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Why Is electricity cheaper at night?

Wednesday, September 3, 2014

Why Is electricity cheaper at night?


A lot of us will have heard about the Economy 7 (and possibly the Economy 10 tariff). If you havn’t, it’s:

“A tariff where you get cheaper electricity for 7 or 10 hours a day, mostly during the night”

It is essentially an electricity equivalent of off-peak train tickets. A savvy electricity user will be able to save a load of money through an Economy 7 tariff and to find out more about ways to use an Economy 7 tariff to its maximum potential then see another of our articles here.

What we’re going to look into here is why electricity is cheaper at night, and it all starts with the UK’s daily usage graph, sourced directly from the national grid[1].


As you can see, at our peak, in the morning and evening, we use nearly double the amount of electricity that we use at night. A single power station can only produce a small part of this power, and so the higher our maximum need is, the more power stations are required. The Economy 7 tariff is here to encourage people to flatten the curve above to look something like this:


Even though we would be using the same amount of electricity we would be using fewer power stations, which would mean that we wouldn’t have to build as many, maintain as many and do all the other things needed in running an entire plant! So that is out first reason:

  1. By using electricity at night instead of in the day, we can reduce the number of power stations we need in the UK, which saves the electricity companies money!

The next part of the conundrum requires the introduction of the three different types of power plants: base load, load following, and peak load.

Base load power plants are on all the time, day and night. They hardly ever turn off and they tend to be the most efficient when compared to others of the same fuel type (i.e. we’re not comparing coal and nuclear here). Renewables like wind and solar, as well as nuclear tend to contribute a lot towards base load energy because they are relatively cheap to run and much harder to turn off than other power sources.

Load following power plants are those which are turned on when the demand exceeds that which can be supplied by the base load plants. The cheapest ones to run are turned on first, and then the more expensive ones are turned on last.

Peaking power plants (a.k.a peakers) are only turned on when we really need them (like when we turn on the kettle at the Coronation Street adverts[2]). These guys tend to be oil guzzling, carbon farting, money wasting machines. Some even run on diesel and are the most expensive to run.

If you’re really interested, the National Grid has a great, live monitor of where our energy is coming from right now, including how much we get from those on the other side of the English Channel.

Below is how our daily demand may be split into the three categories introduced above.

So this brings us to reason number two for cheaper electricity at night:

  1. By using electricity at night, we can use more of the efficient, base load power plants, and less of the expensive peaking power plants.

So now we know why we pay less for electricity at night if we’re on Economy 7!

If you want to know more about how to use Economy 7 to your advantage, then check out our forum conversations and our other articleson the subject!

If you’re interested in finding out more about the future of our energy and the world, then there is a fantastic book that presents only facts and no gossip called Renewable Energy: Without the Hot Air, by David Mackay and it’s available for free online!

[1] National Grid Article

[2] Manchester Evening News Article

  • Alex Buckman
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    Alex Buckman
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