The parameters on the Thermal Storage page describe the properties thermal energy storage system. Dispatch controls are on the System Control page.
The power tower storage model requires that the heat transfer fluid volume, tank loss coefficients, and tank temperatures be specified. SAM calculates the storage tank geometry to ensure that the storage system can supply energy to the power block at its design thermal input capacity for the number of hours specified by the Full Load TS Hours variable.
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 power, MWt
The thermal power required at the power cycle inlet for it to operate at its design point.
Cycle Thermal Power (MWt) = Design Turbine Gross Output (MWe) ÷ Cycle Thermal Efficiency
Hot storage cold temperature, °C
The temperature of the cold heat transfer fluid at the hot tank inlet when the power cycle operates at its design point.
Hot storage hot temperature, °C
The temperature of the hot heat transfer fluid at the hot tank outlet when the power cycle operates at its design point.
Hours of storage, hours
The nominal thermal storage capacity expressed in hours at full load: The number of hours that the storage system can supply energy at the cycle's design point.
SAM displays the equivalent storage capacity in MWht on the Installation Costs page.
Hot storage cold temperature, °C
The temperature of the cold heat transfer fluid at the cold tank inlet when the power cycle operates at its design point.
Hot storage hot temperature, °C
The temperature of the hot heat transfer fluid at the cold tank outlet when the power cycle operates at its design point.
Hot/Cold Temperature Thermal Energy Storage
The hot temperature and cold temperature thermal energy storage parameters are for the hot and cold storage tanks, respectively.
Hot/Cold Storage Fluid
The storage fluid used for the hot and cold storage tanks.
Property table for user-defined hot/cold storage fluid
When you choose User-defined from the storage fluid list, you can specify a table of material properties of a storage fluid. You must provide values for two temperatures (two rows of data) of specific heat, density, viscosity, and conductivity values. See Custom HTF for details.
TES thermal capacity
The nominal thermal capacity of the storage system.
TES Thermal Capacity = Hours of Storage at Power Cycle Full Load × Cycle Thermal Input Power at Design
Available HTF volume, m³
The total volume of storage fluid in both storage tanks.
SAM calculates the total heat transfer fluid volume in storage based on the storage hours at full load and the power block design turbine thermal input capacity. The total heat transfer fluid volume is divided among the total number of tanks so that all hot tanks contain the same volume of fluid, and all cold tanks contain the same volume of fluid.
Tank height, m
The height of the cylinder-shaped heat transfer fluid volume in each tank. SAM calculates the height based on the diameter and storage volume of a single tank.
Tank fluid minimum height, m
The minimum allowable height of fluid in the storage tank(s). The mechanical limits of the tank determine this value.
Parallel tank pairs
The number of parallel hot-cold storage tank pairs. Increasing the number of tank-pairs also increases the volume of the heat transfer fluid exposed to the tank surface, which increases the total tank thermal losses. SAM divides the total heat transfer fluid volume among all of the tanks, and assumes that each hot tank contains an equal volume of fluid, and each cold tank contains and equal volume.
Tank diameter, m
The diameter of the cylinder-shaped heat transfer fluid volume in each storage tank.
Initial Hot HTF Percent, %
The fraction of the storage heat transfer fluid in the hot storage tank at the beginning of the simulation.
Wetted loss coefficient, W/m²/K
The thermal loss coefficient that applies to the portion of the storage tank holding the storage heat transfer fluid.
Estimated heat loss, MWt
Heat loss from the storage system at the design-point.
Cold tank heater temperature set point, °C
The minimum allowed cold tank temperature. Whenever the heat transfer fluid temperature in storage drops below the set-point value, the system adds sufficient thermal energy from an electric tank heater to storage to reach the set-point.
Cold tank heater capacity, MWe
The maximum electric load of the cold tank electric heater.
Hot tank heater temperature set point, °C
The minimum allowed hot tank temperature. Whenever the heat transfer fluid temperature in storage drops below the set-point value, the system adds sufficient thermal energy from an electric tank heater to storage to reach the set-point.
Hot tank heater capacity, MWe
The maximum electric load of the hot tank electric heater.
Custom HTF
If the heat transfer fluid you want to use in the solar field is not included in the Field HTF Fluid list, you can define a custom heat transfer fluid using the User-defined option in the list. To define a custom fluid, you need to know the following properties for at least two temperatures:
•Temperature, ºC
•Specific heat, kJ/kg-K
•Density, kg/m³
•Viscosity, Pa-s
•Kinematic viscosity, m²-s (not required, see note below)
•Conductivity, W/m-K
•Enthalpy, J/kg (not required, see note below)
Note. The kinematic viscosity and enthalpy data in the table are not used by the CSP models. These properties are redundant: Kinematic viscosity is the ratio of viscosity to density, and the heat balance equations use specific heat instead of enthalpy.
To define a custom heat transfer fluid:
1.In the Field HTF fluid list, click User-defined.
2.In the Edit Material Properties table, change Number of data points to 2 or higher. The number should equal the number of temperature values for which you have data.
3.Type values for each property in the table.
You can also import data from a text file of comma-separated values. Each row in the file should contain properties separated by commas, in the same the order that they appear in the Edit Material Properties window. Do not include a header row in the file.
Notes
Each row in the materials property fluid table must be for a set of properties at a specific temperature. No two rows should have the same temperature value.
SAM calculates property values from the table using linear interpolation.
The rows in the table must sorted by the temperature value, in either ascending or descending order.
The physical trough model uses the temperature, specific heat, density, viscosity, and conductivity values. It ignores the enthalpy and kinematic viscosity values (the empirical trough model does use those values).
For the physical trough model, if you specify user-defined HTF fluids with the same properties for the solar field and thermal storage system, on the Thermal Storage page, SAM disables the Hot side HX approach temp and Cold side HX approach temp inputs, and sets them to zero internally to represent a system with no heat exchanger. (When the hot and cold side approach temperatures are zero, Thermal storage exergetic efficiency is one.)
