Wholesale electricity markets

Learning objectives

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

Understand the purpose of wholesale electricity markets.
Explain who participates in wholesale electricity markets.
Understand how electricity is bought and sold before it reaches consumers.
Recognise how wholesale prices are formed.
Appreciate both the strengths and limitations of wholesale market design.
Understand that wholesale markets coordinate electricity generation but do not directly control the physical electricity system.

Introduction

When you switch on a light, electricity does not come directly from the power station owned by your electricity supplier.

Instead, electricity is traded between companies in a wholesale electricity market before it reaches consumers.

Wholesale markets form the commercial heart of modern electricity systems.

They determine:

Which generators are paid to produce electricity.
How much electricity is bought and sold.
The wholesale price of electricity.

Importantly, wholesale markets do not determine where electricity physically flows.

Electricity follows the laws of physics.

Wholesale markets simply determine the commercial agreements between market participants.

Why do wholesale markets exist?

Following liberalisation, electricity generation was no longer owned by a single organisation.

Instead, many independent companies owned power stations.

These generators needed a way to sell electricity.

Retail suppliers needed a way to purchase electricity for their customers.

Wholesale electricity markets provide the mechanism that brings buyers and sellers together.

They allow electricity to be traded in a transparent and organised manner.

Who participates?

Wholesale electricity markets involve many different organisations.

These include:

Generators

Companies that produce electricity using:

Gas.
Nuclear.
Wind.
Solar.
Hydroelectricity.
Biomass.

Their objective is to sell electricity.

Retail suppliers

Retail companies purchase electricity in wholesale markets before selling it to households and businesses.

Large industrial consumers

Some very large consumers purchase electricity directly from wholesale markets.

Traders

Specialist trading companies buy and sell electricity without necessarily generating or consuming it themselves.

They help manage financial risk and improve market liquidity.

Market operators

Independent organisations administer the market, collect bids and determine market outcomes.

What is traded?

Although we often say electricity is traded, market participants are actually trading contracts for future delivery of electricity.

For example:

A retailer may agree to purchase:

100 MWh

during a particular half-hour tomorrow.

A generator agrees to supply that quantity if dispatched.

The actual electrons flowing through the network cannot be labelled or directed.

Only the commercial obligation is traded.

Matching buyers and sellers

At its simplest, a wholesale market performs a familiar function.

Buyers submit bids indicating:

How much electricity they wish to purchase.
The maximum price they are willing to pay.

Generators submit offers indicating:

How much electricity they can produce.
The minimum price at which they are willing to generate.

The market operator matches supply and demand.

The objective is to satisfy demand while respecting the market rules.

Supply and demand

Electricity markets rely upon the same basic economic principles as many other markets.

When demand is low:

Relatively inexpensive generators may be sufficient.

Wholesale prices tend to be lower.

When demand increases:

More generators must operate.

Some of these generators have higher operating costs.

Wholesale prices generally increase.

The market price therefore reflects the balance between available supply and electricity demand.

An example

Imagine electricity demand during one particular hour is:

500 MW.

Three generators submit offers.

Generator	Capacity	Offer Price
Wind Farm	200 MW	£0/MWh
Nuclear Plant	200 MW	£35/MWh
Gas Plant	300 MW	£90/MWh

To satisfy demand:

The wind farm produces 200 MW.
The nuclear plant produces 200 MW.
The gas plant supplies the remaining 100 MW.

All three generators are required to meet demand.

The wholesale market price is determined by the highest-priced generator required to satisfy demand—in this case, the gas plant.

This approach is known as marginal pricing, and we will examine it in much greater detail later in the course.

Why prices change

Wholesale electricity prices vary continuously because electricity systems are constantly changing.

Prices respond to factors such as:

Electricity demand.
Weather conditions.
Generator availability.
Fuel prices.
Transmission constraints.
Unexpected equipment failures.

As these conditions change, the balance between supply and demand changes, and so do market prices.

Supply stacks

It is often useful to imagine generators arranged in order of increasing operating cost.

This is known as the merit order.

