Resource mapping of solar energy An overview of available data in Norway

Transcription

1 Resource mapping of solar energy An overview of available data in Norway Report: KVT/OB/2013/R046

2

3 Content 1 Introduction Properties of solar radiation THE SOLAR RADIATION SPECTRUM 2.2 DEFINITIONS OF QUANTITIES 3 Observations of solar radiation SURFACE OBSERVATIONS Global radiation Diffuse radiation Direct radiation Radiation measurements for solar energy Sunshine duration SATELLITE 4 Existing resource mapping projects PHOTOVOLTAIC GEOGRAPHICAL INFORMATION SYSTEM (PVGIS) SATEL-LIGHT SODA - SOLAR RADIATION DATA HelioClim HelioClim NASA-SSE METEONORM SOLEMI ENMETSOL TIER IRSOLAV STRÅNG 17 5 Description of stations included in the database NETWORKS MEASURING SOLAR RADIATION IN NORWAY AND SWEDEN Bioforsk, Norway Meteorological Institute, Norway Energinettet, Norway Norwegian Radiation Protection Authority, Norway SMHI s radiation network in Sweden Fagklim, UMB, Ås Geophysical Institute, University of Bergen Norwegian University of Science and Technology (NTNU) Institute for Physics, University of Oslo Agder Photovoltaic Lab, University of Agder Norut, Narvik Norwegian Water Resources and Energy Directorate (NVE) Akershus Energi, Lillestrøm Brødrene Dahl, Larvik Jotun, Sandefjord Teknova, Kristiansand Glava Energy Center, Arvika Norwegian Meteorological Institute, METAR Akershus Energi, Lillestrøm RADIATION MEASUREMENTS STATIONS 5.3 CLOUD OBSERVATIONS 5.4 SOLAR ENERGY PRODUCTION DATA 5 5 2/55

4 5.4.2 Hedmark University College, Evenstad Production data from Swedish solar plants Summary and suggestions for future work References Appendix A List of stations A.1 BIOFORSK STATIONS A.2 METEOROLOGICAL INSTITUTE A.3 OTHER STATIONS /55

5 1 Introduction Accurate estimates of solar radiation are essential in order to give good estimates of the potential power production form a solar power plant. The solar radiation is dependent in particular on the cloud and particle climate and angle of incident varying with geographic position and time of day and time of year. This can give large differences in daily average solar radiation received over short distances. Over the latest years we have seen a large growth in the utilization of solar energy for power production in European countries (Both photovoltaic production of electricity and solar collectors for solar heat). We also see a large growth in solar energy plants installed in Sweden and Denmark, however several of the tools used to estimate the power output from such installations in Norway shows that the solar resource in Norway is quite low. This may be one of the reasons why development of solar power installations has not experienced a similar growth in Norway as in our neighboring countries. Some of the commonly used tools to estimate energy production from solar energy plants are based on a limited number of data for estimating the solar resource in Norway. In the PVGIS tool (described in Chapter 4.1) only one station of solar radiation is included for Norway. Meteonorm (a licenced software from Meteotest described in Chapter 4.4) has only got 3 stations in Norway out of a database of 1200 stations worldwide. In addition to the ground stations satellite measurements of solar radiation at the ground is available. The satellite data is found to be quite accurate in Europe. The quality of the satellite data is however reduced at higher latitudes because of a low viewing angle. In this project we will perform a screening to find and describe the solar radiation data in Norway. We aim to build up a database of such data, which will be essential for future solar resource estimates, model validation purposes, the use as reference stations and improvement of the mapping of solar resources in Norway. 4/55

6 2 Properties of solar radiation 2.1 The solar radiation spectrum The energy spectrum of the solar radiation is shown in Figure 2-1. The spectrum shows how the solar energy is distributed on different wavelengths, with a maximum in the visible part (~ nm). The yellow part of the graph is an indication of the wavelengths that are absorbed through the atmosphere. The red area represents the energy spectrum of solar radiation received at sea level. The absorption bands of the atmospheric gasses, O 2, O 3, H 2 O and CO 2 are marked. In addition to absorption by gasses, particles and aerosols also contribute to the absorption in the atmosphere. Figure 2-1 the solar radiation spectrum. The energy of the solar radiation for different wavelengths at top of atmosphere (yellow) and at sea level (red) is shown. Also shown is the blackbody spectrum for 5250 C, which represents the theoretical spectrum of emitted radiation from the sun. Image created by Robert A. Rohde / Global Warming Art. 2.2 Definitions of quantities Solar irradiance is defined as the power of solar radiation incident on a surface and is given as the power per unit area (watts per square meters, Wm -2 ). The integral of solar irradiance over a time period is solar irradiation or insolation and is measured in Jm -2 (3600 Jm -2 = 3600 Whm -2 ). The albedo is defined as the reflection coefficient and it represents the amount of incoming radiation that is reflected from the ground. The albedo is typically given as a value between 0 5/55

