Process¶

The Process component is used for controllable energy conversion processes between two or more buses with arbitrary energy carriers (bus0, bus1, bus2, etc.). It serves as an alternative to Link with a different parameterisation for multi-carrier processes like electrolysis, heat pumps, or combined heat and power (CHP) plants.

The Process component has one internal dispatch variable p and one or more power outputs p0, p1, p2, etc. associated with the buses bus0, bus1, bus2, etc. The power at each bus is determined by pX = rateX * p, where rateX is the corresponding rate parameter. Positive rates produce energy at the bus, negative rates consume energy from it.
p_nom constrains the internal dispatch p and also determines how capital_cost and marginal_cost are accounted.
For consistency, the internal dispatch carries the same unit as the output at an optional reference bus, chosen by setting its corresponding rateX to 1. or -1..
The columns bus2, rate2, bus3, rate3, etc. in n.processes are automatically added to the component attributes.
For delayed energy transport, use the attribute delay0, delay1, ... which postpones the output at bus0, bus1, ... in terms of elapsed time, taking snapshot weightings into account. See this example.

Comparison with Link

The key difference to Link is that efficiency, efficiency2, ... are replaced by rate0, rate1, rate2, ... with a single sign convention: the power output at busX is always rateX * p. This avoids the implicit sign convention of Links where bus0 is always the input and efficiencies for additional inputs must be negative.

Process for an electrolyser

An electrolyser consuming electricity at bus0 and producing hydrogen at bus1 with 70% efficiency:

n.add(
    "Process",
    "electrolyser",
    bus0="electricity",
    bus1="hydrogen",
    rate0=-1,          # consumes 1 unit of electricity (reference bus)
    rate1=0.7,         # produces 0.7 units of hydrogen
    p_nom_extendable=True,
    capital_cost=100,  # cost per MW of electricity input
)

Process for a CHP plant

A combined heat and power plant taking gas as input and producing electricity and heat. This example illustrates sector coupling with processes including a CHP plant.

n.add(
    "Process",
    "CHP",
    bus0="gas",
    bus1="electricity",
    bus2="heat",
    rate0=-1,          # consumes 1 unit of gas
    rate1=0.3,         # produces 0.3 units of electricity
    rate2=0.5,         # produces 0.5 units of heat
    p_nom_extendable=True,
    capital_cost=50,
)

Process for the Haber-Bosch process

The Haber-Bosch process consumes electricity and hydrogen and produces ammonia. Using the ammonia output as reference bus (rate1=1):

n.add(
    "Process",
    "Haber-Bosch",
    bus0="electricity",
    bus1="ammonia",
    bus2="hydrogen",
    rate0=-costs.at["Haber-Bosch", "electricity-input"],
    rate1=1,           # reference bus
    rate2=-costs.at["Haber-Bosch", "hydrogen-input"], # in tH2/tNH3
    p_nom_extendable=True,
    capital_cost=costs.at["Haber-Bosch", "capital_cost"], # in Eur/(tNH3/h)
    marginal_cost=costs.at["Haber-Bosch", "VOM"], # in Eur/tNH3
)

