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PVGIS users manual

1.Introduction

This web page explains how to use the PVGIS web interface to produce calculations of solar radiation and PhotoVoltaic (PV) system energy production. We will try to show how to use PVGIS in practice. There is much more information about PVGIS available.  You can also have a look at the methods used to make the calculations or at a brief "getting starting" guide.

This manual describes PVGIS version 5.

What is PVGIS

PVGIS is a web application that allows the user to get data on solar radiation and photovoltaic (PV) system energy production, at any place in most parts of the world. It is completely free to use, with no restrictions on what the results can be used for, and with no registration necessary.

PVGIS can be used to make a number of different calculations. This manual will describe each of them. To use PVGIS you have to go through a few simple steps. Much of the information given in this manual can also be found in the Help texts of PVGIS.

Input and output in PVGIS

The PVGIS user interface is shown below.

 PVGIS interface
PVGIS interface when you first access the web application, before doing anything.

©PVGIS © European Communities, 2001-2017

Most of the tools in PVGIS require some input from the user, this is handled as normal web forms, where the user clicks on options or enters information, such as for example the size of a PV system.

Before entering the data for the calculation the user must select a geographical location for which to make the calculation. This is done by:

  • By clicking on the map, perhaps also using the zoom option.
  • By entering an address in the "address" field below the map
  • By entering latitude and longitude in the fields below the map. Latitude and longitude can be input in the format DD:MM:SSA where DD is the degrees, MM the arc-minutes, SS the arc-seconds and A the hemisphere (N, S, E, W). Latitude and longitude can also be input as decimal values, so for instance 45°15'N should be input as 45.25. Latitudes south of the equator are input as negative values, north are positive. Longitudes west of the 0° meridian should be given as negative values, eastern values are positive.

PVGIS allows the user to get the results in a number of different ways:

  • As number and graphs shown in the web browser. All graphs can also be saved to file.
  • As information in text (CSV) format. The output formats are described separatelly in the "Tools" section.
  • As a PDF document, available after the user has clicked to show the results in the browser.
  • Using the non-interactive PVGIS web services. These are described further in the "Tools" section.

2. Using horizon information

The calculation of solar radiation and/or PV performance in PVGIS can use information about the local horizon to estimate the effects of shadows from nearby hills or mountains. The user has a number of choices for this option, which are shown to the right of the map in the PVGIS tool.

Options for the horizon information in PVGIS
Options for the horizon information in PVGIS

©PVGIS © European Communities, 2001-2017


The user has three choices for the horizon information:

  1. Do not use the horizon information for the calculations. This is the choice when the user unselects both the "calculated horizon" and the "upload horizon file" options.
  2. Use the PVGIS built-in horizon information. To choose this, select "Calculated horizon" in the PVGIS tool. This is the default option.
  3. Upload your own information about the horizon height. The horizon file to be uploaded to our web site should be a simple text file, such as you can create using a text editor (such as Notepad for Windows), or by exporting a spreadsheet as comma-separated values (.csv). The file name must have the extensions '.txt' or '.csv'. In the file there should be one number per line, with each number representing the horizon height in degrees in a certain compass direction around the point of interest. The horizon heights in the file should be given in a clockwise direction starting at North; that is, from North, going to East, South, West, and back to North. The values are assumed to represent equal angular distance around the horizon. For instance, if you have 36 values in the file, PVGIS assumes that the first point is due north, the next is 10 degrees east of north, and so on, until the last point, 10 degrees west of north. An example file can be found here. In this case, there are only 12 numbers in the file, corresponding to a horizon height for every 30 degrees around the horizon.

Most of the PVGIS tools (except the hourly radiation time series) will display a graph of the horizon together with the results of the calculation. The graph is shown as a polar plot with the horizon height in a circle. The next figure shows an example of the horizon plot. A fisheye camera picture of the same location is shown for comparison.

Horizon graph in PVGIS; fisheye camera picture of the same location.
Left: an example of the horizon graph in PVGIS. Right: fisheye camera picture of the same location.

© PVGIS © European Communities, 2001-2017

3. Choice of solar radiation database

The solar radiation databases (DBs) available in PVGIS are:

Database Type Start Year End Year

Spatial  res.

