Example 1: Independent parametric

ICON_Under-Construction

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 independent parametric group. The independent group is useful for analysis that includes either a single parametric variable, or two or more parametric variables that are not related to each other. It is based on the first case in the sample file Parametrics Examples.sam.

Does the rule of thumb for optimal photovoltaic array orientation "due south at latitude tilt" apply to a residential photovoltaic system in Boulder, Colorado? To answer this question, we will define Tilt as an independent parametric variable and assign it a range of values. Solar Advisor will calculate a the complete set of results for the system using each array tilt angle value. To answer the question, we will examine graphs of annual output and LCOE to find the optimal array orientation.

Notes. The following procedure begins with the sample file Standard PV Systems.sam, and walks through the process of setting up an independent parametric group, running Solar Advisor, and then examining graphs of the results. The first case in the sample file Parametrics Examples.sam is what your file should look like after completing the example described below.

Although this example is for a photovoltaic system, the procedure would be the same for parametric variables for other technologies.

Define Tilt as an independent parametric variable:

1.	Open Standard PV Systems.sam. The file should be in the Solar Advisor Samples 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 A.sam.

3.	Rename the residential case: right-click the Residential Flat Plate System tab, click Rename on the shortcut menu, and type "Example 1 - Independent Parametric" in the Rename Case window.

4.	Delete the remaining cases in the file: right-click each tab and click Delete on the shortcut menu.

5.	When you finish deleting the cases, the file should contain a single case. Deleting the other cases will make your file less cluttered as you add more cases.

6.	On the Climate page, choose CO Boulder.tm2 in the Location list.

Notice that the View Results button turned red and changed to Run Analysis, indicating that you changed the value of an input variable.

7.	On the Case menu, click Define Parametrics to open the Define Parametric window.

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

9.	In the Add Variable window, scroll to the Array section of the list and click Tilt to define it as a parametric variable.

The Add Variable window displays a list of all Solar Advisor variables that you can define as parametric variables. The variables are grouped into the same categories that appear on the main window's Navigation menu.

10.	Click OK to return to the Define Parametric window.

11.	In the Define Parametric window, under Independent Parametrics, Click Edit Values. (The Tilt box should have a green background indicating that it is active.)

12.	In the Edit Variable window, under Specify Range, type the numbers 0 in Start, 60 in End, and 10 in Increment.

Solar Advisor automatically displays a list of the values that you have assigned to the parametric variable in the table under Enter Values. In this case, the minimum value of the tilt variable is 0, and there are seven values ranging from 0 to 60 degrees in increasing increments of 10 degrees.

Tip. You can also enter values for the parametric variable by hand by clicking a row in the table under Enter Values, pressing the Insert key, and typing values directly in the table. You can delete values from the list by selecting the value and pressing the Delete key.

13.	In the Edit Variable window, in the table under Enter Values, click the box next to the value 40. An asterisk will appear in the box indicating that 40 degrees is the base value of the parametric variable.

14.	Although parametric variables have a range of values, only a single value, the variable's base value, is displayed in boxes on the data input pages.

15.

Click OK to close the Edit Variable window, and again to close the Define Parametric window. On the Array page, notice that Solar Advisor displays the Tilt box with a brown background, indicating that it is a parametric variable. The Array box in the navigation menu also appears with a brown background, indicating that the Array page contains one or more parametric variables. The Tilt box shows the parametric variable's base value, 40.

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

So far, we have defined a single parametric variable, Tilt, and assigned it seven values ranging from 0 to 60 degrees in increments of 10 degrees. We defined the base value to be 40 degrees. In Solar Advisor, a tilt of zero degrees represents a horizontal array. A tilt of ninety degrees would be vertical.

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.

In the Information window, note that the number of TRNSYS simulations is equal to the number of values we assigned to tilt. Solar Advisor will perform a complete simulation for each of the seven tilt values.

3.	Click Yes to start the simulations.

After running a simulation for each tilt value, Solar Advisor displays the Results Summary page. Note that the LCOE and other metrics that appear in the Base column of the Metrics table are calculated using the base value of each parametric variable. In this case, we set the base value of Tilt to 40 degrees, so the LCOE and other metrics reflect that value. The cash flow and other results in the project summary (Project summary on the View menu) also reflect the parametric variable's base value.

4.	Because we defined Tilt as a parametric variable, Solar Advisor creates a set of new standard graphs in the Graphs list. The new graphs are Annual Output vs Tilt, LCOE vs Tilt, and Cost stacked bar vs Tilt.

5.	In the Graphs list on the Results Summary page, click *LCOE vs Tilt.

6.	Save the file.

The results of this parametric analysis show that given the assumptions for this project, an array tilt of 40 degrees (from the horizontal) results in the highest system annual output in kWh for tilt values of between 0 and 60 degrees. Thus, the optimal value of tilt is 40 degrees, which is what the rule of thumb suggests for Boulder, whose latitude is approximately 40 degrees north.

Note: You can also use sliders to examine the impact of Tilt on different results. For example, you could add a slider for the tilt variable to the Cashflow graph to explore how changes in the array tilt affect the cash flow. See Sliders for more information.