How are data accessed/downloaded in POWER?

Solar and meteorological parameters can be accessed in the POWER web site via the Data Access Viewer (DAV) at  https://power.larc.nasa.gov/data-access-viewer/.  When the DAV page opens you may click the “Access Data” box and/or check the “Do not show ..” box to avoid loading the splash Page on subsequent visits. 

• In the DAV page that is now visible, in Section 1 select the User community appropriate for the desired data parameters.
• Choose the appropriate Temporal Average in Section 2.
• Enter the site latitude and longitude in Section 3
• Note that if Climatology time period is selected in Section 2, there is not need to enter a time period in section 4 since by default monthly values are averaged over the climatological time period.
• In Section 5, Select Output File Format.
• In Section 6, the parameters that are available for the Select User community and Temporal period are listed in Parameters Folders. Each folder can be opened by clicking on the intersection of the horizontal and vertical branch associated with each folder. Individual data parameters are selected/deselected by clicking on each parameters or all parameters in a folder can be selected/deselected by clicking on the folder itself.
• Click the “Submit” button in Section 7. The resulting page will provide time series plots of the selected data parameters. To download data in the previously selected format click the appropriate box under the "Output Files".

You may also download all data parameters using API calls described at https://power.larc.nasa.gov/docs/v1/.

What is the spatial resolution of the POWER data?

The POWER solar data were initially produced on a 1° latitude/longitude grid and subsequently re-gridded via data replication to a 0.5° latitude, longitude grid cells. The latitude, longitude value for the cell is at the lower left corner of the cell.

The POWER meteorological data were initially produced on a 1/2° by 2/3° global grid and then bi-linearly interpolated by the POWER project to a global 0.5° grid. The latitude, longitude value for the cell is at the center of the cell.

What is the temporal resolution of the POWER data?

The POWER solar data are initially produced on 3-hourly time increments which are averaged to provide daily values. The daily averaged values are used to calculate climatologically averaged monthly values.

The meteorological data are initially produced on 1-hourly time increments which are averaged to provided daily values. The daily averaged values are used to calculate climatologically averaged monthly values.

Where is this data derived?

The POWER solar data are inferred via radiative transfer models from satellite observations. Solar data are taken from the NASA GEWEX SRB and the FLASHFlux projects. Specific time periods associated with each project are listed in the methodology documentation.

The POWER meteorological data are taken from the most current NASA’s Global Model and Assimilation Office assimilation model. The most current model is given in the methodology documentation.

How do I access a requested file (ASCII, CSV, ICASA, GeoTIFF, NetCDF) from the API?

JSON is the default response for all data requests. Please see the 'outputs' section at the bottom of the JSON response for a link to the requested file.

What are the different ways to access the POWER data?

The POWER data can be downloaded as daily time series files or as climatologically monthly averaged values.

Who do I contact if I have a question?

Inquiries regarding the POWER data can be made at power-project@lists.nasa.gov.

Why is the elevation given for the POWER data different from the surface station values?

The POWER data, including the elevation value, represent average values over 1/2° latitude, longitude grid cells. In complex terrain, such as mountains, the averaged elevation of the grid cell can be substantially different from the local elevation of a local surface site.

Are sunshine data (sunshine hours /day; or percentage insolation) and Solar Radiation Global available in POWER?

Yes. The annual averaged global solar radiation and the monthly averaged daylight hours are available via the POWER Data Access Viewer in the Sustainable Buildings community.

Can one access/download POWER data from multiple locations without entering an individual latitude, longitude coordinate?

Contact the POWER project office at power-project@lists.nasa.gov for help in downloading data files from multiple surface sites.

Does the POWER solar insolation represent net radiation or solar radiation requiring an additional cloud term?

The POWER solar values are the downward solar radiation reaching the earth's surface for all sky conditions. The influence of clouds has been taken into account in computing the solar values. The POWER data does not provide the net radiation defined as difference between the incoming and outgoing radiation.

Are hourly data available?

Hourly data are not available at this time

Do the solar insolation values include cloudiness?

The all sky values do include cloudiness. The clear sky values are determined for various cloud 'free' conditions.

What is the accuracy of the POWER solar and/or meteorology data?

The accuracy of both the solar and meteorology data are evaluated through direct comparisons with surface site observations. Results from the comparisons are documented in the methodology documentation.

Can I get global gridded data?

Monthly and annual climatologies for most of the POWER parameters can be downloaded via the POWER Data Access Viewer (DAV) Global Downloads widget which can be access by clicking on the ball icon in the lower center portion of the DAV.

