Hybrid offshore hub

Please note: General documentation concerning hybrid offshore wind can be found in the Hybrid offshore wind documentation. This documention is focused on the configuration and hourly calculations of hyrbid offshore wind in the ETM.

Hybrid offshore hubs represent an offshore renewable electricity production facility combined with an electrolyser for hydrogen production. It is connected to the mainland power grid via a subnautical power cable. The electrolyser is connected to the mainland hydrogen network via a subnautical pipeline.

Configuration of hybrid offshore hub

Nodes

A hybrid offshore hub in the ETM requires 6 nodes:

1. Producer: This represents renewable electricity production (e.g. wind farm or solar farm) which produce electricity according to a production profile. At the moment, the ETM only incorporates a hybrid offshore hub based with renewable electricity production from offshore wind farms.
2. Electrolyser: Depending on the WTP of the electrolyser and the capacity of the electrolyser,power cable and producer, hydrogen production will take place.
3. Curtailment: Energy is diverted here when the electrolyser cannot use all generated energy due to its capacity constraints, and when onshore electricity demand is too low.
4. Cable offshore-onshore: The producer transports electricity to the cable node so it can be transported to the onshore power grid.
5. Cable onshore-offshore: This cable transports electricity from the onshore power grid to the offshore electrolyser. This cable will be deployed when the WTP of the electrolyser is higher than the national electricity price and when there is still undeployed electrolyser capacity available. In reality, this cable is the same cable as the cable offshore-onshore (and therefore has the same specs), but is added as a seperate node for modelling purposes.
6. Hydrogen offshore pipeline: Hydrogen that is produced by the electrolyser will be transported to the onshore hydrogen network by this node.

Edges

The edge-types of the edges between the nodes can be found in the picture below. As can be seen in the legend, a 'dashed' edge has the 'reversed' attribute set to true.

For more information about edge-types please visit the Graph components documentation. Some of the configured edge-types are further explained here:

• Producer > Electrolyser: constant. Through the constant edge a specific amount of energy is set through this edge. The model uses this characteristic to sum all electricity that has flown from the producer to the electrolyser in each hour of the year.
• Producer > Curtailment: reversed share. With the reversed share the model sets the annual demand of the curtailment node equal to the sum of curtailed energy for each hour of the year, at the same time when the amount through the edge from Producer to Electrolyser is set.
• Producer > Cable from offshore network: inversed_flexible. The remaining produced energy from the Producer is subsequently allocated to the cable with the inversed_flexible edge.
• Cable > Electrolyser: flexible. When the electrolyser node does not yet meet its yearly demand it is given by the merit module, cable node will deliver this deficit through the flexible edge.

Node attributes

Producer node

The producer requires the following merit_order attributes:

• group: The name of the profile to be used to shape the hourly load from the producer.
• level: The level at which the technology appears in the electricity network.
• type: Always set to producer.
• subtype: Always set to hybrid_offshore.
• relations.curtailment: The key of the curtailment node.
• relations.output: The key of the output cable node.
• relations.input: The key of the input cable node.
• relations.converter: The key of the converter node (in this case the electrolyser).

All attributes are required.

For example:

- merit_order.group = dynamic: wind_offshore
- merit_order.level = hv
- merit_order.type = producer
- merit_order.subtype = hybrid_offshore
- merit_order.relations.curtailment = energy_power_hybrid_curtailed_electricity
- merit_order.relations.output = energy_power_hybrid_from_offshore_network_electricity
- merit_order.relations.input = energy_power_hybrid_to_offshore_network_electricity
- merit_order.relations.converter = energy_hydrogen_hybrid_electrolysis_wind_electricity

Electrolyser node (converter)

The electrolyser node requires the following merit_order attributes:

• level: The level at which the technology appears in the electricity network.
• type: Always set to flex.
• subtype: Always set to satisfied_demand.
• relations.input: The key of the consumer node.
• max_consumption_price: The maximal cost per MWh electricity that the electrolyser is willing to pay.

