Optimization Wizard |

| To start the power tower optimization wizard, first click Heliostat Field on the main window's navigation menu to view the Heliostat Field page, and then follow the instructions below. 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 tower optimization wizard simplifies the task of choosing values for the relatively large number of input parameters required to specify the power tower solar field and receiver. Because the heliostat field is typically the most capital intensive part of a power tower project, often accounting for 30-40% of the total installation cost, optimizing the heliostat field size is a critical step in minimizing overall project cost. The optimization wizard searches for a set optimal system parameter values, where the optimal system is defined as the one that results in the lowest levelized cost of energy. Note that the optimization process is separate from the simulation process. When you run the wizard, it populates some of the input variables in the Solar Advisor input pages (listed below) with optimal values. Before running simulations, you can choose to either keep the values generated by the wizard or modify them. The wizard's underlying code is based on the DELSOL3 code from Sandia National Laboratory (Kistler 1986, see References), and is implemented in SAM through the PTGen program described in the thesis Simulation and Predictive Performance Modeling of Utility-Scale Central Receiver System Power Plants (Wagner 2008) http://sel.me.wisc.edu/theses/wagner08.zip (33 MB). To use the optimization wizard:
1. | On the Tower System Costs page, enter values for the capital costs.
2. | On the Heliostat Field page, click Start Wizard to start the wizard.
Solar Advisor initially populates the variables in the wizard with values from the Heliostat Field, Tower and Receiver, and Power Cycle pages. Solar Advisor assigns values to variables that don't appear elsewhere, such as Minimum Tower Height and Maximum Tower Height, using either default values or values based on the last time the wizard ran.
3. | Enter values to define the parameters of the optimization.
4. | Click Optimize Solar Field.
5. | After the wizard finishes running, click Close.
6. | Review the variables on the input pages. Modify any values as needed, and then configure and run simulations to simulate the system(s) and display annual production, levelized cost of energy, and other results on the Results page.
| Input Variable Reference
Solar Field Solar Multiple The ratio of of the receiver's design thermal output to the power block's design thermal input. For systems with no storage, the solar multiple should be close to or equal to one. Receiver and Tower The receiver and tower optimization variables determine the optimization search range and step size for the receiver and tower dimensions. Receiver and Tower Min Receiver Diameter (m) The minimum value for the range of receiver diameter values that the wizard will search for an optimal solution. Max Receiver Diameter (m) The maximum value for the range of receiver diameter values that the wizard will search for an optimal solution. Optimization Levels for Receiver Diameter The number of receiver diameter values to evaluate in the search for an optimal solution. The maximum allowed number of optimization levels is 10. Min Receiver Height / Diameter Ratio The minimum receiver height to receiver diameter ratio for the range of values that the wizard will search for the optimal solution. Max Receiver Height / Diameter Ratio The maximum receiver height to receiver diameter ratio for the range of values that the wizard will search for the optimal solution. Optimization Levels for Receiver H/D Ratio The number of receiver height to diameter ratio values to evaluate in the search for an optimal solution.The maximum allowed number of optimization levels is 10. Min Tower Height (m) The minimum value for the range of tower height values that the wizard will search for an optimal solution. Max Tower Height (m) The maximum value for the range of tower height values that the wizard will search for an optimal solution. Optimization Levels for Tower Height The number of tower height values to evaluate in the search for an optimal solution. The maximum allowed number of optimization levels is 10.
| Overview of the Optimization Process
For each variable that is specified as a range in the optimization wizard, the wizard searches for the value within the range that meets the performance requirements at the lowest levelized cost of energy. The wizard searches discrete combinations of options based on the "optimization level" of each optimized variable. For example, if the minimum tower height is specified as 150 m and the maximum 250 m, and the tower height optimization level is 10, the wizard will simulate 10 systems with unique tower heights evenly incremented between 150 m and 250 m. Be sure to choose reasonable ranges and step sizes to minimize the number of calculations the wizard must perform. The solar multiple is the ratio of of the receiver's design thermal output to the power block's design thermal input. The optimization wizard uses the solar multiple to calculate the receiver's thermal rating, which is equal to the solar multiple multiplied by the power cycle nameplate electric capacity divided by the rated cycle conversion efficiency, both of which are on the Power Cycle page. The wizard holds the following variables constant as it searches for the optimal system:
• | Solar Multiple on the Optimization Wizard window.
