System Design#
The System Design page shows inputs for design point parameters that determine the system’s nameplate capacity. Use the System Design inputs to define the nominal ratings of the system, and then specify details for each part of the system on the appropriate input pages.
Note
All of the system design inputs are nominal values, or values at the system’s design point. SAM calculates actual values during simulation and reports them in the results.
Design Point Parameters#
Solar Field#
- Boiling
The solar field delivers two-phase steam.
- Subcooled
The solar field delivers sub-cooled, pressurized water with single-phase liquid at the outlet.
- Field outlet steam quality
The field outlet steam quality is used to calculate the mass flow rate of steam. Steam quality is two-phase at outlet and completely condensed at inlet. This value represents the fraction of fluid exiting the solar field that is in vapor phase. The balance of the unevaporated fluid recirculates to the inlet of the solar field and is mixed with the subcooled feedwater from the process heat application.
- Subcooled dT, °C
Temperature difference for the Subcooled option.
- Target outlet temperature, °C
Target outlet temperature calculated based on the boiling or subcooled option.
- Design-point DNI, W/m**2**
The direct normal irradiance (DNI) available at the design point.
Increasing this value indicates that fewer heliostats are needed to achieve the reference condition power, while decreasing this value has the opposite effect. The design-point DNI value should represent the DNI at which your plant should achieve the specified thermal rating, including thermal and piping losses
For design-point calculations involving solar irradiance, SAM uses the design-point DNI value with the sun position at noon on the summer solstice (June 21 north of the equator, and December 21 south of the equator).
- Target Solar multiple
The field aperture area expressed as a multiple of the aperture area required to meet the thermal load.
- Target receiver thermal power, MWt
The thermal power required at the receiver outlet to meet the design thermal load.
Receiver Thermal Power (MWt) = Solar Multiple × Heat Sink Power (MWt)
This set of inputs defines the design-point operating conditions of the steam in the solar field. The field inlet and outlet temperatures, the pressure constraints, and the boiler outlet quality (if applicable) are used to calculate the enthalpy of steam during the annual performance calculation at each collector module in the loop.
- Field inlet temperature, °C
The estimated temperature of feedwater from the power cycle at the inlet of the solar field. This value is used to calculate estimated thermal losses from the solar field at design, and is not directly used in calculating the hourly performance for the annual simulation. The field inlet temperature is calculated during performance runs based on the power cycle conversion efficiency and the steam temperature at the inlet of the power cycle.
Heat Sink#
The heat sink parameters describe the process heat application’s thermal load.
- Heat sink power (MWt)
Thermal input to the heat sink at design. Together with the target solar multiple, this value determines the receiver design conditions.
- Heat sink inlet pressure (bar)
The steam pressure at the heat sink inlet.
- Heat sink fractional pressure drop
The pressure drop across the heat sink.
System Availability#
System availability losses are reductions in the system’s output due to operational requirements such as maintenance down time or other situations that prevent the system from operating as designed.
Note
To model curtailment, forced outages or reduction in power output required by the grid operator, use the inputs on the Grid Limits page. The Grid Limits page is not available for all performance models. For the PV Battery model, battery dispatch is affected by the system availability losses. For the PVWatts Battery, Custom Generation Profile - Battery, and Standalone Battery models, battery dispatch ignores the system availability losses.
To edit the system availability losses, click Edit losses.
The Edit Losses window allows you to define loss factors as follows:
Constant loss is a single loss factor that applies to the system’s entire output. You can use this to model an availability factor.
Time series losses apply to specific time steps.
SAM reduces the system’s output in each time step by the loss percentage that you specify for that time step. For a given time step, a loss of zero would result in no adjustment. A loss of 5% would reduce the output by 5%, and a loss of -5% would increase the output value by 5%.