Comments
PVGIS-SARAH Satellite 2005 2016

0.05° x 0.05° (~ 5 km)

  Default DB for Europe, Asia, Africa and South America (below 20 S)
PVGIS-NSRDB Satellite 2005 2015

0.038° x 0.0.38° (~ 4 km)

  Default DB for the Americas (above 20 S)
PVGIS-CMSAF Satellite 2007 2016

0.025° x 0.025° (~ 2.5 km)

  This operational database is not produced any more. Please, use PVGIS-SARAH instead.
PVGIS-ERA5

 Reanalysis

2005 2016 0.25° x 0.25° (~ 25 km)   Default DB for Europe above 60 N
PVGIS-COSMO

 Reanalysis

2005 2015

0.055° x 0.055° (~ 5 km)

  Alternative to ERA5 (high-resolution regional reanalysis over Europe)

All databases provide hourly solar radiation estimates.

Most of the solar radiation data used by PVGIS have been calculated from satellite images. There exist a number of different methods to do this, based on which satellites are used. The choices that are available in PVGIS at present are:

  • PVGIS-SARAH This data set has been calculated by CM SAF and the PVGIS team. This data cover Europe, Africa, most of Asia, and parts of South America.
  • PVGIS-NSRDB This data set has been provided by the National Renewable Energy Laboratory (NREL) and is part of the National Solar Radiation Database.
  • PVGIS-CMSAF This data set has been calculated by the CM SAF collaboration for the area covering Europe and Africa, as well as parts of South America. The data cover the period 2007-2016.

Some areas are not covered by the satellite data, this is especially the case for high-latitude areas. We have therefore introduced two additional solar radiation databases for Europe, which include northern latitudes:

  • PVGIS-ERA5 This is the new reanalysis product from ECMWF. Coverage is worldwide at hourly time resolution and a spatial resolution of 0.28° lat/lon. At the moment, in PVGIS we are making this database available for Europe.
  • PVGIS-COSMO COSMO-REA6 is a regional reanalysis product, covering Europe at hourly time resolution and a spatial resolution of about 6km (we use 3' lat/lon in PVGIS). The original data set is available here

More information about the reanalysis-based solar radiation data is available.

For each calculation option in the web interface, PVGIS will present the user with a choice of the databases that cover the location chosen by the user.

The figure below shows the areas covered by each of the solar radiation databases.

 Geographical extent of solar radiation data sets
Geographical extent of the solar radiation data sets in PVGIS

©PVGIS © European Communities, 2001-2017

Based on the different validation studies performed the databases recommended for each location are the following:

These databases are the ones used by default when the raddatabase parameter is not provided in the non-interactive tools. These are also the databases used in the TMY tool.

4. Calculation of grid-connected PV system performance

Photovoltaic (PV) systems convert the energy of sunlight into electric energy. Although PV modules produce direct current (DC) electricity, often the modules are connected to an Inverter which converts the electricity into AC, which can then be used locally or sent to the electricity grid. This type of PV system is called grid-connected PV. The calculation of the energy production assumes that all the energy that is not used locally can be sent to the grid.

Inputs for the PV system calculations

PVGIS needs some information from the user to make a calculation of the PV energy production. These inputs are described in the following:

Input fields for the grid-connected PV system calculation
Input fields for the grid-connected PV system calculation

©PVGIS © European Communities, 2001-2017

PV Technology

The performance of PV modules depends on the temperature and on the solar irradiance, but the exact dependence varies between different types of PV modules. At the moment we can estimate the losses due to temperature and irradiance effects for the following types of modules: crystalline silicon cells; thin film modules made from CIS or CIGS and thin film modules made from Cadmium Telluride (CdTe).

For other technologies (especially various amorphous technologies), this correction cannot be calculated here. If you choose one of the first three options here the calculation of performance will take into account the temperature dependence of the performance of the chosen technology. If you choose the other option (other/unknown), the calculation will assume a loss of 8% of power due to temperature effects (a generic value which has found to be reasonable for temperate climates).

PV power output also depends on the spectrum of the solar radiation. PVGIS can calculate how the variations of the spectrum of sunlight affects the overall energy production from a PV system. At the moment this calculation can be done for crystalline silicon and CdTe modules. Note that this calculation is not yet available when using the NSRDB solar radiation database.

Installed peak power

This is the power that the manufacturer declares that the PV array can produce under standard test conditions, which are a constant 1000W of solar irradiation per square meter in the plane of the array, at an array temperature of 25°C. The peak power should be entered in kilowatt-peak (kWp). If you do not know the declared peak power of your modules but instead know the area of the modules and the declared conversion efficiency (in percent), you can calculate the peak power as power = area * efficiency / 100. See more explanation in the FAQ.

