How is electricity provided to our homes and what happens to it when not in use?

[Panchy]

Our electric energy is provided by power-station,for example a water power station.My question is,the water power station doesn't produce electricity all the time,then what provide the voltage in our houses?Do they store the electricity?(It seem to be impossible)In addition,if it begins to produce electricity,and nobody use it at that time,how to deal with these electricity?
I want to know the details.Thanks.

 

[Ouabache]

Welcome to PF forums! Feel free to check out the various subforums, you will find some fascinating and informative discussions.

I believe you are wondering how electrical energy is stored. Just do a web search with key words such as "grid energy storage"

 

[SirAskalot]

Generated power is always the same as consumed power. Where else would the energy goes? In some isolated locations there may be some sort of energy bank, but normaly there is just the power plant, grid and consumer.

If a power plant isn't running, some other power plants on the same grid is running and supplying the demanded load. If you live in the US, over 1000 power plants are connected and share your demand. If you turn on a light switch and demands 60W, some power plant needs to produce 60W more. Turn it of again, and the power plant reduces its production.

 

[vk6kro]

In a water powered (hydroelectric) power station, spare electricity is sometimes used to power pumps, which pump the water back up to a high reservoir.

Then when a burst of electical power is anticipated, this water can be released back into the turbines of the mains generators and provide the torque needed for the heavily loaded machines.

In Britain, there is a TV show that has a huge following. When this program finishes, there is a mass migration from lounge rooms to the kitchen to make a warm drink with a kettle.

To meet this demand, the water from these high reservoirs is released all over Britain and even in far-away Scotland. This has to be precisely timed by arrangement with the TV stations as the power has to be available when it is needed.

For normal minute-to-minute load variations, with a fuel powered power station, automatic speed regulators are used on the engines that drive the big generators. So, when demand drops, the driving engine is given less fuel, so it maintains constant speed.

 

[SirAskalot]

This might be the case in GB, but normaly, pumping water back into raservoir is only done when the power company can buy cheap electricity for this use, and sell the electricity (water stored) with a profit some months later.

Energy efficiency, electric prices throughout the year and propability of rainfall and demand for the coming months, are key aspects in this decision. Mostly its a economic decision for long term income for the power company.

 

[sophiecentaur]

Panchy
A very good question and the fact is you can't 'store' electrical energy at all. It's the only real disadvantage in using electricity. Pump storage and batteries is not very efficient and intermittent supplies can be a real embarrassment.
I am amazed that the UK government seems to think Wind Turbines are 'the' solution to all our energy problems. It seems a very naive view. They are huge and very visible - so that may be the main reason that politicians like them so much. Each one is a visible monument to the statesman who got it placed there.

The best possible way to organise the Electricity supply is to control demand in addition to supply. A large proportion of our demands need not be supplied at any particular time. Many homes (mine included) have radio 'teleswitches' which can turn on and off the supply to stored water heaters and 'night-store' room heaters and are controlled by digital signals carried on the 198kHz Radio 4 transmissions. When cheap / 'free' energy is available and surplus to regular needs, the loads can be switched in. The energy, in this case, is stored as heat which can be very good value in a heat store installation with lots of insulation and large thermal mass.

 

[Ouabache]

As I mentioned above, doing a web search using key words 'grid energy storage'
reveals several methods used for storing electrical energy.Two of them have been mentioned
vk6kro - pumping water up to a reservoir
sophie - thermal storage

Here are five more ways that have been used, to store electrical energy
(1) converting to compressed air
(2) converting to mechanical inertia in a flywheel
(3) converting to hydrogen
(4) storage in a magnetic field using a superconductive coil
(5) storage in batteries

 

[SirAskalot]

But why bother! Storing electrical energy is a poor solution, in almost every way.

Using energy sources which must be used there and now such as windgenerators, solarsecells and thermalheaters, should be prioritized when energy is available. For then to stop electrical production from controlled sources such as hydroelectric, nuclear, coal and LNG. This is the best "energy storage" solution, ie. not convert excess electrical energy in the first place, but not the cheapest one.