attribute	type	unit	default	description	status
name	string	nan	nan	Unique name	Input (required)
bus0	string	nan	nan	Name of first bus to which process is attached.	Input (required)
bus1	string	nan	nan	Name of second bus to which process is attached. Further buses (`bus2`, `bus3`, etc.) are automatically expanded as needed.	Input (required)
type	string	nan	nan	Placeholder for process type. Not implemented.	Input (optional)
carrier	string	nan	nan	Carrier of the process describing its technology (e.g. gas boiler, electrolyser, HVDC process).	Input (optional)
rate0	static or series	per unit	-1	Rate of energy transfer at `bus0` relative to internal power `p`. Can be time-dependent (e.g. to represent temperature-dependent heat pump COP). `Rate`s for further buses (e.g. `bus2`, `bus3`, etc.) are automatically expanded as needed (e.g. `rate2`, `rate3`, etc.).	Input (optional)
rate1	static or series	per unit	1	Rate of energy transfer at `bus1` relative to internal power `p`. Can be time-dependent (e.g. to represent temperature-dependent heat pump COP). `Rate`s for further buses (e.g. `bus2`, `bus3`, etc.) are automatically expanded as needed (e.g. `rate2`, `rate3`, etc.).	Input (optional)
active	boolean	nan	True	Whether to consider the component in basic functionality or not	Input (optional)
build_year	int	year	0	Build year	Input (optional)
lifetime	float	years	inf	Lifetime	Input (optional)
p_nom	float	MW	0	Limit of power which can pass through process (in units of `bus0`). Ignored if `p_nom_extendable=True`.	Input (optional)
p_nom_mod	float	MW	0	Unit size of process module (e.g. fixed blocks of 100 MW).	Input (optional)
p_nom_extendable	boolean	nan	False	Switch to allow capacity `p_nom` to be extended.	Input (optional)
p_nom_min	float	MW	0	If `p_nom_extendable=True`, set its minimum value.	Input (optional)
p_nom_max	float	MW	inf	If `p_nom_extendable=True`, set its maximum value.	Input (optional)
p_nom_set	float	MW	nan	If `p_nom` is extendable in optimization, set its value.	Input (optional)
p_set	static or series	MW	nan	The dispatch set point for `p0` of the process (for optimisation and power flow).	Input (optional)
p_init	static	MW	nan	Active power used as a starting point for limiting the ramp in the very first snapshot (for optimisation)	Input (optional)
p_min_pu	static or series	per unit of p_nom	0.	Minimal dispatch per unit of `p_nom` for the process. Can also be negative.	Input (optional)
p_max_pu	static or series	per unit of p_nom	1.	Maximal dispatch per unit of `p_nom` for the process. Can also be negative.	Input (optional)
capital_cost	float	currency/MW	0	Fixed period costs of extending `p_nom` by 1 MW (unit of `bus0`, e.g. annuitized investment costs). Used directly unless `overnight_cost` is specified. Any `length` factor must already be included.	Input (optional)
overnight_cost	float	currency/MW	nan	Overnight (upfront) investment cost per MW (unit of `bus0`). If specified, PyPSA calculates annuity using `discount_rate` and `lifetime`. Takes precedence over `capital_cost`.	Input (optional)
discount_rate	float	per unit	nan	Discount rate for annuity calculation when using `overnight_cost`. Supports 0% rate (simple depreciation).	Input (optional)
fom_cost	float	currency/MW	0	Fixed period operation and maintenance costs per MW (unit of `bus0`), added to annuitized investment cost.	Input (optional)
marginal_cost	static or series	currency/MWh	0.	Marginal cost of 1 MWh consumption from `bus0` (e.g. including variable operation and maintenance costs of an electrolyser but excluding electricity costs).	Input (optional)
marginal_cost_quadratic	static or series	currency/MWh	0.	Quadratic marginal cost for 1 MWh of consumption from `bus0`.	Input (optional)
stand_by_cost	static or series	currency/h	0.	Stand-by cost for operating the process. This cost is incurred whenever the status is 1 (including when dispatch decision is zero).	Input (optional)
length	float	km	0	Length of the process. Useful for calculating `capital_cost` for HVDC connections.	Input (optional)
terrain_factor	float	per unit	1	Terrain factor for increasing `capital_cost` calculated from `length`.	Input (optional)
