# Carriers
ESDL allows you to describe a list of carriers with parameters that are used inside your model
There are two types of carriers:
* Commodities
* Energy carriers
They serve different purposes but can be combined in the same model if required. Choices depend on the scope of the model.
The `Carriers` class is a collection of the abstract class `Carrier`. The `Carrier` class can have the following parameters:
* an `id` paramater that is used for referring to carriers.
* a `name` parameter to describe the name of the carrier.
* a `cost` paramater of type GenericProfile (allows both a fixed value as a profile that changes over time).
* a `dataSource` parameter to document the origin of the information you're using
The `Commodity` and `EnergyCarrier` classes are subclasses of `Carrier`.
## Commodity
The `Commodity` class is an abstract class, with the following subclasses:
* ElectricityCommodity: can be used for electricity. If required a distinction between different voltage levels can be made (LV, MV, HV, ...). A `voltage` parameter can be specified.
* GasCommodity: can be used for natural gas, biogas, carbon dioxide (CO2), hydrogen (H2), and so on. Distinction is done based on the `name` parameter.
* HeatCommodity: can be used for heat. If required a distinction between different temperature levels can be made (LT, MT, HT, ...). A `temperature` parameter can be specified.
* EnergyCommodity: can be used for describing energy balances (expressed in Joules, independent of the specific commodity).
## EnergyCarrier
The `EnergyCarrier` class has the following parameters:
* an `energyContent` parameter: allows the specification of the energy content of the energy carrier
* an `energyContentUnit` parameter: the unit of the `energyContent` paramater
* an `emission` parameter: allows the specification of emission values per energy content
* an `emissionUnit` parameter: the unit of the `emission` parameter
* an `energyCarrierType` parameter: an enumeration with options `UNDEFINED`, `RENEWABLE`, `FOSSIL`
* a `stateOfMatter` parameter: an enumeration with options `UNDEFINED`, `SOLID`, `LIQUID`, `GASEOUS`
This class is based on the [list of energy carriers](https://www.rvo.nl/sites/default/files/2018/03/Nederlandse%20energiedragerlijst%202018.pdf) as published by RVO:
An example ESDL file with this information looks like:
```markup
```
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