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# PVGIS user 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.

### 1.1 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.

### 1.2 Input and output in PVGIS

The PVGIS user interface is shown below.

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 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 (API 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.

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.

## 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-SARAH2 Satellite 2005 2020 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-ERA5 Reanalysis 2005 2020 0.25° x 0.25° (~ 25 km) Default DB for rest of the world without coverage from satellite-based DBs PVGIS-SARAH Satellite 2005 2016 0.05° x 0.05° (~ 5 km) This operational database is not updated any more. Please, use PVGIS-SARAH2 instead.

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-SARAH2 This data set has been calculated by CM SAF to replace SARAH-1. 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-SARAH This data set was calculated by CM SAF and the PVGIS team. This data has a similar coverage than PVGIS-SARAH2.

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

• PVGIS-ERA5 This is an reanalysis product from ECMWF. Coverage is worldwide at hourly time resolution and a spatial resolution of 0.28° lat/lon.

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.

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.

### 4.1 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:

### 4.2 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.

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:

## 5. Calculation of sun-tracking PV system performance

### 5.1 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.

## 6. Calculation of off-grid PV system performance

### 6.1 Inputs for the off-grid PV calculations

PVGIS needs some information from the user to make a calculation of the PV energy production.

These inputs are described in the following:

### 5.2 Calculation outputs for the off-grid PV calculations

PVGIS calculates the off-grid PV energy production taking into account the solar radiation for every hour over a period of several years. The calculation is done in the following steps:

• For every hour calculate the solar radiation on the PV module(s) and the PV power
• If the PV power is greater than the energy consumption for that hour, store the rest of the energy in the battery.
• If the PV power is less than the energy consumption, get the missing energy from the battery.
• If the battery becomes full, calculate the energy "wasted" i.e. the PV power could be neither consumed nor stored.
• If the battery becomes empty, calculate the missing energy and add the day to the count of days on which the system ran out of energy.

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:

• Monthly average of the daily energy output as well as the daily average of the energy not captured because the battery became full
• Monthly statistics on how often be battery became full or empty during the day.
• Histogram of the battery charge statistics

These are accessed via the buttons:

The following are some explanatory notes for the off-grid results:

i) PVGIS does all the calculations hour by hour over the complete time series of solar radiation data used. For example, if you use PVGIS-SARAH2 you will be working with 15 years of data. As explained above, the PV output is estimated.for every hour from the received in-plane irradiance. This energy goes directly to the load and if there is an excess, this extra energy goes to charge the battery.

• In case the PV output for that hour is lower than the consumption, the energy missing will be taken from the battery.
• Every time (hour) that the state of charge of the battery reaches 100%, PVGIS adds one day to the count of days when the battery becomes full. This is then used to estimate the % of days when the battery becomes full.
• Similarly, when the battery state of charge reaches the cut off limit, PVGIS adds one day to the count of days when the battery becomes empty.

ii) In addition to the average values of energy not captured because of a full battery or of average energy missing, it is important to check the monthly values of Ed and E_lost_d as they inform about how the PV-battery system is working.

• Average energy production per day (Ed): energy produced by the PV system that goes to the load, not necessarily directly. It may have been stored in the battery and then used by the load. If the PV system is very big, this value is maximum the value of the load consumption.
• Average energy not captured per day (E_lost_d): Energy produced by the PV system that is lost because the load is less than the PV production. This energy cannot be stored in the battery, or if stored cannot be used by the loads as they are already covered.
• The sum of these two variables is the same even if other parameters change. The sum only depends on the PV capacity installed. For example, if the load would be 0, the total PV production will be shown as "energy not captured". Even if the battery capacity changes, and the other variables are fixed, the sum of those two parameters does not change.

iii) Other parameters

• Percentage days with full battery: the PV energy not consumed by the load goes to the battery, and it can get full
• Percentage days with empty battery: days when the battery ends empty (at the discharge limit), as the PV system produced less energy than the load
• "Average energy not captured due to full battery" indicates how much PV energy is lost because the load is covered and the battery full. It is the ratio of all the energy lost over the complete time series (E_lost_d) divided by the number of days the battery gets fully charged.
• "Average energy missing" is the energy that is missing, in the sense that the load cannot be met from either the PV or the battery. It is the ratio of the energy missing (Consumption-Ed) for all days in the time series divided by the number of days the battery gets empty i.e. reaches the set discharge limit.

iv) If the battery size is increased and the rest of the system stays the same, the average energy lost will decrease as the battery can store more energy that can be used for the loads later on. Also the average energy missing decreases. However, there will be a point at which these values increases. As the battery size increases, so more PV energy can be stored and used for the loads but there will be less days when the battery gets fully charged, increasing the value of the ratio “Average energy not captured”. Similarly, there will be, in total, less energy missing, as more can be stored, but there will be less number of days when the battery gets empty, so the average energy missing increases.

v) In order to really know how much energy is provided by the PV battery system to the loads, one can use the monthly average Ed values. Multiply each one by the number of days in the month and the number of years (remember to consider leap years!). The total shows how much energy goes to the load (directly or indirectly via the battery). The same process can be used to calculate how much energy is missing, bearing in mind that the average energy not captured and missing is calculated considering the number of days the battery gets fully charged or empty respectively, not the total number of days.

vi) While for the grid connected system we propose a default value for the system losses of 14%, we don’t offer that variable as an input for the users to modify for the estimations of the off-grid system. In this case, we use a value a performance ratio of the whole off-grid system of 0.67. This may be conservative estimation, but it is intended to include losses from the performance of the battery, the inverter and degradation of the different system components

## 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

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:

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

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.

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
• Air preassure
• Dry bulb temperature (2m temperature)
• Wind speed
• Wind direction (degrees clockwise from north)
• Relative humidity

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).