The Grid 2025 Challenge - Introduction - University of Glasgow

Legislation
The UK Government is working towards providing a greater proportion
of the National Grid ("the grid")'s electricity via renewable
energy sources in order to reduce the UK's greenhouse gas emissions
from fossil fuel power plants. Under the Climate Change Act signed into
law in 2008, the government set out targets to cut greenhouse gas
emissions by 80% compared to 1990
levels by 2050.[1]
In Scotland, the government has been considering plans "to meet an
equivalent of 100% demand for
electricity from renewable energy by 2020".[2]
The European Union also has a directive which legislates that the
United Kingdom should increase production of electricity from renewable
energy sources from 1.3% in 2005 to 15% by 2020.[3]
The Current Grid
A 400kV power
line, part of the distribution network that forms part of the National
Grid in Great Britain.
Electricity is supplied to homes and businesses in Britain from a
series of interconnected power stations, substations and other
infrastructure connected to consumers. At any given moment, there is a
specific demand created by the electrical devices connected to the
grid, and a specific power being supplied by the various interconnected
generators from power plants. Keeping these two factors in balance is
extremely important to prevent mismatches between electricity supply
and demand. National Grid plc,
the independent body responsible for maintaining the grid on the United
Kingdom government's behalf, are tasked with keeping the supply and
demand of electricity in balance.
At present, electricity is mostly produced from traditional fossil
fuel power plants such as coal or nuclear. These usually provide a
large, stable source of power that is, to a large extent, not directly
influenced by the weather. While some power plants in use in Britain
rely on renewable energy sources, they represent only a small
proportion of the total generating capacity of the grid and so
fluctuations in power production from these plants are reasonably easy
to accommodate in the present grid.
Supply and Demand Pattern
Electricity demand in the UK follows a reasonably predictable
pattern (as can be seen in the 'Typical Weekly Demand' figure).
National Grid controllers forecast demand using a number of
measurements such as weather patterns, time of year, day of the week
and time of day. Naturally, demand for electricity is greatest in the
colder months when households need more heat, and particularly in the
daylight hours when offices are lit and heated, and when people use
productive equipment such as computers. The whole country's demand
throughout the day will tend to fluctuate only gradually, as occasions
where additional power is required are offset by other reductions in
demand, such as a kettle being switched on in one household as another
household's kettle switches off (this is known as the diversity of
demand or diversity factor[4]).
British electricity demand across a week in
2011. At the weekend, the power demand is roughly 15% lower and there is a more gradual morning
spike than during the week. Apart from these differences, demand
follows the same pattern every day. The shape of the demand across this
week, but not necessarily the magnitude, is typical of most weeks.
The Future Grid
The increasing use of renewable energy sources presents a problem to
grid controllers in being able to maintain the balance between supply
and demand. The grid infrastructure itself provides only a very limited
ability to store energy, so when electricity is being consumed, it has
to be generated at the very same moment. Some renewable energy sources,
such as wind power via turbines and solar power via photovoltaic cells,
can suffer from fluctuations in their output due to the variability of
the underlying sources of energy. For example, wind turbines rely on
air flow, and the wind does not always flow at a steady rate. Solar
cells do not always receive a constant level of sunlight, as it can be
attenuated through clouds in the sky.
Future Challenges
Unfortunately, electricity demand does not necessarily follow
electricity supply. When the wind stops blowing and the Sun goes down,
consumers do not consciously adjust their electricity demand
accordingly. The National Grid controllers can predict quite reasonably
the electricity demand in the short term future based on temperatures,
day of the week and time of the year, among other factors.
Variability of Renewable Energy
Sources
The grid controllers cannot predict the weather to a great deal of
precision. This problem is especially compounded with local variations
in wind, clouds and rain. This means that renewable energy sources that
rely on the weather, such as wind and solar, can provide large
fluctuations in their output when the weather is changeable. Across an
entire country, the local variations in weather can reduce the overall
fluctuations in the power being provided from renewable energy sources.
However, still the overall fluctations will be significantly larger in
an electricity grid mainly based on renewable energy sources compared
to an grid mainly based on non-renewable energy sources.
Influence of Renewable Energy Sources
on the Grid
The electricity generation fluctuations produced by some renewable
energy sources present a problem to the National Grid. While it is in
principle possible to build enough renewable energy generation capacity
to match the maximum electricity demand, it is impossible to create a
renewable energy source which is able to provide its maximum output at
all times. Variations in electricity supply from renewable energy
sources can result in occasions where there is either too little or too
much electricity being produced. Such variations can occur over short
periods (such as a quick gust of wind providing additional electricity
production from turbines) and over long periods (such as the Gulf
Stream moving north during winter, causing a lack of wind across the
whole country).
The Solution?
An example of a supply surplus and a supply
deficit occurring on the same day. The y-axis shows the deficit between
supply and demand, with positive values indicating a lack of required
electricity being supplied. There are at first two periods of supply
surplus, and later a period of supply deficit. A potential solution to
the deficit would be to somehow store the initial surplus for use later
on.
While it would theoretically be possible to build enough renewable
energy sources with enough average generation capacity to meet the
current demand at all times, such a plan would require a large fleet of
conventional power plants in standby mode, ready to take over when the
renewable energy sources cannot satisfy the demand, or build huge
facilities (such as pumped storage or batteries) for long duration
electricity storage. Both of these approaches require costly hardware
to be built and maintained. A much more elegant solution is to find a way to store surplus
energy in times of abundant supply, for use in times when supply is
limited.
There exist a few ideas which can help mitigate the fluctuations
caused by renewable energy sources. For instance, dynamic demand
control is a technique which seeks to limit an appliance's
electricity consumption in times when there is limited supply, instead
only using electricity when it is plentiful. Some research papers
outline techniques involving devices such as fridges or electric cars. To
model the effect that such techniques have, though, we need an idea of
the frequency and magnitude of the fluctuations the grid based entirely
on renewable energy sources would experience.
Our Dataset
The dataset available on this website provides a 1 year long time
series of the simualted electricty supply to demand ratio for the year
2025, assuming all electrcity is produced from renewable energy
sources. This data set can be used as a benchmark to assess the
regularity and size of the fluctuations the future grid might
experience, hopefully providing insight into the usefulness of various
new technologies, including, among others, dynamic demand control
devices.
A description of the dataset and how it was produced can be
found on the Data page.