Generator Fixed Load

Units:	MW
Mode:	Input Only
Multi-band:	False
Default Value:	0
Validation Rule:	Any Value
Key Property:	No
Description:	Fixed load

Generator Fixed Load defines a fixed profile of Generation from the facility i.e. it constrains the Generation to be exactly this value subject to availability.

How the value of Fixed Load is interpreted depends on the Fixed Load Global setting. It controls whether the value is across all units at the facility or unit-by-unit.

Fixed Load is commonly used:

In benchmarking exercises when you want dispatch to follow exactly the historical market dispatch in some or all periods of the simulation.
To model non-scheduled resources such as solar or wind.

Fixed load is treated specially in the simulator. It over-rides other constraints such as Min Stable Level, Start Profile, Max Ramp Up, and Max Ramp Down. When offers are defined the Fixed Load over-rides the Offer Quantity e.g. if there is insufficient capacity offered to meet the Fixed Load the size of the last offer band is extended automatically.

How Fixed Load values of zero are interpreted is controlled by the Fixed Load Method setting. By default:

if the value is zero the dispatch constraint is ignored, but
if the value is non-zero the simulator will dispatch the unit to exactly the given level.

This interpretation is based on the rules of some self- commitment markets where Fixed Load is used to model units on test for a period of time and zero indicates that the unit is not on test. However you may wish to enforce Fixed Load value of zero. In this case you will need to set Fixed Load Method = "Enforce Zero Values". If you want Fixed Load to be ignored in some time periods you can set the Fixed Load value to -1. Any negative values used for Fixed Load property, will relax the Fixed Load constraint and return the generator to normal dispatch optimization.

In the example in Table 1 the generator will be dispatched to follow the given profile (15 MW in hour 1 of Monday and 25 MW on hour 2 Monday) while the unit runs up to its minimum stable level, and beyond that it will follow dispatch according to its cleared energy offers.

Table 1: Example of Fixed Load when Fixed Load Method = "Relax When Zero"
Property	Value	Units	Band	Timeslice
Units	1	-	1
Max Capacity	250	MW	1
Offer Quantity	40	MW	1
Offer Quantity	210	MW	2
Offer Price	0	$/MWh	1	WEEKDAY
Offer Price	30	$/MWh	1	WEEKEND
Offer Price	30	$/MWh	2
Fixed Load	15	MW	1	W2,H1
Fixed Load	25	MW	1	W2,H2

In the example in Table 2 the generator will follow a series of values defined in the Data File "FIXED" but only for the specific date ranges shown, other times the dispatch is optimized normally.

Table 2: Example of Fixed Load when Fixed Load Method = "Enforce Zero Values"
Property	Value	Units	Band	Date From	Date To	Data File
Fixed Load	-1	MW	1
Fixed Load	0	MW	1	Tuesday, 1 December 2009 06:00:00	Tuesday, 4 May 2010 06:00:00	FIXED
Fixed Load	0	MW	1	Friday, 7 May 2010 06:00:00	Saturday, 8 May 2010 06:00:00	FIXED

By default the Fixed Load constraint is a hard constraint meaning that no violations are allowed. You can optionally make the constraint 'soft' and introduce a penalty price with the property Fixed Load Penalty. The frequency, quantity and cost of violations are reported in the properties:

Note that Fixed Load is automatically derated by the Generator Forced Outage Rate and Maintenance Rate in non-chronological simulation phases e.g. when LT Plan or MT Schedule are using load duration curves. This is done to simulate the effect of outages on the ability of the station to meet the Fixed Load requirement.