7 and 1 (or percentage) where 0 represents a black body which reflects no radiation, while 1 represents a reflection of all incoming solar radiation. The global irradiance on a horizontal surface on Earth consists of the direct irradiance E dir and diffuse irradiance E dif. On a tilted plane, there is another irradiance component: E ref, which is the component that is reflected from the ground: E = E dir + E dif + E ref The direct radiation is the radiation received directly from the sun, this is the main part of the radiation on a clear day. The direct radiation is directed from the sun s location on the sky. The diffuse radiation is the part of the solar radiation that has been scattered in the atmosphere before it reaches the surface. The scattering is caused by the atmospheric gas components, particles (aerosols) or clouds. The scattering of the solar radiation is typically larger at low solar angles compared to high solar angles. During cloudy days the diffuse radiation may constitute the largest part of the global radiation. The diffuse radiation is often considered to be non-directional. Measured on a horizontal plane the reflected component will be negligible, but for a tilted plane this component also must be considered. The reflected component will depend on the sun s angle, the angle of the plane, the angle of the reflecting surface and the ground albedo. 6/55

8 3 Observations of solar radiation 3.1 Surface observations The typical method to measure solar radiation is by using a thermopile detector. The detector has a black coating that absorbs the incoming radiation. This leads to a temperature rise in the detector that depends on the intensity of the radiative flux (irradiance) received by the detector. For solar energy purposes the solar panels are tilted at an angle to optimize the power production from the installation. In order to estimate the solar resource this tilting must be considered. It is therefore important to separate the solar energy into the direct and diffuse components. The direct radiation will be increased by tilting of the panel compared to horizontal surface, while the non-directional diffuse radiation received by the panel will not be modified by the tilting Global radiation Global irradiance is measured with a pyranometer. An example of a pyranometer is shown in Figure 3-1. The instrument consists of the thermopile detector which is located at the center of the two glass domes. The pyranometer needs to be mounted horizontally to measure global irradiance. The spectral response of a thermopile pyranometer is typically independent of wavelength and measures in the range ~ nm. Figure 3-1 Kipp & Zonen CMP11 pyranometer (ref Kipp & Zonen, Maintenance of the pyranometer: The instrument must be cleaned regularly to ensure the translucence of the glass dome. The leveling of the instruments must be checked regularly. Kipp and Zonen advise the user to recalibrate the instruments every two years ( 7/55

9 Other challenges with the instrument are frost or dew forming on the dome. The instruments can be equipped with extra ventilation that ensures that the air is kept above the dew-point. Snow can be another challenge in the winter months. Regular cleaning and inspection of the instruments reduces these problems. But a thorough inspection and filtering of the data is advised as part of the analysis of such data. According to ISO9060 the pyranometers are classified according to their performance giving a list of specifications that must be fulfilled. The ISO9060 compliant pyranometers are grouped in 3 classes, Second Class, First Class and Secondary Standard. Pyranometers of the Secondary Standard classification follows the highest performance criteria for a pyranometer. For solar energy purposes it is recommended to use anemometers classified at least as First Class Diffuse radiation Measurements of diffuse radiation are more challenging than global radiation measurements. The diffuse radiation is also measured by the pyranometer. But the direct radiation must be blocked out. This is typically done by using a sun-tracker. The sun tracker is a mechanical devise which is set up to follow the sun s movement across the sky during the day and during the year. The sun tracker contains a disk that is set up to block the direct solar radiation. An example of a sun tracker is shown in Figure 3-2. Figure 3-2 Kipp & Zonen SOLYS 2 sun tracker (ref Kipp & Zonen, 8/55

