Capacity

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Overview

Capacity refers to the maximum amount of electrical power that a generation unit can produce, typically measured in megawatts (MW). Understanding the different types of capacity measurements helps in analysing the true potential and operational constraints of electricity generators.

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Types of Capacity

In the Australian electricity market, there are two primary capacity measurements tracked by AEMO (Australian Energy Market Operator):

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Registered Capacity

Registered capacity represents the normal operational capacity of a generation unit. This is the capacity registered with AEMO for standard market operations.

• For solar farms, this typically reflects the aggregate capacity of all solar panels installed
• For fossil fuel plants, this often represents the design capacity or Maximum Continuous Rating
• This is the standard measure used for most capacity analysis

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Maximum Capacity

Maximum capacity is used by AEMO for bid validation in market systems and may differ from registered capacity.

• For solar farms, this is often lower than registered capacity due to grid connection constraints
• For fossil fuel plants, this may represent a temporary higher output achievable at reduced efficiency
• This capacity might only be sustained for limited periods

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Why Do These Capacities Differ?

The differences between registered and maximum capacity vary by generation technology: Solar Farms often have registered capacity greater than maximum capacity due to:

• Intentional oversizing of solar panel installations
• Grid connection limitations that constrain output
• Economic optimisation considering varying solar conditions

Fossil Fuel Plants sometimes have maximum capacity greater than registered capacity because:

• They can temporarily operate above normal ratings
• Higher outputs may come with reduced efficiency
• Operators typically avoid this except during high-price events

For a detailed technical discussion of these capacity measures, see WattClarity’s analysis: Analytical Challenge – choosing what measure to use, for ‘Installed Capacity’

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Accessing Capacity Data

OpenElectricity provides capacity information through multiple interfaces:

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Facility Pages

Individual facility pages display detailed capacity information. For example, the Bayswater Power Station page shows registered capacity in its capacity chart: View Bayswater Power Station The facility page displays:

• Current registered capacity for each generation unit
• Unit-level details including fuel technology
• Operational status and performance metrics
• Capacity factors for each unit

Note that the charts display registered capacity rather than maximum capacity, providing the standard operational capacity for analysis. This is better demonstrated when viewing battery facilities, such as the Waratah Super Battery in New South Wales. View Waratah Super Battery The generation does not come near the registered capacity of the unit, but likely does approach the maximum capacity.

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Capacity Charts

OpenElectricity’s capacity charts provide comprehensive views of capacity across networks and fuel technologies: Explore Capacity Charts These advanced charts offer:

• Historical capacity trends by fuel technology
• Combined view of both NEM and WEM markets
• Interactive filtering and time range selection
• Breakdown by renewable and non-renewable sources

Advanced charting features allow you to view capacity history by fueltech over time in proportion view, change view, and more.

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API Access

For programmatic access, capacity data is available through the OpenElectricity API at the facilities endpoint. The API provides:

• Real-time capacity information
• Historical capacity data
• Both registered and available capacity values
• Detailed unit-level information

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Capacity Factors

Capacity factor is a crucial metric that measures how much electricity a generator actually produces compared to what it could produce if operating at full capacity continuously. It’s expressed as a percentage: Capacity Factor = (Actual Energy Output) ÷ (Maximum Possible Energy Output) × 100%

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What Capacity Factors Tell You

A capacity factor reveals the operational characteristics and performance of a power station:

• High capacity factors (70-90%) indicate baseload generators that run continuously
• Moderate capacity factors (30-60%) suggest peaking plants or weather-dependent renewables
• Low capacity factors (10-30%) typically indicate backup generators or highly variable renewables

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Typical Capacity Factors by Fuel Technology

Carbon-based

• Coal: 70-85% - Designed for continuous operation
• Gas: 10-70% - Combined cycle plants often run as mid-merit generation or as peaking plants
• Diesel: 0-10% - Used in emergency situations

Renewables

• Hydro: 30-50% - Varies significantly based on water availability and market needs
• Wind: 30-45% - Dependent on wind resource quality and location
• Solar (Utility): 25-35% - Limited by daylight hours and weather often better oriented and placed
• Solar (Rooftop): 15-20% - Lower than utility

Storage

• Battery: 10-30% - Used for arbitrage and grid stabilisation rather than continuous output
• Pumped Hydro: 20-40% - Cycles between generation and pumping modes

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Interpreting Capacity Factors

Capacity factors help assess:

1. Economic Performance: Higher capacity factors generally mean better return on investment
2. Resource Quality: For renewables, higher factors indicate more optimal unit locations
3. Operational Strategy: Low factors may be intentional for peaking plants
4. Maintenance Patterns: Declining factors might indicate ageing equipment
5. Market Conditions: Economic factors such as price spikes or surges in demand influence when generators operate

For more detailed facility information and real-time generation data, explore the Facilities Guide.