Using heat as bus0 of heat pumps messes with pypsa.statistic.optimal_capacity()

[vla-climact]

Version Checks (indicate both or one)

• I have confirmed this bug exists on the lastest release of PyPSA-Eur.

• I have confirmed this bug exists on the current master branch of PyPSA-Eur.

Issue Description

Hi everyone,

I have been experiencing trouble using pypsa.statistics.optimal_capacity with recent changes on the heat bus allocation for heat pumps. When calling optimal capacity for a specific carrier (e.g. low voltage), I get a positive capacity whereas I should get a negative one, as for any other (heat) link consuming "low voltage". Heat capacities are as well reversed (negative instead of positive). Energy balance are computed properly though

My guess, then, is that this comes from:

1. Using p_max_pu = 0 / p_min_pu = -cop <0, but with a positive efficiency
2. How optimal_capacity is implemented (using port_efficiency)

Maybe should we instead use a negative efficiency and p_min_pu = 0 / p_max_pu = cop, like for DAC ?

NB : This remark applies as well to heat vents, which use a efficiency = 1 but a p_max_pu = 0 / p_min_pu = -1.

Reproducible Example

>>> n = pypsa.Network(...) # optimized network

>>> n.statistics.optimal_capacity(bus_carrier="low voltage")

component  carrier                         
Generator  solar rooftop                        27992.80489
Link       BEV charger                        -296126.89025
           V2G                                 133257.10061
           electricity distribution grid        -7974.74833
           home battery charger                    -1.55432
           home battery discharger                  1.55432
           rural air heat pump                   3193.75522
           rural ground heat pump               43602.10090
           rural resistive heater              -15485.35487
           urban central air heat pump          15920.37297
           urban central resistive heater      -15618.98691
           urban decentral air heat pump       124346.99806
           urban decentral resistive heater    -65188.19632
dtype: float64

>>> n.statistics.optimal_capacity(bus_carrier="rural heat")
component  carrier                     
Generator  rural heat vent                     1.78074
           rural solar thermal                 0.55727
Link       rural air heat pump             -3193.75522
           rural ground heat pump         -43602.10090
           rural water tanks charger         -30.72206
           rural biomass boiler             2962.42039
           rural gas boiler                36835.83436
           rural oil boiler                30667.91043
           rural resistive heater          13936.81938
           rural water tanks discharger       30.72206
dtype: float64

Expected Behavior

>>> n.statistics.optimal_capacity(bus_carrier="low voltage")
component  carrier                         
Generator  solar rooftop                        27992.80489
Link       BEV charger                        -296126.89025
           V2G                                 133257.10061
           electricity distribution grid        -7974.74833
           home battery charger                    -1.55432
           home battery discharger                  1.55432
           rural air heat pump                   - 3193.75522
           rural ground heat pump               - 43602.10090
           rural resistive heater              -15485.35487
           urban central air heat pump          - 15920.37297
           urban central resistive heater      -15618.98691
           urban decentral air heat pump       - 124346.99806
           urban decentral resistive heater    -65188.19632
dtype: float64

>>>n.statistics.optimal_capacity(bus_carrier="rural heat")
component  carrier                     
Generator  rural heat vent                     -1.78074
           rural solar thermal                 0.55727
Link       rural air heat pump             3193.75522
           rural ground heat pump         43602.10090
           rural water tanks charger         30.72206
           rural biomass boiler             2962.42039
           rural gas boiler                36835.83436
           rural oil boiler                30667.91043
           rural resistive heater          13936.81938
           rural water tanks discharger       30.72206
dtype: float64

Installed Versions

Details

Replace this line.