Is the power grid too big? Right-sizing the grid could reduce blackout risk

Apr 08, 2014
The overall operational "Risk" as a function of the system size (N), showing a decrease at first as the system becomes more efficient with size followed by an increase as the risk of large failures starts to dominate. The optimal size is then the minimum point in the curve. Credit: B.A. Carreras/BACV Solutions

Some 90 years ago, British polymath J.B.S. Haldane proposed that for every animal there is an optimal size—one which allows it to make best use of its environment and the physical laws that govern its activities, whether hiding, hunting, hoofing or hibernating. Today, three researchers are asking whether there is a "right" size for another type of huge beast: the U.S. power grid.

David Newman, a physicist at the University of Alaska, believes that smaller grids would reduce the likelihood of severe outages, such as the 2003 Northeast blackout that cut to 50 million people in the United States and Canada for up to two days.

Newman and co-authors Benjamin Carreras, of BACV Solutions in Oak Ridge, Tenn., and Ian Dobson of Iowa State University make their case in the journal Chaos, which is produced by AIP Publishing.

Their investigation began 20 years ago, when Newman and Carreras were studying why stable fusion plasmas turned unstable so quickly. They modeled the problem by comparing the plasma to a sandpile.

"Sandpiles are stable until you get to a certain height. Then you add one more grain and the whole thing starts to avalanche. This is because the pile's grains are already close to the critical angle where they will start rolling down the pile. All it takes is one grain to trigger a cascade," he explained.

While discussing a blackout, Newman and Carreras realized that their sandpile model might help explain behavior.

The Structure of the U.S. Power Grid

North America has three power grids, interconnected systems that transmit electricity from hundreds of power plants to millions of consumers. Each grid is huge, because the more power plants and power lines in a grid, the better it can even out local variations in the supply and demand or respond if some part of the grid goes down.

On the other hand, large grids are vulnerable to the rare but significant possibility of a grid-wide blackout like the one in 2003.

"The problem is that grids run close to the edge of their capacity because of economic pressures. Electric companies want to maximize profits, so they don't invest in more equipment than they need," Newman said.

On a hot days, when everyone's air conditioners are on, the grid runs near capacity. If a tree branch knocks down a power line, the grid is usually resilient enough to distribute extra power and make up the difference. But if the grid is already near its critical point and has no extra capacity, there is a small but significant chance that it can collapse like a sandpile.

This is vulnerable to cascading events comes from the fact that the grid's complexity evolved over time. It reflects the tension between economic pressures and government regulations to ensure reliability.

"Over time, the grid evolved in ways that are not pre-engineered," Newman said.

Backup Power Versus Blackout Risk

In their new paper, the researchers ask whether the grid has an optimal size, one large enough to share power efficiently but small enough to prevent enormous blackouts.

The team based its analysis on the Western United States grid, which has more than 16,000 nodes. Nodes include generators, substations, and transformers (which convert high-voltage electricity into low-voltage power for homes and business).

The model started by comparing one 1,000-bus grid with ten 100-bus networks. It then assessed how well the grids shared electricity in response to virtual outages.

"We found that for the best tradeoff between providing backup power and blackout risk, the optimal size was 500 to 700 nodes," Newman said.

Though grid wide blackouts are highly unlikely, they can dominate costs. They are very expensive and take longer to get things back under control. They also require more crews and resources, so utilities can help one another as they do in smaller blackouts.

In smaller grids, the blackouts are smaller and easier to fix because utilities can call for help from surrounding regions. Overall, small grid blackouts have a lower cost to society," Newman said.

The researchers believe their insights into sizing might apply to other complex, evolved networks like the Internet and financial markets.

"If we reduce the number of connected pieces, maybe we can reduce the societal cost of failures," Newman added.

Explore further: Keeping the lights on: Mechanical engineer finds a way to predict cascading power outages

More information: The article, "Does size matter?" by B. A. Carreras, D. E. Newman, Ian Dobson appears in Chaos: An Interdisciplinary Journal of Nonlinear Science (DOI: 10.1063/1.4868393). It will be published online on April 8, 2014. http://scitation.aip.org/content/aip/journal/chaos/24/2/10.1063/1.4868393

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User comments : 12

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Eikka
not rated yet Apr 08, 2014
If "small" is 100 and "big" is 1000, the 500-700 node grid is not small.

And how does this work with renewable energy, which needs a very large grid to smooth out local variability?
Doug_Huffman
not rated yet Apr 08, 2014
See N. N. Taleb on fragility and Antifragile: Things That Gain from Disorder.

