What Happens to Unused Electricity in Distribution Transformers?

[Venkata Satish]

I Have a Dumb Question. If Electricity Supplied from Substation to Feeder to Transformer and Under Transformer If There Are Many Consumers. Assuming That many Consumers Went on for a Holiday, Does Utility Still Pay for the Electricity to the Generation company for the Electricity they Supplied?

Technically, what had happened to electricity which was passed till transformer? Is it earthed?

 

[anorlunda]

The rate of energy produced is adjusted to match the rate on energy consumed (plus losses) all the time,

On holidays, less is made and less is used.

 

[Venkata Satish]

But how ?
the generator company had already sent the electricity. Am i missing something here?

 

[Venkata Satish]

What I understand it the generation company continues to send standard electricity say 10MW, whether the down stream systems use it or not. Electricity is already produced it can not be taken back or stored

 

[anorlunda]

Yes, you missed a lot. Your understanding is wrong.

There is a PF Insights article that addresses your question. Read that first, then come back if you have more questions.

https://www.physicsforums.com/insights/what-happens-when-you-flip-the-light-switch/

 

[Venkata Satish]

Yes ..I have read the link you have indicated

Assuming if they opt for DAM, assuming utility orders 5MW for that day and for a argument sake assume that many people went for vacation. And the consumer level only 2 MW. So what happens to the 3 MW..i think utility steel needs to pay for 5MW

Still i am missing somrhing? I am sorry i am not an electrical engineer. It may be stupid question to you

i am trying to understand Demand Response concepts

1 day: The Day-Ahead-Market (DAM)

Reference https://www.physicsforums.com/insights/what-happens-when-you-flip-the-light-switch/

 

[anorlunda]

Actually, that is a very good question. In your first post, you asked about earthing the excess power. Excess power is never generated.

But now you make it clear that you are asking about payment. Yes, if the power plant contracts 100MW in the day-ahead market but only 95MW is needed in real time, he is still paid for 100. But consumers pay only for the energy they use.

Where does the money come from four that 5MW difference? All power plants and all utilities contribute to a fund to pay for someone to run that DAM market. The money comes from that fund.

Suppose the power plant sold 90MW in the DAM market but the next day 95 is needed. The extra 5MW are purchased on the real time RT market where prices may be different than DAM prices. The RT market is calculated every 15 minutes.

The markets are motivated to be as accurate as possible in how much they buy in advance.

Edit: demand response can be thought of as a negative way to balance load and generation. If an extra 10MW is needed, the market can pay a power plant to make 10 more, or it can pay demand response to demand 10 less. Demand response is not normally sold in the DAM but only in the RT market. The prices paid for demand response are much higher than power plant purchases. Therefore demand response is not used unless an emergency is near.

 

[sophiecentaur]

What I understand it the generation company continues to send standard electricity say 10MW, whether the down stream systems use it or not. Electricity is already produced it can not be taken back or stored

This answer is a more elementary response to your question than the other posts and I think this is the answer you 'need': (It may not be so simple for a generator that's part of a network but we should get this straight first).
On a basic level, that statement is wrong. Energy can only be dissipated in the Resistive Part of a Load. If the resistance is infinite (open circuit`) then no power can be supplied.. The 10MW that you quote is a maximum possible. No load and the generator will either speed up and jump off its bed or the regulation will kick in and limit the amount of fuel supplied to the amount needed to overcome the very small losses in the system.
An easier equivalent would be a 13A plug, with the appliance switched off. The "13A" just refers to the current at which the fuse will blow. It is the Voltage of the supply, along with the resistance of the load that determine the power dissipated / transferred. Any 240V appliance can be fed from a 13A plug as long as it doesn't need more than 13A.
The term "Electricity" that you use is not a Quantity. You mean Electrical Power (I think) and the amount of Power supplied will depend, as I said, above. on the generator volts and the load resistance. It's not like a chef who produces 10 pies per hour, which pile up on the counter if no one eats them. The chef only produces a pie if he has been asked for one and his maximum per hour is ten.

