residential, commercial, institutional, or industrial structures (or a mix of these occupancies). Its purpose is to integrate multiple on-site DG energy sources, such as photovoltaic (PV) arrays and energy storage systems, into a functional power system that can serve the facility load reliably. In urban areas, a microgrid will most often operate in parallel with the serving utility but can also operate off-grid when traditional utility service is not available in a rural area or where the owner wants to be utility-grid independent. In the past, if a grid-tied facility lost its supply, DG energy production sources were required to shut down to protect emergency responders from hazardous shocks and other dangers. Today, there is a movement to develop safety procedures and controls that can isolate or “island” a facility so it can continue operating and supporting the local community using DG energy sources even if the utility grid is out of service.
Until recently, customer facilities typically incorporated a single DG energy source, such as a rooftop PV array, to take advantage of government and utility financial incentives, achieve a third-party green building certification, or demonstrate dedication to the environment. However, outages have left facility owners, operators and communities looking for a more reliable energy supply.
Today, there are many DG options available to meet the EC’s customer requirements, and those options are both scalable and economical when compared with utility retail rates. These DG sources are both renewable and nonrenewable (e.g., fuel cells that operate on natural gas). As a result, facility owners and operators are exploring the use of multiple on-site energy production sources whose characteristics complement one another to economically improve system reliability.
At first glance, a microgrid appears to be merely a looped distribution system that ties together all of a facility’s distributed energy production and storage sources in parallel with its traditional utility service to serve the facility’s load. Simply paralleling a single DG source with the traditional utility service is possible because the inverter controls of the DG source. Since peak PV production usually coincides with the serving utility’s peak load at midday, all of the energy produced by the PV system will either be offset by the facility’s load or help the utility reduce its peak system load through net metering or an established feed-in tariff. However, when multiple DG sources and storage systems are serving a facility with different operating characteristics, paralleling these sources will not result in optimal system operation and could even result in problems.
As a result, the microgrid’s heart is the control system that integrates a number of disparate energy sources to take advantage of each source’s unique operating characteristics so that the microgrid operates optimally in terms of safety, reliability and economics. A number of electrical equipment manufacturers are producing and selling microgrid control systems. These microgrid control systems can be installed to operate a microgrid made up of any number and type of distributed energy production and storage sources and that can interface with the serving utility. The microgrid control system determines when and how much energy is supplied by a particular DG source or energy storage device, balancing supply and load and providing any excess energy to the serving utility.
Getting ahead of the curve
Commercial and institutional facilities, as well as communities and cities, see microgrids as a way to keep a variety of facilities—including critical operation, healthcare, emergency services, water treatment and supply, traffic control and public lighting for safety and crime prevention—operating when the utility power supply is damaged or fails.
Understanding microgrids and their control systems could be the basis for expanding the EC’s energy services through service and new construction.
For more, check out the feature on Microgrids by Chuck Ross, October 2013, or at www.ecmag.com/ross1013.