System loss

The estimated system losses are all the losses in the system, which cause the power actually delivered to the electricity grid to be lower than the power produced by the PV modules. There are several causes for this loss, such as losses in cables, power inverters, dirt (sometimes snow) on the modules and so on. Over the years the modules also tend to lose a bit of their power, so the average yearly output over the lifetime of the system will be a few percent lower than the output in the first years.

We have given a default value of 14% for the overall losses. If you have a good idea that your value will be different (maybe due to a really high-efficiency inverter) you may reduce this value a little.

Mounting position

For fixed (non-tracking) systems, the way the modules are mounted will have an influence on the temperature of the module, which in turn affects the efficiency. Experiments have shown that if the movement of air behind the modules is restricted, the modules can get considerably hotter (up to 15°C at 1000W/m2 of sunlight).

In PVGIS there are two possibilities: free-standing, meaning that the modules are mounted on a rack with air flowing freely behind the modules; and building- integrated, which means that the modules are completely built into the structure of the wall or roof of a building, with no air movement behind the modules.

Some types of mounting are in between these two extremes, for instance if the modules are mounted on a roof with curved roof tiles, allowing air to move behind the modules. In such cases, the performance will be somewhere between the results of the two calculations that are possible here.

Slope of PV modules

This is the angle of the PV modules from the horizontal plane, for a fixed (non-tracking) mounting.

For some applications the slope and azimuth angles will already be known, for instance if the PV modules are to be built into an existing roof. However, if you have the possibility to choose the slope and/or azimuth, PVGIS can also calculate for you the optimal values for slope and azimuth (assuming fixed angles for the entire year).

Slope of PV modules

Azimuth (orientation) of PV modules

The azimuth, or orientation, is the angle of the PV modules relative to the direction due South. - 90° is East, 0° is South and 90° is West.

For some applications the slope and azimuth angles will already be known, for instance if the PV modules are to be built into an existing roof. However, if you have the possibility to choose the slope and/or azimuth, PVGIS can also calculate for you the optimal values for slope and azimuth (assuming fixed angles for the entire year).

Azimuth (orientation) of PV modules

Optimizing slope (and maybe azimuth)

If you click to choose this option, PVGIS will calculate the slope of the PV modules that gives the highest energy output for the whole year. PVGIS can also calculate the optimum azimuth if desired. These options assume that the slope and azimuth angles stay fixed for the entire year.

PV electricity cost calculation

For fixed-mounting PV systems connected to the grid PVGIS can calculate the cost of the electricity generated by the PV system. The calculation is based on a "Levelized Cost of Energy" method, similar to the way a fixed-rate mortgage is calculated. You need to input a few bits of information to make the calculation:

  • The total cost of buying and installing the PV system, in your currency. If you entered 5kWp as the system size, the cost should be for a system of that size.
  • The interest rate, in % per year, this is assumed to be constant throughout the lifetime of the PV system.
  • The expected lifetime of the PV system, in years.

The calculation assumes that there will be a fixed cost per year for maintenance of the PV system (such as replacement of components that break down), equal to 2% of the original cost of the system.


Calculation outputs for the PV grid-connected system calculation

The outputs of the calculation consist of annual average values of energy production and in-plane solar irradiation, as well as graphs of the monthly values. 

Calculation outputs for fixed-mounted grid-connected PV system
Calculation outputs for fixed-mounted grid-connected PV system. Left: table with annual summary. Right: graph of PV energy output by month.

©PVGIS © European Communities, 2001-2017

In addition to the annual average PV output and the average irradiation, PVGIS also reports the year-to-year variability in the PV output, as the standard deviation of the yearly values over the period with solar radiation data in the chosen solar radiation database. You also get an overview of the different losses in the PV output caused by various effects.

When you make the calculation the visible graph is the PV output. If you let the mouse pointer hover above the graph you can see the monthly values as numbers. You can switch between the graphs clicking on the buttons: 

Graphs have a download button in the top right corner. In addition, you can download a PDF document with all the information shown in the calculation output.

