Time to Rightsize the Grid?

Does Size Matter Source CarrerasLast week a team of systems scientists known for counter-intuitive insights on power grids delivered a fresh one that questions one of the tenets of grid design: bigger grids, they argue, may not make for better grids. University of Iowa electrical engineering professor Ian Dobson and physicists David Newman and Ben Carreras make the case for optimal sizing of power grids in last week’s issue of the nonlinear sciences journal Chaos.

In a nutshell, the systems scientists use grid modeling to show that grid benefits such as frequency stabilization and power trading can be outweighed by the debilitating impacts of big blackouts. As grids grow larger, they become enablers for ever larger cascading blackouts. The Northeast Blackout of 2003 was a classic case. From a tripped line in northern Ohio, the outage cascaded in all directions to unplug more than 50 million people from western Michigan and Toronto to New York City.

This week’s findings are more conceptual, however, than some news outlets would have us believe. NBC News, in an online article entitled Researchers Suggest It’s Time to Downsize Power Grid, misjudged the Chaos report as a call to break up the dual grids that interconnect most of eastern and western North America. “It’s not possible to really make that statement,” says Carreras, who runs Oak Ridge, TN-based consulting firm BACV Solutions and is a visiting professor at Madrid’s Universidad Carlos III.

NBC misinterpreted Carreras et al’s simulations showing that grids with just 700-1000 nodes (over 15 times smaller than North America’s big grids) maximize interconnection benefits while minimizing blackout costs (see above chart). The researchers say this could indicate that some real grids are too large, but there are two big reasons to be cautious about drawing conclusions.

Carreras stresses that the model nodes are not necessarily representative of those on a real grid. Many of the group’s simulations, for example, use scale models of the Western grid in which each node in the model represents, on average, 10 nodes on the real grid.

Newman, a physics professor at the University of Alaska in Fairbanks, notes that the specific models used in this Chaos study were idealized, homogeneous systems. As such, he says, they bear little resemblance to the heterogeneity of real grids with their diversity of voltage levels, branching patterns and other features. “700-1000 nodes was the optimal size for the artificial network we had constructed,” says Newman.

Media hype is a problem that has dogged this team of system scientists since they gained notoriety over a decade ago by identifying cascading failures as an innate feature of power grids. Their simulations, which I covered in a Spectrum cover story ten years ago, show that economic pressure to maximize return on investment loads power grids to levels that leave them at heightened risk of costly blackouts.

The researchers delivered a complex systems view of blackouts that they hoped would spur novel thinking about the costs and benefits in grid design, and novel approaches to blackout prevention. But their message was often misinterpreted as an attack on the quality of grid engineering, or an argument that trying to prevent blackouts was futile.

Carreras et al argue that this week’s report has important conceptual value, if one gets beyond the hype. For one thing, blackout risks should be factored into the cost-benefit calculation when grid planners consider expanded interconnection. This could be applicable in developing countries as well as in Europe, which recently expanded its grid to include Turkey’s and is considering extensions to North Africa and Russia.

It’s also possible that grid design could be engineered to enable extended interconnection without expanding cascading blackout risk. Newman points to the possibility that weak links could be deliberately placed within grids to confine cascading blackouts to their region of origin. The team’s next step, says Newman, is to study just that possibility by simulating and optimizing heterogeneous networks.

This post was created for Energywise, IEEE Spectrum’s blog on green power, cars and climate

Minnesota Finds Net Metering Undervalues Rooftop Solar

Utilities should be paying more for their customers’ surplus solar power generation according to a solar pricing scheme approved by Minnesota’s Public Utility Commission last month and expected to be finalized in early April. Minnesota’s move marks the first state-level application of the ‘value of solar’ approach, which sets a price by accounting for rooftop solar power’s net benefits, pioneered by the municipal utility in Austin, TX.

Minnesota is one of 43 U.S. states that requires utilities to pay retail rates for surplus solar power that their customers put on the grid. Utilities across the U.S. are fighting such net metering rules, arguing that they fail to compensate the utility for services that their grid provides to the distributed generator. So last year pro-solar activists and politicians in Minnesota called the utilities’ bluff, passing legislation tasking the state’s Department of Commerce with calculating the true value of rooftop solar power. Continue reading

Blackouts Ahead on Our Unruly Power Grids

ImageTen years after the Northeast Blackout that shut off power in seven U.S. states and Ontario cascading power grid failures remain a fact of life. And, as I argue today on Spectrum’s Energywise blog, engineers are little closer to predicting and preventing them.

The good news is that engineers are beginning to accept that they have a complex system problem on their hands — an insight that could help them find solutions.

Such understanding was in short supply one year after the Northeast blackout, as I discovered with the publication of my August 2004 cover story for IEEE Spectrum commemorating its one-year anniversary profiling the apparent mathematical inevitability of cascading power-system failures. That message raised a firestorm of protest from engineers who saw their can-do creed under attack.

Today, however, the black sheep who spotted the tell-tale signs of a chaotic self-organizing system in blackout databases have come in from the cold. The University of Wisconsin’s Ian Dobson, for example, says he is having success attracting grants — no mean feat for interdisciplinary research targeting the uber-unsexy field of power transmission. And the IEEE set up a task force on cascading failures (with Dobson at the table).

