Power Block

To view the SCA / HCE page, click Power Block on the main window's navigation menu. Note that for the Power Block page to be available, the technology option in the Technology and Market window must be Concentrating Solar Power - Parabolic Trough System.

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.

Contents

►	Input Variable Reference describes the input variables and options on the Power Block page.

►	Power Cycle Library Options describes the reference steam turbines included in the default power block library.

►	Equations for Calculated Values describes the equations used to calculated the calculated values on the Power Block page.

Input Variable Reference

Plant Characteristics

Name	Description	Units
Rated Turbine Net Capacity	Nameplate capacity of turbine. SAM does not use this variable in energy calculations, but does use it as the system capacity to calculate costs on the system costs page.	MWe
Design Turbine Gross Output	Gross electric output of turbine, typically 110% of rated turbine net capacity. Used to calculate the design turbine thermal input, which is displayed in the power cycle group with a blue background and described below. Also used to calculate the energy from the backup boiler.	MWe

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.

Name	Description	Units
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	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.	MWt
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	The maximum thermal energy that can be delivered to the power block by the solar field, thermal energy storage system or both.	MWt
Min Thermal Input	The minimum thermal energy that can be delivered to the power block by the solar field, thermal energy storage system or both.	MWt
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.	--

Power Cycle Library Options

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 22. Power cycle reference systems.

Reference System	Approximate Solar Field Size Range m2	Approximate Operating Temperature ºC	Suggested Modeling Application
APS Ormat 1 MWe 300C	10,000	300	Organic Rankine-cycle power block
Nexant 450C HTF	-	450	High-temperature heat transfer fluid (molten salt)
Nexant 500C HTF	-	500	High-temperature heat transfer fluid (molten salt)
SEGS 30 MWe Turbine	180,000 - 230,000	300 - 400	Typical applications
SEGS 80 MWe Turbine	460,000 - 480,000	400	Typical applications
Siemens 400C HTF		400	High-temperature heat transfer fluid

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 23. Reference system parameters.

Parameter Name	SEGS 30	SEGS 80	APS ORC	Nexant 450	Nexant 500	Siemens 400
Rated Turbine Net Capacity	30	80	1	100	100	50
Design Turbine Gross Output	35	89	1.160	110	110	55
Design Turbine Thermal Input	93.3	235.8	5.600	278.0	269.9	147.2
Design Turbine Gross Efficiency	0.3749	0.3774	0.2071	0.3957	0.4076	0.3736
Max Over Design Operation	1.15	1.15	1.15	1.15	1.15	1.15
Minimum Load	0.15	0.15	0.15	0.15	0.15	0.15
Turb. Part Load Therm to Elec F0	-0.0571910	-0.0377260	-0.1593790	-0.0240590	-0.0252994	-0.0298
Turb. Part Load Therm to Elec F1	1.0041000	1.0062000	0.9261810	1.0254800	1.0261900	0.7219
Turb. Part Load Therm to Elec F2	0.1255000	0.0763160	1.1349230	0.0000000	0.0000000	0.7158
Turb. Part Load Therm to Elec F3	-0.0724470	-0.0447750	-1.3605660	0.0000000	0.0000000	-0.5518
Turb. Part Load Therm to Elec F4	0.0000000	0.0000000	0.4588420	0.0000000	0.0000000	0.1430
Turb. Part Load Elec to Therm F0	0.0565200	0.0373700	0.1492050	0.0234837	0.0246620	0.044964
Turb. Part Load Elec to Therm F1	0.9822000	0.9882300	0.8521820	0.9751230	0.9744650	1.182900
Turb. Part Load Elec to Therm F2	-0.0982950	-0.0649910	-0.3247150	0.0000000	0.0000000	-0.563880
Turb. Part Load Elec to Therm F3	0.0595730	0.0393880	0.4486300	0.0000000	0.0000000	0.467190
Turb. Part Load Elec to Therm F4	0.0000000	0.0000000	-0.1256020	0.0000000	0.0000000	-0.130090

Equations for Calculated Values

Design Turbine Thermal Input

Where,

hDesignTurbineGross	Design Turbine Gross Efficiency
QDesignTurbineGross (W)	Design Turbine Gross Output
QDesignTurbineThermalInput (W)	Design Turbine Thermal Input

Max Thermal Input

Where,

QtoPBMax (W)	Max Thermal Input
QPBDesign (W)	Design Turbine Thermal Input
FET(0-4)	Turbine Part Load Elec To Therm coefficients
FPBMax	Max Over Design Operation

Min Thermal Input

Where,

QtoPBMin (W)	Min Thermal Input
QPBDesign (W)	Design Turbine Thermal Input
FET(0-4)	Turbine Part Load Elec To Therm coefficients
FPBMax	Minimum Load