5. Calculation of sun-tracking PV system performance

Inputs for the tracking PV calculations

The second "tab" of PVGIS 5 lets the user make calculations of the energy production from various types of sun-tracking PV systems. Sun-tracking PV systems have the PV modules mounted on supports that move the modules during the day so the modules face in the direction of the sun. The systems are presumed to be grid-connected, so the PV energy production is independent of local energy consumption. 

Input fields for the tracking PV system calculation
Input fields for the tracking PV system calculation

©PVGIS © European Communities, 2001-2017

Installed peak power

This is the power that the manufacturer declares that the PV array can produce under standard test conditions, which are a constant 1000W of solar irradiation per square meter in the plane of the array, at an array temperature of 25°C. The peak power should be entered in watt-peak (Wp). Note the difference from the grid-connected and tracking PV calculations where this value is assumed to be in kWp. If you do not know the declared peak power of your modules but instead know the area of the modules and the declared conversion efficiency (in percent), you can calculate the peak power as power = area * efficiency / 100. See more explanation in the FAQ.

Battery capacity

This is the size, or energy capacity, of the battery used in the off-grid system, measured in watt-hours (Wh). If instead you know the battery voltage (say, 12V) and the battery capacity in Ah, the energy capacity can be calculated as Energy capacity=voltage*capacity.

The capacity should be the nominal capacity from fully charged to fully discharged, even if the system is set up to disconnect the battery before fully discharged (see next option).

Discharge cutoff limit

Batteries, especially Lead-acid batteries, degrade quickly if they are allowed to completely discharge too often. Therefore a cutoff is normally imposed, so that the battery charge cannot go below a certain percentage of full charge. This should be entered here. The default value is 40%.

Consumption per day

This is the energy consumption of all the electrical equipment connected to the system during a 24 hour period. PVGIS assumes that this daily consumption is distributed in a way over the hours of the day, corresponding to a typical home use with most of the consumption during the evening. The hourly fraction of consumption assumed by PVGIS is found here.

Upload consumption data

If you know that the consumption profile is different from the one assumed by PVGIS you have the option of uploading your own. The hourly consumption information in the uploaded file should consist of 24 hourly values, each on its own line. The values in the file should be the fraction of the daily consumption that takes place in each hour, with the sum of the numbers equal to 1. The daily consumption profile should be defined for the standard local time, without consideration of daylight saving offsets if relevant to the location. The format is the same as the default consumption file.

Calculation outputs for the off-grid PV calculations

As for the other PV calculation tools in PVGIS, the outputs for the off-grid PV tool consist of annual statistical values and graphs of monthly system performance values.

There are three different monthly graphs,

accessible via the buttons: 

  • A graph showing the monthly average of the daily energy output as well as the daily average of the energy not captured because the battery became full
  • A graph of monthly statistics on how often be battery became full or empty during the day.
  • A histogram of the battery charge state

7. Monthly average solar radiation data

This tab allows the user to visualize and download monthly average data for solar radiation and temperature over a multiyear period.

Input options in the monthly radiation tab

Input fields for the monthly solar radiation tab
Input fields for the monthly solar radiation tab

© PVGIS © European Communities, 2001-2017

The user should first choose the start and end year for the output. Then there are a number of options to choose which data to calculate:

Global horizontal irradiation

This value is the monthly sum of the solar radiation energy that hits one square meter of a horizontal plane, measured in kWh/m2.

Direct normal irradiation

This value is the monthly sum of the solar radiation energy that hits one square meter of a plane always facing in the direction of the sun, measured in kWh/m2, including only the radiation arriving directly from the disc of the sun.

Global irradiation, optimal angle

This value is the monthly sum of the solar radiation energy that hits one square meter of a plane facing in the direction of the equator, at the inclination angle that gives the highest annual irradiation, measured in kWh/m2.

Global irradiation, selected angle

This value is the monthly sum of the solar radiation energy that hits one square meter of a plane facing in the direction of the equator, at the inclination angle chosen by the user, measured in kWh/m2.

Ratio of diffuse to global radiation

A large fraction of the radiation arriving at the ground does not come directly from the sun but as a result of scattering from the air (the blue sky) clouds and haze. This is known as diffuse radiation.This number gives the fraction of the total radiation arriving at the ground which is due to diffuse radiation.

Monthly radiation output

The results of the monthly radiation calculations are shown only as graphs, although the tabulated values can be downloaded in CSV or PDF format.

