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Bechtel engineer shares advice on microgrid design

Strategies for navigating likely mishaps included

Rockville, MD (November 9, 2015) – Microgrids are still at the point where the benefits and potential pitfalls need to be weighed, Henrik Johansen, assistant chief engineer at Bechtel Infrastructure & Power, told Smart Grid Today – the leading independent, daily, professional news journal of the smart grid industry – recently. Smart Grid Today publisher Modern Markets Intelligence Inc. is sharing the story here, free of charge.

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" programmed into the design of a microgrid's controls, issues can easily arise during failures.  

"When you have, let's say, two generators on and both are trying to hold frequency, they can get into a sympathetic oscillation." In such extreme cases, "it should ultimately trip the grid off without damaging any equipment.

"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?"

OK to get some help

One answer is contracting with an engineering firm. The benefits of microgrids will drive the engineering community to solve the problems.

The old-school electric utility remains "probably the best way to back yourself up" in the near future, Johansen said.  If such grids do diminish, backup power sourcing will need to be reassessed.

Bechtel, whose smart grid credentials include transmission lines in Alberta, Canada, and a potential offshore HVDC link between Norfolk Virginia to New York City, is not yet focused on microgrids as a separate business.  

In part, this is due to the small scale. In the US, microgrids only number around 200, which adds up to less than 2,000 MW – "not even one big power plant," he added, noting that, by EPRI's definition, a microgrid is 10 MW or smaller. "That is like 3,500 homes."

Bechtel builds microgrids

Bechtel has the chance to incorporate microgrids into larger infrastructure projects it undertakes. For example, the government of Gabon hired Bechtel for its National Infrastructure Master Plan, including some of that African nation's smart cities.

"Those cities, including the capital, Libreville, are going to be candidates for microgrids."

His firm is also providing engineering for a new city in Saudi Arabia called Waad Al Shamal. "That is a greenfield site, ground up. It is going to have 'fiber to the home' and a smart grid and probably a microgrid – or at least, a smart grid with microgrid concepts."

Meanwhile, Bechtel is helping install the infrastructure needed for smart cities and smart apps. For example, the firm is working with Google to bring fiber to the home in several US cities, including Atlanta, Charlotte, Raleigh-Durham and Nashville, Johansen said.  

On the renewable energy side, Bechtel worked with BrightSource Energy, Google and NRG to build a 377-MW solar thermal plant called Ivanpah. The Southern California site, which will produce enough clean, renewable power to run 140,000 homes, was included in the Fray's music video, for the group's song "Love Don't Die," he added.

This story was originally published in Smart Grid Today (http://www.smartgridtoday.com/public/Bechtel-engineer-shares-advice-on-microgrid-design.cfm?ref=PressRelease) on November 4, 2015, and has been slightly edited for this format. To read more articles like this one, sign up for a Free Trial to Smart Grid Today.

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