Example 3: Combination parametric |  |  |  |

| This topic describes SAM 3.0 and has not been revised for SAM 2009 Beta. You may find useful information, especially if you are new to SAM, but some of the information may be inconsistent with the new version.

This example illustrates the use of the combination parametric group, which is useful for parametric analyses involving related variables that you want to appear in a single graph, but whose values are not dependent on each other. It is based on the third case in the sample file Parametrics Examples.sam.

In Example 1, we found that for Boulder, Colorado, the array tilt suggested by the photovoltaic system design rule of thumb "due south at latitude tilt" is correct. Is the due south array azimuth rule of thumb also correct for Boulder? To find out, we will define a combination parametric group that contains the both the Tilt and Azimuth variables. Adding Tilt and Azimuth to a combination group will allow us to create a contour graph of system output versus tilt and azimuth. We can then use the graph to find the values of both tilt and azimuth that result in the highest annual system output.

Define Tilt and Azimuth as combination parametric variables:

1. | Open Standard PV Systems.sam. The file should be in the Solar Advisor Sample folder, which is C:\SAM\Samples by default.

2. | On the File menu, click Save As and choose a name for the file, such as Parametric Examples B.sam.

3. | Rename the residential case: right-click the Residential Flat Plate System tab, click Rename on the shortcut menu, and type "Example 3 - Array Orientation" in the Rename Case window.

4. | Delete the remaining cases to reduce clutter in your file by right-clicking each case's tab and clicking Delete on the shortcut menu.

5. | On the Climate page, change the location to CO Boulder.tm2.

6. | On the Array page, right-click the variable box for Tilt.

7. | In the Tilt Input Type window click next to Parametrics.

8. | In the Define Parametric window, under Combination Parametrics, click Add Variable.

9. | In the Add Variable window, scroll to the Array section and click both Azimuth and Tilt to define them as parametric variables.

10. | Click OK to return to the Define Parametric window. Notice that the tilt and azimuth variables appear in the Combination Parametrics 1 box. Solar Advisor created a second box named Combination Parametrics 2 to allow for additional parametric groups.

11. | In the Define Parametric window, click Edit Combo to display the Edit Group window.

12. | In the Edit Group window, under Azimuth, click Edit Values to open the Edit Variable window. The window displays the current values of each variable.

13. | In the Edit Variable window, under Specify Range, type -30 for Start, 30 for End, and 10 for Increment.

Solar Advisor automatically displays a list of the values that you assigned to the parametric variable in the table under Enter Values. In this case, the minimum value of the azimuth is -30 degrees, with seven values ranging from -30 to +30 degrees in increasing increments of 10 degrees.

14. | In the Edit Variable window, in the table under Enter Values, in the row containing the value 0, click the box next to the value. An asterisk will appear in the box indicating that 0, or due south, is the base value of the azimuth parametric variable.

15. | Click OK to return to the Edit Group window.

16. | In the Edit Group window, under Tilt, click Edit Values and specify a range that starts with 0, ends with 60, and has an increment of 10.

17. | Set 40 as the base case. Boulder's latitude is approximately 40 degrees North.

18. | Click OK to return to the Edit Group Window. Solar Advisor displays the azimuth and tilt variables and their values side by side so that you can quickly check their values.

Tip. In this example, using the same number of values for the two variables will help the appearance of the graph we will create later by ensuring that the tilt and azimuth axes have the same number of ticks. When deciding on a number of values to use for Combination Parametrics, keep in mind the graph's appearance.

19. | Click OK to close the parametric variable windows and return to the Array page. On the Array page, notice that the tilt and azimuth variable boxes appear with brown backgrounds, indicating that they are parametric variables. The Array box in the navigation menu also appears with a brown background, indicating that the Array page contains one or more parametric variables.

Tip. You can define and edit parametric variables by either using the Define parametrics command on the Case menu, as we did in the steps above, or by right-clicking a variable name and clicking next to Parametrics in the Input Type window.

20. | Save the file.

Run the simulation and view results:

1. | Click Run Analysis.

2. | If the Inverter Size Issue window appears, click Run All. The message indicates that the inverter's rated capacity is slightly less than the array's rated capacity, which for the purposes of this exercise, is not a problem.

Solar Advisor displays an Information window telling you the number of TRNSYS simulations and approximate time the analysis will take, in this case 49 simulations. Because we assigned seven values each to azimuth and tilt, the analysis requires 7 × 7 = 49 simulations Solar Advisor will perform a complete simulation for each combination of tilt and azimuth we specified.

3. | Click Yes to start the simulations. When Solar Advisor finishes calculations, the Results Summary page appears.

4. | When the results are complete, save the file.

After running the simulations, Solar Advisor displays the Results Summary page. Solar Advisor calculates values that appear in the results summary table using the base value of each parametric variable in the analysis. In this case, we set the base value of the array tilt variable to 40 degrees and of the array azimuth to 0 degrees, so the LCOE and other metrics in the table reflect a system with an array at latitude tilt pointing due south. The cash flow, time series data, and other results in the project summary (Project summary on the View menu) all reflect the parametric variable's base value.

5. | In order to view the impact of array orientation on system output, we will create a contour graph of system output versus tilt and azimuth.

6. | On the Results Summary page, click Add to open the Graph Info window.

7. | In the Graph Info window, type "Array Orientation" in the Name box, select Contour in Graph Type, Azimuth in X Values, Annual Output (kWh) in ZValues, and Tilt in YValues.

8. | Click OK to create the graph.

Solar Advisor makes the calculations necessary to display the custom graph and then displays it on the main window. The custom graph name also appears in the list of graphs.

9. | Check Legend under the graph to display a color key on the graph. You can right click the graph to copy an image of the graph to the clipboard for use in other applications.

10. | Save the file

As you can see on the contour graph (and in the table under the graph), the orientation that results in the highest annual output is a tilt of 40 degrees and azimuth of -10 degrees. Note that the optimal azimuth is ten degrees east of south, not due south as the rule of thumb suggests. This may be due to late afternoon effects of sun setting over mountains and summer afternoon thunderstorms. The optimal tilt, on the other hand, is about 40 degrees north, approximately the latitude of Boulder, Colorado, and consistent with the rule of thumb.