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Smart Power Grid Could Wreak Havoc On Itself
MrSeb writes "Smart power grid monitoring that lets you pick the exact cheapest time to run the dishwasher or recharge your electric car may put too much power (so to speak) in the hands of the consumer, according to a new study by MIT. Researchers say that users receiving minute-by-minute pricing information might cycle off-peak power use more rapidly than utilities can spool up their power plants. In other words, it's OK if you're the only person charging your Chevy Volt at 2am in the morning, but if a whole town does it exactly the same time... there will be issues."
they will quickly become peak hours, I have the upmost faith in our utilities to gouge us for whatever they can
The big question that seemed/seems lost in all this "The electric car is gonna save the world!" hype is how an energy grid that can barely handle our energy needs AS IT IS is supposed to function when a significant portion of the population replaces their evil petroleum cars with electricity-draining electrics. When I've asked that question in the past to my usual suspect lineup of hippie friends (who also think that organic food and wind turbines are going to save us all too), the only answer I ever got was a vague "Well, most of that'll be happening at night, when the power demand is down anyway." But we're talking HUGE power usage spikes with those cars. Think of how much our system is already taxed when HVAC units have to cool a 10-degree-higher heat wave. Now imagine half the population plugging cars into the gird every night that draw WAY more power than any consumer HVAC unit.
SJW: Someone who has run out of real oppression, and has to fake it.
You could be charging your car at 2AM in the afternoon!
These researchers clearly misunderstood the idea of a "smart" power grid. It is not intended to let you control when you consume your electricity so as to save money. It is intended to let the government/corporations control when you consume electricity.
The truth is that all men having power ought to be mistrusted. James Madison
I doubt that the few people with the intelligence to do this will even get close to being involved with the "smart grid." Be prepared for a decade of power more unreliable than we have now (almost every company I work with has a backup generator).
If I used a sig over again, would anyone notice?
The rest of the world already has peak and off peak tariffs. This is really no different.
Given not everyone will get a smart meeter at once, it should be easy for them to map how usage changes along with price and time of day. The suppliers can know before customers what price changes are about to happen, and should be able to adjust their supply accordingly.
Existing grid can *already* support converting 70% of all the cars to electric, provided that they all charge at night. You really do not appreciate the difference in power usage difference between day and night. Build more power plants & transmission lines and you can get that number even higher. The article is a troll, btw.
___
If you think big enough, you'll never have to do it.
We need to store power so that we can only use that power at a constant rate 24/7.
we have more then what is needed on the generation side but what is lacking is the power transmission that needs to have alot more wires / links.
He's right! And if everyone in town flushes their toilet at the same time, all the pipes will burst and we'll all die!
The solutions here are a case of "No shit Sherlock." Put in a random offset in the update cycling - They do the same thing for automatic software updates already. If you schedule for an update every half hour it might actually update anywhere from 15 minutes to 45 minutes (adjust delay as needed for application). The random staggering keeps everyone from grabbing an update (and thus cycling their power hungry appliances on) at the same time.
Get a web developer
I was at a talk last year about how to solve this issues. The proposed solution was to take the decision to use/not use power out of the hands of the consumer by having smart appliances that could be regulated from an outside source. Basically you would nominate "desires" and the "system" would attempt to optimize power usage to meet those desires over the entire local neighborhood (IE delay running the dryer now to put a quick charge in the car so you can go out to dinner, as dinner is more important to you now than the dried clothes are). This was being proposed in order to smooth out the demand peaks that are being expected when everyone in the street had electric cars and wanted to charge them all up at once, and how this affects the local power infrastructure. The talk presented some interesting data that showed that with minor tweaking you can readily smooth out major peaks.
The question I raised was basically "Yep the technology works, but how are you going to change the mindset of people away from ME ME ME to US US US?".
I am Slashdot. Are you Slashdot as well?
I think the fear is that devices will be programmed to start running when electricity drops below a certain cost. So, say the price drops below 10c/kwh suddenly everyone's electric car will start charging at once, and that surge could cause problems for the supply network. Of course it's also easily dealt with by introducing random small delays in the price update time or other programmatic methods.
In order to successfully mitigate congestion in a network requires the sender having detected packet loss to cut transmission rates exponentially and then linearly increase transmission rates until congestion is detected (exponential back off). I suspect that power congestion response in a smart grid would be similar, perhaps by doubling the current price if demand is exceeding production but only linearly decreasing the price as production exceeds demand.