But how cares about the best solution when there are more cheaper ways to do things!

 

[Panchy]

I asked a professor,his answer is,if nobody use the electricity the stations generate,then they will be wasted.Because it is not practical to store that much electricity.Of course,we have some ways to save on electicity just as vk6kro mentioned above.Thanks for all your replys!

 

[SirAskalot]

This reminds me of a Norwagian sitcom, funny for us who understand the topic. But for the general public this might seem real.

Short summary for none Scandinavian people:
<<Norwegian "end-current" is a place where excess electricity ends up for destruction, 1500W excess production means the have to turn on a vacuum cleaner and so forth>>

 

[Averagesupernova]

But why bother! Storing electrical energy is a poor solution, in almost every way.

Using energy sources which must be used there and now such as windgenerators, solarsecells and thermalheaters, should be prioritized when energy is available. For then to stop electrical production from controlled sources such as hydroelectric, nuclear, coal and LNG. This is the best "energy storage" solution, ie. not convert excess electrical energy in the first place, but not the cheapest one.

But how cares about the best solution when there are more cheaper ways to do things!

So let me get this straight. You think it is better to go ahead and use wind, solar, whatever renewable source we have when the wind is blowing, sun is shining, etc. But when those sources are not producing, just burn up the non-renewable fuels and screw storage? What about prolonging the supply of non-renewable fuels? Isn't energy storage from renewable sources a better solution from that standpoint? Do you handle your money the same way? If you don't need to spend it at the moment do you turn away the income?

 

[MisterX]

Panchy
Pump storage and batteries is not very efficient

According to what I have read:
Batteries are very efficient (90 +%), but are expensive. Pump storage is 70 to 85% efficient. It is more cost effective to operate, though capital costs depend on geology of the area where the storage resivoir is to be built.

 

[SirAskalot]

So let me get this straight. You think it is better to go ahead and use wind, solar, whatever renewable source we have when the wind is blowing, sun is shining, etc. But when those sources are not producing, just burn up the non-renewable fuels and screw storage? What about prolonging the supply of non-renewable fuels? Isn't energy storage from renewable sources a better solution from that standpoint? Do you handle your money the same way? If you don't need to spend it at the moment do you turn away the income?

We can't be discussing the same subject? I am talking about installed power in todays world, and electrical power in relation to the power grid. Right now, wind, solar and other periodic energy sources can't supply our electrical energy demand alone. In other words there is no excess energy from those sources to store. If you choose to store this energy, some other energy source (non periodic) has to supply the equal amount of energy to the consumer.

Calculation with efficiency its easy to see that the total amount of energy "used" is larger with energy storage (from losses) than with the direct use of electrical energy. The use of fossil fuels are also higher with storage.

In relation to isolated objects where there are excess electrical energy, storage is a good solution. But this aint a problem with normal households in countries with enough installed power, which can supply peak demands and have electrical demands higher than periodic sources supply at all time.

To use your money analogy, you have just enough money to pay your bills, but instead you choose to put some money in a bank savings account, but to manage to pay your bills you have to take up a loan with higher interest rates than your bank savings. In the end you loosing money.

 

[Averagesupernova]

If you have ever been close to a wind farm you will notice that often times not all of the turbines are turning. Probably because there is not enough transmission line available to transport the power where it can be utilized. So, to me it would make sense to provide a place close to a wind farm to store energy and load the wind turbines at capacity. When the demand is there and the wind isn't blowing dump power into the grid from storage. Don't get me wrong, I'm certainly not saying if we upgrade the transmission lines that we can shut down all nukes and fossil plants. That simply is not true. What I have more of a problem with is what I see as your attitude that all energy storage is a joke. Please forgive me if I am wrong about that.
-
I seen something similar to this with regard to large capacitors on the power input of 12 volt loads with wildly varying current demand. Some say the capacitor smoothes out the demand from the source while others say it is a band-aid approach and what really needs to be done is to have a bigger power supply and wires feeding the load. There are advantages and disadvantages to both approaches.