10 3.1.3 Direct radiation Direct radiation is measured by a pyrheliometer. The instrument contains a thermopile sensor, but the sensor has a 5 field of view with a flat window. The pyrheliometer needs to be installed on a high accuracy sun-tracker in order to always be directed towards the sun. Typical accuracy of the sun-tracker should be less than 0.5. An example of a pyrheliometer is shown in Figure 3-3. In Figure 3-2 the instrument can be seen mounted on a sun tracker. Figure 3-3 Kipp & Zonen CPH 1 Pyrheliometer (ref Kipp & Zonen, Radiation measurements for solar energy Measurements of the solar resource for a solar energy purposes is often performed by mounting a pyranometer on a tilted surface. By tilting the pyranometer it does not measure global radiation, but rather the potential energy that is available for the solar panels. With such instrumentation set up one will not separate between direct and diffuse radiation, but rather potential energy valid for the given tilting angle. With such a setup reflection from the ground and albedo effects can be an additional challenge since the ground surface becomes a larger part of the instruments viewing angle Sunshine duration Sunshine duration sensors can be used to provide the number of sunshine hours per day. Several of the meteorological stations are equipped with sunshine duration sensors. The output from the sensor separates sunny from non-sunny weather. The accuracy of such a sensor is around 10 %. An example of a sunshine duration sensor is shown in Figure 3-4. The value from this sensor is often reported as minutes of sunshine during the last 1 hour. The data from this sensor might be useful in combination with data on global radiation to model the direct and diffuse components. 9/55

11 Figure 3-4 Kipp & Zonen CSD 3 sunshine duration sensor (Kipp & Zonen, Satellite Global radiation can also be derived from satellite measurements. The Heliosat method (Cano et al, 1986) uses the visible images of the geostationary satellites to derive the surface global radiation. The Heliosat method assumes that the albedo of a cloudy atmosphere is higher than from the land surface and ocean. Based on the albedo measured by the satellite a cloud index for the given location is calculated. The cloud index is used to estimate the global radiation in time steps of minutes. The global radiation calculations are done using data from the Meteosat satellites. Two generations of this satellite have been operative. The first generation was operative until 2005 with a resolution of the satellite images of up to 2.5 x 2.5 km, the second generation Meteosat has been in operation since 2005 and has a spatial resolution up to 1 km x 1km. The resolution is highest at the equator just below the satellite location. The resolution is reduced by increasing distance from this point since the viewing angle becomes lower. The geostationary satellites are thus not the best suited to monitor areas at high latitudes, because of a low viewing angle. The uncertainty of such data does therefore increase northward. At low sun elevation it becomes difficult to distinguish between cloudy and cloud free conditions. The first generation Meteosat had a sampling rate of twice per hour, while the second generation has a sampling rate of four times per hour. Ineichen (2011) has made an intercomparison between several of the different Meteosat satellite products available for 23 ground stations in Europe between N for data covering It was shown that the global irradiance was retrieved with a negligible bias and with a standard deviation around 16 % for the best algorithm. For the beam irradiance the bias is several percent with a standard deviation of around 35%. The work of Hagen (2011) has shown that the satellite data gives a quite good estimate of the global radiation measured at several locations in Norway and Sweden. The methodology has some difficulties in distinguishing between clouds and snow cover. This contributes to an underestimation of the global radiation by the satellite. Some differences arise from the fact that the satellite does not take into consideration the horizon as viewed at the measurement site, which leads to some overestimation of the radiation by the satellite. It was shown in 10/55

12 Hagen (2011) that the satellite data on average had a positive bias compared to radiation measurements. It is not known to what extent polar orbiting satellites have been used to create similar products. The problem using polar orbiting satellites is that they pass over an area only 2 times per day, and that the area covered by the satellite at each passing may also vary. The geostationary satellites deliver a snapshot of the same area every minutes, and will thus give a reliable description of the variation in solar radiation over the day. The polar orbiting satellites are however better suited to map areas at high latitudes with a higher resolution than is available from geostationary satellites. Studies to estimate solar radiation at the ground form polar orbiting satellites have been carried out by e.g. Godøy (2012) and Liu & Liu (2012). 11/55