• | Nameplate Capacity on the Power Cycle page.
• | Heliostat Width on the Heliostat Field page.
• | Heliostat Height on the Heliostat Field page.
• | Maximum Receiver Flux on the Tower and Receiver page.
The wizard searches within the specified ranges to find optimal values of the following variables on the Tower and Receiver page.When the wizard finishes running, Solar Advisor populates the variables with the optimal values.
• | Receiver Diameter
• | Receiver Height (calculated as a function of the receiver height to the receiver diameter ratio)
• | Tower Height
Solar Advisor also populates the following variables on the Heliostat Field page with values from the wizard:
• | Radial Step Size for Layout
• | Total Reflective Area
• | Number of Heliostats
• | Number of heliostats per radial zone in the field layout table
The optimization wizard uses the following values from the input pages, but does not change their values. From the Heliostat Field page:
• | Heliostat Width
• | Heliostat Height
• | Ratio of Reflective Area to Profile
• | Mirror Reflectivity and Soiling
• | Use Round Heliostats
• | Max Distance from Tower
• | Min Distance from tower
• | Image Error
• | Number of Radial Zones
• | Number of Azimuthal Zones
From the Tower and Receiver page:
• | Coating Absorptivity
• | Max Receiver Flux
From the Power Cycle page:
• | Nameplate Capacity
• | Rated Cycle Conversion Efficiency
It is possible that the wizard will not find an optimal field layout given a set of values that you provide. Finding an optimal set of input parameters is often an iterative process that may require you to run the optimization wizard and adjust input value ranges several times until the wizard finds a reasonable field layout for your analysis. When the wizard cannot find an optimal layout, it displays a message with suggestions for adjustments. Typically, the suggestions include adjusting the upper or lower limits of optimization variables, and ensuring that the minimum and maximum heliostat distance from tower values are reasonable. Keep in mind that because the wizard uses capital costs from the Tower System Costs page in the optimization process, unreasonable cost values may also prevent the wizard from finding an optimal field layout. In some cases, wizard will fail to find an optimal design and exit without notice. When that happens, check to see if the values of optimized variables shown on the input pages are outside of the range specified for those variables in the wizard, and try adjusting the ranges you specified and rerunning the wizard.
| Guidelines for Choosing Variable Ranges for Optimization
The optimization wizard does its best to find parameter values for an optimal system within the search ranges you specify on the wizard input tabs. Because the wizard searches a discrete number of values within the range for each parameter, defining too broad of a range increases the chances that the optimal value lies between the values included in the search. On the other hand, defining too narrow a range increases the chances that the optimal value lies outside of the search range. The ability of the optimization wizard to find an optimal system is sensitive to the following variable ranges:
• | Receiver diameter range, defined by Minimum Receiver Diameter and Maximum Receiver Diameter.
• | Receiver height to diameter ratio range, defined by Minimum Receiver Height/Diameter Ratio and Maximum Receiver Height/Diameter Ratio.
• | Tower height range, defined by Minimum Tower Height and Maximum Tower Height.
• | Heliostat distance from tower range, defined by Maximum Distance from Tower and Minimum Distance from Tower values on the Heliostat Field page.
The following rules of thumb may be helpful in choosing search ranges for these variables, although they may not apply to some systems.
• | Tower height: The tower height typically falls between 15 m for very small systems (5 MWe) and 300 m for very large systems (150 MWe). For example, a reasonable range for a 30 MWe system with a solar multiple of 1.0 would be between 40 m and 120 m.
• | Receiver diameter: The optimization wizard searches for a receiver diameter value that maximizes absorbed radiation from the heliostat field within the flux limit defined by the maximum value on the Receiver/Tower page. Like the tower height, the receiver area typically scales with system's design thermal power. For very small systems, the optimal receiver diameter is typically between 1 m and 3 m, while very large systems may require a diameter of 25 m.
• | Receiver height to diameter ratio: This ratio should generally fall between 0.5 and 2.0.
• | Heliostat distance from tower: If the minimum distance is too small, the inner zones in the heliostat will contain no heliostats (the first rows in the field layout table on the Heliostat Field page contain zeros), which will cause the simulation to fail. If the maximum distance is too large, the outer zones will contain no heliostats. On the other hand, if the maximum distance is too small, all of the outer zones will contain heliostats. For very small systems, the maximum distance might be set to 300 m, and for very large systems, a distance of 2000 m might be appropriate.