# Activity costs¶

## Costs for operation a boiler¶

### General description¶

This example illustrates the effect of activity_costs.

There are the following components:

• demand_heat: heat demand (constant, for the sake of simplicity)

• boiler: gas firing, consumes (paid) gas

Notice that activity_costs is an attribute to NonConvex. This is because it relies on the activity status of a component which is only available for nonconvex flows.

### Code¶

Download source code: `activity_costs.py`

Click to display code
```import matplotlib.pyplot as plt
import numpy as np
import pandas as pd

from oemof import solph

def main():
##########################################################################
# Calculate parameters and initialize the energy system and
##########################################################################
periods = 24
time = pd.date_range("1/1/2018", periods=periods, freq="H")

demand_heat = np.full(periods, 5)
demand_heat[:4] = 0
demand_heat[4:18] = 4

activity_costs = np.full(periods, 5)
activity_costs[18:] = 0

es = solph.EnergySystem(timeindex=time)

b_heat = solph.Bus(label="b_heat")

sink_heat = solph.components.Sink(
label="demand",
inputs={b_heat: solph.Flow(fix=demand_heat, nominal_value=1)},
)

fireplace = solph.components.Source(
label="fireplace",
outputs={
b_heat: solph.Flow(
nominal_value=3,
variable_costs=0,
nonconvex=solph.NonConvex(activity_costs=activity_costs),
)
},
)

boiler = solph.components.Source(
label="boiler",
outputs={b_heat: solph.Flow(nominal_value=10, variable_costs=1)},
)

##########################################################################
# Optimise the energy system
##########################################################################

# create an optimization problem and solve it
om = solph.Model(es)

# solve model
om.solve(solver="cbc", solve_kwargs={"tee": True})

##########################################################################
# Check and plot the results
##########################################################################

results = solph.processing.results(om)

# plot data
data = solph.views.node(results, "b_heat")["sequences"]
ax = data.plot(kind="line", drawstyle="steps-post", grid=True, rot=0)
ax.set_xlabel("Time")
ax.set_ylabel("Heat (arb. units)")
plt.show()

if __name__ == "__main__":
main()
```

### Installation requirements¶

This example requires oemof.solph (v0.5.x), install by:

```pip install oemof.solph[examples]
```