What do Power Plants do at Night?

[Puppyjump]

I caught the tail end of a radio talk show where it was mentioned that power plants don't "throttle down" at night, even though grid loads decrease. Instead of dropping power output to meet the demands of a lower grid consumption, the power plants bleed off the excess power into the ground. In other words, the power plant always operates at 100% output regardless of the grid demand.

This sounds unlikely to me (talk radio is often inaccurate), or at the very least, very generalized since there is no such thing as a "power plant", rather "what kind of power plant".

Questions:

1) Is it true that some power plants always run at 100% output, thereby bleeding excess power as waste that the grid is not pulling (such as at night)?
2a) What kind? Hydro, coal, nuclear?
2b) Do all power plants of a certain type operate this way?
3) How can you determine the approximate amount of power in your region that may come from such plants?

If it is true that certain power plants waste energy during periods of low demand, then it would be a good thing to plug in EVs at night to collect power that otherwise would have basically been thrown away. Further, it would mean that EV's charged this way would truly be emissions-free as the "long emissions tailpipe" argument would be invalid given the power plant always generates the same levels of power and pollution.

 

[voicecoils]

I suggest you do a bit of goggling on power generation, grid infrastructure, and energy markets.

To start you off, have a look at the attached document. It gives some insight into what baseload, intermediate, and peak power demands are and how they can be met.

I suspect the talk show was describing one of the primary sources of baseload power: coal fired power stations. They aim to operate close to their continuous power rating all the time. Doing so maximises the powerstation's efficiency and longevity. They may vary their output by small amounts. They also break down (as mentioned in the attachment) and may be off line for days or weeks.

Since the energy demands of customers does vary, other generators who can ramp power up and down faster will do so. They get paid higher prices for their ability to do this. Natural gas turbine generators, hydroelectric, wind, and others will meet peaking demands or shut down as necessary.

 

[voicecoils]

Lastly, if you generate power, it has to go somewhere.

If there is excess power, I'm not aware of any way to 'bleed it into the ground'. You need a load, whether it is a bank of resistors, batteries, pumping water up a dam, etc.

 

[Puppyjump]

Lastly, if you generate power, it has to go somewhere.

If there is excess power, I'm not aware of any way to 'bleed it into the ground'. You need a load, whether it is a bank of resistors, batteries, pumping water up a dam, etc.

I interpreted the show's statements that it was a resistive load, i.e., wasted energy. Perhaps cooled by the ground, or more likely a body of water?

Pumping water up a hydroelectric dam or storage in batteries would be a good thing whereas the radio program was making a point that the energy was being wasted, not stored.

Given that the media is often weak technically, I don't believe that there is a significant amount of energy wasted this way, but I just wanted to find out with certainty.

I plan on some Google searching, but was hoping to get some info here first as I suspect power experts read these posts.

 

[Puppyjump]

I suggest you do a bit of goggling on power generation, grid infrastructure, and energy markets.

To start you off, have a look at the attached document. It gives some insight into what baseload, intermediate, and peak power demands are and how they can be met.

I suspect the talk show was describing one of the primary sources of baseload power: coal fired power stations. They aim to operate close to their continuous power rating all the time. Doing so maximises the powerstation's efficiency and longevity. They may vary their output by small amounts. They also break down (as mentioned in the attachment) and may be off line for days or weeks.

Since the energy demands of customers does vary, other generators who can ramp power up and down faster will do so. They get paid higher prices for their ability to do this. Natural gas turbine generators, hydroelectric, wind, and others will meet peaking demands or shut down as necessary.

Thanks for the .pdf info. I never considered the pollution associated with the supply and support of a nuclear power plant....

 

[Doctorbass]

I know two things about powerplant at night:

First, at around midnight, some country correct the phase or total cycles generated in a day to ensure that the total: 60 cycle /sec give always the same total of 86400cycles a day to ensure that AC synchronous clock dont take any advance or retard.

In other words, many clock still use the 60hz to keep their speed constant.. but sometime to compensate the low and high load the frequency of the generator change a little bit and in one entire day the total Hz generated is not exactly 86400.. so to keet clock up to date they increase or decrease speed of the generator for a fraction of a second giving like 61, 62 or 59 or 58Hz to the first second of the next day at 0:01am...


Also, i think this is false about always keeping same load for a power plant... just imagine.. sometime the variation of that load could be like 40 or 50% from 8h(high liad of the morning and 23h low load...

so the balance load wold be too importnat to build a compensating load that can absorb all that power!!!

+ in hydro electricity, the energy stored is the water in the reservoir.. so they can regulate it!.. and not waste it in waste load...
I'm pretty sure hydro regulate the output fonction of the load... and for nuclear, i guess the nuclear reaction is controlled too and probablu regulated

Doc

 

[Tiberius]

Hi Puppyjump,

There's a good discussion of the very subject on http://www.withouthotair.com

Some types of power plant can be throttled up and down relatively easily, some can't. A lot of renewable energy sources are intermittent; some, such as tidal lagoons or hydro, can be controlled and throttled up and down to meet demand.

