How much electricity is created but unused at night by power utilties?

Question

I want to estimate how much electricity goes to waste each night by utilities that keep their electrical generators going (they take too long to spin up otherwise), but ultimately isn't used.

I'm heading toward estimating how much of that wasted electricity could be used to charge plug-in hybrid cars (or purely electric cars). And, then, how many such cars could be charged.

It's not a trivial issue--that electricity, because it's already generated, doesn't add to greenhouse gas production or further use of coal. It's "free" in other words.

Perhaps someone has already done that calculation, or there are web sites that have the information.

TIA!

Answer 1

In general, utilities don't generate power that isn't used.  They may run generators at very inefficient power levels, but the actual output all goes to the grid.  The worst I've heard of is that steam is dumped if turbines can't take it, but only for transients (e.g. the powerplant goes off line).

For some information about dealing with uncertain demand conditions, see the section on "firming value" at the link.

Operating plants at very sub-optimal efficiency might as well be throwing power away, though.  This is one reason why electric cars with utility-controlled chargers are the grid manager's wet dream; instead of having to meet demand in real time within a few megawatts, the manager could turn demand up and down to follow the output of the most efficient powerplants just as long as the right number of megawatt-hours was delivered overnight.

Another plus:  switching off a gigawatt of vehicle chargers is equivalent to a gigawatt of spinning reserve, and it doesn't take a bit of fuel to have it available.  If the vehicles can feed power back to the grid (Vehicle To Grid, or V2G) the usefulness to the grid manager would be even greater.

Answer 2

There is no excess electricity produced at night.

The load on the electrical grid is constantly changing from warm to cold, day to night.

When the load starts to drop for any reason there are control and transmission operators that forecast the demand based on real time information and send out calls to all power plants to adjust load levels to meet the demand on the system.

It is simply accomplished by reducing the firing rates on the boilers in the system so less power is produced or increasing firing rates so more is produced.

There are also many natural gas fired peaking plants on the grid that can be brought up to full load fairly rapidly or brought off - line as needed.

Answer 3

Engineer-poet's answer is fantastic.  I couldn't add anything else to it.  Bravo.

Answer 4

You've got some bad info, bud.  There is little effeiciency difference whether the generators are at full capacity or not.  If the load is light there is less pull on the generators then it takes much less power to keep them turning.

Leveling the load throughout the day IS an issue though since you need to make the most of your capacity.  This is done in a number of ways.  

Ice-bank airconditioning systems are a prime example.  At night, refrigeration systems produce ice stored in brine tanks.  Then during the day, during peak loads, they don't have to run their compressors to cool the building.  

Commercial electric rates are often negotiated and you can get electricity much cheaper during off-peak hours.

Answer 5

Comparably little...as demand goes down, the turbines are turned down as well, and what goes into the net but is not used locally, is sold to other jurisdictions that use more power at night. Any company operating a blast furnace, for example, tends to operate at night because it's cheaper (utility cost wise), and there is less demand to cause them to loose power.

As for spinning-up the generators...it doesn't take as long as you might think. After all, hydro dams regularily allow turbines to spin-down when demand is low. So do nukes.

Good Luck!

Answer 6

NO !!!   NO  There is no electricity that is generated that is not used. If a 60,000 watt generator is ruining it does not produce electricity that is not used.  A 40 hp. motor is ruining with a 10 hp. load the motor only uses 10 hp of electricity to pull the load. When u say a 40 hp. motor that is the max load of the motor.

Answer 7

you have know idea how the power system works.

there are two types of power plants.

main line plants and peaking plants.

main line plants are steam type plants and are built as needed to supply the minimum load. nuke, coal, and oil fired

peaking plants are plants like hydro  geothermal and gas turbine plants that can be turned on and off as needed.

the power companies turn on peaking plants as needed to build load above minimum that is made by the mainline plants

wind and solar are nether of these as you only can make power when you have wind or sun.

this is why you can not rely on them.

this is why building solar and wind plant ONLY will not work.

if the have wind or solar then they may not have to turn on some of the peaking plants.

if they do not have them then they must use the peaking plants.

what that means is that there is no wasted power.

and anyone that believes there is is full of bull.

that is likely why you can not find the info on the web.

more misinformation that helps the power companies justify building more main line plants.