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Follow on Google News |  Bechtel engineer shares advice on microgrid design, strategies for navigating likely mishapsBy: Smart Grid Today These grids are typically smaller than 10 MWs. Microgrids offer many opportunities for efficiency and environmental improvements for the production and use of power, Johansen said. "If you are using a thermal source and if you're setting it close to a community or campus-type environment, you can use combined heat and power and actually use the waste heat. "It really helps on efficiency and is also good for reducing GHG emissions," he added. Demand-side participation is a lot higher with a microgrid than the standard power grid, Johansen said. "If the microgrid starts to run a little low on power, maybe you can simply shed some load. "Maybe you are not going to charge plug-in hybrid cars. Maybe you will turn off the street lights. As the internet of things (IOT) permeates everything, it gets far more possible to control everything – almost to the household-solar level." Johansen offered some design cautions. The adage "failing to plan is planning to fail" works here – with a twist, he added. No equipment can be considered infallible, so the controls may need to implement compromises in microgrid operation in response to failures. "Maybe the frequency is allowed to not be as precise. Maybe you are going to go on droop control or something like this so you aren't quite there in system frequency but it will be good enough until you get things repaired." [EDITOR'S NOTE: Droop control is a control strategy commonly applied to generators for primary frequency control – and occasionally voltage control – to allow parallel generator operation such as load sharing.] "On a case-by-case basis, you have to get in there with controls and look at what happens when things fail," Johansen said. "You can have failures in the control. You need to go through graceful degradation of the controls. "If some piece of equipment packs it in, you can't just say, 'It's okay to blackout.' You need to have something properly engineered into both the overall microgrid and the individual generator controls." As more microgrids come online, it will be crucial to get the controls right "so a microgrid can operate autonomously, control its frequency and do things correctly," he added. Johansen believes that without "graceful degradation" "When you have, let's say, two generators on and both are trying to hold frequency, they can get into a sympathetic oscillation." "Usually the protection is designed for that, but that is an example of a non-graceful degradation. "Or, you could have something where you don't manage to match load and generation well enough and the frequency slides and, as it slides up or down far enough, you may end up again having a grid blackout." Sympathetic oscillations, off-normal frequency operation and loss of generation are all common potential problems, Johansen said. "The reason people don't know about them is we have been very successful engineering them out," he added. Not replacing the grid Since microgrids have so many potential applications for efficiency and resilience, they could proliferate to the point where the conventional utility grid is economically squeezed out, Johansen said, but he believes complete elimination of the grid is unlikely. Renewable resources are distributed in a scattered way and the resulting power-cost differences and/or power surpluses "may well continue to make long-haul power transmission viable," he added. Where microgrids do take off, diverse ownership and control could shape up as big coordination issues. Microgrid participants will need to designate experts to handle extreme weather events and other potential serious disruptions to the power supply. "While full-scale utilities can afford to have a handful of high quality engineers looking after the system, when you divorce your grid from that and it is owned by some small community, it's probably very hard to justify even one position," Johansen said. "So when things go wrong, who are you going to turn to?" This entire story was originally published in Smart Grid Today (http://www.smartgridtoday.com/ ABOUT SMART GRID TODAY Smart Grid Today, the publication of record for the smart grid industry since 2009, delivers daily, unbiased, comprehensive and original reporting on emerging trends, applications and policies driving the modern utility industry. Our signature format features highly concise and easy-to-understand news copy based on trusted reporting, exclusive interviews, informed analysis and strategic insights that our subscribers rely on to succeed every business day. Modern Markets Intelligence Inc publishes Smart Grid Today. CONTACTS Sam Spencer Publisher Modern Markets Intelligence Inc. 1-888-980-4446 sam@mminews.com Season Crawford VP of Marketing Modern Markets Intelligence Inc. 1-888-678-4480 season@mminews.com End
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