Managing the electricity supply/demand through the daily and seasonal cycles is quite an art, but its possible. The author in the link I posted discusses how a fleet of electric vehicles, with intelligent night time charging, can play a part.

I've posted the link before, but it doesn't hurt to do it again.

Nick

 

[dogman dan]

I think nuclear can be turned up or down relatively quick, but coal fired boilers are very hard to change the output of. It may be a lot like a steel mill, where the furnace will be ruined if it ever is allowed to completely cool off.

There are other types of generators that can be switched on or off pretty quick. Emergency units are often just jet engines, that run on regular jet fuel. They can be turned on and off just about instantly and are used to fill in when demand peaks. Here in NM, we have lots of natural gas, either wells, or the pipeline to california from texas. Along the pipeline there are numerous power plants built just for the purpose of feeding california with more power when the summer spikes in use happen on hot days. Like the jet engines, they can go on line in a relatively short time. They use a gas turbine, so it can start up and shut off daily easy.

It would be cool though, if lithium prices fell enough to make it practical for tv's, computers, etc, to use a battery that automaticly charged after midnight so the bit of power they use could be taken from the grid at night. Right now it would get a bit pricy to do that.

 

[paultrafalgar]

Hi Puppyjump,

There's a good discussion of the very subject on http://www.withouthotair.com
...

People might like to know, Tiberius, that that book "Without Hot Air" by Cambridge professor David Mackay can be downloaded free (383pages) as a pdf from that site. If anyone wants to discuss what he says about CHP with me (or us) please let me know.

 

[dak664]

I think nuclear can be turned up or down relatively quick, but coal fired boilers are very hard to change the output of. It may be a lot like a steel mill, where the furnace will be ruined if it ever is allowed to completely cool off.

My knowledge is probably outdated, but so are most US nuke plants...
I think it's the other way around. Coal plants can track a load pretty well, just change air intake and the output changes a few seconds later. A fission plant can oscillate due to the water also being the moderater so once it reaches stable thermal production the operators like to leave it there 24/7. Startup/Shutdown is another thing entirely, it takes a lot longer in both cases. Nuke plants stay at around 7% thermal output even when shut down due to spontaneous decay of built-up fission products, and that heat is generally dumped using external electricity for the pumps.

 

[TPA]

Most heat engines are difficult to start up after shut down, so they usually only shut them down for serious overhaul.

and...

you can discharge to ground, that is why you have a grounding rod by your electric service. Take a hot wire from your electric service and connect it to your grounding rod and watch your meter spin! (really...do not try this at home.)

 

[spinningmagnets]

I don't think it so much the coal-burners that cant be quickly throttled, as it is the steam half of the plant is best to be kept hot.

few new coal plants are built, so they are often used for base-loads as far as I know (plus coal is cheap). Often, many cities use natural gas burned in gas turbines (jet engines) to generate electricity during peak loads as it is reasonably affordable, and they can be easily and quickly be ramped up and down without damage.

 

[TPA]

Yea, its the steam turbines that cannot be throttled. If you reduce the heat to a steam turbine you run the risk of condensation inside the turbine, which causes turbine blade impingement.

Also, some gas turbines are used as a topping cycle for a steam turbine (waste heat from the gas turbine is used to heat water to steam, creating a second cycle for "free") so if the gas turbine is throttled back, the steam cycle would be affected.

 

[dnmun]

talk radio. a place rush limburger can call home.

i gotta admit i could not stop laughing about the idea that they just connected the grid to ground to soak up the excess energy. how dumb has our country become?

anyhow, nuclear and coal fired plants are always carrying the baseload, running flat out, and the hydro and gas turbines are tweaked to balance the load. you can see it at bonneville dam and grand coulee when the airconditioners are all running in california. the outflow from the turbines in the dams like hoover and bonneville just increases dramatically from flat water to roaring gyres in the river downstream.

 

[ElectricEd]

Here in Melbourne Victoria (Oz) we have the ability to generate about 6.5GW. In summer our demand recently peaked near 8.5GW. The power companies buy the excess power from other states to make up the difference.
Between Victoria there is an undersea DC cable called "BassLink". We buy at peak cost hydro power from Tasmania during the day and send the excess power from our brown coal power stations at night back over BassLink to pump the water back up the hill. Tassie wins on both counts. Lucky Tasmania!
We used to mainly have off peak electric hot water systems that used the excess power and were turned on and off by a timer and billed through a separate meter. Nowadays most households are on gas from Bass Strait, so the excess power is mainly used to pump hydro water in the Snowy Mountains in NSW and Tasmania. Some larger companies have extra shifts so that they can use cheaper power at night. There is also a special metering for the charging up of electric forklifts and electric fleet vehicles at night. It'd be nice if we could use this rate for charging personal EVs.

 

[dogman dan]

yup, you guys are right, even if you can just put the rods in on a nuke plant, that doesn't mean they like to do it. The steam end issues for one, and also, it's nice with a nuke to get it just right and then don't mess with it! Chernobyl was a shutdown test.

