Link - Inputs

Links represent controllable power connections between two buses. Unlike lines (passive AC flow), links allow explicit control over power transfer and can convert between carriers. Below are all input attributes that you can set for link components.

Basic

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
type	string	n/a	n/a	No	static	Placeholder for link type. Not yet implemented.
carrier	string	n/a	(empty)	No	static	Carrier type transported by the link: "DC" for electrical HVDC links, or "heat" or "gas" for thermal links. Used for categorization and energy balance constraints.
active	boolean	n/a	True	No	static	Whether this link is active and should be included in network calculations. Set to False to temporarily disable the link without deleting it.

Capacity

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
p_nom	float	MW	0	Yes	static	The maximum active power capacity of the link in MW. This sets the limit for power flow through the link.
p_nom_mod	float	MW	0	No	static	The unit size for capacity expansion. When extending the nominal power (p_nom), it can only be increased in multiples of this module size.
p_nom_extendable	boolean	n/a	False	No	static	Switch to allow the nominal power (p_nom) to be extended in optimization.
p_nom_min	float	MW	0	No	static	If the nominal power (p_nom) is extendable in optimization, set its minimum value.
p_nom_max	float	MW	inf	No	static	If the nominal power (p_nom) is extendable in optimization, set its maximum value (e.g. limited by technical potential or right-of-way constraints).
build_year	int	year	0	No	static	The year when the link can be built or commissioned. Essential for multi-year capacity expansion planning models, which determine optimal investment timing and link retirement schedules.
lifetime	float	years	inf	No	static	The operational lifetime of the link in years. Essential for multi-year capacity expansion planning models, which use this to determine when links retire (build year + lifetime). Set to "inf" for links that never retire.

Energy

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
efficiency	float	per unit	1	No	static or timeseries	The efficiency of power transfer from bus0 to bus1. A value of 1.0 means no losses, while lower values represent transmission losses. Can be time-varying to model temperature-dependent performance (e.g., heat pump Coefficient of Performance).

Power Limits

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
p_set	float	MW	0	No	static or timeseries	Fixed active power flow that the link must transfer from bus0 to bus1. Used when the link power flow is predetermined rather than optimized.
p_min_pu	float	per unit	0	No	static or timeseries	The minimum power flow per unit of the nominal power (p_nom). Negative values allow reverse flow (from bus1 to bus0). Can be static or time-varying.
p_max_pu	float	per unit	1	No	static or timeseries	The maximum power flow per unit of the nominal power (p_nom). Negative values allow reverse flow (from bus1 to bus0). Can be static or time-varying.

Unit Commitment

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
committable	boolean	n/a	False	No	static	Enable unit commitment, allowing the link to be turned on or off with associated start-up and shutdown costs. Only available when the nominal power (p_nom) is not extendable.
start_up_cost	float	currency	0	No	static	Cost to start up the link. Only read if committable is True.
shut_down_cost	float	currency	0	No	static	Cost to shut down the link. Only read if committable is True.
stand_by_cost	float	currency/h	0	No	static or timeseries	Stand-by cost for operating the link at null power flow.
min_up_time	int	snapshots	0	No	static	Minimum number of snapshots for status to be 1. Only read if committable is True.
min_down_time	int	snapshots	0	No	static	Minimum number of snapshots for status to be 0. Only read if committable is True.
up_time_before	int	snapshots	1	No	static	Number of snapshots that the link was online before network.snapshots start. Only read if committable is True and min_up_time is non-zero.
down_time_before	int	snapshots	0	No	static	Number of snapshots that the link was offline before network.snapshots start. Only read if committable is True and min_down_time is non-zero.

Ramping

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
ramp_limit_up	float	per unit	1	No	static or timeseries	Maximum power flow increase from one snapshot to the next, per unit of the nominal power (p_nom). Ignored if 1.
ramp_limit_down	float	per unit	1	No	static or timeseries	Maximum power flow decrease from one snapshot to the next, per unit of the nominal power (p_nom). Ignored if 1.
ramp_limit_start_up	float	per unit	1	No	static	Maximum power flow increase at start up, per unit of the nominal power (p_nom). Only read if committable is True.

Costs

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
capital_cost	float	currency/MW	0	No	static	The cost per MW of adding new link capacity. Includes investment costs (spread over the planning period) and fixed operations & maintenance costs. Only relevant when p_nom_extendable is True.
marginal_cost	float	currency/MWh	0	No	static or timeseries	The variable cost of transferring 1 MWh from bus0 to bus1 (before efficiency losses). Used by the optimizer to determine economic dispatch. Only meaningful if p_max_pu >= 0 (unidirectional flow).
marginal_cost_quadratic	float	currency/MWh²	0	No	static or timeseries	Quadratic term for non-linear cost curves. When set, the total cost includes a quadratic component that increases with the square of power flow, modeling increasing marginal costs at higher transfer levels.

Electrical

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
length	float	km	0	No	static	The physical length of the link in kilometers. Used for calculating capital costs, especially for transmission lines or pipelines.
terrain_factor	float	per unit	1	No	static	Multiplier for capital cost to account for difficult terrain. Values greater than 1 increase the capital cost to reflect higher construction costs in challenging terrain (e.g., mountains, water crossings).