In this week’s Industry Perspectives, Ameresco’s Jim Bishop explores engineering risks in microgrid technology and why picking the right technical partner or partners can be key to success.
Today’s advanced microgrids are flexible, multi-functional and complex. Taken together with their relatively cutting edge underlying software intelligence, and it is clear why some energy customers see microgrid technology as daunting.
Companies, schools, hospitals, research centers and government agencies want the benefits of microgrids, but worry that they lack expertise to navigate the complexity of developing and then operating them.
The good news is that there are ways to achieve the energy reliability, resiliency, emissions reductions and cost management offered by a microgrid without shouldering the development and operational risk of microgrid technology.
Those who see microgrid management as too far outside of their core competency may turn to knowledgeable partners for help with their design, engineering, financing, equipment procurement and deployment.
Those who see microgrid management as too far outside of their core competency may turn to knowledgeable partners for help with their design, engineering, financing, equipment procurement and deployment.
Successful microgrid development benefits not only from technologically advanced hardware and software, but also requires application of specific technical expertise to achieve the desired outcome.
One or more partners?
Choosing the microgrid’s generation source — renewables, fossil fuel or some combination — is often a primary decision for the new microgrid customer. The choice reflects corporate and institutional priorities. Is the customer seeking reliability, resiliency, lower costs, sustainability, energy security or a combination of these benefits from the microgrid?
Some organizations prefer choosing microgrid technology solutions provided by a single vendor, mainly because it may simplify decision-making and project development and accountability for successful implementation.
Using a single technology vendor may also mean sacrificing fuel diversity and efficiency. Using multiple technologies — and therefore multiple vendors — opens the opportunity to create a microgrid that incorporates more than one generation technology, perhaps some combination of solar, wind, combined heat and power (CHP), natural gas or energy storage. More importantly, a microgrid host should assure that their selected solution can appropriately integrate not only varying technologies, but also consider and incorporate existing systems and design features in their facility.
A microgrid that uses a complete, customized, engineered solution, is likely to exceed expectations, with components operating in a coordinated fashion for reliability and resiliency in an uncertain operating environment.
There is strong value in seeking a partner that brings a holistic, custom-engineered systems approach to microgrid project design and development, one that acts in a technology and vendor-agnostic fashion to meet the customer’s goals.
The importance of built environment history
Selecting new generating technology is one facet of project planning. Another is evaluation of existing energy infrastructure on the site.
Most facilities were designed for a specific purpose and to accommodate the expected or existing needs of the client. Some legacy energy and distribution assets may be able to be upgraded and configured into a new microgrid, but it’s important to thoroughly assess the state of the existing equipment.
Accommodating expansion, technological advances, and adapting mission, the built environment may be modified to suit new objectives and evolve from the original facility design intent. Perhaps a building’s wiring and electrical systems were upgraded to handle the higher loads that result from increased host activity, and a wider variety, of electronic and electrical devices. Over time, system additions, upgrades, and repairs to accommodate changes in use and activity may pull the design of a building away from its original intent. A comprehensive evaluation of the existing facility, modified to its present use, and with a view toward future needs, is essential in executing a successful microgrid.
Safety: The Delta-Y transformer problem
Microgrids are often targeted at continuity of energy supply in an environment of contingencies, however those very contingencies can introduce conditions that weren’t originally part of a facility’s design. Particularly, customer-side generation sources may introduce two-way flow of electricity. One specific example revolves around ubiquitous delta-Y transformers, and the way customer-side generation responds to ground faults and short circuits.
Sending electricity upstream to a utility grid, or distributing it to serve on-site loads, a building or facility’s existing grid-tied power generation and distribution network will behave differently when powered exclusively by variable, renewable power generation resources, such as solar PV or battery-based energy storage rather than the utility. An organization and its microgrid project managers need to ensure that all aspects, devices and components of a microgrid function effectively and as expected to ensure reliable operation and continuity of safety features.
Existing on both the utility and customer sides of the meter, transformers are core components of any electrical system. Referring to the form in which a transformer’s internal wiring is connected, so-called delta transformer windings are commonly found on the utility or campus distribution side of an electrical service. Wye transformer windings are commonly found on the customer side. Delta and wye transformers differ in several respects, one being their behavior when an unintentional ground fault or short occurs in the customer wiring beyond the transformer.
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Most customer-side generation equipment includes the capability of automatically shutting down or disconnecting when a short circuit occurs on the system. These sensing systems may not always operate as expected when a short circuit occurs on a delta-connected side of a transformer. The generation source could therefore unintentionally stay online during certain short circuit conditions. Specific protective settings or devices may need to be deployed, or the transformer may need to be replaced or modified to assure safe operation in an isolated microgrid.
An added consideration is that many electrical protective devices are sensitive to the amount of current that flows in a system. Current flows that are within design parameters flow uninterrupted. Flows that are slightly over design limits are interrupted after several seconds or minutes. Very high flows, as when a short circuit occurs, are tripped in milliseconds. Protective devices are at various branches of the electrical system, and are coordinated when the facility is designed so that only the closest device to a problem responds, minimizing interruption. Utility sources have a high capacity to provide current, which makes it relatively simple for protective equipment to distinguish an acceptable condition from a dangerous one. Modern customer generation such as solar (PV) equipment, battery systems, and even most backup or cogeneration generators cannot produce these large currents for more than a few seconds if at all, and so protective devices may not operate as expected. Protective device coordination should therefore be reviewed considering each of the power sources in a microgrid system to ensure predictable and safe operations.
Choosing a microgrid partner
While there are risks associated with installing a new microgrid project, especially if energy is not the owner/operator’s core expertise, there are also significant benefits.
Finding the right microgrid development partner is critical to mitigating the risks and harnessing those benefits. It’s particularly important to find one that is technology agnostic and offers the expertise and experience to properly evaluate each new and existing system component.
Today, there are a variety of expert partners to choose from. These include microgrid project developers, engineering, procurement and construction (EPC) companies, third-party system owners and operators, and electrical equipment and systems vendors. Many of these partners also arrange customized financing options, such as power purchase agreements (PPA) and leases with third-party microgrid operators.
With the right partner, microgrid customers can enjoy the benefits without grappling with the complexities of development and operations.
Jim Bishop is team leader – engineering at Ameresco.
