NOTE: Annuities are only computed if the Discount Rate is non-zero.

In all other respects a generation project is the same as a normal Generator. Thus the location of the project is defined by the Generator Nodes memberships i.e. if you have identical project types that can be built in one of multiple locations you must define a Generator at each location.

The production cost model for new generators is identical to that used by MT Schedule and is fully featured, meaning you can model anything that can be modelled in normal simulations, including but not limited to:

• energy and capacity factor constraints
• emissions costs and limits
• fuel constraints
• unit commitment and technical limits

You define these limits in the normal way and the simulator takes care of invoking them only when the unit is actually built.

2. CHP, Cogeneration and other Constrained Resources

Generators with special restrictions, such as Combined Heat and Power (CHP), can be modelled using the normal Generator properties. For example, a CHP plant might have a Min Load restriction representing its heat load. The simulator takes care of only imposing this constraint once the plant is built. For example:

Property	Value	Unit
Max Capacity	300	MW
Min Load	150	MW

Other generators, such as cogeneration, might have known operating regimes that can be represented with multi-band offers like this:

Property	Value	Unit	Band
Offer Quantity	100	MW	1
Offer Quantity	75	MW	2
Offer Price	0	$/MWh	1
Offer Price	25	$/MWh	2

Again the simulator ensures that the offer only 'exists' once the plant is built. Offers are always per generating unit, so the amount offered will automatically increase as the number of units built increases.

3. Hydro, Geothermal and other Energy Constrained Resources

LT Plan can model new hydro, geothermal and other energy constrained resources. For example a 'simple' hydro generation project with capacity, energy limits and run-of-river generation varying by month could be defined as follows:

Property	Value	Unit	Timeslice
Max capacity	20	MW
Rating	18	MW	M01
Rating	20	MW	M02
Rating	16.5	MW	M03
...	...	...
Rating	17	MW	M12
Min load	1	MW	M1
Min load	3	MW	M2
Min load	7	MW	M3
...	...	...	...
Min load	0.5	GWh	M12
Max Energy MONTH	8	GWh	M01
Max Energy MONTH	9.5	GWh	M02
Max Energy MONTH	7.1	GWh	M03
...	...	...	...
Max Energy MONTH	5	GWh	M12
Max Units Built	1	-
Max Units Built	1500	$/kW
Economic Life	30	years
WACC	12	%

This simplified approach can work well for small hydro with limited storage, but when modelling a system with larger hydro or where the hydro provides a significant proportion of the total energy demand it is necessary to model the variability in hydro energy more directly—see Stochastic Optimization.

4. Wind and other Intermittent Resources

Intermittency of generation affects the amount of installed capacity that can be relied upon at peak times. This particularly applies to wind. Here is a typical set of input properties for a wind generation candidate:

Property	Value	Unit	Filename
Max Units Built	300	-
Max Capacity	1	MW
Rating	0	MW	Normalized Wind.csv
Firm Capacity	0.07	MW

Here the Filename reference points to a normalized series of wind power for the location i.e. an hourly series. The Firm Capacity defines how much of the installed capacity counts towards capacity reserves in Equation 5.

When modelling with load duration curves, wind intermittency has more of an effect on the short-term energy balancing than the aggregate energy balance implied by the LDC, thus a single 'expected value' wind profile is generally adequate unless the amount of wind capacity is large in which case it may be worthwhile to model wind variability directly in the LT Plan formulation - see Stochastic Optimization.

5. Retirements

Retirements can be economic, planned, or part of a logical sequence of project stages.

5.1. Planned Retirements

If the unit's retirement is planned and the retirement date is known, then the Units property is all that is needed, as in the following example:

Property	Value	Unit	Date from
Units	1	-
Units	0	-	1/01/2016

In this example the generator is 'in service' from the start of the planning horizon (no date given for Units = 1), and goes out of service on January 1, 2016.

