Yes, but power plants are inefficient when they are operating at less than their designed capacity, and they have to be sized to meet the maximum expected instantaneous demand. So if you’ve got a ridiculous 24-hour variation in power demand, your plant is expensive to build because it’s huge, and the actual instantaneous cost per kilowatt-hour during off-peak hours is high because of the inefficiencies. Power companies try to get around this by smoothing out demand in a couple of ways:
-build energy storage capacity, or
-sell off-peak power for less, encouraging customers to shift some of their own demand to off-peak times by changes in how they operate, or by customers building their own energy storage systems.
With the demand smoothed out like that, you can build a smaller power plant and operate it at closer to its design load (i.e. closer to peak efficiency) most of the time.
I have heard of commercial HVAC systems that use cheap off-peak power to crease ice or chilled brine, and then use that cold reservoir to keep the building cool during the day, when electrical power cost is high. This is an example of a customer shifting some of their own demand to off-peak times to smooth out the 24-hour demand cycle.
It’s only on a small scale at present, but the technology is being developed and some is in service. There are plenty of good links from theEnergy Storage Association you could peruse.
In addition to what Machine Elf said, power companies will use the grid to divert power to places that have higher demand. Companies may even buy power from other utilities to transmit to their customers since they are all connected.* Mostly.
In addition to what has been mentioned, there is some work on flow-batteries. In these batteries, all the chemical change occurs in a liquid electrolyte, and does not involve the plates. This means the electrolyte can be charged and removed to a tank external from the battery, and then flowed through the plates when the power is needed. This makes for a fairly cheap and expandable system. Increasing storage capacity means only adding more tanks of electrolyte. Of course more plate cells are needed if peak power has to be increased.
The general answer to your question is “Only for a very small fraction of the energy produced.”
As many of the replies above have stated there are all kinds of technology applications which are storing energy and then putting it back on the grid. But these applications are usually not cost effective except for special cases.
The actual output from stored energy sources is a drop in the bucket compared to the on-line resources generating power using conventional methods.
For practical purposes electrical power is a commodity that is manufactured and consumed within the same instance.
The inability to reliably and cost-effectively store energy is the reason why the US/Canada and to a certain point, Mexico, have a shared grid. They can “transfer” from one coast to the other. Usually by providing power to adjacent grids to help with their peak loads as people come home and then go to sleep.
Actually, there are 4 grids. See Gedd’s link in 23 above. Coast to coast transfers are possible but way too costly for practical purposes. The grids are separated by DC converter ties. Scheduling power through the ties is expensive as is the losses and cost to transmit power a great distance. Most dispatch operating regions within each grid have adequate generation to meet peak needs so the transfer of power is based primarily on economics of generation and not on peak load time differences.
Grid transfers do happen constantly but those are pure economic choices which are only partly influenced by shifts in peak timing.
In in my contract, if you want a feed in tariff from the power companies they don’t allow you to store power, your connecting to their grid, the conditions are up to the power company.
So based on what has been posted, it sounds like the batteries are more a method to smooth out power fluctuations and needs, allowing existing plants to run at a more efficient rate, and for new ones to be designed to a more steady capacity, rather than for pronounced peaks and valleys of demand?
A key driver for development of economic, large-scale storage is the growth of intermittent renewables (wind and solar). This is especially pressing in Ireland, which is an island market with limited interconnection and a high penetration of renewables. Hawaii would probably be similar.
In this context, the distinction you are making is not clear to me. A grid-scale storage solution capable of storing energy over a timescale of hours or days would allow surplus generation to be timeshifted to times of high demand (and high price), and would also allow thermal generators to run at steadier loads.
A more important distinction is that between short-term storage, providing voltage control by smoothing out fluctuations on a timescale of seconds, and long-term storage of the kind I mentioned in the previous paragraph.
We are currently planning to install on a pilot basis at one of our wind farms a multi-MW storage facility that will include both Li-ion and NaS batteries to provide capability in both shorter and longer timescales.
Something I’ve never quite understood: How do modern power grids handle balancing supply & demand? If electricity can’t be stored how does it perfectly match demand with little to no brown-outs as demand increases? And if demand suddenly goes down significantly what exactly happens at a generating station to compensate? Are the generators’ (actually alternators) fields simply linked to the demand so that they get ‘de-energized’ and stop making electricity even though they remain spinning? (or words to that effect…)
No one has ever attempted to position solar or wind power as sources for base load. We already have excellent solutions for that, such as hydroelectric and nuclear power.
When electrical load increases, the generator becomes harder to turn. (You have to put more energy in to get more energy out.) Power plants are designed to keep their generators turning (in North America) at something very close to 60 cycles per second. When load increases, the power plant must increase the inputs by the same amount to keep the generator turning at the right speed.
The fact that all generators are synchronized together in a grid makes this a little easier. If a generator for whatever reason starts to slow down, all the other generators on the network will feed power to it, causing it to become a motor. The generator wants to stay synchronized with the grid, which is much more powerful than any one generator. This property helps smooth things out while operators bring additional capacity online. Usually they’re pretty good about forecasting demand and can have the proper capacity available at the proper time. Forecasting does get a little more difficult with the increasing prevalence of unpredictable supplementary sources like solar and wind.
There will also be small fluctuations in the power of the grid, as the load changes. When you flip the switch to turn on the light bulb in your kitchen, the voltage on the grid is decreased ever so slightly for a moment. Nobody ever notices, of course, because on average, there are the same number of people turning off switches and turning them on. There is some variation over the course of the day, but when you’re averaging over a whole city, that variation is mostly predictable and taken into account by the power companies.
Also, generators aim to achieve 60 Hz exactly–but only on average. A wall clock that uses the power frequency as a timebase will be as accurate as an atomic clock over the course of many days, but during any one day it may be off by around a second (IIRC). During high load times the generators may slow down as you say; plant operators then run slightly faster than 60 Hz at low load times to make up for the deficit.
I think there’s been some talk about relaxing this constraint since wall clocks are less common now, but I don’t know if anything’s come of it.
It’s still not completely clear to me. When demand for energy is low, does a hydro-electric plant still produce the same amount of energy as when demand is high? If so, is the excess energy “wasted”? Or do they have a way to limit how much energy is produced if there’s no way for it to be used?
They have valves that can limit the flow of water through the turbines, limiting electrical power production. There’s no point in producing more electrical power than can be used at any given moment because then they would have to dissipate it somewhere, e.g. a gigantic load bank.
If the flow through the turbines is less than the flow into the reservoir from upstream, then the difference simply collects in the reservoir. If the reservoir is already at its height limit, then water is released from a spillway.