One obvious cause for rising consciousness is the fact that blackouts just keep happening Continue reading

German Parliament OKs Bold HVDC Grid Upgrade

Germany’s bold transmission plan is a go. The Bundesrat, Germany’s senate, has accepted the plan’s enabling legislation forwarded to it by the Bundestag (Germany’s parliament), according to the authoritative German Energy Blog. There is every reason to expect that the plan’s core element — four high-voltage direct current or HVDC transmission lines profiled by Spectrum last month — will get built.

That is good news for Germany’s grid and those of its neighbors. All are straining to manage powerful and variable flows from the wind turbines and solar panels that provided 12 percent of Germany’s power generation last year.

Elements of both the HVDC system design and the legislation should ease construction of the HVDC systems. On the design side, Germany’s transmission system operators have specified advanced converters whose ability to arrest and clear DC line faults will reduce the risk of running overhead lines. This means the HVDC lines can use existing rights-of-way used by AC lines. In fact, they can be hung from the same towers. Read the May 2013 story for extensive discussion of the advanced modular multilevel converters.

The enabling legislation, meanwhile, will simplify line permitting by making a federal court in Leipzig the only forum for legal disputes concerning the projects. Separate legislation passed by the Bundesrat and Bundestag makes  Germany’s federal networks regulator, the Bundesnetzagentur or BNetzA, the sole permitting authority for power lines that cross Germany’s state or national borders. These measures — for better or worse — cut out state-level officials that face greater pressure from local project opponents and may be more sympathetic to their concerns.

Add it all up and Germany is en route to become the first country with HVDC lines playing a critical role at the core of their power grid. It is arguably the first real challenge to AC’s century-plus reign as the top dog in power transmission since DC-advocate Thomas Edison lost the War of Currents. Tesla and Westinghouse may just be rolling over.

This post was created for Energywise, IEEE Spectrum’s blog on green power, cars and climate

Germany Jumpstarts the Supergrid


Power Core: Spectrum’s infographic take on Germany’s HVDC transmission plans

New developments in high-voltage DC electronics could herald an epic shift in energy delivery

By Peter Fairley

Stuttgart is one of the last places you’d expect to find in a power pinch. This south German city’s massive automotive plants run 24-7 without a hiccup, efficiency measures have held industrial power consumption flat, and solar panels flash from atop its major buildings. But now all that is at risk. The country’s accelerated shift from nuclear power and fossil fuels to renewable resources, such as wind and solar, has exposed a huge gap in its transmission capacity. If they are to survive, Stuttgart’s factories—and power consumers across southern Germany—will need to import a lot more power from the north, and Germany’s grid is already at capacity.

To fill the gap, Germany is considering an aggressive plan that would push high-voltage direct current, or HVDC, from its conventional position on the periphery of AC grids to a central role. The primary reason is simple: For the first time, HVDC seems cheaper than patching up the AC grid. But Germany’s transmission planners also have another motivation: They want to provide as much performance and reliability as they can to an AC grid that’s already strained by excess wind power. For that, they’re considering implementing power electronics that are capable of doing something that’s never before been done on a commercial line: stop DC current in milliseconds flat.

Germany’s plan could mark the beginning of something much bigger: a “supergrid” of inter connected DC lines capable of transporting electricity on a continental scale, ferrying energy from North Sea turbines, dams in Scandinavia, or Mediterranean solar farms to wherever demand is greatest at that moment…

Published in the May issue of IEEE Spectrum. Read the story at Spectrum.com.

Supergrid Technology Beats Expectations

HVDC breaker Source AlstomAn industrial research consortium that is a who’s-who of the European power industry says development of technologies to produce high-voltage DC (HVDC) supergrids accelerated in 2012 — “surpassing expectations.” The assessment comes in the supergrids technology roadmap updated earlier this month by Friends of the Supergrid, whose members include power equipment suppliers such as Siemens, ABB and Alstom, as well as transmission system operators and renewable energy developers.

Summarizing the conclusions of an expert group within the International Council on Large Electric Systems — better known as CIGRE, its French acroynm — the Friends of the Supergrid says there is now no doubt as to the feasibility of HVDC networks ferrying renewable energy resources from wherever they are in surplus to wherever they are needed: “CIGRE Working Group B4–52 considered this question, specifically whether it was technically and economically feasible to build a DC Grid, and the answer was yes.” Continue reading

AC/DC 101

Much of your editor’s reporting in 2012 focused on the re-emergence of direct current or DC power — through pieces in IEEE Spectrum, Technology Review, and Power & Energy Magazine — and there is more in the works. Some of you, however, may still be wondering what DC power is and how it differs from the alternating current or AC power flowing from most electrical sockets. So here are some answers.

The questions were posed by Andrew Huang, a 9th grader at High Technology High School in Lincroft, NJ, who recently interviewed me for a history project on Nikola Tesla and Thomas Edison’s late-19th Century War of Currents. (Check out The Oatmeal’s Why Nikola Tesla was the greatest geek who ever lived for a rather tilted yet entertaining take on a key combattant in this epic tech tussle.)

What are some differences between the physics of AC and DC? Continue reading