Can multi-temporal raster files be downloaded from the POWER for analysis using ArcGIS?

We recommend using the Regional API tool and exporting the data as NetCDF. Once you have the data downloaded to your computer use the “Make NetCDF Raster Layer (Multidimension)” Tool to import the data to ArcGIS. An example of the API URL to download daily data in NetCDF from a rectangular region bounded on the left upper corner at 35N x 10W and the lower right corner at 31N x 6W

Does the regional download return the average of the region rather than the average for each 0.5 x 0.5 degree grid within the specified region?

The Regional tool returns the location and the average of each 0.5 x 0.5 degree grid within the given bounding box. It does not provide a regional average.

Does POWER provide wind speed data products?

Yes. For all three User communities Daily, Interannual, and Climatologically monthly averaged wind speed data products are available at an elevation of 10 meters and 50 meters above the earth’s surface. Wind data products at 2-meter elevation are also available through the Agroclimatology community.

How can I download data from large geographical regions without entering the latitude, longitude coordinate for each half-degree grid box within the region?

The POWER region widget allows data to be downloaded from a maximum area of 4.5 x 4.5 degrees. For regions larger than this maximum you can contact the POWER team at power-project@list.nasa.gov for assistance.

When I make an HTTP API request to the services for a JSON result, how do I access the data file?

In the JSON output returned by the API request search for the file format requested (e.g. ASCII, NetCDF, ect.) and copy and paste the associated URL in a web browser to get the requested output file.

What are the terms for use of the POWER data?

Use of POWER Data: When POWER data products are used in a publication, we request the following acknowledgment be included: "These data were obtained from the NASA Langley Research Center (LaRC) POWER Project funded through the NASA Earth Science/Applied Science Program."

Reprints Please: The POWER Project kindly requests that Users of the POWER data send a reference, web link and/or a reprint of any published papers or reports or a brief description of other uses (e.g., posters, oral presentations, etc.) of the POWER data products to power-project@list.nasa.gov.

Redistribution of Data: To assist the POWER Project in providing the best service to the scientific community, we request notification if you transmit POWER data to other researchers.

Why are solar data missing from the daily products?

Solar data are typically missing because the satellite observational data are missing and irretrievable.

Are the solar minimum and maximum insulation values on a tilted surface available from the POWER data archive?

Yes. The climatologically monthly averaged maximum and minimum solar irradiances incident on equatorial facing tilted surfaces are currently available (as of 11/7/2018) through the POWER DAV and API services for a surface tilted at an angle equal to the user requested latitude ± 15-degree. See section 6.2.1 in the Methodology document for a more detailed discussion of how the POWER data compares to the old values from the old SSE web site. (https://power.larc.nasa.gov/documents/POWER_Data_v9_methodology.pdf)

Do you run webinars to introduce the tools and provide some background for beginners?

Currently there is no on line webinar, however there are online instructions describing how and where to access the POWER data parameters. For example the User Guide (https://power.larc.nasa.gov/data-access-viewer/POWER_DAV_USER_GUIDE.pdf) and the link associated with “How to Find My Parameters of interest?” on the power home page (https://power.larc.nasa.gov/)

Is it possible to get the monthly average relative humidity only during the daytime (for example from 7 or 8 am to 8 or 9 pm) from the website Power?

The short answer is no. Hourly data is not “officially” available at the POWER web site at this time. However, we can provide limited hourly surface parameters directly from MERRA-2 atmospheric reanalysis for a small set of locations and a limited time range. If a long time series or large to global regions is needed, then it is recommend that the MERRA data set be obtained from the NASA Goddard data archive and process to obtain the required data.

Is the data in Solar Irradiance for Equator Facing Tilted Surfaces suitable for a tilted panel (or surface) fixed during the day, or is it more suitable for tilted surface with vertical axis rotation (From east to west)?

The current (10/15/2018) POWER solar data incident on tilted panels is only valid for a fixed tilted surface. The SI_EF_Optimum solar insolation is only valid for fixed surfaces at the optimum tilt angle. Currently the POWER site does not provide the solar insolation for surfaces oriented East or West of the vertical axis.

Is the DNI (i.e. DNR) the same as the Optimal Solar Irradiance (i.e. SI_EF_OPTIMAL) for an Equator Facing Tilted Surface?

