Power Cycle |

| To view the Power Cycle page, click Power Cycle on the main window's navigation menu. Note that for the power tower input pages to be available, the technology option in the Technology and Market window must be Concentrating Solar Power - Power Tower System.
| Overview
The power cycle converts thermal energy to electric energy. The power cycle is assumed to consist of a Rankine-cycle steam engine, two open feed-water heaters, and a pre-heater, boiler and super-heater. The parameters on the Power cycle page describe the steam turbine size and other properties. Page numbers relevant to this section from the Wagner (2008) and Kistler B (1986) references are:
• | Wagner 83, 86, 114, 164
• | Kistler 224
The power cycle page displays variables that specify the design operating conditions for the steam Rankine cycle used to convert thermal energy to electricity.
| Input Variable Reference
Plant Capacity Design gross output (MWe) The power cycle's design output, not accounting for parasitic losses. 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, 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 Block Design Point Rated cycle conversion efficiency The thermal to electric conversion efficiency of the power cycle under design conditions. Design Thermal Power (MWt) The turbine's design thermal input. It is the thermal energy required at the power block inlet for it to operate at its design point, as defined by the value of the nameplate electric capacity and an estimate of the parasitic losses: Design thermal power = nameplate electric capacity + total parasitic loss estimate. (See the Parasitics page for a description of the total parasitic loss estimate.) Design HTF Inlet Temp (°C) The design temperature in degrees Celsius of the hot heat transfer fluid at the power block inlet.p 114. design htf inlet temperature can be different from receiver outlet temperature when power block design specifications require a different inlet temperature for maximum efficiency. The design values are the operating conditions at which the power block operates at its nameplate capacity. Design HTF Outlet Temp (°C) The design temperature in degrees Celsius of the cold heat transfer fluid at the power block outlet.p 114 The design values are the operating conditions at which the power block operates at its nameplate capacity. Boiler Steam Pressure (Bar) The saturation pressure of the steam as it is converted from liquid to vapor in the boiler or steam generator. Solar Advisor uses this value to determine the steam's saturation temperature and thus the superheating capability of the heat exchangers. The temperature difference that drives the steam mass flow rate in the Rankine cycle is the difference between the hot heat transfer fluid inlet temperature and the saturation temperature of the steam boiler pressure. Boiler LHV Efficiency The boiler's lower heating value efficiency, used to calculate the quantity of gas required by the boiler. Steam cycle blowdown fraction The fraction of the steam mass flow rate in the power cycle that is extracted and replaced by fresh water. This fraction is multiplied by the steam mass flow rate in the power cycle for each hour of plant operation to determine the total required quantity of power cycle makeup water. The blowdown fraction accounts for water use related directly to replacement of the steam working fluid. The default value of 0.013 for the wet-cooled case represents makeup due to blowdown quench and steam cycle makeup during operation and startup. A value of 0.016 is appropriate for dry-cooled systems to account for additional wet-surface air cooling for critical Rankine cycle components. Plant Control Min Temp to Load (°C) The lowest heat transfer fluid temperature allowed at the power cycle inlet. Whenever the fluid temperature falls below this point, the power cycle shuts down. Low-Resource Standby Period (hours) During periods of insufficient flow from the heat source due to low thermal resource, the power block may enter standby mode. In standby mode, the cycle can restart quickly without the startup period required by a cold start. The standby period is the maximum number of hours allowed for standby mode. This option is only available for systems with thermal storage.p 164 Standby Mode Thermal Fraction The fraction of the turbine's design thermal input required from storage to keep the power cycle in standby mode. This thermal energy is not converted into electric power. Turbine Startup Time (hours) The time in hours that the system consumes energy at the startup fraction before it begins producing electricity. If the startup fraction is zero, the system will operate at the design capacity over the startup time. Turbine Startup Energy Fraction The fraction of the turbine's design thermal input required by the system during startup. This thermal energy is not converted to electric power. Minimum Load Fraction The fraction of the nameplate electric capacity below which the power block does not generate electricity. Whenever the power block output is below the minimum load and thermal energy is available from the solar field, the field is defocused. For systems with storage, solar field energy is delivered to storage until storage is full. (field control 1 aimed at tower, <1, fraction that is displayed are aimed toward the tower. field could be defocused if power block is not large enough, storage too small, max htf velocity through tower is exceeded)The default value is 0.15. Max Over Design Operation The maximum allowable power block output as a fraction of the electric nameplate capacity. Whenever storage is not available and the solar resource exceeds the design value of 950 W/m2, some heliostats in the solar field are defocused to limit the power block output to the maximum load. The default value is 1.1. Cooling System Condenser type Choose either an air-cooled condenser system (dry cooling) or evaporative cooling system (wet cooling). Ambient temp at design (ºC) The ambient temperature at which the power cycle operates at its design-point-rated cycle conversion efficiency. For the air-cooled condenser option, use a dry bulb ambient temperature value. For the evaporative condenser, use the wet bulb temperature. Ref. Condenser Water dT (ºC) For the evaporative type only. The temperature rise of the cooling water across the condenser under design conditions, used to calculate the cooling water mass flow rate at design, and the steam condensing temperature. Approach temperature (ºC) For the evaporative type only. The temperature difference between the circulating water at the condenser inlet and the wet bulb ambient temperature, used with the ref. condenser water dT value to determine the condenser saturation temperature and thus the turbine back pressure. ITD at design point (ºC) For the air-cooled type only. Initial temperature difference (ITD), difference between the temperature of steam at the turbine outlet (condenser inlet) and the ambient dry-bulb temperature. Condenser pressure ratio For the air-cooled type only. The pressure-drop ratio across the air-cooled condenser heat exchanger, used to calculate the pressure drop across the condenser and the corresponding parasitic power required to maintain the air flow rate.