Do power companies store excess energy during times of low demand?

Question

Power companies always shut down generation plants when there is low demand in the power grid, but they always have to maintain a safety margin - perhaps 10% or more power than the grids demand.

Do they STORE this excess/unused power? what happens to unused power.

Answer 1

A power company in Texas had compressed air in a salt dome in the '80's.    They were going to greatly expand the useage of compressed air since it worked so well, but then power prices fell and it just wasn't worth the trouble.

Answer 2

No the AC power is available but that doesn't mean U use it. The load on the generator is just the load that is put on it. The generator could be much larger. The load on the generator is reflected back to the motor.

Answer 3

The majority of the power grid is AC (alternating current).  The electric power that is produced by the power plants is the electric power that is being used at that moment in time while maintaining the grid frequency at 60 Hz.  There is no unused electrical power.

There is no storage of the electric power once has been produced.  At times of low system demand hydroelectric plants will pump water from afterbays back into the reservoir in order to be able to reuse the water during the next day's peak system demand, but energy and power plants other than hydroelectric power has to be used to do this.  Perpetual motion is a great concept but physically impossible.

The safety margin of 10% that you speak of is the power company's ability to provide for unseen spikes in demand.  They do this by having 'rolling reserve'.  In the case of the power plant where I work we are capable of 230MW but the utility usually runs us at 200MW, but since all of our generators are 'rolling' and are capable of an additional 30MW we have 30MW of 'rolling reserve' that the utility can tap into.

Answer 4

In a few places they pump water into a reservoir at night during the low demand period so they have more water available during the day high demand period.  It's a net loss of energy but since they charge more during the day it is profitable.  That's about the only way they can do it.

Answer 5

I read up a bit on this and here what I've found:

Like your car's Alternator there is no "extra" power that is created without demand. Meaning if everyone shuts off their A/C's in a big city the power plant's generators simply slow down or shut off.

The safety margin is that they try to preemptively have power "potential" that is on the ready - maybe some turbines spinning, ready to accept load. Given, running a power generation source without load is wasteful but it is acceptable since even the power companies cannot tell when exactly or how much demand will change. They usually make up the needed power from providers while they increase capacity - if they can.

You car's alternator is good example - once you get up to speed above an idle, it is making more power than the engine, the basic accessories and the battery needs. If you could monitor the drag or draw of the alternator on your car as you turned devices on a off you would see how load makes the alternator put out more power - while spinning at the same rate. Your engine has to absorb the drag of the alternator by increasing fuel consumption or idle speed. Your alternator is simply using regulating the voltage going out and its’ speed determines the amperage potential. At about 2500 rpm your alternator is putting at about 70% of capacity.

The easiest way to see this is turn on all your accessories at idle and you should see the headlights dim a bit. Raise the engine speed and notice that they brighten but only so much.

Overall the generators that power company's use are far more efficient than the alternator in your car so any waste is simply there to feed our ravenous need for power.

The only utilities that are planning for storage for solar and wind, since the sun sets and winds change. Those methods range from air compression, to molten salt to flywheels and many others.

Answer 6

Today we have few ways to store electricity and if it is not use it is gone. But one way is to build motor/generators and at night pump water to an upper dam and when needed let the water out producing power. California has several of these but needs many today as wind power is added and many times this power is at night. Electric cars will soon be another way to convert overproduction to usable energy. Check out some of the new superconductor technologies that will save us 25% on demand and produce 30% more supply at CoolingEarth.org