Which is why, absent mega-watt-hour storage for electric power, wind and PV solar are not useful sources of grid electricity. Once they get above a few percent of the capacity of the grid, their instability currently(*) requires another source of energy that can react quickly when they go up or down in contribution to the grid.
(*) Sorry...
To a Lisp hacker, XML is S-expressions in drag.
I've been looking at a (commercial grade) battery backup for my house, and my thought is, why not let the battery backup pay for itself by charging itself every day at 2 AM (or whenever the power's cheapest) and discharge it at 5:30 PM when the power price is the highest and make 8 - 10 cents/kWh a day. Unfortunately, my utility doesn't have smart meters, so I'm stuck with the flat rate, so I haven't done too much research beyond an initial glance. Has anyone looked into this more in depth? Could arbitraging the electricity price more than pay for itself over time?
In mulitcast network code it is common to randomize scheduling by a factor of +/- 50% in order to reduced synchronization effects.
Similarly, power use scheduling could be randomized across some range.
Perfect solution. Charge capacitor whenever you want at the lowest cost hours. Use said stored charge to power any devices you want at home including your car.
Yeah i know doesn't exist now/yet. But i don't see why it couldn't, you're moving capacity from the grid to the end point.
Systems can be built to deal with this problem, calling it the end of the idea is simply short sighted.
Where genius and insanity become confused true wisdom is found
While not a technically simple answer, this could be solved with "reservations". Your car wants to charge at 2am for 4 hours, it uses the (given) network to ask for that much power at that time. If it is granted the reservation, that many kWh are counted at the smart meter and sold at a discounted rate. If a large amount of power is drawn without a reservation, it's charged at the base rate. If your car *must* charge for 4hrs at 2am and is refused a reservation, you might get a partial discount "for trying". To make the system actual able to load-balance, your car asks for 4hrs of charging anywhere between e.g. 11pm and 7am, and the utility tells it when it get that block. If the meter was actually designed to separately keep track of a few key load circuits *separately* ("the house", car, HVAC), this would work "better" in that the kWh's being charged for can actually be *accounted* to a given device.
The utilities have been doing this in reverse for a long time, with a "utility curtailment" signal sent to HVAC systems to turn them off. However, to my understanding those are typically done in the form of rolling blackouts, neighborhood at a time....
....what?
My local power company pays me (or rather, discounts my bill slightly) to let them mount a remote switch on my house A/C unit. This lets them shut it off for short periods during peak demand.
Installing a similar circuit on e-vehicle charging systems would take care of oddly-timed peaks if everyone in the neighborhood is charging their car at the same time.
tl;dr - just make the grid smarter.
-- Alastair
I got my smartmeter here in Texas more than a year ago. So far the best data I can get is delayed by 2 days and at 15 minute intervals.
There are some mythical devices called HAN that you are supposed to buy somewhere to use for instant monitoring inside your house but I have yet to find anybody selling them.
HTML is obsolete. It's time for a new, simpler and richer markup language.
Both storage and production should be distributed as widely as possible. If half the homes in your neighborhood have solar panels, wind turbines, and on-site storage, then there will be much less need for the coal-fired "utility" plant to adjust to localized spikes.
XML is like violence. If it doesn't solve your problem, you're not using enough of it. --AC
Upmost is a b-grade peripherals manufacturer in Taiwan. I think you meant utmost instead. ;-)
XML is like violence. If it doesn't solve your problem, you're not using enough of it. --AC
of course, but it is afar manageable then most people seem to believe' OTOH, most people who complain about this have no idea what ti takes to charge an electric cars. It's takes lot less electricity then they 'think' it does.
The Kruger Dunning explains most post on
What we need to do is stop being superstitious about nuclear power and build safe nuclear power plants, and actually operate them with the emphasis on safety, rather than the emphasis on cost-cutting (read as: profitability). "Alternative" energy solutions are fine and dandy, but they'll either never catch up with demand, or will catch up too slowly. We may yet have fusion power, but it's still far enough away that we can't make that part of the equation. Nuclear fission may not be the best long-term solution, but it's the best solution we have right now.
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with the right metering scheme, they basically pass their commodity pricing to you. so, you get to decide whether or not you should run the dishwasher when you get home from work, or on a saturday morning, based on what you want to pay. If you want to pay less, you'll run the dishwasher when it's cheaper for you if you're given the ability to make that differentiation. As it stands you have no financial incentive not to run your dishwasher at peak times, so you run it whenever.
regarding the system, it's about load leveling. current systems strain to meet peak energy demand. if they could incentivize shifting energy from that peak, it makes the system's ability to meet peak demand easier. (otherwise we'd need to build more power plants. then NIMBY takes hold.)
my bad, and thanks for not being a dick about it ... thats pretty rare
Price variations on this case are not based on speculation
They are based on the fact that, at night, power consumption drops considerably.
