Module 10 — A New Approach to Market Design
Lesson 8 of 10
Energy, capacity and reliability products
Learning objectives
By the end of this lesson you should be able to:
- Understand the distinction between energy, capacity and reliability.
- Explain why these services provide different forms of value.
- Recognise why consumers may require different combinations of these services.
- Appreciate how separating electricity into distinct products can improve market design.
- Understand how differentiated products support consumer choice and investment.
Introduction
Electricity is often discussed as though it were a single product.
Consumers purchase electricity.
Generators produce electricity.
Markets trade electricity.
However, the service that consumers actually receive is more complex.
A household does not simply require units of energy.
It also requires electricity to be available when needed and delivered with an appropriate level of reliability.
This suggests that electricity can be viewed as a combination of several distinct services rather than a single product.
One possible framework separates these services into:
- energy,
- capacity, and
- reliability.
Energy
Energy represents the amount of electricity consumed over time.
It is typically measured in kilowatt-hours (kWh) or megawatt-hours (MWh).
Examples include:
- charging an electric vehicle,
- heating a home,
- operating industrial equipment,
- powering household appliances.
Energy answers the question:
"How much electricity is required?"
Capacity
Capacity represents the ability to deliver electricity when it is needed.
It reflects the maximum rate at which electricity can be supplied.
Capacity is commonly measured in kilowatts (kW) or megawatts (MW).
For example:
A household may consume relatively little energy over an entire day while still requiring high power for a short period.
Similarly, an industrial facility may require a large electrical connection even if it does not operate continuously.
Capacity therefore answers the question:
"How much power may be required at any one time?"
Reliability
Reliability describes the confidence that electricity will be available when required.
Examples include:
- maintaining supply during periods of scarcity,
- minimising interruptions,
- ensuring critical services remain available,
- supporting essential infrastructure.
Different consumers place different values on reliability.
For example, a hospital may require a much higher level of reliability than a domestic electric vehicle charger.
Reliability therefore answers the question:
"How certain should the service be?"
Different services for different needs
Not every consumer values these three services equally.
Consider the following examples.
A household battery may:
- require moderate energy,
- moderate capacity,
- relatively flexible reliability.
A data centre may require:
- very high energy,
- high capacity,
- extremely high reliability.
A domestic water heater may require:
- modest energy,
- relatively low capacity,
- flexible timing and reliability.
Although each consumes electricity, the services they require are clearly different.
Why distinguish between products?
Treating electricity as a single product can make it difficult to recognise these different requirements.
Separating energy, capacity and reliability allows participants to express more accurately the service they require.
This can improve:
- consumer choice,
- resource allocation,
- investment decisions,
- system planning,
- transparency.
Participants purchase the services they value rather than paying for a single undifferentiated product.
Supporting different technologies
Modern electricity systems include many different technologies.
Examples include:
- renewable generation,
- batteries,
- demand response,
- conventional generators,
- interconnectors,
- flexible industrial loads.
Each technology contributes differently.
Some primarily supply energy.
Others provide capacity during periods of high demand.
Others improve system reliability by responding rapidly to unexpected events.
Distinguishing between different products allows these contributions to be recognised more explicitly.
Consumer choice
Different consumers may choose different service combinations depending on their own requirements.
Some may prefer:
- lower costs with greater flexibility.
Others may prefer:
- guaranteed availability at higher cost.
Others may prioritise:
- uninterrupted service for critical applications.
Rather than assuming every consumer requires exactly the same service, differentiated products allow individuals to select the combination that best matches their needs.
Building on previous lessons
Earlier lessons introduced:
- stateful allocation,
- continuous clearing,
- network-feasible allocation,
- distributed pricing,
- fairness memory,
- forward requests.
Energy, capacity and reliability products provide the services that these mechanisms allocate.
Forward requests describe the service required.
The allocation mechanism determines how that service is delivered while respecting network constraints and coordinating with other participants.
Investment signals
Separating electricity into distinct products also provides clearer signals for investment.
If the system requires additional energy, market signals encourage investment in energy-producing resources.
If additional capacity is needed, technologies capable of delivering power during peak demand become more valuable.
If greater reliability is required, resources that improve security of supply receive stronger incentives.
In this way, different products encourage investment in the specific capabilities the electricity system requires.
A service-oriented perspective
This framework encourages a different way of thinking about electricity markets.
Rather than trading a single commodity, the market coordinates multiple services that together deliver the overall electricity experience expected by consumers.
Energy determines how much electricity is used.
Capacity determines how much power can be delivered.
Reliability determines the confidence with which that service can be provided.
Together, these services define the quality of electricity supplied.
A key insight
Electricity is more than a quantity of energy.
Consumers also value access to power and confidence that it will be available when needed.
Treating energy, capacity and reliability as distinct but complementary products allows electricity services to better reflect the diverse needs of modern consumers and the capabilities of modern power systems.
Key takeaways
- Electricity services can be viewed as combinations of energy, capacity and reliability.
- Energy describes how much electricity is consumed.
- Capacity describes the maximum rate at which electricity can be delivered.
- Reliability describes the confidence that electricity will be available when required.
- Different consumers require different combinations of these services.
- Distinguishing between products improves consumer choice, resource allocation and investment signals.
- A service-oriented perspective provides a richer description of electricity than treating it as a single commodity.
Looking ahead
Having separated electricity into distinct products, the next lesson examines how markets can provide investment signals that encourage the development of the resources needed to deliver these services efficiently over the long term.