The too-smart-for-its-own-good grid

August 4, 2011 By Larry Hardesty
A 'heat map' depicting the rates charged by electricity producers on the Eastern seaboard and across the Midwest — in which colors at the red end of the spectrum represent high prices and colors at the blue end low prices — demonstrates how drastically the wholesale-energy market can change in as little as five minutes. Credit: Mardavij Roozbehani

In the last few years, electrical utilities have begun equipping their customers’ homes with new meters that have Internet connections and increased computational capacity. One envisioned application of these “smart meters” is to give customers real-time information about fluctuations in the price of electricity, which might encourage them to defer some energy-intensive tasks until supply is high or demand is low. Less of the energy produced from erratic renewable sources such as wind and solar would thus be wasted, and utilities would less frequently fire up backup generators, which are not only more expensive to operate but tend to be more polluting, too.

Recent work by researchers in MIT’s Laboratory for Information and Decision Systems, however, shows that this policy could backfire. If too many people set appliances to turn on, or devices to recharge, when the price of crosses the same threshold, it could cause a huge spike in demand; in the worst case, that could bring down the power grid. Fortunately, in a paper presented at the last IEEE Conference on Decision and Control, the researchers also show that some relatively simple types of price controls could prevent huge swings in demand. But that stability would come at the cost of some of the efficiencies that real-time pricing is intended to provide.

Today, customers receive monthly electrical bills that indicate the cost of electricity as a three- to six-month average. In fact, however, the price that power producers charge utilities fluctuates every five minutes or so, according to market conditions. The electrical system is thus what control theorists call an open loop: Price varies according to demand, but demand doesn’t vary according to price. Smart meters could close that loop, drastically changing the dynamics of the system.

Taking control

Research scientist Mardavij Roozbehani and professors Sanjoy Mitter and Munther Dahleh assumed that every consumer has a “utility function” describing how inconvenient it is for him or her to defer electricity usage. While that function will vary from person to person, individual utility functions can be pooled into a single collective function for an entire population. The researchers assumed that on average, consumers will seek to maximize the difference between the utility function and the cost of electricity: That is, they’ll try to get as much convenience for as little money as possible.

What they found was that if consumer response to price fluctuation is large enough to significantly alter patterns of energy use — and if it’s not, there’s no point in installing smart meters — then price variations well within the normal range can cause dangerous oscillations in demand. “For the system to work, supply and demand must match almost perfectly at each instant of time,” Roozbehani says. “The generators have what are called ramp constraints: They cannot ramp up their production arbitrarily fast, and they cannot ramp it down arbitrarily fast. If these oscillations become very wild, they’ll have a hard time keeping track of the demand. And that’s bad for everyone.”

The researchers’ model, however, also indicates that at least partially shielding consumers from the volatility of the market could tame those oscillations. For instance, Roozbehani explains, utilities could give consumers price updates every hour or so, instead of every five minutes. Or, he says, “if the prices in the wholesale market are varying very widely, I pass the consumer a price that reflects the wholesale market conditions but not to that extent. If the prices in the wholesale market just doubled, I don’t give the consumer a price that is double the previous time interval but a price that is slightly higher.” According to Roozbehani, the same theoretical framework that he and his colleagues adopt in their paper should enable the analysis and development of practical pricing models.

The trade-off

But minimizing the risks of giving consumers real-time pricing information also diminishes the benefits. “Possibly, when you need an aggressive response from the consumers — say the wind drops — you’re not going to get it,” Roozbehani says.

One way to improve that trade-off, Roozbehani explains, would be for customers to actually give utilities information about how they would respond to different prices at different times. Utilities could then tune the prices that they pass to consumers much more precisely, to maximize responsiveness to fluctuations in the market while minimizing the risk of instability. Collecting that information would be difficult, but Roozbehani’s hunch is that the benefits would outweigh the costs. He’s currently working on expanding his model so that it factors in the value of information, to see if his hunch is right.

“As far as I know, very, very few people are analyzing the dynamics of electricity markets with experience from control theory,” says Eugene Litvinov, senior director of business architecture and technology at ISO New England, the organization that oversees the operation of the electrical grid in the six New England states. “I think we should encourage these kinds of studies, because regulatory bodies and government are pushing for certain things, and they don’t realize how far they can push. For example, they want to have 30 percent wind penetration by 2020, or something like this, but that could cause serious issues for the grid. Without that kind of analysis, the operators would be very uncomfortable just jumping over the cliff.”

But, Litvinov adds, an accurate model of the dynamics of energy consumption would have to factor in consumers’ responses, not only to changing electricity prices, but also to each other’s responses. “It’s like a game,” Litvinov says. “People will have to start adopting more sophisticated strategies. That whole dynamic is itself a subject for study.” Roozbehani agrees, pointing out that he, Dahleh, Mitter, and colleagues have already published research that begins to examine exactly the questions that Litvinov raises.

Explore further: Texas Tech researchers gauge new Chinese cotton policy shift

Related Stories

Texas Tech researchers gauge new Chinese cotton policy shift

April 27, 2011

China’s textile mill demand for cotton played a critical role in driving cotton prices to a record $2.27 last month, up 175 percent over the year before. But now cotton producers are wary of lower cotton prices in the ...

CSIRO Builds Smart Energy System

March 22, 2006

CSIRO technology will help to reduce black-outs and improve the reliability and efficiency of the electricity grid while reducing greenhouse emissions. It will also complement smart electricity meters promising consumers ...

Solar leader sees bright future

December 10, 2010

Zhengrong Shi, an engineer turned entrepreneur, has become one of China’s richest citizens by betting heavily on the future of solar power. In a talk on Tuesday at MIT, he outlined his vision for how he believes solar ...

Combine carbon consensus with income tax cuts: study

March 15, 2011

A carbon pricing proposal can find consensus and would allow income tax cuts, as long as industry handouts can be kept in check, according to a new report from The Australian National University.

Recommended for you

Samsung to disable Note 7 phones in recall effort

December 9, 2016

Samsung announced Friday it would disable its Galaxy Note 7 smartphones in the US market to force remaining owners to stop using the devices, which were recalled for safety reasons.

Swiss unveil stratospheric solar plane

December 7, 2016

Just months after two Swiss pilots completed a historic round-the-world trip in a Sun-powered plane, another Swiss adventurer on Wednesday unveiled a solar plane aimed at reaching the stratosphere.

Solar panels repay their energy 'debt': study

December 6, 2016

The climate-friendly electricity generated by solar panels in the past 40 years has all but cancelled out the polluting energy used to produce them, a study said Tuesday.


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Aug 04, 2011
Most people are either at work or sleeping a substantial part of the day, so the only way to regulate usage is to automate it. My A/C in Las Vegas, NV had remote shutoffs back in the 1980s. It was never shut off for more than 15 minutes a day and I never noticed it. Other candidates for remote control would be water heaters and plug-in cars.
5 / 5 (1) Aug 04, 2011
Most people are either at work or sleeping a substantial part of the day, so the only way to regulate usage is to automate it. My A/C in Las Vegas, NV had remote shutoffs back in the 1980s. It was never shut off for more than 15 minutes a day and I never noticed it. Other candidates for remote control would be water heaters and plug-in cars.

You argue for central control of demand. But if prices double, I will just cut off my A/C by hand. No matter what, substantial demand will be driven at the customer level.
not rated yet Aug 04, 2011
Other candidates would be refrigerators and to a lesser extent dish and clothes washers dryers etc.
not rated yet Aug 06, 2011
Many modern clothes washers and dishwashers have a delay function that would do just as well. Just study the price fluctuations for a week and see about what time it'd be best to run them.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.