 

[russ_watters]

Yes ..I have read the link you have indicated

Assuming if they opt for DAM, assuming utility orders 5MW for that day and for a argument sake assume that many people went for vacation. And the consumer level only 2 MW. So what happens to the 3 MW..i think utility steel needs to pay for 5MW

Still i am missing something?

The utility doesn't pre-purchase power and the generating company doesn't generate it willy-nilly. The grid's production is continuously adjusted to match the load. It has to be, otherwise, the generators wouldn't stay in sync and you'd have problems like voltage and frequency fluctuations. So, quite literally, if there is too much power being supplied to the grid, someone closes a valve on the dam and reduces its power output.

The way this works in a market setting is with variable pricing. If the grid gets oversupplied, the value of the electricity drops, in real time, to the point where it becomes uneconomical to keep selling it, so the producers reduce their output. It is rare that there is ever a true surplus, but when that happens, the price can actually go negative (the electric company will pay customers to use electricity) or large suppliers that don't throttle well, like nuclear plants, can dump the excess heat into the atmosphere instead of using it to make electricity (can't find a reference for that, so I don't know how common it is).

In some cases, power can be exported long distances, but here's an example of it being sold at a loss:
http://business.financialpost.com/fp-comment/ontarios-power-trip-power-dumping

Here's an incident with a negative price:
http://cleantechnica.com/2015/10/01/texas-electricity-prices-going-negative/
Wind power is particularly susceptible to negative pricing because unlike solar, it doesn't necessarily peak when the grid peaks.

 

[anorlunda]

The utility doesn't pre-purchase power

Yes they do. Read the Insights article https://www.physicsforums.com/insights/what-happens-when-you-flip-the-light-switch/

About 50% of energy is traded in long term (5-10 years) advance contracts, 40% in the DAM (day-ahead-market), and 10% in real time.

 

[anorlunda]

It is rare that there is ever a true surplus, but when that happens, the price can actually go negative (the electric company will pay customers to use electricity) or large suppliers that don't throttle well, like nuclear plants, can dump the excess heat into the atmosphere instead of using it to make electricity (can't find a reference for that, so I don't know how common it is).

By the way, that statement is also wrong. The wholesale market participants are generators and utilities. Retail customers are insulated from that. When prices go negative, the generator pays the market, rather than being paid. Negative prices usually persist only for an hour or two.

Retail customers pay rates to the electric company according to tariffs submitted by the utility and approved by the PUC. The tariff rates typically hold the prices constant for a year or two. Those rates are never negative.

In other words, the wholesale market is much more volatile than the retail market.

 

[Venkata Satish]

Let me explain me in simple terms

Assuming that Utility consumer does have manual meters. Which means the meter reads are only captured every month and the difference of old reading and new reading is the consumption of the specific customer. And that particular customer is charged based on the tariff .

Meaning Bill Amount = Number of units consumed * cost per unit

So basically, you don not know the consumption of each customer on the hourly basis, or daily basis because they are manual meters

Assume that there 100,000 such customer is some city. How do Utility calculate the total consumption would be? Per day how much electric they order? As per the below if a utility orders DAM of say 50MW, if customers consume only 40MW. Utility gets money for only 40MW usage from customers(ignore losses for a moment). but they have to pay for 50MW to utility is that right?

----------------------------------------------------------------------------
About 50% of energy is traded in long term (5-10 years) advance contracts, 40% in the DAM (day-ahead-market), and 10% in real time.
----------------------------------------------------------------------------

1. I am still not clear what happened to the electricity power of difference of 10 MW. The generator would have created by burning coal , or by hydro or nucelar etc. Or the power itself is not created in the first place?
2. What if the consumption of customers go high. Say if they consume 60MW, will the generation company still supply the extra 10MW? (above and beyond what utility promised)
3. With Manual meters we can't predict the real time energy. Is that right?
4. DAM is not possible with manual meters. Is that right?

Just assume that all 100,000 customers are equipped with smart meters and smart meters sends consumption data every 15 minutes, we can order the energy as per DAM and real-time . This way utility saves money. Is my understanding correct?