He might say that many small failures are less risky than a system too big to fail.

Alternative/renewable energy is a small failure that can be tolerated but for the magnitude of the Ponzi-investment of capital.
Eikka
not rated yet Apr 08, 2014
Alternative/renewable energy is a small failure that can be tolerated


That depends. Weather systems are easily a thousand miles across, so the independent nodes aren't actually all that independent.
antialias_physorg
5 / 5 (1) Apr 09, 2014
The graph show the optimum at 300, not 500-700. Or am I missing something?

And how does this work with renewable energy, which needs a very large grid to smooth out local variability?

If your buffer/storage infrastructure is similarly decentralized then grid size shouldn't have any effect at all.
Eikka
not rated yet Apr 09, 2014
The graph show the optimum at 300, not 500-700. Or am I missing something?


Yes. It's a logarithmic scale. The arrow is a bit past 400.

If your buffer/storage infrastructure is similarly decentralized then grid size shouldn't have any effect at all.


If you have any.
antialias_physorg
not rated yet Apr 09, 2014
Yes. It's a logarithmic scale. The arrow is a bit past 400.

True ...that still isn't in the 500-700 region, though.

If you have any.

Buffer systems are a must. No one in the renewable energy business is denying that.
(Buffer systems are a must also for the old types of energy production, BTW: They're called 'National reserves' and hydro powerplants)
Eikka
not rated yet Apr 09, 2014
No one in the renewable energy business is denying that.


I find they'd rather just not talk about it and keep building more windmills.

(Buffer systems are a must also for the old types of energy production, BTW: They're called 'National reserves' and hydro powerplants)


Not in the same sense and same extent. The grid systems works perfectly fine without any significant energy buffers because all or most of the power is dispatchable on demand. The existing hydro plants hold only a tiny amount of energy, and in the case of a major disruption the larger energy users are simply required to drop off the grid until additional spare capacity gets kicked up online.

This system is entirely insufficient and unsuitable in dealing with large scale fast power variation on the grid as a result of using renewable power. It's an entirely different sort of problem.
ryggesogn2
1 / 5 (1) Apr 09, 2014
" Overall, small grid blackouts have a lower cost to society," "
Cost to 'society'?
antialias_physorg
5 / 5 (1) Apr 09, 2014
The grid systems works perfectly fine without any significant energy buffers because all or most of the power is dispatchable on demand.

The old types require steady input of fules. If you're not the producer of these fuels you need a buffer system. If you fall out with countries that supply those fuels to you then you're out of luck. How much buffer system would you need? 10 years worth? 20 years worth? (Read: enogh time to switch over to some other from of energy). For renewables it's 3 days' worth. AND the measn of production are all in your own hands.

So in terms of energy security the old kind are MUCH worse. Or are you just assuming that you'll be able to extract fossil fuels from your own soil...forever? Really?
Z99
not rated yet Apr 13, 2014
aa seems to be confused. Power needs happen second-by-second, minute-by-minute. Considerations about "energy security" have no immediate relevance to this discussion.
"Green" power provides insufficient buffering, and we have no economic storage technology.
Transition from hydrocarbons will require decades - once sufficiently cost-efficient alternatives are available. Today they are not. If you want to construct straw-man arguments ("or are you just assuming that you'll be able to extract fossil fuels ...forever?"), why waste our and your time? You remind me of the FDA which prevented the use of superglue to stop bleeding in Vietnam because of the "long term" risks. Yeah, lets put long term cancer risk ahead of saving the patient's life.
The real problem with this type of study is the virtual lack of sufficient testing of their model and modeling assumptions. Getting the model "right" would take a lot more than 3 professors and a couple of hours supercomputing time.
Bob_Wallace
not rated yet Apr 13, 2014
The grid it too small. The bigger the better - it gives more ability to share supply and storage.

What needs to be done is to make the grid smarter. Build in mechanisms that isolate problems rather than allow cascading outage.

We're starting to do that.
Bob_Wallace
not rated yet Apr 13, 2014
aa seems to be confused. Power needs happen second-by-second, minute-by-minute. Considerations about "energy security" have no immediate relevance to this discussion.
"Green" power provides insufficient buffering, and we have no economic storage technology.
Transition from hydrocarbons will require decades - once sufficiently cost-efficient alternatives are available. Today they are not.


Beg to differ. Pump-up hydro offers very economic storage.

Transition off fossil fuels for grid power could be done in a couple decades were we adequately scared. I think fossil fuels will be largely gone in about three decades. Some will likely still be around as deep backup.

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