Open Cycle Gas Turbine

Open Cycle Gas Turbine#

The OpenCycleGasTurbine class models an open-cycle gas turbine (OCGT), also known as a peaker plant or simple-cycle gas turbine. Since this class is focused on peaker plant behavior, this class was developed based on aeroderivative engines. It is a subclass of ThermalComponentBase and inherits all state machine behavior, ramp constraints, and operational logic from the base class.

Set component_type: OpenCycleGasTurbine in the component’s YAML section. The section key is a user-chosen component_name (e.g. open_cycle_gas_turbine); see Component Names, Types, and Categories for details.

For details on the state machine, startup/shutdown behavior, and base parameters, see Thermal Component Base.

OCGT-Specific Parameters#

The OCGT class provides default values for natural gas properties from [6]:

Parameter

Units

Default

Description

hhv

J/m³

39050000

Higher heating value of natural gas (39.05 MJ/m³) [6]

fuel_density

kg/m³

0.768

Fuel density for mass calculations [6]

The efficiency_table parameter is optional. If not provided, default values based on approximate readings from the SC1A curve in Exhibit ES-4 of [5] are used. All efficiency values are HHV (Higher Heating Value) net plant efficiencies. See Thermal Component Base for details on the efficiency table format.

Default Parameter Values#

The OpenCycleGasTurbine class provides default values for base class parameters based on References [1-5]. Only rated_capacity and initial_conditions are required in the YAML configuration.

Parameter

Default Value

Source

min_stable_load_fraction

0.40 (40%)

[4]

ramp_rate_fraction

0.10 (10%/min)

[1]

run_up_rate_fraction

Same as ramp_rate_fraction

—

hot_startup_time

420 s (7 minutes)

[1], [5]

warm_startup_time

480 s (8 minutes)

[1], [5]

cold_startup_time

480 s (8 minutes)

[1], [5]

min_up_time

1800 s (30 minutes)

[4]

min_down_time

3600 s (1 hour)

[4]

hhv

39050000 J/m³ (39.05 MJ/m³)

[6]

fuel_density

0.768 kg/m³

[6]

efficiency_table

SC1A HHV net efficiency (see below)

Exhibit ES-4 of [5]

Default Efficiency Table#

The default HHV net plant efficiency table is based on approximate readings from the SC1A (simple cycle) curve in Exhibit ES-4 of [5]:

Power Fraction

HHV Net Efficiency

1.00

0.39 (39%)

0.75

0.37 (37%)

0.50

0.325 (32.5%)

0.25

0.245 (24.5%)

OCGT Outputs#

The OCGT model provides the following outputs (inherited from base class):

Output

Units

Description

power

kW

Actual power output

state

integer

Operating state number (0-5), corresponding to the STATES enum

efficiency

fraction (0-1)

Current HHV net plant efficiency

fuel_volume_rate

m³/s

Fuel volume flow rate

fuel_mass_rate

kg/s

Fuel mass flow rate (computed using fuel_density [6])

Efficiency and Fuel Rate#

HHV net plant efficiency varies with load based on the efficiency_table. The fuel volume rate is calculated as:

\[ \text{fuel\_volume\_rate} = \frac{\text{power}}{\text{efficiency} \times \text{hhv}} \]

Where:

  • power is in W (converted from kW internally)

  • efficiency is the HHV net efficiency interpolated from the efficiency table

  • hhv is the higher heating value in J/m³ (default 39.05 MJ/m³ for natural gas [6])

  • Result is fuel volume rate in m³/s

The fuel mass rate is then computed from the volume rate using the fuel density [6]:

\[ \text{fuel\_mass\_rate} = \text{fuel\_volume\_rate} \times \text{fuel\_density} \]

Where:

  • fuel_volume_rate is in m³/s

  • fuel_density is in kg/m³ (default 0.768 kg/m³ for natural gas [6])

  • Result is fuel mass rate in kg/s

YAML Configuration#

Minimal Configuration#

Required parameters only (uses defaults for hhv, efficiency_table, and other parameters):

open_cycle_gas_turbine:
  component_type: OpenCycleGasTurbine
  rated_capacity: 100000  # kW (100 MW)
  initial_conditions:
    power: 0  # 0 kW means OFF; power > 0 means ON

Full Configuration#

All parameters explicitly specified:

open_cycle_gas_turbine:
  component_type: OpenCycleGasTurbine
  rated_capacity: 100000  # kW (100 MW)
  min_stable_load_fraction: 0.4  # 40% minimum operating point
  ramp_rate_fraction: 0.1  # 10%/min ramp rate
  run_up_rate_fraction: 0.05  # 5%/min run up rate
  hot_startup_time: 420.0  # 7 minutes
  warm_startup_time: 480.0  # 8 minutes
  cold_startup_time: 480.0  # 8 minutes
  min_up_time: 1800  # 30 minutes
  min_down_time: 3600  # 1 hour
  hhv: 39050000  # J/m³ for natural gas (39.05 MJ/m³) [6]
  fuel_density: 0.768  # kg/m³ for natural gas [6]
  efficiency_table:
    power_fraction:
      - 1.0
      - 0.75
      - 0.50
      - 0.25
    efficiency:  # HHV net plant efficiency from SC1A in Exhibit ES-4 of [5]
      - 0.39
      - 0.37
      - 0.325
      - 0.245
  log_channels:
    - power
    - fuel_volume_rate
    - fuel_mass_rate
    - state
    - efficiency
    - power_setpoint
  initial_conditions:
    power: 0  # 0 kW means OFF; power > 0 means ON

Logging Configuration#

The log_channels parameter controls which outputs are written to the HDF5 output file.

Available Channels:

  • power: Actual power output in kW (always logged)

  • state: Operating state number (0-5), corresponding to the STATES enum

  • fuel_volume_rate: Fuel volume flow rate in m³/s

  • fuel_mass_rate: Fuel mass flow rate in kg/s (computed using fuel_density [6])

  • efficiency: Current HHV net plant efficiency (0-1)

  • power_setpoint: Requested power setpoint in kW

References#

  1. Agora Energiewende (2017): “Flexibility in thermal power plants - With a focus on existing coal-fired power plants.”

  2. “Impact of Detailed Parameter Modeling of Open-Cycle Gas Turbines on Production Cost Simulation”, NREL/CP-6A40-87554, National Renewable Energy Laboratory, 2024.

  3. Deane, J.P., G. Drayton, and B.P. Ó Gallachóir. “The Impact of Sub-Hourly Modelling in Power Systems with Significant Levels of Renewable Generation.” Applied Energy 113 (January 2014): 152–58. https://doi.org/10.1016/j.apenergy.2013.07.027.

  4. IRENA (2019), Innovation landscape brief: Flexibility in conventional power plants, International Renewable Energy Agency, Abu Dhabi.

  5. M. Oakes, M. Turner, “Cost and Performance Baseline for Fossil Energy Plants, Volume 5: Natural Gas Electricity Generating Units for Flexible Operation,” National Energy Technology Laboratory, Pittsburgh, May 5, 2023.

  6. I. Staffell, “The Energy and Fuel Data Sheet,” University of Birmingham, March 2011. https://claverton-energy.com/cms4/wp-content/uploads/2012/08/the_energy_and_fuel_data_sheet.pdf

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