For example:

Wind.
Solar.
Nuclear.
Hydroelectricity.
Coal.
Gas.

As demand increases, progressively more expensive generators are required.

The wholesale price therefore tends to rise as higher-cost generators enter the market.

In reality, the ordering is more complex and depends on many operational factors, but the merit order provides a useful way of understanding wholesale price formation.

Wholesale prices are not retail prices

Consumers rarely pay the wholesale electricity price directly.

A household electricity bill typically includes many additional costs.

For example:

Network charges.
Environmental levies.
Capacity payments.
Balancing costs.
Supplier operating costs.
Taxes.

Wholesale electricity is therefore only one component of the final retail price.

The role of forecasting

Unlike many other commodities, electricity cannot easily be stored in large quantities.

Generators and suppliers must therefore forecast future conditions.

These forecasts include:

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

Wholesale markets depend heavily upon accurate forecasting because electricity must be available precisely when consumers require it.

Markets versus physical operation

One of the most common misunderstandings about electricity markets is that they directly control the power system.

They do not.

Wholesale markets determine:

Commercial transactions.
Financial payments.
Scheduled generation.

The physical electricity system is operated separately by the system operator, whose responsibility is to maintain:

Frequency.
Voltage.
Security.
Reliability.

The market creates a schedule.

The system operator ensures that schedule remains physically achievable.

Strengths of wholesale markets

Wholesale electricity markets offer several important advantages.

Competition

Multiple generators compete to supply electricity.

Transparency

Market prices provide information about supply and demand conditions.

Investment signals

High prices may indicate that additional generation capacity would be valuable.

Efficient dispatch

Under ideal conditions, lower-cost generators are generally used before higher-cost generators.

Limitations

Wholesale markets also have important limitations.

Electricity is not an ordinary commodity

Supply and demand must remain balanced continuously.

Physical constraints

Electricity networks contain transmission limits, voltage constraints and stability requirements that markets alone cannot manage.

Forecast uncertainty

Electricity demand and renewable generation cannot be predicted perfectly.

Missing services

Wholesale markets primarily reward energy production.

Many other valuable services—including reserves, flexibility and reliability—often require additional markets or payment mechanisms.

These topics will be explored later in the course.

Wholesale markets and the energy transition

When many wholesale electricity markets were first designed, most electricity came from large thermal power stations.

Today the situation is changing.

Electricity systems increasingly include:

Wind generation.
Solar power.
Batteries.
Flexible demand.
Distributed Energy Resources.

These technologies possess characteristics very different from conventional generators.

This has raised important questions about whether traditional wholesale market designs remain well suited to increasingly decentralised electricity systems.

Throughout the remainder of this course we will examine these questions in detail.

A key insight

Wholesale electricity markets exist to coordinate commercial transactions between electricity producers and consumers.

They answer questions such as:

Who generates electricity?
How much is generated?
What payments are made?

They do not directly determine:

Where electricity flows.
Whether the network remains secure.
Whether the schedule is physically feasible.

Those responsibilities remain governed by the engineering of the electricity system.

Understanding the distinction between commercial coordination and physical operation is one of the most important concepts in electricity market design.

Key takeaways

Wholesale electricity markets allow generators and buyers to trade electricity before it reaches consumers.
Participants include generators, retailers, industrial consumers, traders and market operators.
Market participants trade contracts for future electricity delivery rather than physical electrons.
Wholesale prices reflect the balance between electricity supply and demand.
Many wholesale markets use marginal pricing, where the highest-cost generator needed to meet demand sets the market price.
Wholesale electricity prices form only one component of consumers' electricity bills.
Wholesale markets coordinate commercial transactions, while system operators maintain the physical security of the electricity system.
Modern electricity systems are raising new questions about whether traditional wholesale market designs remain appropriate.

Looking ahead

Not all electricity is traded through organised wholesale markets.

Many companies buy and sell electricity directly through long-term agreements or organised exchanges.

In the next lesson, we explore bilateral contracts and power exchanges, examining the different ways electricity companies manage price risk and secure future electricity supplies.