We’ve all
heard about the surge in demand for electricity that comes at half time during
the big match as everyone brews up a cup of tea, but how much higher is the
peak demand for electricity than the lowest level on a normal day? Have a guess.
A lot is
written about the “how much” of energy use, but the “when” is also of great
interest –particularly in relation to energy supplies like photovoltaic solar power and wind
power that you can’t just switch on and off.
National Grid
(the company in charge of getting electricity from the generator to the user in
the UK) publishes detailed statistics on electricity demand.
Electricity
Demand Follows a Predictable Daily Pattern
The first graphic
shows a plot of the half-hourly instantaneous power consumption of the UK
electricity grid for 5th January and 29th June 2011.
Both are
working days, but obviously one is in the depths of winter, and one in
summer. What’s striking is how similar
the curves are.
From about 6am, the
country begins to wake up and switches on heating, kettles and toasters. Power demand rises to about 10am as people
head off for work and school, and then flattens for the rest of the working
day. The daily peak in demand follows at about 5:30pm as
people arrive home and switch on domestic appliances, while offices and shops remain
open. This peak is much more pronounced
in the winter as people are more likely to be indoors and have the lights and heating on.
From 5:30pm,
demand falls as the offices and shops close and then people turn off lights and
appliances and head off to bed.
But demand
doesn’t fall so much as you might think through the night, many industrial
processes continue 24 hours, and people time the use of appliances and storage
heaters to take advantage of cheaper overnight electricity.
...and a Weekly Pattern
The second
chart shows the energy demand from two weeks from the summer of
2011. A saw-tooth pattern is evident,
with lower demand at weekends as offices and businesses are closed. Weekend demand is around five to ten percent
lower than week-day demand.
...and a Seasonal Pattern
The third chart shows the daily energy demand for the whole of 2011, and shows the difference between summer demand and winter
demand. Electricity demand in the winter is around 30% higher than the summer. Summertime
air-conditioning loads are more than offset by the increased use of electrical
space heating, lighting, and clothes drying in winter.
So, was your
guess close? If it wasn’t you’re in good
company. A straw poll around the office yielded guesses that ranged from peak demand being six times more to a hundred
times more than the lowest demand on the same day.