 

[russ_watters]

Yes they do. Read the Insights article https://www.physicsforums.com/insights/what-happens-when-you-flip-the-light-switch/

About 50% of energy is traded in long term (5-10 years) advance contracts, 40% in the DAM (day-ahead-market), and 10% in real time.

Yeah, I knew that wasn't really right after I said it -- I was trying to find a way to say that electric companies don't just run their generators willy-nilly because they already sold the power. Contracts or not, they constantly adjust their output.

 

[russ_watters]

So basically, you don not know the consumption of each customer on the hourly basis, or daily basis because they are manual meters

Assume that there 100,000 such customer is some city. How do Utility calculate the total consumption would be?

The utility company does not have to just guess ahead of time and live with the guess: the generators feel the load. Look at the graph on the right, halfway down the page, where it says "real time statistics":
http://www.pjm.com/

1. I am still not clear what happened to the electricity power of difference of 10 MW.

Again, such a thing never happens. They are constantly adjusting (well...10MW isn't much, so there may be fluctuations of that amount...).

Or the power itself is not created in the first place?

Right.

3. With Manual meters we can't predict the real time energy. Is that right?

Yes, but they can feel the real time load.

 

[sophiecentaur]

Yes, but they can feel the real time load.

. . . . . and that load will only consume what it wants. The 'system' cannot supply any more than that - in whatever way the input is shared by all the generators. I have been interpreting the thread title in that way, rather than including interactions within the grid.
If someone can, somehow, insist on supplying an additional 10MW when the system is in a steady state, then someone else has to supply 10MW less. That has to be obvious, doesn't it?

 

[Venkata Satish]

If I understand correctly, i a very lay man's terms as soon as switch on the bulb in the bed room the demand information all the way propagated to transformer to Feeder to transmission lines to Generation station . Is that right?
This way Generator know how much to produce in the output and supply
Sorry - But still my question is, the extra resources are already used like coal, nuclear etc. I know they are controlling output

On the commercial front, if utility could not predict the consumption correctly they end up paying more to Generator company and losing the money. Kindly confirm my understanding. So smart meters is the way to predict real time demand. Correct me if i am wrong

 

[sophiecentaur]

Sorry - But still my question is, the extra resources are already used like coal, nuclear etc. I know they are controlling output

Yes. I get your point. There is always a time lag between a change in load and the generator output. There is some 'slop' / 'inertia' in the system that will allow, for instance, the steam pressure in the boilers to build up over a short time before the rate of fuel supply is adjusted. In the whole network, there are generators with fast responses (gas turbines, for example) and they will react faster and reduce their output quickly. If there is not enough fast adjustment available, the generators would all speed up and some of the unwanted input energy will turn up as kinetic energy of rotation. Also, the other loads will experience a higher voltage so they will dissipate more power. Likewise, a massive increase in load can result in the generators slowing down, the volts reducing and everyone's lights going dim - until they feed more coal / fuel into the boilers etc..
I remember talking to a guy (wayyy back) who was doing a study into dumping the power produced by a nuclear power station, in the event of the (single) grid supply line being damaged. Nuclear Power stations are the slowest to respond to controls and you could get melt down (apparently) if a load is suddenly removed. The solution being studied was to use massive motors for a pump storage system into a lake in nearby mountains.
So your question is very valid and it can be a serious problem.
Our PF friends with more practical knowledge of these things can probably give you more (an infinite amount of) info on this. I think it may be a time to cue Jim ?