 

[russ_watters]

Note that if the energy is going to be wasted anyway, the efficiency of the storage doesn't matter at all in answering the question of if it would conserve energy. The only question is if it is cost effective.

Beyond that, even if you can throttle a power plant, it still may make more sense to build pumped storage because then you don't have to build as big of a power plant.

 

[Averagesupernova]

Russ. I couldn't agree more.

 

[mheslep]

But why bother! Storing electrical energy is a poor solution, in almost every way.

Because the load varies significantly, both over a 24 hour day and seasonally, and power plants cost money to build. The problem of varying load has been an issue for commercial electric generation since Edison. An electric utility operator has essentially two goals for economic operation for a given power plant type:
1. Build as few plants as possible, and once built
2. Run the existing plants as much as possible to maximize return on the investment.

Consequently operators are loath to build new plants that just operate during the day at peak demand, that they'll then have to idle at night. Energy storage is a major solution to the problem, and by far the most significant storage scheme in the US is hydro power of various kinds, in which the utility can use the hydro facility as a generating source during the day and peak load time, and then at night either allow water to back up or route the power from some coal or nuclear plant to pump water back up to the resovoir. The largest such facility in the world http://en.wikipedia.org/wiki/Bath_County_Pumped_Storage_Station" with a rated power of 2.7 GW(e).

 

[mheslep]

Note that if the energy is going to be wasted anyway, the efficiency of the storage doesn't matter at all in answering the question of if it would conserve energy. The only question is if it is cost effective.

Beyond that, even if you can throttle a power plant, it still may make more sense to build pumped storage because then you don't have to build as big of a power plant.

Yep.

 

[russ_watters]

Also note that the in-progress switch to hourly-rate billing will shift much of the incentive to store energy from producers to consumers. IOW, electricity will cost so much less at night and so much more during the day that there will be a substantial incentive to store it.

 

[dlgoff]

There is a way to take of some of the peak demands when generation isn't available without adding another generator. It's called load shed. Kind of scary.

Even my little REA is offering lower rates if they can control my air-conditioner (turn it off and on at 15 minute intervals). Sounds a lot like load shed to me.

 

[Averagesupernova]

In general, isn't stockpiling of anything usually advantageous? I don't see how not.

 

[sparkey]

as far as having a surplus available for demand spikes, yea stockpiling is good. its just a matter of whether or not the means of stockpiling is cost effective. does it cost as much or less than having more generators on standby for spikes? consider transmission, maintenance, and the cost of running generators at all hrs, peak and non, to generate the power necessary to stockpile.

 

[dlgoff]

Some times keeping a generator/boiler idling is better than shutting it down. It takes quite a bit of energy to get them up from a cold start.

 

[sparkey]

agreed. and it is quite stressful on the generator as well which adds to the maintenance cost.

 

[mheslep]

Some times keeping a generator/boiler idling is better than shutting it down. It takes quite a bit of energy to get them up from a cold start.

Some not so much. Gas turbines and hydro, for instance, are mostly throw a switch when you need it.

 

[SirAskalot]

I can see my statement might seem deterministic, but i understand off course that for some use, energy storage is the best solution with regards to cost and practical solutions. As you all have mentioned.

But putting costs, politics and other non physical restrictions aside I still believe energy storage in concern with electrical power grids are a poor solutin with respect to efficiency.

Transmission line capacity is of course the big bottleneck, and in a region with high demands for a period, low energy supply (ie. empty reservoir) and a poor line capacity, a energy storage of pumping water back in the reservoir in front of the period is a good solution. But a better solution would be a line capacity upgrade or in some cases not draining the reservoir in front of the winter. (better energy politics)

Two generators or more are in many situations a good thing, its more efficient to run a generator at it "best point" rather than running at 60%, and depending on the market it may be most cost effective. Also down time (service and maintenance) are less. And the additional cost from storage system have to be taken in account. But again, it vary from country to country, and region to region.