13 4 Existing resource mapping projects 4.1 Photovoltaic Geographical Information System (PVGIS) PVGIS is a project of the Institute for Energy and Transport of the Joint Research Centre (JRC) under of the European Commission. The project provides assessments of the solar energy resources in Europe with the aim to contribute to the implementation of solar energy. From the PVGIS web site 1 solar resource maps can be downloaded as yearly global irradiance values on horizontal and optimally inclined surfaces [kwh m -2 ]. The maps are presented for each country for a horizontal plane and for the optimal inclination ( Figure 4-1). The web page also consists of an interactive resource map (a screen dump is shown in Figure 4-2) which allows the user to extract information about the monthly and daily radiation parameters for a chosen location. An interactive estimation of the PV energy production can also be done for the chosen location using the interactive web tool. The steps that have been used to calculate the resource maps are the following: 1. Calculation of the clear sky global irradiance. Linke turbidity (Remund et al., 2003) represents the atmospheric absorption and scattering under clear skies conditions. The solar radiation at the top of the atmosphere has been integrated down to the surface representing clear sky conditions using the Linke turbidity from SoDa 2. Elevation data from a digital elevation model is used to represent local shadowing effects for low solar angles and as a correction of the Linke turbidity values at high elevations. 2. Calculation and interpolation of the clear sky index to estimate the real sky irradiance. The clear sky index represents the reduction of the total radiation on the ground by clouds. The clear sky index is calculated based on the ratio between the measured global irradiance and the computed clear sky global irradiance from met stations in Europe (ESRA database). The clear sky indices from the met stations are spatially interpolated to a map of 1km x 1km for each month. Most of the European countries are covered by a dense network of stations. From a total of 566 stations in Europe only one is located in Norway (Bergen). Sweden has 11 stations which are also used in the interpolation of clear sky indexes in Norway. See Figure 4-3 for a map of the stations used. 3. Calculations for surfaces inclined at different angles. Calculation of the energy density at different angles requires that the global radiation is divided into direct and diffuse components following empirical relations (cf. Scharmer and Greif, 2000, Kasten and Czeplak 1980, Hrvoľ 1991). The maps have been validated by comparing the interpolated maps with the measurement of radiation at the different stations (Figure 4-3). A cross-validation of the maps was performed by leaving out some of the stations in the calculation of the maps, and then to use these left-out stations for validation. The cross-validation was performed for a large number of combinations of stations to finally reach a level an uncertainty level in the maps presented. The average yearly bias (MBE) for all stations were found to be 1 Wh/m 2 (0.03%), but with higher biases for /55

14 the monthly values. The root-mean square error (RMSE) from the cross validation was found to be within the interval Wh/m 2 /day ( %). The PVGIS website ( contains a detailed description of the models and interpolation routines that are used to create the maps. The project is currently active and the site and models are regularly updated. Figure 4-1 Global irradiation and solar electricity potential for horizontally (left) and optimally inclined (right) PV modules. From PVGIS, JRC, European Community. 13/55

15 Figure 4-2 Interactive map interface to output monthly and daily radiation values from the PVGIS database and tool for estimation of energy from a PV system. Screen dump from the PVGIS web site. Figure 4-3 Map of the ESRA ground stations used for calculation of the clear sky indices and for validation of the final calculations. From PVGIS web pages. 4.2 Satel-light The Satel-Light project gives access to solar radiation data based on data from the Meteosat satellites for all over Europe up to approximately 66 N. The project was funded by the 14/55

16 European Union from 1996 until 1998, and one of the goals of the project was to provide a database with satellite images. The database consists of data covering the period with half hourly resolution. The work of Hagen (2011) shows that the satellite data gives a quite good estimate of the global radiation measured at several locations in Norway and Sweden. The project is no longer funded but the web site and database is in operation and is available at From the web site it is possible to acquire time series of satellite data for any given position. The resolution of the satellite data in the database is approximately 5 x 16 km at 60 degrees latitude. 4.3 SoDa - Solar Radiation Data The SoDa web services gives access to solar radiation data as timeseries or maps for free and for purchase from their web site ( Available data is from HelioClim1, HelioClim3, and NASA-SSE HelioClim3 The data from the HelioClim3 project for solar irradiance is given as global, direct and diffuse components on a horizontal plane, on an inclined plane or on a plane normal to the sun rays. The temporal resolution is 15 minutes. Also hourly, daily, weekly and monthly values are given. Data for the period is available without cost from the SoDa web page. Data after can be purchased through the SoDa web page. The HelioClim3 data have a spatial resolution up to 3 km x 3km and a spatial coverage as shown in Figure 4-4. Figure 4-4 Extent and spatial resolution of HelioClim3 (from SoDa, 15/55