 

[256bits]

If I understand correctly, i a very lay man's terms as soon as switch on the bulb in the bed room the demand information all the way propagated to transformer to Feeder to transmission lines to Generation station . Is that right?
This way Generator know how much to produce in the output and supply
Sorry - But still my question is, the extra resources are already used like coal, nuclear etc. I know they are controlling output

On the commercial front, if utility could not predict the consumption correctly they end up paying more to Generator company and losing the money. Kindly confirm my understanding. So smart meters is the way to predict real time demand. Correct me if i am wrong

For a fully supply and demand electical market, it can work the same way as any financial market, so that risk is spread out amongst the players.
Not all power generation and utility servicing regions operate under such a market, as there may be controls in place from the government as in any industry.
To protect themselves from fluctuations in demand and supply, and the resulting fluctuations in price in a market, a secondary market consisting of hedges and options appears.
See,
https://en.wikipedia.org/wiki/Hedge_(finance )
Sme examples.
1. Producer and utility may contract at a price and volume of energy delivered, with an option for the utility to purchase x amount more at the same or different price.
2. A "ceiling" price is agreed upon for x amount of product. If the spot price is above the ceiling the producer pays the buyer the difference. If the spot is below the spot price, the purchaser pays the producer.
3. A clearinghouse would be set up to coordinate the financial transactions between the players if there are many producers and buyers. With an area with only one producer and one utility transactions would be necessarily in both's favour. Neither would want to put the other out of business, jeopardizinng their own viability.

So evaluation of risk factor, and the people employed by the companies had better take that into account when buying and selling a product.

 

[anorlunda]

If I understand correctly, i a very lay man's terms as soon as switch on the bulb in the bed room the demand information all the way propagated to transformer to Feeder to transmission lines to Generation station . Is that right?
This way Generator know how much to produce in the output and supply
Sorry - But still my question is, the extra resources are already used like coal, nuclear etc. I know they are controlling output

On the commercial front, if utility could not predict the consumption correctly they end up paying more to Generator company and losing the money. Kindly confirm my understanding. So smart meters is the way to predict real time demand. Correct me if i am wrong

You are re-asking the same questions answered and confirmed in earlier posts.

The answers to all your questions are all in the insights articles.
https://www.physicsforums.com/insights/what-happens-when-you-flip-the-light-switch/
https://www.physicsforums.com/insights/ac-power-analysis-part-2-network-analysis/

The instantaneous unbalance between generation and load becomes rate of change of frequency. Frequency is the feedback signal used to adjust generation, not smart meters. It has worked that way since 1889.

 

[256bits]

. So smart meters is the way to predict real time demand. Correct me if i am wrong

Do smart meters show electrical power usage?
The utility bills you for energy consumption.

The time lag between the smart meter reading and the demand curve for the power stations just isn't there. The utility company can use meter reading to see trends horly, daily, monthly, yearly, to set up the major portion of how much electricty they should buy, but since no-one can predict mother nature it really isn't all that much use in the spot market.

 

[Jeff Rosenbury]

Maybe I'm off base here, but I think some basics may help.

Electric companies sell power which is different from voltage. Voltage is in many ways much cheaper than power. Power is the product voltage times current. So when people "go on vacation" they still get voltage, but no current.

The power company is responsible for making sure the voltage is constant. But that is cheap to make (neglecting the infrastructure costs which are already paid).

There is some parasitic current needed to run things like transformers. The power company eats these minor costs if no one wants power.

Large consumers of electricity are billed differently from consumers, so the pricing model is different. It varies by whatever contracts they sign.

 

[anorlunda]

Large consumers of electricity are billed differently from consumers, so the pricing model is different. It varies by whatever contracts they sign.

That's true but the contracts must fit within the confines of the published tariff rates. The tariffs cover both small consumers and large ones. That prevents secret sweet deals for cronies.

The biggest violation of that principle that I know of is in the State of New York. 22 cities and towns in NY are allocated blocks of Niagara Falls power by law. They are historically grandfathered in. Consumers in those communities pay only 10% as much as consumers in the rest of the state. 2004 was the last time I checked that this was still true.

In several parts of the world, electric power theft is a large fraction of the load. That underscores the need to separate regulation of the grid, from the flow of payments. Even when stolen, it must still be regulated.

 

[russ_watters]

The instantaneous unbalance between generation and load becomes rate of change of frequency. Frequency is the feedback signal used to adjust generation, not smart meters. It has worked that way since 1889.

Does voltage also vary with load or is that separate? A function of magnetic field strength instead of rpm?

 

[anorlunda]

Does voltage also vary with load or is that separate? A function of magnetic field strength instead of rpm?

