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To view the PVWatts Solar Array page, click PVWatts Solar Array on the main window's navigation menu. Note that for the PVWatts Solar Array page to be available, the technology option in the Technology and Market window must be Photovoltaics - PVWatts Performance Model.
The PVWatts Solar Array page displays variables for Solar Advisor's implementation of NREL's PVWatts model.
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Solar Advisor includes an implementation of NREL's PVWatts model to facilitate comparing results calculated by Solar Advisor's three other photovoltaic module performance models with PVWatts results, and to generate results based on the PVWatts performance model but using Solar Advisor's cost and financial model and assumptions.
Note. NREL's PVWatts model is a web-based simulation model for grid-connected photovoltaic systems. To use the model or find out more about it, visit the PVWatts website at http://www.nrel.gov/rredc/pvwatts/. The model is also described in Marion (2002).
Input Variable Reference
PVWatts System Inputs
The system inputs define the size of the system, derate factor, and the array orientation. For information about choosing values for the PVWatts input variables, see the PVWatts website at http://www.nrel.gov/rredc/pvwatts/changing_parameters.html.
Variable
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Description
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Units
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DC Rating
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The array's nameplate DC power rating in kilowatts under standard test conditions (STC). The DC rating is equal to a single module's DC power rating in watts at 25°C and 1,000 W/m2 multiplied by the number of modules in the array divided by 1,000.
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DC to AC Derate Factor
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A factor accounting for conversion of the array's DC nameplate capacity to the system's AC power rating at STC. The default value is 0.77. For help calculating the derate factor, see the PVWatts derate factor calculator at http://rredc.nrel.gov/solar/calculators/PVWATTS/derate.cgi.
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Array Tracking Mode
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The three array tracking modes are:
| • | A fixed array is fixed at the tilt and azimuth angles defined by the Tilt and Azimuth variables. |
| • | A one-axis tracking array is fixed at the tilt angle defined by the Tilt variable and rotates from east in the morning to west in the evening to track the daily movement of the sun across the sky. |
| • | A two-axis tracking array rotates from east in the morning to west in the evening to track the daily movement of the sun across the sky, and from north to south to track the sun's seasonal movement throughout the year. |
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Tilt
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Applies only to fixed arrays and arrays with one-axis tracking. The array's tilt angle in degrees from horizontal, where zero degrees is horizontal, and 90 degrees is vertical. As a rule of thumb, system designers often use the location's latitude as the optimal array tilt angle. The actual tilt angle will vary based on project requirements.
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degrees
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Azimuth
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Applies only to fixed arrays with no tracking. The array's east-west orientation in degrees. An azimuth value of zero is facing the equator in both the northern and southern hemispheres. In the northern hemisphere, an azimuth of positive 90 degrees is facing due west, and negative 90 degrees is facing due east. As a rule of thumb, system designers often use an array azimuth of zero, or facing the equator.
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degrees
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