Defining Reliability
Overview
Reliability has traditionally been viewed as a property of the electricity system.
Network operators build sufficient infrastructure to minimise interruptions, while generators maintain enough capacity to satisfy expected demand.
Consumers receive electricity whenever they request it.
This approach has served society well for many decades.
However, it implicitly assumes that every electricity service requires exactly the same level of reliability.
In reality, different applications have very different requirements.
FP-AMM therefore treats reliability as a measurable and programmable property of an electricity service rather than a fixed characteristic of the electricity system.
What is Reliability?
In its simplest form, reliability describes the likelihood that a requested electricity service will be delivered when required.
For traditional electricity systems this question was relatively simple.
Will electricity be available when the customer turns on an appliance?
Modern electricity systems require a more nuanced definition.
Flexible devices often possess multiple opportunities in which they can consume electricity.
For example, an electric vehicle arriving home at 6:00 pm may only require a full battery before 7:00 am the following morning.
The question is therefore no longer
"Can electricity be supplied immediately?"
Instead it becomes
"Can this service be delivered before its required deadline?"
Reliability therefore becomes associated with the successful completion of a requested service rather than the continuous supply of electrical power.
Reliability Depends on the Service
Different electricity services tolerate different levels of delay.
For example,
| Device | Typical Reliability Requirement |
|---|---|
| Medical equipment | Immediate, continuous supply |
| Lighting | Immediate supply |
| Refrigeration | Continuous supply |
| Electric vehicle charging | Complete before departure |
| Hot water heating | Complete before required use |
| Battery charging | Flexible within operating limits |
Each service possesses its own acceptable operating window.
Treating all of these requirements identically unnecessarily increases system costs while reducing the opportunity to utilise renewable energy and flexible demand.
Reliability is Separate from Energy
An important principle of FP-AMM is that energy and reliability are different products.
Energy answers the question:
How much electricity is required?
Reliability answers the question:
How confidently should that request be fulfilled?
Two customers may request exactly the same amount of energy.
However, one may require immediate delivery while the other is happy for delivery to occur at any point over several hours.
Although the energy requirement is identical, the reliability requirement is completely different.
Recognising this distinction allows the market to coordinate flexible demand far more efficiently.
Reliability is a Probability
FP-AMM represents reliability as the probability that a requested service will be successfully completed within its agreed operating window.
A higher reliability therefore represents a stronger commitment from the electricity system.
For example,
- a highly reliable service is expected to be delivered almost every time,
- a more flexible service may occasionally be delayed when genuine scarcity exists.
This probabilistic interpretation reflects the physical reality of modern electricity systems.
Absolute guarantees are neither technically achievable nor economically efficient.
Instead, the objective is to provide transparent and measurable service commitments.
Reliability is Continuously Updated
Reliability is not determined once and then forgotten.
As the electricity system evolves, forecasts improve, renewable generation changes and new market requests arrive.
The probability of successfully completing each service therefore changes continuously.
FP-AMM continuously updates these reliability estimates as part of the market clearing process.
Participants always observe the most up-to-date assessment of their requested service.
Reliability Enables Better Coordination
Making reliability explicit provides several important advantages.
It allows:
- customers to select services appropriate for their needs,
- flexible devices to participate without compromising essential demand,
- renewable generation to be utilised more effectively,
- network capacity to be allocated more efficiently,
- market incentives to reflect the true value of flexibility.
Reliability therefore becomes an active coordination mechanism rather than a hidden engineering objective.
Reliability is a Contract
Within FP-AMM, reliability is not merely an operational metric.
It forms part of the agreement between the customer and the electricity provider.
When a customer enrols a flexible device into the market, they agree the level of reliability required for that service.
The market continuously attempts to satisfy these commitments while responding to changing system conditions.
Most of the time, every requested service can be delivered successfully.
Only during periods of genuine scarcity do trade-offs become necessary.
Those trade-offs are governed by the Service Level selected by the customer and the Fair Play mechanism described later in this documentation.
From Reliability to Service Levels
Reliability provides a quantitative measure of how likely a service is to be successfully delivered.
Customers, however, should not be expected to purchase abstract probabilities.
Instead, FP-AMM groups reliability commitments into clearly defined Service Levels.
Each Service Level specifies the reliability commitment associated with a particular class of flexible service, allowing customers to select the balance between cost, flexibility and certainty that best meets their requirements.
The following sections describe how these Service Levels are defined and incorporated into customer contracts.