Solar potential map – does the installation of photovoltaic modules make sense?

The installation of photovoltaic modules has been especially popular in recent years. The common use of this type of energy generation is mainly influenced by the idea of saving money by using renewable energies, which is also supported by subsidies, e. g. from the “My Energy” programme. Solar radiation can be converted into electrical energy or used for water heating. However, the optimal use of photovoltaic modules requires a sufficient amount of solar energy, and unfortunately the location of the house and the weather conditions might not be conducive to energy generation. The answer to these doubts is a solar potential map.

Fundamentals of solar potential mapping

The solar potential map was created by geodesy engineers and enables to check the amount of energy that can be extracted from the roof surfaces. It is based on the Digital Surface Model (DSM) and meteorological data, including insolation analyses. Digital Surface Model is a point-by-point representation of the land surface with objects that occur on that area, i.e. buildings, trees and other infrastructure elements. DSM is created by LIDAR laser scanning (Light Detection and Ranging) during Airborne Laser Scanning (ALS). LIDAR transmits the laser light to the target and measures its reflection. The spot at which the beam bounced off the object is the point. The scanned object is represented by a cloud of points with specific coordinates, which can be further edited and modelled. Poland is fully covered with ALS data of varying point densities – from 4 points/m2 in rural areas to 20 points/m2 in urban areas.

PICTURE 1. WARSAW CENTER – CLOUD OF POINTS

source: mapy.geoportal.gov.pl

In addition to the Digital Surface Model, meteorological data, including insolation and shadow analyses, are required to create a map of solar potential. Although the data on solar insolation dates back several years, they do not include all the relevant information affecting the efficiency of the use of photovoltaic modules. However, an important information for mapping solar potential is sunshine duration and insolation.

Sunshine duration is the time in which radiation coming directly from the solar disk enters a certain place in a certain period. In Poland, the annual solar radiation is between 1 390 and 1 900 hours (source: PVGIS). Insolation is the amount of solar energy that falls on a certain surface at a certain time. In Poland, the average insolation is between 1 100 and 1 300 kWh/m2/year (source: PVGIS).

In addition, variable angles of incidence of the sun’s rays (solar motion), scattering of light through the atmosphere, inclination of roof surfaces, building structures, adjacent objects and vegetation, statistical weather conditions and altitude above sea level can be taken into account for the calculation.

Solar potential map in Poland

The insolation of the roofs was generated with the use of above data and Digital Surface Model. The data prepared in this way are displayed on the solar potential map, which can be found on the city Geographics Information System. In Poland, this map was created for several cities, such as Warsaw, Wroclaw, Poznan, Katowice and Bydgoszcz. It contains aggregated data on the amount of energy falling on individual roof areas, eg. on an annual or monthly basis.

The solar potential map of Wroclaw, for example, shows radiation data with regard to:

• Direct Horizontal Irradiation (IDH), i.e. the proportion of radiation that has reached the Earth’s surface and passed through the atmosphere without interacting with its components such as clouds, aerosols, etc.
• Scattered Horizontal Irradiation (ISH), i.e. the amount of radiation scattered (changed direction) by contact with atmospheric components.
• Total Horizontal Irradiation (ITH), i.e. the sum of direct and scattered irradiation.

PICTURE 2. SOLAR POTENTIAL MAP OF WROCLAW

source: gis.um.wroc.pl

The solar potential map for Poznan was created in a 3D model and also contains information on the average total solar radiation for the roof area.

PICTURE 3. SOLAR POTENTIAL MAP OF POZNAN

source: http://sip.poznan.pl/model3d/#/legend

Solar potential in the world

Renewable energy sources are playing an increasingly important role in environmental protection. Their use is not only financially profitable, but also makes it easier to move away from conventional energy sources such as coal, wood or natural gas. To promote this idea, the Photovoltaic Geographical Information System (PVGIS) was developed, covering all of Europe and Africa, as well as parts of Asia and America. Among other things, this system allows the verification of the power generation potential of different photovoltaic technologies, as well as the average monthly and daily solar radiation and temperature.

Because the solar potential maps in Poland are created by using the Digital Surface Model, they contain ready-made information about the amount of energy that can be stored on roof surface. In PVGIS, the user determines whether the panels are placed on the ground or on the roof, enters data such as the inclination of the panels and the azimuth, and the system calculates the amount of solar energy.

Summary

The solar potential map shows how different the solar radiation is on roof surfaces and provides information on whether it is worthwhile to install photovoltaic modules on the roof or not. Since the maps are publicly available, everyone has the opportunity to see how much electricity may be generated from a photovoltaic system. If the radiation on the roof is very low, it should be considered whether the energy from the sun is enough to heat at least the water or not. It is possible that the location of the building and the roof construction are not favourable and that the panels will only have a decorative function.

Daria Łaskowska
Maintenance and Development SpecialistCentrum AMRON