 

[sophiecentaur]

-
I seen something similar to this with regard to large capacitors on the power input of 12 volt loads with wildly varying current demand. Some say the capacitor smoothes out the demand from the source while others say it is a band-aid approach and what really needs to be done is to have a bigger power supply and wires feeding the load. There are advantages and disadvantages to both approaches.

Large decoupling capacitors are put at the input of devices like amplifier to cope with large current drain at rates corresponding to the signal frequencies (audio frequencies of a few Hz). They are not just a "band aid" but an economic and well engineered way to produce an effective low supply impedance without spending too much on thick supply leads and massive PSU components. The 'averaging' is over a period of less than one second and to cope with the need for the supply rail not to sag at the peaks of current demand when handling large amplitude low frequency audio signals. This has no bearing on the question of how to cope with large scale electricity supplies, in which the timescales are in hours.
Such difference in timescale means that the best solutions are not necessarily the same for both cases.

 

[sophiecentaur]

Some not so much. Gas turbines and hydro, for instance, are mostly throw a switch when you need it.

Gas turbines are hideously expensive to run (and wear out pretty quickly too) and would only be invoked in a serious emergency, after all other generating sources were flat out.

Reserve Hydro power is along the lines of pump storage - except that the rain provided the water up there.

 

[mheslep]

Gas turbines are hideously expensive to run (and wear out pretty quickly too) and would only be invoked in a serious emergency, after all other generating sources were flat out.

Not an emergency, just peak load in the Summer. About 15% of the total US generating fleet by nameplate power is gas turbine.
http://www.eia.doe.gov/cneaf/electricity/page/capacity/existingunits2008.xls
CF is ~5-30%. And the cost of gas has come down, expect the CF to increase. In any case I mentioned them because they come on line almost immediately when called upon.

 

[sophiecentaur]

Would that be when the big stations are off line for maintenance, perhaps?
I am right about the relatively short lifetime of gas turbines though, aren't I?

 

[mheslep]

Would that be when the big stations are off line for maintenance, perhaps?
I am right about the relatively short lifetime of gas turbines though, aren't I?

Compared to boilers, I don't really know, but turbine life is on the order of years for land based industrial use.

 

[Averagesupernova]

Large decoupling capacitors are put at the input of devices like amplifier to cope with large current drain at rates corresponding to the signal frequencies (audio frequencies of a few Hz). They are not just a "band aid" but an economic and well engineered way to produce an effective low supply impedance without spending too much on thick supply leads and massive PSU components. The 'averaging' is over a period of less than one second and to cope with the need for the supply rail not to sag at the peaks of current demand when handling large amplitude low frequency audio signals. This has no bearing on the question of how to cope with large scale electricity supplies, in which the timescales are in hours.
Such difference in timescale means that the best solutions are not necessarily the same for both cases.

I know exactly why they are put there and I know exactly what the benefits are. You are correct in that they are not a band-aid. Just because the times involved are hours vs. fractions of seconds does not mean there are not enough significant similarities to make comparisons.

 

[sophiecentaur]

I know exactly why they are put there and I know exactly what the benefits are. You are correct in that they are not a band-aid. Just because the times involved are hours vs. fractions of seconds does not mean there are not enough significant similarities to make comparisons.

Fair enough. I thought that you probably knew all that but, in the light of several comments in this thread, I thought it worth pointing out (to the world in general) that all the 'options' that have been mentioned are not necessarily applicable to the original question which seemed to be, essentially, about the Electricity Supply Industry.
As usual, the thread has meandered a bit. . . . :)

 

[Averagesupernova]

As usual, the thread has meandered a bit. . . . :)

Hey that's what makes a good thread. A little bit of meandering can bring in new ideas. Of course, there is a limit.

 

[sophiecentaur]

Hear hear - twice.