17 The data is given as csv-files compatible with PVsyst HelioClim1 The data from HelioClim1 is given as daily, weekly and monthly values of global radiation on a horizontal plane for the period 1985 to The data has a horizontal resolution of approximately 20 km x 20 km. The data is freely available from the SoDa web page. The data coverage is the same as for HelioClim NASA-SSE Data is provided as time series of global radiation on a horizontal plane with grid cells of 1 degree x 1 degree from 1983 to Data is available worldwide. The data is available as daily values from the SoDa web page. 4.4 Meteonorm Meteonorm, provided by Meteotest, uses a synthetication method that combines satellite images and ground observations and deliver resource maps in addition to hourly and sub-hourly time series of solar radiation and other meteorological parameters with a spatial resolution down to 1km x 1km. The meteonorm database contains data from more than 8300 meteorological stations, where approximately 1200 of these stations contains measurements of solar irradiance. In Norway the database contains the solar irradiance data from Bergen, Bodø and Tromsø. In addition a number of meteorological stations without solar irradiance measurements are available. Data from Meteonorm can be purchased from their web site: Solemi Solemi can deliver hourly timeseries based on satellite data worldwide up to 66 degrees latitude. Solemi is provided by DLR (Deutsches Zentrum für Luft- und Raumfahrt - German Aerospace Center). The temporal coverage for the time series is for Europe. The data has a geographical resolution up to 2.5 x 2.5 km 2. Data after 2005 has a geographical resolution up to 1 x 1 km 2. The parameters given from Solemi are global horizontal irradiance and direct normal irradiance. A free sample of data is given from the year 2005, and can be acquired from the web page: EnMetSol From the University of Oldeburg satellite derived irradiance data are available as timeseries and maps trough the EnMetSol methodology. They use the Heliosat method by calculating the cloud indexes from the Meteosat satellite images. The final product is global horizontal, diffuse horizontal and direct normal irradiance given as time series using the satellite resolution. Data is available for purchase Tier 3Tier provide a dataset on solar radiation based on Meteosat. They use the Heliosat method, but also include daily snow cover datasets to distinguish clouds and snow cover. The data is calibrated for each satellite based on ground observations. Data is available for purchase. 16/55

18 4.8 IrSolAv IrSolAv is based on Meteosat using the Heilosat method. The cloud index is derived using the methodology developed by Dagestad and Olseth (2007) with some modifications. The clear sky conditions are identified with an algorithm by Polo et al (2009). A resource map based on IrSolAv is presented in an interactive web page on More information is available from Data is available for purchase. 4.9 STRÅNG STRÅNG is a model for solar radiation developed by SMHI (Swedish Meteorological and Hydrological Institute) based on meso scale simulations. This model produces instantaneous fields with 11 x 11 km horizontal resolution and 1 hour temporal resolution of global radiation, direct solar radiation, photosynthetically active radiation, UV radiation, and sunshine duration, covering the entire Scandinavia. Measurements of global radiation and direct solar radiation from the radiation network of SMHI have been used for tuning and validation of the model. The error when comparing hourly model data with point observations is approximately 30 % for the global and the UV irradiance, while it is about 60% for the direct irradiance and the sunshine duration, as it is stated in the STRÅNG system database. STRÅNG data is publicly available for download through the STRÅNG system database ( The data can be returned as hourly, daily, monthly or yearly time series covering the period 1999 and onward. Data prior to have a horizontal resolution of 22 x 22 km 2, instead of 11 x 11 km 2. Based on data from STRÅNG combined with information of the positioning and roof angle of every building in Stockholm, a solar energy potential map of Stockholm has been made (Figure 4-5). The map shows the incoming solar radiation on each roof of each building in the city. The map is available from 17/55

19 Figure 4-5 A screen dump of Stockholms solkarta, 18/55

20 5 Description of stations included in the database 5.1 Networks measuring solar radiation in Norway and Sweden Bioforsk, Norway A total of 47 stations in the Bioforsk network measures solar radiation today. 46 of these stations have long timeseries of global radiation (more than 10 years). Several of the stations have data back to the 1980 s. Several of the stations also measure sunshine duration. The data from Bioforsk is available from their database at A list of the stations, including measurement equipment, location and duration of measurements can be found in Appendix A. Today most of these stations are equipped with Kipp and Zonen pyranometers (CM11, ISO9060 Secondary Standard), while some stations uses Kipp and Zonen CM3 (ISO9060 Second Class) or CNR1 (ISO9060 Second Class). The sensors at these stations are not ventilated which can give condensation in the instruments during some meteorological conditions giving erroneous measurements. Routines for the operation of the stations are described by Instrumenttjenesten (ITAS) in a Technical memorandum. The pyranometer is cleaned weekly during the summer season, while monthly during the winter season. Figure 5-1 Typical setup of a Bioforsk station (From ITAS Teknisk Notat, LMT værstasjon Type 2) 19/55

