Notation and units

Unit mistakes in energy modelling produce plausible-looking, completely wrong results. This page is the book's single source of truth for symbols and units.

Units

Quantity	Unit	Notes
Power	MW	Instantaneous rate. Dispatch targets, availability, limits
Energy	MWh	Power × time. 10 MW for one 5-minute interval = 0.833 MWh
Price / value	$/MWh	Australian dollars unless stated
Value rate	$/h	$/MWh × MW. Multiply by interval length in hours to get $
Shadow price of a MW limit	$/MWh	($/h) per MW
State of charge	MWh, or % of usable energy capacity	Always say which
Time	NEM market time (AEST, UTC+10, no daylight saving)	Stored timezone-aware where possible

Intervals

Concept	Length	Notes
Dispatch interval	5 min	288 per day
Settlement (trading) interval	5 min since 1 Oct 2021 (5MS)	Earlier data: 30 min
Interval label	AEMO labels intervals by their end time	The library documents which convention each dataset uses

Symbols

Symbol	Meaning
\(P_i\)	Power exported by unit \(i\) [MW]
\(\bar P_i\)	Available capacity of unit \(i\) [MW]
\(L\)	Network / connection limit [MW]
\(a_i\)	Participation coefficient of unit \(i\) in a limit [–]
\(v_i\)	Value to the owner of one MWh from unit \(i\) [$/MWh]
\(\lambda\)	Shadow price (dual value) of a constraint
\(\Delta t\)	Interval length [h] (5 min = 1/12 h)

Availability is not one thing

Keep these separate; they are frequently and wrongly treated as equal:

Term	Meaning
Physical capability	What the plant could produce if nothing else limited it
Technical availability	Capability minus outages and derates
Commercial / market availability	What is offered to the market
Dispatch target	What the dispatch process instructs
Actual generation	What was metered