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There is always a debate around Earth Hour every year, and the opposite side of Earth Hour usually claims that

The (sudden) decrease and increase of the power usage in the start and end of Earth Hour will cause much more power loss (than the save of power), and even do damage to the power supply system.

Is this statement true? To what extent?

Thank you very much.

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Depends on how smart the engineers were. :P – Mateen Ulhaq Mar 26 '11 at 2:44

4 Answers 4

Probably not, lighting uses a decreasing proportion of the power load these days.

In the UK the grid used to carefully monitor TV, during the commercial breaks in popular soaps the power draw would go up by giga-watts as everybody made tea! This was in the days when 20M people watched the same show and in a country with electric kettles.

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The grids can take turning the lights off, by experimental observation: everyday all over the world the lights come up at about the same time for each geographical region, and turn off at about the same time due to the similar sleep schedule of millions.

Total black out might overload the system, but the percentage of people who take part in the game is small so even then dangers are minimal.

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"Total blackout...." wrong. – Georg Mar 26 '11 at 19:14
Don't forget that people use computers at 12PM, which compensates for the lack of lights on. – Mateen Ulhaq Mar 27 '11 at 4:22
@muntoo: Don't forget that your local power company keeps close tabs on overall consumption (go google it, I'm sure it's around somewhere). And that graph of consumption over time is not flat for any particular day. – Ernie Jul 27 '11 at 0:08

It is unlikely that the Earth Hour will cause substantial damage to the power supply system. However, it will require a lot of energy and manpower to adjust the power plants to the changes.

First of all, generators are automatically taken off the grid if it is detected that the power supply is higher than the current demand.

When the Earth Hour ends, power generation companies will have to turn the generators on (which also consumes time and energy) is such a way that they can supply energy to all those who turn their lights on. But they can't do this too rapidly, or the generators will automatically shut down again.

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Different types of power plants have different rates that they can respond to changes. Coal is usually the slowest, but any thermal plant has components that effectively store heat. These plants may be in a semi-idle state, and are referred to as spinning reserve. In this state fuel is still being burned to maintain temperatures, but the fuel load and power output are both reduced. There is a market for power storage of various durations, from seconds to hours, that is used for grid stabilization. – Omega Centauri Mar 26 '11 at 18:43
Also earth hour is during the evening, when power demand is falling off. To a certain degree it just advances the power demand curve by an hour. So if earth hour was planned for 8-9PM, then a power plant that had been planned to be idled at 9PM, can instead be idled at 8PM, and left off at the end of the interval. This process won't be perfect, but I'd bet most of the demand reduction (but not all) translates into lower fuel consumption. – Omega Centauri Mar 27 '11 at 3:47

As the vast majority of people aren't stupid enough to fall for the scam/hoax, the effects will be miniscule. And of those who do, as said, their electric lights are only a small percentage of their total power consumption (and most likely they'll compensate by turning to other electrical appliances that consume more electricity than those lights).

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In what way is this a scam/hoax? It's not that you are lied to by people who want your money. – Lagerbaer Mar 28 '11 at 2:19
you have in fact been lied to by the entire "environmental movement" who're only interested in scamming you out of your freedom. – jwenting Mar 28 '11 at 10:21
I agree that this is hard nowadays, but one should not reject the true, scientific environmental movement because of noisy people with their crazy actions. – mbq Apr 3 '11 at 13:10
the problem is that that "true, scientific, movement" no longer exists, and is certainly not the one that's promoting "earth hour" (or anything else that promotes humanity going back to the stone age in order to "save the planet"). – jwenting Apr 4 '11 at 9:59

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