DNR is the solar insolation incident on a surface at a normal angle (e.g. 90-degrees). SI_EF_OPTIMAL, as well as the remainder of the solar tilt insolation values, are characterized as “All-Sky”-Insolation”. The All-Sky-Insolation = (DNR) x COS(THMT) + DIFF where THMT is the solar zenith angle and DIFF is the diffuse insolation resulting from atmospheric scattering of the solar insolation as it passes through the earth’s atmosphere. A more detailed explanation of the POWER method of estimating the various components of the solar insolation can be found in the Methodology documentation at htps://power.larc.nasa.gov/documents/POWER_Data_v8_methodology.pdf.

Is it possible to build a solar insolation schedule per the hour of the particular day?

The POWER archive does not provide hourly solar insolation, however the following comments are offered relative to the application of hourly solar data. The true hourly series is most useful for system management and analysis to assess the output of the solar system relative to the time of day. This is particularly useful if the building is connected to the grid and the utility has different charges by hour. The HOMER decision support tool (https://www.homerenergy.com/products/pro/index.html) does require hourly data for a “year” but it focuses on integrating solar, wind, and other conventional power source (i.e., diesel, propane, etc.) for off grid and on-grid systems. HOMER downloaded the old SSE monthly averaged data set and used statistical models to create hourly data for a “year”. HOMER also uses hourly typical design years. Currently, the geosynchronous data that POWER solar irradiance is derived from does not have hourly data before 2000 and thus we do not produce hourly data for the long-term series. POWER may consider adapting an hourly data set from another data source but this has not been completed. We should note that the RETScreen Expert design package (https://www.nrcan.gc.ca/energy/software-tools/7465) does use daily data and long-term monthly data for it’s data management and feasibility design packages. Thus, the current POWER data holdings are readily sufficient to support RETScreen functionality, if using RETScreen is an option for the user. Lastly, we do provide climatological averages of the 3-hourly solar irradiance by month and location. With this information a user can better understand, at least to a 3-hourly interval how the solar diurnal cycle varies on average in that location.

Overview of Parameters Available in the POWER Data Portal

The purpose of this document is to provide Users of the POWER data portal a brief reference guide on what and where specific solar and meteorological parameters can be accessed, and is intended to be a supplement to POWER Data Access Viewer (DAV) User Guide. Additionally, API documentation have been developed to facilitate the use of the various download capabilities of the new web portal, and extensive documentation on the source and validation of the various parameters can be found in the online methodology documentation.

On June 13, 2018 a new the NASA data web portal with improved solar and meteorology data and greatly enhanced capabilities to facilitate access to NASA's solar insolation and meteorological data parameters, was inaugurated. The new POWER data portal is designed to accommodate numerous User requests for more options to access and download data in multiple formats; remove several security issues in the old system; and to combine data portals from three separate User communities. In particular, the new POWER home page provides access to data previously available through separate home pages to the SSE-Renewable Energy (SSE), the Sustainable Buildings (SB), and the Agroclimatolgy (AG) communities via a single site. The new POWER data archive offers all parameters on a ½ x ½ degree global grid through a GIS-enabled Data Access Viewer (DAV), ArcGIS Image Services, and an Application Program Interface (API) service that provides data in a number of formats including CSV, ASCII, JSON, ICASA, NetCDF, and geoTIFF. The new POWER data portal provides direct access to NASA's solar insolation and meteorological data parameters customized for application to the Sustainable Buildings (SB), Agroclimatology (AG), and Renewable Energy (SSE) communities.

The solar and meteorological parameters in POWER are organized based upon the three user communities that POWER serves (Table 1); SSE-Renewable Energy (SSE), the Sustainable Buildings (SB), and the Agroclimatolgy (AG) communities. Within each community, parameters can be accessed with a temporal averaging period of Daily, Interannual, or Climatological. The daily time period can be used to download the time series of the daily averaged values of the selected parameters over the selected time period. The interannual time period can be used to download a time series of the monthly averaged value of the selected parameter for each year in a selectable time period. The climatological time period gives the monthly climatological average for each selected parameters over a climatological time period (currently set by default to July 1983 – June 2005).

For each User community and Temporal Averaging period, the parameters available in POWER are organized into parameter groups and presented in a directory tree style with the name of each folder identifying in very generic terms the parameters in each folder. Each folder in the directory structure can be expanded or collapsed by double clicking on the folder name to expose the parameters that can be selected/deselected individually by clicking on the parameter name, or selecting/deselecting all parameters in a folder by single clicking on the folder name. (Note that currently there is a limit of 20-parameters that can be downloaded at a time.)