21 KVT/OB/2013/R Meteorological Institute, Norway Meteorologisk Institutt has a large number of stations in their eklima database. A total of 70 of these stations are equipped with either pyranometers or sunshine duration sensors. The 70 stations from Meteorologisk Institutt include also the 47 Bioforsk stations. An overview of the location, station type and length of data from the Meteorological Institute is shown in Figure 5-2. From eklima the data is available as hourly values for the latest years, for earlier periods data is typically available every 3 hours. Several of the stations in the database from Meteorologisk Institutt also includes visibility measurements and cloud observations. Meteorologisk Institutt is also responsible for collecting METAR data which is the meteorological data used for aviation. The data is typically collected at airports, but also at other stations. Since the data is intended for aviation cloud observations are an essential part of the METAR. Solar radiation is however not included in the METAR. A total of 68 METAR stations are found in the database from Meteorologisk Institutt. Figure 5-2 The locations of the stations operated by Meteorological Institute which have global radiation or sunshine duration. The circles denote stations where global irradiance is measured; the squares denote the stations where sunshine durability is measured. The triangles denote the stations where both sunshine duration and global irradiance are measured. The colors denote the length of data at each station Energinettet, Norway This is a network of weather stations located mainly at different schools in Norway. The weather stations are operated by teachers and students. The data from a total of 32 stations 20/55

22 are collected in a database, and is available for download from The data also includes measurements of solar radiation. The instruments used are however instruments of lower quality (non ISO9060 compliant) with a different spectral response than the thermopile pyranometers, and with a cutoff at around 1100 nm Norwegian Radiation Protection Authority, Norway Norwegian Radiation Protection Authority (Statens Strålevern) operates 10 stations in Norway where they perform measurements of UV radiation in several spectral bands. Currently they have no pyranometer measurements at their stations, but they are planning to install pyranometers at 3 of the stations in the near future. Data and information from the stations are available from The contact at Statens Strålevern is Bjørn Johnsen SMHI s radiation network in Sweden Figure 5-3 shows the location of the SMHI (Swedish Meteorological and Hydrological Institute) stations measuring solar radiation in Sweden. Stations marked with yellow circles measure only sunshine duration; yellow triangles mark stations measuring sunshine duration and global radiation; yellow squares mark stations that also measure longwave radiation; the stations that also measure direct and diffuse radiation, as well as the aerosol optical depth are marked with orange circles. Stations in bold compose the main network, while the stations in grey compose the supplement network. Global radiation and sunshine duration data are available back to Data from earlier years may also be available but are most probably affected by artificial variations caused by changes in the measuring systems that occurred during the earlier years. Data from SMHI s radiation network may be purchased from SMHI. However, SMHI plans to make these data freely available through the webpage in the near future. 21/55

23 Figure 5-3 Location of the SMHI s stations measuring radiation. Stations marked with yellow circles measure only sunshine duration; while yellow triangles mark stations measuring sunshine duration and global radiation; yellow squares mark stations that also measure longwave radiation; the stations that also measure direct and diffuse radiation, as well as the aerosol optical depth are marked with orange circles. Stations in bold compose the main network, while the stations in grey compose the supplement network. From SMHI. 22/55

24 5.2 Radiation measurements stations The large networks of measurement stations in Norway or Sweden were listed in Chapter 5.1. There are however other stations as well. Some are advanced measurement stations operated by research institutes, while other stations are privately owned stations where data can be made available on request Fagklim, UMB, Ås A field station for agroclimatic studies is located at Sørås at UMB (Universitetet for Miljø- og Biovitenskap). The station includes advanced measurements of solar radiation in addition to other meteorological parameters. Global irradiance is measured at this station since 1950, while diffuse irradiance is measured since Albedo measurements have also been performed since Radiation in 5 different spectral bands has been measured since The instruments currently used are the Eppley Precision pyranometers for global, reflected, diffuse and for 3 of the spectral bands ( nm, nm and nm. The band nm (photosynthetical active radiation) is measured by a Li-Cor Quantum Sensor. UV radiation in the band nm is carried out with an Eppley Ultra-Violet Pyranometer. The instruments at this station are ventilated. The instrumentation of the station is shown in Figure 5-4. Figure 5-4 Solar radiation instrumentation at the Fagklim site at Ås (Source: UMB) Data are available as hourly average values since Earlier data is available only as daily values. Data with 10 minute frequency can also be received from this station. More information can be found at: Data requests can be made to Signe Kroken ( , signe.kroken[at]umb.no). 23/55

