The Power Block parameters describe the equipment in the system that converts thermal energy from the solar field or thermal energy storage system into electricity. The power block is based on a steam turbine that runs on a conventional Rankine power cycle and may or may not include fossil fuel backup. Power block components include a turbine, heat exchangers to transfer heat from the solar field or thermal energy storage system to the turbine, and a cooling system to dissipate waste heat. Solar Advisor considers the thermal energy storage system to be a separate component, which is described on the Thermal Storage page.

The input variables on the Power Block page are divided into two groups. The turbine ratings group determines the capacity of the power block, and the power cycle group defines the performance parameters of the reference turbine.

For a more detailed description of the model, please download the CSP trough reference manual from the Solar Advisor website's support page: https://www.nrel.gov/analysis/sam/support.html.

Plant Characteristics

Design gross output (MWe)

The power cycle's design output, not accounting for parasitic losses. Solar Advisor uses this value to size system components, such as the solar field area when you use the solar multiple to specify the solar field size.

Estimated gross to net conversion factor

An estimate of the ratio of the electric energy delivered to the grid to the power cycle's gross output. Solar Advisor uses the factor to calculate the power cycle's nameplate capacity for capacity-related calculations, including the estimated total cost per net capacity value on the System Costs page, capacity-based incentives on the Payment Incentives page, and the capacity factor reported in the results.

Estimated net output design (nameplate) (MWe)

The power cycle's nameplate capacity, calculated as the product of the design gross output and estimated gross to net conversion factor.

Power Cycle

The variables in the power cycle group describe a reference steam turbine. SAM uses the reference turbine specifications to calculate the turbine output, and then scales the actual output based on the turbine rating variables. Each set of reference turbine specifications is stored in the reference turbine library.

Current power block

Name of the reference turbine. Selecting a reference system determines the values of the other power cycle variables.

Design Turbine Thermal Input (MWt)

The thermal energy required as input to the power block to generate the design turbine gross (electric) output. SAM uses the design turbine thermal input to calculate several power block capacity-related values, including the solar field size, power block design point gross output, and parasitic losses.

Design Turbine Gross Efficiency

Total thermal to electric efficiency of the reference turbine. Used to calculate the design turbine thermal input.

Max Over Design Operation

The turbine's maximum output expressed as a fraction of the design turbine thermal input. Used by the dispatch module to set the power block thermal input limits.

Minimum Load

The turbine's minimum load expressed as a fraction of the design turbine thermal input. Used by the dispatch module to set the power block thermal input limits.

Turbine Start-up Energy

Fraction of the design turbine thermal input required to bring the system to operating temperature after a period of non-operation. Used by the dispatch module to calculate the required start-up energy.

Boiler LHV Efficiency

The back-up boiler's lower heating value efficiency. Used by the power block module to calculate the quantity of gas required by the back-up boiler.

Max Thermal Input (MWt)

The maximum thermal energy that can be delivered to the power block by the solar field, thermal energy storage system or both.

Min Thermal Input (MWt)

The minimum thermal energy that can be delivered to the power block by the solar field, thermal energy storage system or both.

Turb. Part Load Therm to Elec

Factors for the turbine thermal-to-electric efficiency polynomial equation. Used to calculate the design point gross output, which is the portion of the power block's electric output converted from solar energy before losses.

Turb. Part Load Elec to Therm

Factors for turbine's part load electric-to-thermal efficiency polynomial equation. Used to calculate the energy in kilowatt-hours of natural gas equivalent required by the backup boiler. SAM dispatches the backup boiler based on the fossil-fill  fraction table in the thermal storage dispatch parameters on the Thermal Storage page.

Cooling Tower Correction

Cooling tower correction factor. Used to calculate the temperature correction factor that represents cooling tower losses. To model a system with no cooling tower, set F0 to 1, and F1 = F2 = F3 = F4 =0.

Temperature Correction Mode

In the dry bulb mode, SAM calculates a temperature correction factor to account for cooling tower losses based on the ambient temperature from the weather data set. In wet bulb mode, SAM calculates the wet bulb temperature from the ambient temperature and relative humidity from the weather data.

The power cycle library includes six reference turbines. See Working with Libraries for information about managing libraries.

The reference turbines include five conventional Rankine-cycle steam turbines in a range of sizes, and one organic Rankine-cycle turbine. Conventional Rankine-cycle turbines are similar to those used in coal, nuclear, or natural gas power plants. A heat exchanger transfers energy from the solar field's heat transfer fluid to generate steam that drives the turbine. The organic Rankine-cycle turbine operates on the same principle as the conventional turbine, but uses an organic fluid, typically butane or pentane, to run the turbine instead of water.

Table 19. Power cycle reference systems.

When you choose a turbine from the reference system library, Solar Advisor changes the values of the Power Cycle variables. The following table of shows the power cycle parameters for the standard reference systems. Note that you can use any value for the Rated Turbine Net Capacity and Design Turbine Gross Output variables, Solar Advisor will use the reference system parameters with the rated and design turbine parameters.

Table 20. Reference system parameters.

Design Turbine Thermal Input

Where,

Max Thermal Input

Where,

Min Thermal Input

Where,