There are up to three different graphs which are shown by clicking on the buttons: 

The user may request several different solar radiation options. These will all be shown in the same graph. The user can hide one or more curves in the graph by clicking on the legends.

8. Daily radiation profile data

This tool lets the user see and download the average daily profile of solar radiation and air temperature for a given month. The profile shows how the solar radiation (or temperature) changes from hour to hour on average.

Input options in the daily radiation profile tab

Input fields for the daily solar radiation tab
Input fields for the daily solar radiation tab

© PVGIS © European Communities, 2001-2017

The user must choose a month to display. For the web service version of this tool it is also possible to get all 12 months with one command.

The output of the daily profile calculation is 24 hourly values. These can either be shown as a function of time in UTC time or as time in the local time zone. Note that local daylight saving time is NOT taken into account.

The data that can be shown falls into three categories:

  • Irradiance on fixed plane With this option you get the global, direct, and diffuse irradiance profiles for solar radiation on a fixed plane, with slope and azimuth chosen by the user. Optionally you can also see the profile of the clear-sky irradiance (a theoretical value for the irradiance in the absence of clouds).
  • Irradiance on sun-tracking plane With this option you get the global, direct, and diffuse irradiance profiles for solar radiation on a plane that always faces in the direction of the sun (equivalent to the two-axis option in the tracking PV calculations). Optionally you can also see the profile of the clear-sky irradiance (a theoretical value for the irradiance in the absence of clouds).
  • Temperature This option gives you the monthly average of the air temperature for each hour during the day.
Output of the daily radiation profile tab

As for the monthly radiation tab, the user can only see the output as graphs, though the tables of the values can be downloaded in CSV or PDF format.

The user chooses between the three

graphs by clicking on the relevant buttons:

9. Hourly solar radiation and PV data

The solar radiation data used by PVGIS consists of one value for every hour over a multi-year period. This tool gives the user access to the full contents of the solar radiation database. In addition, the user can also request a calculation of PV energy output for each hour during the chosen period.

Input options in the hourly radiation and PV power tab

There are several similarities to the Calculation of grid-connected PV system performance as well as the tracking PV system performance tools. In the hourly tool it is possible to choose between a fixed plane and one tracking plane system. For the fixed plane or the single-axis tracking the slope must be given by the user or the optimized slope angle must be chosen.

Input fields for the hourly solar radiation tab
Input fields for the hourly solar radiation tab

©PVGIS © European Communities, 2001-2017

Apart from the mounting type and information about the angles, the user must choose the first and last year for the hourly data.

By default the output consists of the global in-plane irradiance. However, there are two other options for the data output:

  • PV power With this option, also the power of a PV system with the chosen type of tracking will be calculated. In this case, information about the PV system must be given, just as for the grid-connected PV calculation.
  • Radiation components If this option is chosen, also the direct, diffuse and ground-reflected parts of the solar radiation will be output.

These two options can be chosen together or separately.

Output for the hourly radiation and PV power tab

Unlike the other tools in PVGIS, for the hourly data there is only the option of downloading the data in CSV format. This is due to the large amount of data (up to 10 years of hourly values), that would make it difficult and time consuming to show the data as graphs. The format of the output file is described here.

10. Typical Meteorological Year (TMY) data

This option allows the user to download a data set containing a Typical Meteorological Year (TMY) of data. The data set contains hourly data of the following variables:

  • Date and time
  • Global horizontal irradiance
  • Direct normal irradiance
  • Diffuse horizontal irradiance
  • Air preassure
  • Dry bulb temperature (2m temperature)
  • Wind speed
  • Wind direction (degrees clockwise from north)
  • Relative humidity
  • Long-wave downwelling infrared radiation

The data set has been produced by choosing for each month the most "typical" month out of 10 years of data. The variables used to select the typical month are global horizontal irradiance, air temperature, and relative humidity.

Input options in the TMY tab

The TMY tool has only one option, which is the time period that should be used to calculate the TMY. At the moment there will be only a few choices, as the time period with data is typically not much more than the 10 years needed to construct the TMY.

Output options in the TMY tab

It is possible to show one of the fields of the TMY as a graph, by choosing the appropriate field in the drop-down menu and clicking on "View".

There are two different output formats available: a generic CSV format, and a format suitable for the EnergyPlus software for building energy performance calculations. This format is technically also CSV but is known as EPW format (file extension .epw).

More information about the output data format is found here.