PVWatts® Viewer | Help

Contact | FAQ | Tutorial | PVWatts® Calculator | Results Explained | Grid Cell Explained


The PVWatts® Viewer is an interactive map providing access to multiple data sets which link directly to their corresponding PVWatts® Calculators, allowing the user to determine energy production and cost savings of grid-connected solar photovoltaic (PV) systems. Both calculators are accessible through the viewer by querying their corresponding data layers, which feature weather data in the form of specific locations (239 TMY2 sites in the United States and 76 international) as well as a 40km x 40km grid which covers the United States.

The PVWatts® Viewer provides easy access to both datasets. This application, built on ESRI Flex Viewer, utilizes an interactive web mapping interface that allows you to query both data sets simultaneously for any specified location. The screenshot below illustrates the various data sets as they are displayed in the PVWatts® Viewer. Station locations are indicated by a black cross with a yellow center and a 40km solar resource grid (yellow to red squares) is overlaid on top of a street map of the United States.

Base Map Viewing Options

You have two viewing options: road base map or satellite base map. A road map is the default base map. You can change the base map at anytime. To change the base map, use these icons located in the upper right corner:

Road Map Click on this icon to display a road map as your base map.
Satellite Map Click on this icon to display a satellite view as your base map.

Grid Visibility/Transparency

A grid visibility/transparency check box and slider in the upper right corner allows you to set the levels of transparency for easier viewing of underlying reference data. By default, it is set to 50%.

Panning and Zooming

Panning is available by just clicking and dragging on the map. You can zoom by using the Zoom Full icon in the upper part of the Viewer, by using the zoom slider, or by using the scroll wheel on your mouse while hovering over any portion of the map. Note: To allow for easy drawing, panning is disabled while using the draw tools.

Zoom Full Click on this icon to return the map to its initial zoom level.
Zoom Slider Click the plus or minus to zoom in or out, drag the slider to the desired zoom level, or click directly on the desired zoom level.

PVWatts® Tool

If not already visible, this icon will open the PVWatts® Tool as shown below:

PVWatts® Tool If not already visible, clicking on this icon will open the PVWatts® Tool as shown below:

Tools Menu

Many additional tools are available to you through the tools menu. To access the menu, click the Tools icon shown below. A menu of available tools will appear. Clicking on a tool will activate it, opening a new panel on the right side of the map. Clicking the green arrow in the upper right of the tool's panel will minimize it and the selected tool will remain active. If minimized, clicking the tool's icon will restore the tool's panel. Note: Some tools have specific actions which will change the functionality of the mouse. The restore the default PV Watts tool, click the PVWatts® tool icon on the main toolbar (see above).

Tools Menu If not already visible, clicking on this icon will open the PVWatts® Tool as shown below:
Help Displays this page.
Overview Map Displays an overview map that helps you locate your current selection on a larger map. Drag the red box in the overview map to change your location.
Print Prints the map. Optional fields allow you to declare a title and subtitle for your map.
Locate Select a specific location to display by ZIP code, address or coordinates. Locating by ZIP code will select the center of the ZIP code.
Draw Customize your map and draw attention to specific areas with a variety of drawing and labeling tools.

Using PVWatts® Veiwer (Tutorial)

From the Viewer, users can access PVWatts® Version 1 (site locations) and PVWatts® Version 2 (40K Monthly Grid Cells) through an interactive map. The directions are the same for both formats. Once sent to the PVWatts® calculator, the difference is that with site locations, users can download hourly values of PV performance. Hourly downloads are not available for grid cells.

  1. Select Location
    There are a variety of ways you can select your location:
    1. PVWatts® Tool Enter a zip code, specific address, or coordinates.
    2. Map Interface While the PVWatts® tool is active, you can pan, click and zoom to find your location.
    3. Locate Tool (Deprecated) The locate tool also allows you to enter a zip code, specific address, or coordinates.
  2. Viewing Results
    Depending on where you click, you may see results from more than one data set. For example, clicking within the US will often produce a site location result as well as a grid cell result. Click the arrows or drag the scroll bar slider on the right of the results panel to view additional results.
    Re-center the map and zoom in on a specific result.
    A direct link to the
    Results Explained section of this help file.
  3. Send to PVWatts®
    Once you've identified the location you are interested in, click the button shown below on the corresponding result to send the location information to the PVWatts® Calculator.
    Send the location information of a result to the PVWatts® calculator.
  4. PVWatts® Calculator
    A separate browser window will open (contents shown below) indicating your system parameters. The default values will automatically be populated. Enter new system parameters, if desired, and press the Calculate button when you are ready to run the PVWatts® Calculator.
    1. Site Location Cell ID, State, Latitude, Longitude
    2. PV System Specifications DC Rating, DC to AC derate factor, array type and Tracking system (array tilt or array azimuth)
    3. Energy Data Cost of electricity (from 2010)
  5. Review Calculated Results
    After running the PVWatts® Calculator, your calculated results will display (shown below) in the window. To output your calculation as text, select the “Output Results as Text” button.

Results Explained

The results generated by querying a point (clicking or searching) fall into one of two primary categories:

Domestic (US TMY2) or International Hourly Site
Displays the latitude, longitude, state, region, location and/or country of the hourly station located closest to the point queried. Additional information such as a WBAN number or Station ID may be provided. This information is sent to PVWatts® for use in the calculator.
40km Grid Cell
Displays the latitude and longitude of the grid cell centroid of the located point. The state shown in the results is the state in which the centroid of the grid cell resides.
Note: The state returned by the grid cell may not match the state at the exact location of the queried point if the grid cell spans more than one state. This has no impact on the PVWatts® calculation results. For more information, see
'Grid Cell Explained' below.

Grid Cell Explained

Each grid cell displayed in the PVWatts® Viewer is a 40km x 40km area of interpolated solar resource data assembled using the Climatological Solar Radiation (CSR) model. Grid cell resolution is driven by the input data base components used to run the model.

40km Grid Cell
A sample grid cell (left) demonstrates the key elements used in the PVWatts® calculation:

Additional Information

PVWatts® Contact

For questions or suggestions regarding the PVWatts® Calculator or the PVWatts® Viewer, contact:
Pamela Gray-Hann