VARs (imaginary flow) regulate voltage. Voltage regulation is discussed explicitly in

https://www.physicsforums.com/insights/ac-power-analysis-part-2-network-analysis/

 

[sophiecentaur]

We've had a long thread and an Insight into VARS and Imaginary power. Could we start one on Imaginary Coal? (Hush mah mouth!)

 

[jim hardy]

If I understand correctly, i a very lay man's terms as soon as switch on the bulb in the bed room the demand information all the way propagated to transformer to Feeder to transmission lines to Generation station . Is that right?

That is EXACTLY right
in theory...
When you switch on the Christmas Tree lights, somewhere a steam valve has to open a little bit more to make that few more watts and a coal pulverizer has to pulverize a little more coal and feed it into the boiler to make that extra steam. We cannot store AC electric energy as AC electric energy ...
I practice, the total mechanical rotating inertia of the generators in the system is so large it can supply that extra few more watts until somebody else switches their Christmas Tree lights off.

I have stood in the control room of a steam power plant watching a summer thunderstorm roll in over Miami. The operators would take bets how many megawatts they'd have to stop making as customers' air conditioners cycled off because of the storms cooling the city. 200 megawatts was not unusual.

The way the "demand information" gets propagated back to the generators is simple conservation of energy.
Think of the "grid" like any other rotating machine. If you take out more energy than is going in the machine slows down. Anorlunda's "Flyball Governors" sense that slowdown and open the steam valves.

Keep your thinking simple. Anything complex is just a lot of simple ones hooked together. We all want to leap straight to an answer without goin through the necessary thinking. The brain can believe stuff that's just not true. So train yourself to think in baby steps.

You can watch here the minute frequency changes across the whole US grid as energy sloshes around. It swings like a wind chime.

http://fnetpublic.utk.edu/gradientmap.html

Bear in mind that map isn't perfect it always shows far west running slow. I don't know why . But short term variations are evident.
I prefer this one showing the phase angle. Blue areas are importing power from red areas. But it doesn't cover "Way out West".
Watch it for a few minutes... it's fascinating.
http://fnetpublic.utk.edu/anglecontour.html

Any help ?

old jim

 

[jim hardy]

The biggest violation of that principle that I know of is in the State of New York. 22 cities and towns in NY are allocated blocks of Niagara Falls power by law. They are historically grandfathered in. Consumers in those communities pay only 10% as much as consumers in the rest of the state. 2004 was the last time I checked that this was still true.

On the other hand, who financed and built the power station? If it was local taxes then the locals should benefit .
My in-laws lived in Niagara Falls. In early seventies the cost per kw of power delivered to Father-In-Law's factory was less than my company's nuclear fuel cost. Way less than 1cent per KWH.

old jim

 

[anorlunda]

Fun stuff, but I think we left the OP in the dust.

The OP was conflating Ohms law with financial payments. Until he separates those in his head, his progress is limited.

 

[jim hardy]

Fun stuff, but I think we left the OP in the dust.

The OP was conflating Ohms law with financial payments. Until he separates those in his head, his progress is limited.

I took this phrase

the demand information all the way propagated to transformer to Feeder to transmission lines to Generation station .

as meaning he thought there was computers and telecommunication and IT departments involved.

Indeed he appears to undersimplify things.

old jim

 

[anorlunda]

On the other hand, who financed and built the power station? If it was local taxes then the locals should benefit .
My in-laws lived in Niagara Falls. In early seventies the cost per kw of power delivered to Father-In-Law's factory was less than my company's nuclear fuel cost. Way less than 1cent per KWH.

old jim

The 22 cities are not all the most local. They got the rights as political pork, favors to their powerful congressmen.

This Wikipedia article tells an interesting history that goes back to 1805, long before electric power. But it fails to mention George Westinghouse and Nikola Tesla. It was my understanding that the first electric plant there was their brainchild, and the origin of the AC/DC feud with Edison.

https://en.m.wikipedia.org/wiki/Niagara_Falls_Hydraulic_Power_and_Manufacturing_Company

 

[Venkata Satish]

Thanks for your reply. Now i agree that no extra energy is generated.