For example:

- merit_order.level = hv
- merit_order.subtype = satisfied_demand
- merit_order.type = flex
- merit_order.relations.input = energy_power_hybrid_wind_turbine_offshore
- max_consumption_price = 30.0

In addition for the electrolyser, hydrogen merit attributes are required:

• group: The name of the profile to be used to shape the hourly load from the producer.
• type: Always set to producer.
• subtype: Always set to must_run.

For example:

- hydrogen.group = self: electricity_input_curve
- hydrogen.subtype = must_run
- hydrogen.type = producer

Cable from offshore and cable to offshore nodes

For both cable nodes, the node must have an electricity_output_capacity attribute which specifies how much energy can flow between this node and the HV network each hour (in MW). It also needs a specified number_of_units, the calculations in the merit module concerning hybrid offshore wind hubs rely on this attribute.

- electricity_output_capacity = 500
- number_of_units = 1

Outputs

The following data can be expected after the merit order has run.

Producer node

• demand: the total amount of electricity produced annually, including curtailed electricity
• electricity_output_curve: the hourly electricity output from the producer, including curtailed electricity

Electrolyser node (converter)

• demand: the total annual amount of energy that flows through the node
• electricity_input_curve: the hourly electricity input to the converter node
• hydrogen_output_curve: the hourly hydrogen output from the converter node

Output node (cable from offshore network)

• demand: the total annual amount of electricity that flows through the node
• electricity_input_curve: the hourly electricity input into the cable (originating from the producer node)

Input node (cable to offshore network)

• demand: the total annual amount of electricity that flows through the node
• electricity_output_curve: the hourly electricity output of the cable (which flows to the converter node)

Curtailment node

• demand: the total annual amount of curtailed energy from the producer
• electricity_input_curve: the hourly curtailed electricity input (originating from the producer node)

Updating values with GQL

The ETM currently provides user inputs that update the number_of_units of the producer node and the electrolyser (converter) node. For the power cable nodes, the electricity_output_capacity can be set.

Change the capacity of the producer

In the ETM, the total installed capacity of the producer node can be set. This input will update the number_of_units of the producer based on the typical input capacity of one producer unit:

UPDATE(
  V(producer_key),
  number_of_units,
  USER_INPUT() / V(electrolyser_key, typical_input_capacity)
)

Change the capacity of the electrolyser

In the ETM, the relative installed capacity of the electrolyser can be set compared to the installed capacity of the producer node. With this setting the total installed capacity of the electrolyser can be calculated and subsequently the total number_of_units of the electrolyser is updated:

UPDATE(
  V(electrolyser_key),
  number_of_units,
  DIVIDE(
    PRODUCT(
      USER_INPUT(),
      V(producer_key, "number_of_units * typical_input_capacity")
    ),
    V(electrolyser_key, typical_input_capacity)
  )
)

Change the capacity of the power cable

Similar to the electrolyser node, the electricity input capacity of the cable nodes can be set through a relative capacity compared to the installed capacity of the producer node. By correcting for the electricity_output_conversion, the electricity_output_capacity is calculated and updated. Note that the total installed output capacity of the cable nodes is set directly via the electricity_output_capacity attribute (so the number_of_units is not applied or updated here). Both nodes need to be updated with the same value since in reality this is the same cable with bi-directional functionality.

EACH(
  UPDATE(
    V(from_offshore_key),
    electricity_output_capacity,
    PRODUCT(
      USER_INPUT() * V(producer_key, "number_of_units * typical_input_capacity"),
      V(from_offshore_key, electricity_output_conversion)
    )
  ),
  UPDATE(
    V(to_offshore_key),
    electricity_output_capacity,
    PRODUCT(
      USER_INPUT() * V(producer_key, "number_of_units * typical_input_capacity"),
      V(to_offshore_key, electricity_output_conversion)
    )
  )
)