Power Cycle#
The power cycle parameters describe the characteristics of the power cycle that absorbs heat from the hot heat transfer fluid (HTF) via the hot thermal energy storage (TES), generates electricity, and heats the cold HTF to be delivered to the cold TES reservoir. The power cycle currently applies a simple approximation to calculate off-design performance as reservoir temperatures and load change. Future work may add more detailed off-design models or allow users to input off-design data.
For a detailed description of the PTES model see:
Neises, T.; Hamilton, B.; Martinek, J.; McTigue, J. (2022) Stand-alone and Hybrid Electric Thermal Energy Storage in the System Advisor Model. 51 pp. NREL/TP-5700-82989. (PDF 2.3 MB)
System Design Parameters#
The system design parameters are from the System Design page, where you can define the design-point parameters of the entire power tower system.
- Cycle thermal input power, MWt
Heat input to cycle at design conditions.
- Hot storage cold temperature, °C
Temperature of the cold tank of the hot reservoir at design. This is also the temperature of the hot HTF entering the heat pump hot heat exchanger at design and the temperature exiting the cycle hot heat exchanger at design.
- Hot storage hot temperature, °C
Temperature of the hot tank of the hot reservoir at design. This is also the temperature of the hot HTF exiting the heat pump hot heat exchanger at design and the temperature entering the cycle hot heat exchanger at design.
- Cycle thermodynamic power, MWe
Net power generated by the working fluid. Additional power consumption like electric motor inefficiency, cooling parasitics, and HTF pumping power are captured in separate inputs on the Power Cycle page and reflected in Net electricity output at design discharge and Net round-trip efficiency.
- Cold storage cold temperature, °C
Temperature of the cold tank of the cold reservoir at design. This is also the temperature of the cold HTF exiting the heat pump cold heat exchanger at design and the temperature entering the cycle cold heat exchanger at design.
- Cold storage hot temperature, °C
Temperature of the hot tank of the cold reservoir at design. This is also the temperature of the cold HTF entering the heat pump cold heat exchanger at design and the temperature exiting the cycle cold heat exchanger at design.
Component Parameters#
Startup#
- Fraction of design power allowed during startup
Fraction of the design cycle thermal power input allowed to bring the cycle up to operating temperature after a period of non-operation. This input is meant to capture ramping constraints.
- Duration of startup at max startup power, hr
The amount of time at the maximum allowed thermal power at startup that is required to reach operating temperature during startup. This input is meant to capture the energy required to reach operating temperature.
Operation#
- Maximum cycle heat input fraction
The maximum cycle thermal power input allowed as a fraction of the design point.
- Minimum cycle heat input fraction
The minimum cycle thermal power input allowed as a fraction of the design point. This input governs minimum part-load.
- Minimum operating fraction
The fraction of the design thermal power required to maintain the cycle at standby. Energy consumed by the cycle during standby does not generate electricity, so standby is rarely used in cases where 1) the penalty for generating electricity at the current timestep offsets the standby energy consumption and 2) standby energy requirements are less than startup energy requirements.
Cycle Parasitics#
- Parasitics (non-pumping) as fraction of thermodynamic power
Electrical consumption of cycle parasitics, not including HTF pumping power, defined as a fraction of the design cycle net thermodynamic power output. Examples of potentially relevant parasitics include electric motor and generator inefficiencies and heat rejection parasitics. At off-design this value is calculated by scaling by the ratio of off-design thermodynamic power to design thermodynamic power.
- Parasitics, MWe
Calculated electrical consumption of cycle parasitics at design conditions, not including HTF pumping power.
Hot HTF Pumping Power#
- Pumping power rate through hot heat exchanger, kWe/kg/s
Electrical power required to move 1 kg/s of hot HTF through the hot side heat exchanger.
- Hot HTF mass flow rate, kg/s
Hot HTF mass flow rate at design conditions.
- Hot HTF pumping power, MWe
Electrical power required to pump hot HTF at design conditions.
Cold HTF Pumping Power#
- Pumping power rate through cold heat exchanger, kWe/kg/s
Electrical power required to move 1 kg/s of cold HTF through the cold side heat exchanger.
- Cold HTF mass flow rate, kg/s
Cold HTF mass flow rate at design conditions.
- Cold HTF pumping power, MWe
Electrical power required to pump cold HTF at design conditions.
Net Metrics
- Net cycle power output, MWe
Net cycle power output calculated by subtracting electrical parasitics from the cycle thermodynamic power.
- Net efficiency
Cycle efficiency calculated using Net cycle power output.