But recently i went to a conference. They put these statement like "Achieved peak savings of 7.2 MW load during DR (Demand Response) Event"

What do they mean by peak savings of 7.2 MW mean? If Produced energy is same as consumed energy where is the saving? Is is commercial savings they are talking about? Meaning they committed to purchase more power but now they reduced it to 7.2 MW because of Demand Response?

Sorry one more question. If utility orders Energy say tomorrow we want 1000MW, are they obligated to buy even thought they have supplied less because of consumption?

 

[sophiecentaur]

What do they mean by peak savings of 7.2 MW mean? If Produced energy is same as consumed energy where is the saving?

I read that as meaning that the 7.2 MW was handled by lower cost generators. High cost, Peak Generation capacity was not needed. Presumably this could be achieved by stoking up coal boilers in good time to catch the peak demand. You can do this with software if you have a sluggish system (predictive techniques) or with human skill and experience. Pedalling fast downhill (forward planning) can help get you up the next hill.

 

[anorlunda]

OP your questions were all answered in post #7.

Beware sales pitches. To my knowledge, payments for demand response are so far limited to large blocks of power, not homeowners. 7,2 MW is about 1000 times more than a house. There is lots of talk about consumer level demand response, but I have not heard of it being implemented yet.

Did you go to the conference as an individual? Representing a company? Representing a city?

 

[jim hardy]

Look at the bullet just above the one you yellowed..
I would guess they remotely switched off 7.2 megawatts of water heaters, airconditioners and clothes dryers.
http://energy.gov/oe/technology-development/smart-grid/demand-response

It also includes direct load control programs which provide the ability for power companies to cycle air conditioners and water heaters on and off during periods of peak demand in exchange for a financial incentive and lower electric bills.

Wikipedia shows this picture of a clothes dryer using a demand response switch to reduce peak demand

 

[Venkata Satish]

i represented the company. My company does software.
I understood the usage of smart meters like to time of usage , if there ant defects in the meters, auto disconnect etc

But still i am not understanding how smart meters can help utilies save money at the distribution place.

Satish

 

[Venkata Satish]

Look at the bullet just above the one you yellowed..
I would guess they remotely switched off 7.2 megawatts of water heaters, airconditioners and clothes dryers.
http://energy.gov/oe/technology-development/smart-grid/demand-response

Wikipedia shows this picture of a clothes dryer using a demand response switch to reduce peak demand

But this as good as not switching the washing machine. So is it addressing financial problem or technical problem.

 

[jim hardy]

But this as good as not switching the washing machine. So is it addressing financial problem or technical problem.

I'm a power plant maintenance guy. So to me it's a technical problem.
At my utility there were days when customers use was pushing our ability to generate so close to the limit that we turned off lights on the boilers and cut out feedwater heaters just for a few extra kilowatts. We sure could have used some gas turbine peaking units but this was 1960's...

To a power company system dispatcher it's a financial problem. If he doesn't have to start one of those horridly inefficient gas turbine peaking units he can save thousands of dollars. 7 megawatts at ten cents per kilowatt for jet engine fuel is S700 an hour. At one time we had a hundred megawatts of those peaking turbines..

 

[Jeff Rosenbury]

I think the key is to understand that different energy sources have wildly different costs. Some hydroelectric plants cost about ½ ¢/kWh while gas peaking plants may run 9 ¢/kWh. Different plants also have different response times. A gas plant can change its power output quickly, but a coal plant takes a few minutes. Nuclear plants can take hours (weeks to shut down, as Fukishima showed us). So power companies want to run the cheap plants full out and use the expensive peaking plants only to balance things when unexpected loads come.

By controlling even a little of the load, the use of expensive peaking power sources is reduced. This saves costs -- a lot of costs.

BTW, lower natural gas costs likely lower these problems. But an increasing reliance on unstable wind and solar power dramatically increases the problem.