Even though most forms of energy generation have a certain level of control over the power generated, at night you can say there is a surplus (since most forms have a generation floor)
how long until
Wouldn't allow everyone to receive the power at one time. If the plants were overloaded, two things could happen, A) pricing jumps up automatically, causing some devices to not consume power due to their price rate limiting.
Second, all the smart equipment in the grid could simply not pass full amperage through to the receiver while the plant is spooling up. The smart meters can provide rolling blackouts as needed to keep the grid under control. These smart devices in the home would be aware of they reduced power availability and simply wait until the grid told them there was sufficient power to activate.
Smart devices that want to turn on at certain times would not turn on exactly at that time, there would be a random number generator which adds some sort of randomized delay so that you set it to run when the price drops to $0.05/hour, and when that occurs, it waits some random amount of time between 0 and 30 minutes. All smart devices do the same thing, effectively giving the grid time to compensate and allow plants to spool up as needed. The smart devices can also be told the grid is overloaded so please wait.
We're talking about a SMART GRID ... you simply program the devices to avoid the problem. If you don't, its not a SMART grid, its just a grid with some silly controllers on it.
Second, once the power company realizes that everyone charges their electric cars at 2am during the price drop ... they simply spool the plants up in advance so they are ready for the load. It'll be rather predictable, kind of like the early morning when everyone gets up and starts using hair dryers and electric ranges, microwaves, electric hot water heaters and all that. They just spool the plants up in advance as the load is rather predictable.
Someone at MIT is missing the tree because they keep looking at the forest.
The grid and these devices are communicating with each other, the grid can simply tell the devices to wait a minute, its not ready, and if they try now they are going to get denied. This isn't a difficult problem to solve, I'm fairly certain it would be trivial to implement the software required on the cheapest of microcontrollers. An Arduino for instance would have no problem dealing with this from both the grid side or the home device side.
Persistent Volume manager for Kubernetes - https://github.com/dwimsey/openshift-pvmanager
I've been saying this for years - despite what boosters of electric cars would have you believe, there isn't a magical well of electrical power available at night.
Yes there is. You've been wrong for years.
The utilities have spent the better part of a century either finding customers for the overnight low demand period or optimizing their networks to not generate unneeded power in the first place.
But they haven't found enough customers for overnight electricity to make the demand anything like during the day. As to "optimising the networks", power station capacity that is there during the day is also there at night. Whilst much of it is currently taken off line, if night time power demands increase, then they can leave more of them on-line at night.
Of course there are consequences to changes. But that's a very different thing from there being catastrophic, or even difficult consequences.
If the end user has programmed their charging to begin at 2am every night, maybe the power company can offer a slight incentive to have people opt in to send their schedules in advance.
This way the utility will know in advance that a ramp up in demand will occur at 2am and in turn schedule their equipment to start up in time.
Not everyone may elect to send in their schedules, but enough may be motivated by the incentives to be able to indicate a general trend which can be extrapolated to the whole user base.
It seems like it would be a reasonable feature for the power meters to incorporate.
Does it bother anyone else that many are proposing that we allow utilities the right to tell us when we can and can not use certain appliances within our own house?
But it's Green, dude.
The odd thing is that most industries want to sell you more stuff, whereas the energy industry keeps trying to sell less stuff and raise prices. Pretty soon we'll be better off running our own generators instead of buying grid power.
I doubt many people consistently drive more than 100 miles a day.
Then you doubt that many people work in parcel delivery or other forms of on-site service. I doubt clients will let service technicians steal their electricity.
Isn't it obvious that if you design the system so people can take advantage of 'off-peak' hours cost it would eliminate that time being 'off-peak'?
Or do people not realize that there are millions of other people in this country alone who in the same system that would be seeking the same monetary savings?
Are we too short sighted to see that in such a system as these same people chase each newer, and shorter 'off-peak' time that it would eventually end up being a system that had NO off-peak time resulting in higher costs for all? Not to mention that in such a system we willingly allow others to dictate what we do with what we pay for after we pay for it like we don't own it to begin with?
Doesn't PV output peak at roughly the same time that demand from air conditioning and business lighting peaks?
I was offered a "deal" on some kind of residential demand metering.