committable	boolean	nan	False	Apply unit commitment constraints. This is only possible with `p_nom_extendable=False`.	Input (optional)
start_up_cost	float	currency	0	Cost to start up the process. Only used if `committable=True`.	Input (optional)
shut_down_cost	float	currency	0	Cost to shut down the process. Only used if `committable=True`.	Input (optional)
min_up_time	int	snapshots	0	Minimum number of snapshots for status to be 1. Only used if `committable=True`. Does not consider snapshot weightings.	Input (optional)
min_down_time	int	snapshots	0	Minimum number of snapshots for status to be 0. Only used if `committable=True`. Does not consider snapshot weightings.	Input (optional)
up_time_before	int	snapshots	1	Number of snapshots that the process was online before network.snapshots start. Only read if `committable=True` and `min_up_time>0`. Does not consider snapshot weightings.	Input (optional)
down_time_before	int	snapshots	0	Number of snapshots that the process was offline before network.snapshots start. Only read if `committable=True` and `min_down_time>0`. Does not consider snapshot weightings.	Input (optional)
ramp_limit_up	static or series	per unit	nan	Maximum increase from one snapshot to the next, per unit of `p_nom`. Ignored if NaN. Does not consider snapshot weightings.	Input (optional)
ramp_limit_down	static or series	per unit	nan	Maximum decrease from one snapshot to the next, per unit of `p_nom`. Ignored if NaN. Does not consider snapshot weightings.	Input (optional)
ramp_limit_start_up	float	per unit	nan	Maximum increase at start up, per unit of `p_nom`. Only used if `committable=True`. Ignored if NaN.	Input (optional)
ramp_limit_shut_down	float	per unit	nan	Maximum decrease at shut down, per unit of `p_nom`. Only used if `committable=True`. Ignored if NaN.	Input (optional)
delay0	int	snapshot weighting units	0	Delay of energy delivery to `bus0` in units of `n.snapshot_weightings.generators`. Energy withdrawn at snapshot `t` arrives at the first snapshot whose cumulative generator weighting start is at least `delay0` units later. Auto-expanded as `delay2`, `delay3`, etc. for additional ports.	Input (optional)
cyclic_delay0	boolean	nan	True	Whether delayed energy wraps cyclically from end to start of the optimization period. If False, energy is lost at the tail and first snapshots receive nothing from delayed processes. Auto-expanded as `cyclic_delay2`, `cyclic_delay3`, etc. for additional ports.	Input (optional)
delay1	int	snapshot weighting units	0	Delay of energy delivery to `bus1` in units of `n.snapshot_weightings.generators`. Energy withdrawn at snapshot `t` arrives at the first snapshot whose cumulative generator weighting start is at least `delay1` units later. Auto-expanded as `delay2`, `delay3`, etc. for additional ports.	Input (optional)
cyclic_delay1	boolean	nan	True	Whether delayed energy wraps cyclically from end to start of the optimization period. If False, energy is lost at the tail and first snapshots receive nothing from delayed processes. Auto-expanded as `cyclic_delay2`, `cyclic_delay3`, etc. for additional ports.	Input (optional)
p	series	MW	0.	Power in component.	Output
p0	series	MW	0.	Power at `bus0` (positive if process is withdrawing from `bus0`).	Output
p1	series	MW	0.	Power at `bus1` (positive if process is withdrawing from `bus1`).	Output
p_nom_opt	float	MW	0	Optimised nominal capacity.	Output
status	series	nan	1.	Status in the snapshot (1 is on, 0 is off). Only returned if `committable=True`.	Output
start_up	series	nan	1.	Whether the unit was started in the snapshot (1 is yes, 0 is no). Only returned if `committable=True`.	Output
shut_down	series	nan	1.	Whether the unit was shut down in the snapshot (1 is yes, 0 is no). Only returned if `committable=True`.	Output
mu_lower	series	currency/MW	nan	Shadow price of lower `p_nom` limit \(-F \leq f\). Always non-negative.	Output
mu_upper	series	currency/MW	nan	Shadow price of upper `p_nom` limit \(f \leq F\). Always non-negative.	Output
mu_p_set	series	currency/MWh	nan	Shadow price of fixed dispatch `p_set`	Output
mu_ramp_limit_up	series	currency/MWh	nan	Shadow price of upper ramp up limit	Output
mu_ramp_limit_down	series	currency/MWh	nan	Shadow price of lower ramp down limit	Output