If you are interested in the financial side, get the annual report from a few power companies (you might want to buy some stock). They go into more detail about costs and how they are reduced. Public utilities are mostly transparent for those willing to do the work of understanding.

 

[anorlunda]

Sigh, we are getting deeper into the woods than I planned.

Electric energy is a fungible commodity, just like shares in a company stock. So all people who buy/sell IBM stock today at 1019 EDT may see a clearing price of $110.27. Some people buy. Some sell. The profit/or loss of each party is not considered. Everybody trades at the same price. If you want a minimum of $120 for your stock, it won't get sold at this moment.

It is the same with generators in the electric markets. If we are forced to start a high cost gas turbine, the clearing price for all generators goes up. Even the low cost generators will be paid the high price until a new price is calculated a short time in the future. In theory, an electric market running along steady at $30/MWH, could spike to $1000/MWH for 15 minutes. In real life (after the year 2000 when California learned the hard way to do it correctly) such extreme spikes almost never happen. A single market clearing price is a simple matter of economic fairness and even handedness. However, it makes it even more expensive to meet a peak demand.

On the wholesale markets, $50/MWH is a typical price paid for an increment of generation. $500/MWH is the price paid for demand response DR. However, those payments are not available to small players, because there is a significant engineering & legal overhead to set up the DR contracts, communications, certification and annual audit.

The law plays a role too. In New York State, the law says that utilities may not consider price when purchasing enough generation to meet the demand. That prevents them from deliberate and involuntary area blackouts as a tactic to avoid price spikes. DR can be considered as a voluntary black out.

(See why I say that these power topics are multidisciplinary? We go from Ohms Law, to Economics 101, to the law almost in the same paragraph.)

My info on DR may be dated. Does anyone know of a homeowner who received a check in the mail for turning off their HVAC under DR control? Time-based rates are not DR. DR is when the grid sends a command DROP YOUR LOAD RIGHT NOW (or there will be a stiff penalty for non-compliance.)

 

[johnbbahm]

I was thinking about what problems a large number of grid attached solar customers will be.
The supply could have much broader swings in a local area.
The power plants can adjust their supply, but only down to zero,
some months in spring and fall, may not have much local load, but a large
surplus of supply.
I am thinking there will need to be some place to dump the surplus, least the heat
harm the grid.

 

[BillyT]

Post 10 has correct answer for a grid, with several generators feeding it.
On a single transformer POV, if all of the customer it supplies disconnect, then the current the transformer takes from the gird drop drastically - only the hysteresis loses in the iron core are being met as the magnetic field alternates. The current in the secondary is zero.

 

[anorlunda]

I was thinking about what problems a large number of grid attached solar customers will be.
The supply could have much broader swings in a local area.
The power plants can adjust their supply, but only down to zero,
some months in spring and fall, may not have much local load, but a large
surplus of supply.
I am thinking there will need to be some place to dump the surplus, least the heat
harm the grid.

Everything you said may become true 20-30 years from now, but for now wind and solar are a tiny fraction of total capacity. 0.6% solar and 4.7% wind in 2015, https://www.eia.gov/tools/faqs/faq.cfm?id=427&t=3
But they are growing rapidly. The northeast USA grids did a study. They found that wind / solar can grow to 20% of total capacity before any drastic changes are needed in the grid operations.

 

[jim hardy]

My info on DR may be dated. Does anyone know of a homeowner who received a check in the mail for turning off their HVAC under DR control?

My utility gives a small discount, around five bucks a month, on the bill for customers who let them install a DR relay on airconditioner and water heater.

My house had one when i moved in but i didnt know what it was. When it failed to "disconnected" state in dead of winter and Fair Anne got a cold shower, i took it out.
That was under threat of "Wrath of the Valkyries" - she thought i'd turned it off on purpose.
I need to call electric company and get one put back in - it's good neighbor policy.

old jim

 

[anorlunda]

utility gives a small discount, around five bucks a month, on the bill for customers who let them install a DR relay on airconditioner and water heater.

Thanks Jim. I am out of date. So now the discussion has to be broadened to wholesale and retail DR. The $500/MWH number I quoted was wholesale. The Supreme Court just decided a case about wholesale DR.