I mean some deal. The off-peak price went down a little, but the on-peak price went up a lot. It is one thing to purchase some kind of switch or Smart Grid interlink so that the dehumidifer only runs at night and that the water heater only runs at night. But the way this deal was structured, I would have to do almost everything -- cook, wash clothes after 11 PM at night to even break even.
If the deal was essentially "revenue neutral" for a common pattern of residential usage and you got a discount for shifting time-of-use, I would have said bring it on. But to raise my electric cost unless I became a total night owl, fuggedaboudit!
The problem is not that we don't have enough power. We have enough power in generation. The problem is nobody wants wires in their backyard so there is no way to upgrade the transmission and distribution systems to meet demand. A decent amount of excess power is actually available to be imported from neighboring states when needed. There is actually a very robust market just for exchange of power. It is really only a couple days out of each year when we get close to capacity of the transmission lines.
"Computers are a lot like Air Conditioners" "They both work great until you start opening Windows"
Why doesn't it dynamically adjust as usage varies? Plug in at the right time and you lock in the price for a determined time (which is shown to you on said smart meter). Problem solved.
Twinstiq, game news
A capacitor stores DC.
Then run 48 V DC over Cat 6 throughout the house and replace various small appliances' power supplies with DC ones. If 48 V DC is good enough for telcos, it ought to be good enough for homes.
Last Call?
Persistent Volume manager for Kubernetes - https://github.com/dwimsey/openshift-pvmanager
You've got 10,000 computers trying to get updates from your host at 12:00am, what do you think is going to happen?
I'm going to use a lot of bandwidth ... 10k hits isn't really that big of a deal for any modern web server. Apache and IIS will both handle it on a single machine if configured properly.
While I don't work for some crappy AV company, I can say that serving 10k users at a single point in time is only marginally difficult if you don't know what you're doing. Trivial if you do. Get back to me when you start talking millions of users wanting updates at a single point in time.
Persistent Volume manager for Kubernetes - https://github.com/dwimsey/openshift-pvmanager
Its not 'no you can't do that' its 'if you do that now it'll cost you $1.50, but if you wait till midnight, it'll cost you $0.25'.
Persistent Volume manager for Kubernetes - https://github.com/dwimsey/openshift-pvmanager
As pointed out in the Risks Forum twenty years ago, we're moving more and more to constant-power loads on the electrical supply. When most power was resistive lighting, dumb motors, and heat, we had a nice positive slope to the load/voltage curve and the system was quite linear. Now we have a rapidly increasing proportion of "smart" loads -- ones which use switching techniques to effectively get constant power. Your computer is one, but so are newer air conditioners, refrigerators, vehicle chargers, etc.
So?
A constant power load has an effective negative impedance: as the voltage goes down, the current goes up. And that's unstable. When the cumulative load line shifts to zero impedance, it all becomes unstable. A brownout will actually result in an increase in current, bringing the system down with no warning.
Sleep tight, chilluns.
Lacking <sarcasm> tags,
SLA = Service Level Agreement. Instead of saying "off peak = midnight - 6am", the utility agrees to provide power for an agreed duration at the off-peak rate, for those purposes e.g. "3+ continuous hours between 10pm and 6am". They can vary the time to suit their loading: some days it might kick in at 10pm, other days at 3am.
Some days you get only the 3h you absolutely need, other days it might be available all night. You don't care if you're asleep, do you, as long as they meet the SLA and the night jobs get done? If they don't, there would be a penalty, of course.
(this is not a
Obviously what we have here is a failure to centrally communicate. A central computer or network of computers can schedule grids to come on and off during off peak hours based on the load in each power grid. Priority could be scheduled by previous usage and trumped by need (emergencies). After a while, spikes of energy will be averaged and plants will be able to anticipate the need.
Google and Amazon network are built not to go down when usage expected to be high, same basic principles apply over time.
Peak Hours will always be peak hours. I work for a power company in rural Nebraska where over half our load is just irrigation. Farmers run their irrigation all night and we control them during peak hours set forth by our wholesale providers. We run more load during off peak hours then we do during controlled peak hours. Big business and farming accounts for well over 75% of our load and revenue , however, households account for over 75% of our customer base. Customer load can't even shake a stick at business loads on any system, I don't care how many Chevy Volts the customers have charging. This article was not well researched and seems to be written by someone that doesn't understand the industry.
off peak power usage is a technology of the 60s-80s, e.g. for heating to use electricity used in industry during the daytime.
i always imagined a smart grid would mean that not everybody turns on at 2am but that you get even a little bit a better rate but letting the company decide when your car will be charged (e.g. sometimes between 1am and 8am).
