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CCUS volumes (t)
===================================

*indexed by: asset, data type, energy, node, technology and test case*

### Description

This indicator is used to analyse the volumes of captured, used and stored CO2 of every asset of the energy system over 
the entire optimization horizon.


<blockquote class="custom-hint">
  <h4>Modelling hint</h4>

  When an asset captures CO2, the resulting production of CO2 captured goes under the *CO2 captured* tag.
  
  When an asset uses or stores some CO2 captured (for instance, in case of a methanation that needs some CO2 captured in
  addition to the hydrogen to produce methane), the resulting consumption of CO2 captured goes under the *CO2 captured
  usage* tag.
</blockquote>


### Calculation

All the equations below are valid for any realization and are therefore implicitly indexed by test case. 
Index *Technology* is directly deduced from the asset and the energy is always *CO2 captured*. 

#### CO2 captured

Let be $x_{a, n}$ the value returned by the data type *CO2 captured* for a given asset $a$ and node $n$.
We can then express $x_{a, n}$ as:

$$
x_{a, n} = \frac{1}{N_h} * \sum_{\text{timestep } t} p_{a, CO_{2} captured, n}(t)
$$

#### CO2 captured usage

Let be $x_{a, n}$ the value returned by the data type *CO2 captured usage* for a given asset $a$ and node $n$.
We can then express $x_{a, n}$ as:

$$
x_{a, n} = \frac{1}{N_h} * \sum_{\text{timestep } t} c_{a, CO_{2} captured, n}(t)
$$

*Global variables and parameters notations definitions can be consulted [here](../notations.md).*


### Indexing

- The asset index refers to the name of the asset 
- The node index of this KPI refers to the node in which the asset produces or uses CO2 captured
- The technology index refers to the technology type of the asset
- The test case index corresponds the test case of the realization variables and parameters are taken from