Day-Ahead, Intraday, Real-Time and Balancing Markets

Learning objectives

By the end of this lesson you should be able to:

Understand why electricity is traded over multiple timescales.
Explain the roles of forward, day-ahead, intraday, real-time and balancing markets.
Recognise how uncertainty changes as delivery approaches.
Compare the European sequential market model with real-time markets such as Australia's National Electricity Market (NEM).
Appreciate why electricity markets continuously update plans rather than making a single decision.
Understand that no forecast is perfect, making real-time system balancing essential.

Introduction

Imagine organising a large outdoor music festival.

Six months before the event, you estimate ticket sales.

One month before, you refine catering orders.

One week before, you update staffing requirements.

The morning of the event, you check the weather forecast.

During the event itself, you continuously respond to changing conditions.

Electricity systems work in much the same way.

No one knows exactly:

How much electricity consumers will use.
How much wind will blow.
How sunny it will be.
Which generators may unexpectedly fail.

Rather than making one decision far in advance, electricity markets continually update their plans as better information becomes available.

Why multiple markets exist

Electricity systems must balance supply and demand every second.

However, participants make decisions over very different timescales.

Some investments are planned:

Years ahead.

Electricity purchases may occur:

Months ahead.

Generator schedules may be finalised:

One day ahead.

Unexpected events may require action:

Seconds before delivery.

No single market can efficiently coordinate all of these decisions.

Instead, electricity markets are organised into a sequence of markets operating progressively closer to real time.

The timeline

A simplified market timeline looks like this:

Time before delivery	Typical market
Months to years	Forward contracts
One day	Day-ahead market
Hours before	Intraday market
Minutes or seconds	Real-time dispatch
During operation	Balancing actions

As delivery approaches:

Forecasts improve.
Uncertainty decreases.
Decisions become more precise.

Forward markets

The earliest trading usually occurs through forward contracts.

These contracts may be agreed:

Months ahead.
Years ahead.

Forward markets help participants manage financial risk.

For example:

A retailer may purchase electricity for next winter long before it is actually required.

Likewise, a generator may secure future revenue by agreeing today to sell electricity it expects to generate next year.

Forward markets therefore provide certainty rather than operational control.

Day-ahead markets

The day-ahead market usually operates one day before electricity is delivered.

By this point, participants possess much better forecasts of:

Electricity demand.
Wind generation.
Solar output.
Generator availability.

Generators submit offers.

Retailers submit demand forecasts.

The market determines a schedule indicating which generators are expected to operate during each trading period the following day.

This schedule becomes the starting point for operating the electricity system.

Why not wait until tomorrow?

One obvious question is:

Why not simply wait until electricity is actually needed?

The answer is that many generators require time to prepare.

For example:

Coal plants may require many hours to start.
Nuclear plants operate most efficiently with stable output.
Fuel must be arranged.
Staff must be scheduled.

Planning ahead allows generators to prepare safely and efficiently.

Intraday markets

Even the best forecasts contain errors.

Weather forecasts improve significantly during the final few hours before delivery.

Consumers may also behave differently from expected.

The intraday market allows participants to update their positions after the day-ahead market has closed.

For example:

A wind farm expecting stronger winds than previously forecast may increase its planned generation.

Alternatively, a retailer expecting higher customer demand may purchase additional electricity.

Intraday trading therefore reduces forecasting errors before real-time operation begins.

Real-time markets

Eventually, forecasts give way to reality.

Electricity must now be generated and consumed.

Some electricity systems operate dedicated real-time markets, where generators continuously submit offers and dispatch decisions are updated every few minutes.

These markets respond directly to actual system conditions rather than forecasts alone.

Australia's National Electricity Market

Australia's National Electricity Market (NEM) provides an example of a real-time electricity market.

Every five minutes:

Generators submit offers.
Demand is measured.
The market is cleared.
Dispatch instructions are issued.

The resulting dispatch schedule reflects current system conditions rather than a schedule determined many hours earlier.