I've been living off the grid on a sailboat for 11 years. I haven't seen a power bill (or a water heater or an AC) that whole time.

 

[AgentCachat]

OK, dummer question still, perhaps off topic. What is base load? Is this related to what the OP asked?

 

[anorlunda]

Base load is that which is there 24x7. However, the definition can be much looser than that.

Think of base load. Peak load and intermediate. Fit your generation source to the closest of those three choices.

 

[sophiecentaur]

As a matter of interest - and someone is bound to have an idea about this - what is the sort of time involved between increasing the rate of coal feed to an increase in generator output? Is it 2 minutes, 10 minutes, 30 minutes? The same figure for a nuclear system would also be interesting (also the reaction time to a drop in fuel input).

 

[Jeff Rosenbury]

I was thinking about what problems a large number of grid attached solar customers will be.
The supply could have much broader swings in a local area.
The power plants can adjust their supply, but only down to zero,
some months in spring and fall, may not have much local load, but a large
surplus of supply.
I am thinking there will need to be some place to dump the surplus, least the heat
harm the grid.

There are some economic activities that thrive on cheap power. Making aluminum is an example. I could easily foresee industrial plants designed to take up the slack.

Another option is energy storage. There are several competing technologies being developed, plus some old fashioned hydo projects. Pump the water uphill when power is cheap and generate peaking power when it's expensive. Still, none of these solutions are inexpensive or likely to get that way soon.

 

[Jeff Rosenbury]

As a matter of interest - and someone is bound to have an idea about this - what is the sort of time involved between increasing the rate of coal feed to an increase in generator output? Is it 2 minutes, 10 minutes, 30 minutes? The same figure for a nuclear system would also be interesting (also the reaction time to a drop in fuel input).

I'm pretty sure power can be cut to a nuclear plant quickly, within a few minutes.

There are three steps. First the fast (prompt) neutrons used in chain reactions are quenched. This takes less than 1ms. That's pretty fast. Next the decay neutrons need to be poisoned. That takes longer. I don't know how long. Finally, about 7% of full power remains due to decay heat. (As opposed to decay neutrons which cause more reactions, but below the breakeven for chain reactions.) This 7% drops off over months, years, decades, centuries, etc.

I seem to recall that Fukishima should have had a month of forced cooling before the fuel rods could boil water on their own without danger.

 

[jim hardy]

As a matter of interest - and someone is bound to have an idea about this - what is the sort of time involved between increasing the rate of coal feed to an increase in generator output? Is it 2 minutes, 10 minutes, 30 minutes? The same figure for a nuclear system would also be interesting (also the reaction time to a drop in fuel input).

Westinghouse plants are designed to "load follow" but they're base loaded because of economics.
i'm having trouble remembering numbers as to procedural limits on rate of load increase/decrease.
I have seen my reactor returned to full power within an hour of a trip. So your "thirty minute" estimate of 3.3% per minute sounds about right for graceful operation.
Smaller changes can go faster. A 10% step change is quite manageable. I've seen step decreases of 50% which, when everything worked as designed our plant handled.

Coal plants - i never worked in one. I'd guess they're similar, 3 to 5 % a minute because that's what the grid needs.

There are three steps. First the fast (prompt) neutrons used in chain reactions are quenched. This takes less than 1ms. That's pretty fast.

It takes a little over a half second for the rods to fall the twelve feet from top of core to bottom. The "prompt" neutrons disappear as the rods fall, and indeed our instruments show flux decreasing in the top half of core first .
That top-to-bottom flux difference propagates through the Reactor Protection System briefly actuating relays whose purpose is to protect the reactor from flux imbalance (for you PWR guys: fΔI term in OPSP and OTSP equations ).
When reviewing post-trip data it's at first confusing why you got those alarms .

A "trip" closes the steam valves as fast as they can move, ~1/10 second and steam bleeds out of the turbine over the next few seconds. So a "trip" puts a near immediate stop to generation.

I hope that helps. Somebody who's more current than i will have better answers.

old jim