But with some lead time, the natural gas plants We have here do throttle down some at night. It's amazing how much house current varies during the day. Back when I was a professional potter, we fired with an electric kiln to 2000 F. If we timed the firing wrong, and it didn't fininsh by 6 am, the firing would take hours longer than normal because the 120 current we had at night would drop when everybody in town turned on coffemakers and tv's. We needed the best possible current to get to the highest temp, and once people woke up, forget it. We definitely had to fire at night, and not start too late the day before.

As I have had it explained to me by linemen, once the power goes into the grid, it's gone in a way, sort of a use it or lose it deal, unless you pump water back up a dam like down under. That is a great idea, I've often wondered why we don't do it, but figured it was an economic thing. I've had this fantasy of millions of wind turbines, pumping excess water from the mississippi river towards the desert, then getting some hydro power back out of it as it goes into the farmers field. No doubt too expensive.

 

[tailwind]

http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity is used all over the world.

Aluminium smelters, desalination plants, pumped storage, charging EVs, are all good uses for low cost electricity at periods of low demand.

To try and answer the original question,

Nuclear plant operates at base-load, as do almost all gas plants. It is the output from coal fired plant which is adjusted to meet the electricity demand on the system. In other words, most 'load following' is carried out by coal-fired plant.

The web site http://www.wattclarity.com.au has some interesting articles about the National Electricity Market in Australia.

Greg

 

[Puppyjump]

talk radio. a place rush limburger can call home.

.

Well, it was NPR talk radio, but still not a reliable source of technical info since its basically hosted by journalists.

 

[dnmun]

doesn't matter. just look at the comments on this thread. even the guy who worked for the electric utility that dogman quoted, all kinda disturbing nobody here knows how our electric grid is managed. no wonder the guys at enron could get away with it.

did any of you know that it was dick cheney who convinced the sierra club to support the use of natural gas turbines for peak load balancing? ever wonder why?

and people like t boone pickens get trashed for trying to get the country to stop wasting the natural gas in generators. what a waste democracy really creates.

so the ground rod is just there to soak up the excess electricity and make your bill go up? hahahaha you guys are too much.

 

[Libellule]

Interesting post here

Power house using steam(that will move the steam turbine, that turn the generator) - heat process(flame) : nuclear, fossil(coal, gas, petrol), can't not be slow down as required by demand, BUT, by heat cycle, meaning, you have to waste the production at night or wish you have some client who will use it!! Has NY power utility that is selling there electricity to Hydro Quebec(water dam) during the night.

Why they don't pump water(reservoir) with it(at night), sure, where the water? Get it, no water to pump, no deal. And please you have to get a fairly ≈high level reservoir.
Other point to keep in mind, the same unit that generate and pump is less efficient, oups, they do exist in the USA.

Reason to use Gaz Turbine(see plane engine, well more robust, yes, and no steam here):
1.- Quick star on demand, really Quick.
2.- Compact installation, thus the reason to install those close to client(city, industry)
3.- Low cost installation
4.- Fast installation

Hope to have answer to some question, interrogation

Ciao

 

[Anonymous]

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[Patriot]

Q: What do power plants do at night?


A: Maintenence. As much as possible.

Otherwise, they throttle down, and alot of resources go to waste.

 

[dnmun]

nukes run at a steady pace, rarely do they get reduced in power, but they can. it is not hard at all to reduce the power in a modern coal fired plant. the coal is ground to a fine powder and blown into the combustion chamber with lotsa air to provide for complete combustion, and it is a computer controller process. not like some guy has to go down to the basement and fiddle with some valves, it is done automatically by the grid management computers. gas turbines are started remotely and automatically when needed, they can respond to load demand in moments actually, but usually they take a few minutes to spin up. i still think the one about how the ground rod is there to soak up the extra electricity is the best though.

 

[Puppyjump]

i still think the one about how the ground rod is there to soak up the extra electricity is the best though.

Be sure not to stand near that ground rod nor recycle your beer near it.

 

[Patriot]

nukes run at a steady pace, rarely do they get reduced in power, but they can. it is not hard at all to reduce the power in a modern coal fired plant. the coal is ground to a fine powder and blown into the combustion chamber with lotsa air to provide for complete combustion, and it is a computer controller process. not like some guy has to go down to the basement and fiddle with some valves, it is done automatically by the grid management computers. gas turbines are started remotely and automatically when needed, they can respond to load demand in moments actually, but usually they take a few minutes to spin up. i still think the one about how the ground rod is there to soak up the extra electricity is the best though.

I used to be a nuke machinist in the Navy. And you are correct, civilian nukes run at a steady pace. At night, the demand drops off majorly, so they have to find ways to manage what they produce. Grounding and load abrsorbing is some of the ways to handle it. The companies are also looking at the cost effectiveness of large Lithium battery banks to store power. I think Altairnano is currently making large commercial battery banks for this reason, along with Navy backup battery banks for ships and submarines. But for now, basically the Turbines still run on the governors, but put out less power.

With the coming electrical automobile infrastructure, the mass charging of cars at night will greatly increase the cost effective efficiency of nuke plants. After 2020, the Next Generation IV reactors will really fit into the new grid modernization program quite nicely.

Good things are ahead.