Just randomly bias each smart meter or print different peak/off peak times on everyones bills.
Realtime minute by minute rates could actually use feedback from the grid to improve reliability or respond to emergencies where n-1 could otherwise not be achived. You just include grid stability in the cost calculation.
Sounds to me that MIT does not know what a smart power grid is, sigh.
Cost free eBook I read (by iBook/Kobo/Amazon/ObookO/Gutenberg etc.): "The Green Odyssey" by Philip Jose Farmer.
Basically, as part of her graduate work in Ecology and Evolution at SUNY Stony Brook (about 1990), my wife (Cynthia Kurtz) did computer simulations of digital organisms, and discovered that sometimes being "dumb" is really being smart, because you don't stick with the smart crowd who ends up competing over the same resource. People did not want to believe her results because they went against all the "foraging theory" of the time. She only got an MA out of that, not a PhD. She presented her results at an early ALife conference. Now people rediscover that effect in smart power grids...
A 21st century issue: the irony of technologies of abundance in the hands of those still thinking in terms of scarcity.
Smart grids don't work like the summary is suggesting! ... it is surplus power that is sold cheap
a) there is no power plant spooled up
b) it is not that you just "activate your dishwasher". It is a market operation: I buy power for the actual price, is the buy order processed, the dishwasher activates.
It is impossible in a smart grid that to many dish waters activate.
Cost free eBook I read (by iBook/Kobo/Amazon/ObookO/Gutenberg etc.): "The Green Odyssey" by Philip Jose Farmer.
This is not about power generation but rather power distribution. Try this: take a common wire, open it up and separate a single copper hair. Use that to bridge an AA battery. It will get hot quickly, as the battery is discharging at its top speed. Now shortcircuit an electrical plug without protections. The hair will melt away quickly. That's what might happen to the grid.
as shown in this graph: http://www.nationalgrid.com/uk/Electricity/Data/Realtime/Demand/Demand8.htm
before, the excuse was that Chernobyl happened because the soviets were reckless and it would never happen in the west.
what's the excuse for Fukishima, which BTW was recently measured at 10+ SV/hr and i have heard unconfirmed reports that 10 was not so much a reading but the maximum that the meters can read out and so it could be any amount higher than 10
Snowden and Manning are heroes.
I have an electronics and engineering background, so I understand the point you're trying to make; however if we had more power plants then distribution wouldn't be a problem anymore. One of the major hurdles preventing more power plants from being built is environmental concerns. I also understand that your average environmentalist would rather have his right arm cut off rather than allow a nuclear power plant to be built, but let's face it: they don't want any power plants built. The more extreme environmentalists don't even want solar or wind generating facilities built because they think even that harms the environment (think of the poor animals!). What I'm saying is that people need to stop having these knee-jerk reactions to nuclear power, and we need to operate them in the most conscientious way possible, because they can and will be a major hazard if mis-managed. Additionally there are cutting-edge designs out there for smaller-scale nuclear reactors that are, compared to current-generation plants, virtually intrinsically-safe, cost a fraction to construct and install, would take a fraction of the time to complete, and could be more widely distributed.
The space program suffered numerous setbacks before we landed men on the moon. Few can debate the benefits we've reaped because of those achievements. I am cognizant that "setbacks" with nuclear power have much longer-lasting and wider-ranging ramifications, but we cannot continue the way we are; we cannot go backwards, we must go forwards.
Are YOU using the TOOL, or is the TOOL using YOU? Think about it!
Believe me I thought that of anybody the Japanese would be meticulous and cautious in managing something like nuclear power, but Mother Nature caught them with their pants down, apparently. What has happened there is regretable, but I don't think the knee-jerk reactions I've been hearing about from all over the world are appropriate or warranted. We need to learn from incidents like in Japan, yes, but we do not need to abandon nuclear power at this time, like Germany is planning on doing.
Read my reply to the comment above yours, if you like. I had more to say on the subject.
Are YOU using the TOOL, or is the TOOL using YOU? Think about it!
Except when the air is still and its cloudy. Then coal and gas would have to work so much harder.
I'm sure someone mentioned it already but it may be possible to shut off everyone's power at exactly the same time.
http://www.ioactive.com/services_grid_research.html
Imagine a worm spreading over the mesh setting all the smart meters in LA to pulse on and off...wonder what that would do...
"If any question why we died, Tell them because our fathers lied."