Financial contracts are still widely used to manage price risk, but the physical operation of the system is driven by a continuously updated real-time market.

European electricity markets

Many European electricity systems follow a different philosophy.

Rather than relying primarily on real-time dispatch, electricity is traded sequentially through:

Day-ahead markets.
Intraday markets.
Balancing mechanisms.

Each stage progressively refines the schedule until electricity is finally delivered.

Both approaches seek to achieve the same objective:

Reliable electricity supply.

They simply organise decision-making differently.

Balancing markets

No forecast is ever perfect.

Unexpected events occur continually.

For example:

A generator unexpectedly fails.
Wind speeds change suddenly.
Consumer demand increases.
Transmission equipment trips offline.

The system operator must respond immediately.

Balancing markets provide the mechanisms needed to make these last-minute adjustments.

Participants capable of rapidly increasing or decreasing generation—or adjusting demand—are paid for providing these services.

Balancing therefore represents the final layer of operational flexibility.

Why balancing is essential

Imagine a city expecting electricity demand of:

10 GW.

Just before delivery, demand unexpectedly rises to:

10.4 GW.

Without additional generation, system frequency would begin to fall.

The system operator therefore calls upon balancing resources to restore the balance between supply and demand.

This process occurs continually throughout every day.

Uncertainty decreases over time

One useful way to think about electricity markets is as a process of gradually reducing uncertainty.

Several months ahead:

Forecasts contain considerable uncertainty.

One day ahead:

Most uncertainty has disappeared.

One hour ahead:

Forecasts become increasingly accurate.

Real time:

The actual operating conditions are finally known.

Each market therefore updates previous decisions using progressively better information.

Markets are continually refining a plan

Rather than viewing electricity markets as separate systems, it is helpful to think of them as successive refinements of the same plan.

Each stage asks:

"Given everything we know now, what is the best schedule?"

As new information becomes available, that answer changes.

Electricity markets therefore operate as a continuous planning process rather than a single optimisation.

Different philosophies

Countries organise this planning process differently.

Some rely heavily on:

Sequential forward scheduling.

Others rely more heavily on:

Real-time optimisation.

Neither approach is universally accepted as superior.

Instead, each reflects different engineering traditions, regulatory philosophies and historical development.

Looking to the future

Historically, electricity demand was relatively predictable and generation came mainly from large thermal power stations.

Today's electricity systems increasingly include:

Variable renewable generation.
Battery storage.
Electric vehicles.
Flexible consumers.
Distributed energy resources.

These technologies introduce both new uncertainties and new opportunities.

As a result, many researchers and policymakers are exploring whether electricity markets should become increasingly continuous, dynamic and responsive.

This remains one of the most active areas of electricity market design.

A key insight

Electricity markets do not make a single decision.

They continually improve their decisions as uncertainty decreases.

Forward markets provide certainty.

Day-ahead markets establish a plan.

Intraday markets refine that plan.

Real-time dispatch implements it.

Balancing actions ensure the electricity system remains secure despite inevitable forecasting errors.

Together, these markets allow electricity systems to cope with uncertainty while maintaining reliable supply.

Key takeaways

Electricity is traded across multiple timescales because uncertainty decreases as delivery approaches.
Forward markets help participants manage long-term financial risk.
Day-ahead markets create the initial operating schedule.
Intraday markets allow participants to respond to improved forecasts.
Real-time markets coordinate electricity generation using current system conditions.
Balancing markets manage unexpected events that occur during operation.
European electricity markets typically use sequential day-ahead, intraday and balancing markets, while Australia's National Electricity Market relies on continuous five-minute real-time dispatch.
Modern electricity systems require continual updating of plans rather than a single market decision.

Looking ahead

So far, we have focused on markets where electricity producers and large buyers trade with one another.

Most consumers, however, do not participate directly in these wholesale markets.

Instead, they purchase electricity from retail suppliers.

In the next lesson, we explore retail electricity markets, examining how suppliers purchase electricity, manage risk and provide services to households and businesses.