5.2. Economic Retirements

LT Plan is able to optimize the timing of retirements. Because building of new generators incurs a significant fixed cost and inefficient existing plant can be 'bypassed' by simply not being dispatched, it is largely the fixed operations and maintenance costs that drive retirements. As plant age, their fixed costs can rise, and their heat rate degrades. This scenario is represented in the following data where the heat rate degrades by 1% p.a. and the operations and maintenance charge increases by 2.5% p.a.:

Property	Value	Unit	Date From
Units	1	-
Max Units Retired	1	-	1/01/2010
Min Units Retired	0	-
Min Units Retired	1	-	1/01/2020
Retirement Cost	9500	$000
Heat Rate	10	GJ/MWh
Heat Rate	10.1	GJ/MWh	1/01/2011
Heat Rate	10.201	GJ/MWh	1/01/2012
...	...	...	...
Heat Rate	10.93685	GJ/MWh	1/01/2020
Fixed O&M Charge	13	$/kW/year
Fixed O&M Charge	13.325	$/kW/year	1/01/2011
Fixed O&M Charge	13.65813	$/kW/year	1/01/2012
...	...	...	...
Fixed O&M Charge	16.23522	$/kW/year	1/01/2020

In the above example the unit is forced to retire no later than 1/01/2020 but no earlier than 1/01/2010 but LT Plan can chose to retire it any time inside that window.

6. Transmission

The planned expansion/retirement of AC and DC lines from the system is enabled using the Line Units property, with the restriction that AC expansion/retirement is only supported by the Variable Shift Factor OPF method. The simulator automatically recomputes the shift factors required to cope with the changes in topography. LT Plan supports all types of transmission constraints including security-constrained Optimal Power Flow.

6.1. Line Additions, Upgrades, and Retirements

Optimized transmission line expansion using the Max Units Built property and retirement using the Max Units Retired property in LT Plan works in much the same way as generation expansion. There are no restrictions on the number of lines that may run between any two nodes, thus the expansion of an existing line can be modelled as the addition of one or more new lines between the same nodes.

The complete replacement of one line with another can be achieved using the Constraint class—see Timing and Staging Constraints.

6.2. Interface Expansion

Expansion of existing transmission interfaces (via the Interface class) is a feature available to all OPF methods. Expansion is done in continuous units of megawatts, thus the only data required are:

• Expansion Cost in $MM/MW
• Max Expansion in MW
• WACC which is the weighted-average cost of capital for interface expansion

Expansion using Interface objects is useful for both zonal/regional transmission and full-nodal AC expansion. In the latter case:

• Define Interface objects for each AC path that can be expanded
• Remove the 'normal' flow limits on the Line objects in the path
• Define the expansion cost parameters and normal limits for the Interface objects
• Set the Transmission Detail option in LT Plan to "nodal"
• Use Transmission settings to control application of other constraints such as SC-OPF

7. Physical Contracts

LT Plan can optimize the purchase of generation and/or load contracts represented by Physical Contract objects. These differ from generator new builds in that the decision to purchase a contract is made at regular intervals, rather than a one-off decision for a generator. You determine the contract interval by setting one of the following properties on the Physical Contract:

• Capacity Charge - for a contract whose quantity can be changed every period
• Capacity Charge DAY - for a contract whose quantity can be changed daily
• Capacity Charge WEEK - for a contract whose quantity can be changed weekly
• Charge MONTH - for a contract whose quantity can be changed monthly
• Capacity Charge YEAR - for a contract whose quantity can be changed annually

The number of 'times' a contract can be 'expanded' is set by either:

• Max Generation Units - for generation contracts
• Max Load Units - for load contracts

These properties are equivalent to Max Units Built for generators and lines. Thus a valid set up of a candidate load contract whose quantity can be renegotiated every month would be:

Property	Value	Unit
Max load	2	MW
Capacity Charge Month	15	$/kW/month
Max Load Units	100	-

Here LT Plan will decide the optimal amount of the contract to take up each month. The total quantity that can be purchased in this case is 200 (2 MW × 100) in increments of 2 MW.

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