It's not the "always on" aspect that causes the problem, it's the fact that the load V/I curve is hyperbolic with a negative slope rather than linear with a positive slope. Since we're primarily concerned with frequencies much less than line, things like power factor aren't really important and since the function is dominated by the real components at those frequencies, it could be called "negative resistance" but too often "resistance" is used to refer to a zero-intercept linear function so the more general "impedance" is less confusing to most. Pedants, of course, can always find something to complain about.
Lacking <sarcasm> tags,
Here is a link to her thesis:
http://www.cfkurtz.com/publications.html
"Kurtz, C.F. 1991. The Evolution of Information Gathering: Operational Constraints. M.A. Thesis, State University of New York at Stony Brook. Also available here. "
http://www.cfkurtz.com/Kurtz_EvolutionOfInformationGathering_1991.pdf
"I present two new approaches to the study of information in foraging theory. First, rather than determine the cost a forager should pay to obtain information, I concentrate on the consequences of information use in an interacting population. I describe a density-dependent model which tracks genotypes with high and low information access through evolutionary time. Stable polymorphisms result. I suggest that the value of information is not monotonically increasing. Second, I present a scheme for partitioning the information used in the decision making process. Three types of information are recognized: internal information, or an individual's internal state; external information, or environmental factors; and relational information, or rules for predicting transformations of internal state. Interactions between the three types are examined in an extension of the basic model."
She says this paper is more succinct, but it is not online: "Kurtz, C.F. 1991. The evolution of information gathering: operational constraints. In From Animals to Animats, eds. Meyer, J.A. and S.W. Wilson. Proc. 1st Int. Conf. on Simulation of Adaptive Behavior, Paris, MIT Press."
A 21st century issue: the irony of technologies of abundance in the hands of those still thinking in terms of scarcity.
It took people who went to MIT to figure we can't have a "smart" grid decide to charge all our cars at the exact same moment? If that was your thesis you should request back all of tuition. And if there is ever an SLA agreement associated with my electric bill that has terms I have to adhere to, I'm going off-grid.
Yep, turns out that operating a gigantic, synchronously operated, dynamic and nonlinear machine with millions of interacting parts in real time and right up to the edge of its limitations ain't so easy to do after all. It's only now that computers+software are getting "smart" enough to keep up with the (supposedly) dumb ol' electric grid.
So, you are looking at runaway prices like when California deregulated the energy market and the automated computer programs all manipulated the price immediately? Or maybe you are referencing the stock market, where automated trading algorithms seem to be designed to respond to eachother to produce price instability?
"power grids and organisms are two different, very different items."
Ture, but I guess I was not clear enough. Consumers of power are like the organisms; the grid is more like the ecosystem. What makes sense individually may be bad both collectively (as a less than global optimum) and also for the individuals (given that other smart individuals do the same thing, which leads to competition or in this case other instability in the system). So those who do the dumb thing may make out better or be better for the system, because there is less competition for what otherwise seems like a good deal to everyone. In general, this is an issue about local optimization by "smart" actors deciding based on local information vs. global optimization. It is part of the reason diversity has value.
It is also an example of both "market failure" and individual failure and probably has applications to financial markets as well. For example, if everyone thinks the same stock sector is undervalued, and starts buying in it, they may bid up the price for stocks there past what they are worth (but as everyone is buying, it becomes a bubble), whereas stock sectors that are not such a bargain might have been better choices for reliable value from dividends.
A 21st century issue: the irony of technologies of abundance in the hands of those still thinking in terms of scarcity.
dE/di = Z(i)
in other words, the slope of the curve at a given point. Now, you can't have a literal negative resistance where a positive current results in a negative voltage -- that generates power. However, it's not at all unusual to have a situation where an increase in current results in a reduction in current. There are even simple primitive semiconductor devices that do that (look up Esaki diodes.)
Now think of what happens when the mains supply has a limited ability to provide current. With a positive impedance load, a drop in the supply voltage results in a drop in current. That's a "brown out." In a power network, it's a simple relationship that makes it fairly easy to manage the load, since the supply voltage isn't guaranteed to be rock-steady. More loads, more current, voltage drops, current drops, balance achieved until they put more generators online.
When you have an actively managed load such as computer power supply (draws as much power as it needs regardless of the line voltage, the current is inversely proportional to the voltage. Which, if you think about it, is a negative impedance relationship. Now when you turn on an extra computer, the network current increases and the voltage drops -- and the current increases, the voltage drops some more, etc.
Crash the electrical grid.
Lacking <sarcasm> tags,