25 KVT/OB/2013/R046 The use of the data in publications should be referenced to Thue-Hansen V. and Grimenes A.A. Meteorologiske data for Ås, Universitetet for Miljø og Biovitenskap 1987 til Geophysical Institute, University of Bergen. At the Geophysical Institute, University of Bergen (GFI) measurements of global and diffuse radiation have been carried out at the roof top of the GFI building since In 1982 the station was also equipped with a pyrheliometer to measure the direct radiation. Sunshine duration has been measured since The data from GFI are available in hourly frequency. The raw data from the measurements have been stored for the latest years, and is available with a 20 second resolution. The instruments are calibrated on an annual basis, cleaning of the instruments are carried out frequently. The instruments are Kipp & Zonen instruments which are ventilated. The instrumentation is shown in Figure 5-5. The contact person at GFI is Jan Asle Olseth (Jan.Olseth[at]gfi.uib.no). Figure 5-5 Instrumentation for solar radiation at the GFI roof top. The left figure shows the pyrheliometers measuring direct solar irradiance. The right figure shows the instruments for diffuse and global irradiance. (Source: Jan Asle Olseth) Norwegian University of Science and Technology (NTNU) Measurements of solar radiation have been carried out at NTNU from The measurement station was located at Institute for Physics at Lade until In 2001 the station was moved to Realfagsbygget at Gløshaugen. Measurements are carried out with a horizontally mounted pyranometer for global irradiance and a pyrheliometer for measurement of the direct component of solar irradiance. The instruments used are Eppley instruments. The station is in addition equipped with a Cimel CE318 spectral band sensor measuring irradiance at wavelengths 340 nm, 380 nm, 440 nm, 500 nm, 670 nm, 870 nm, 936 nm, 1020 nm and 1640 nm; and spectral sensors measuring both direct and global radiation in the range 300 nm to 550 nm. Before the station was moved they experienced some problems with cabling for the pyrheliometer. The routines for cleaning of the instruments were not optimal before 2001, during some periods the instruments may have been covered by snow. The cleaning routines have been improved over the latest years, and cleaning is carried out every 2-3 days or at least 24/55

26 once per week. The station was equipped with a new sun tracker with higher precision in After this, the data from the pyrheliometer is considered to be of high quality. The last calibration of the pyranometer and pyrheliometer was carried out in September Later calibration of the pyranometer and pyrheliometer has not been considered since the data is only used as a support for their spectral instruments. Calibration of the data is however possible as part of post processing of the data since spectral measurements also are available from the station. We have received data dating back to 1991 from these stations. The data are raw data with 1 minute time resolution. The data from Lade is given in W/m -2, while the data from Realfagbygget is given in volts. The data must be calibrated and quality controlled before use. The contact persons at NTNU are Amund Gjerde Gjendem (amund.gjendem[at]ntnu.no) and Oddbjørn Grandum (oddbjorn.grandum[at]ntnu.no). 25/55

27 5.2.4 Institute for Physics, University of Oslo Measurements with pyranometers have been carried out for different master and PhD projects at various locations in Oslo. The measurements have been carried out for shorter time periods (maximum of 2 years) at the different locations. In some of the projects the measurements are carried out with a pyranometer placed horizontally, in other projects they have used a inclined surface. The locations have generally not been optimal for solar irradiance measurements. The instruments have been quite disturbed from surrounding vegetation and buildings, and are as such not representative for solar radiation in Oslo. For more information about the data, and to acquire the data requests can be made to Michaela G. Meir (m.g.meir[at]fys.uio.no) Agder Photovoltaic Lab, University of Agder Since December 2010 measurements of solar irradiance have been carried out on a tilted surface (39 from horizontal) facing almost South (7 East from South). Recently a horizontal sensor was also installed. They use two inclined sensors: a 2 nd -class thermopile pyranometer Kipp & Zonen CMP 3 with a response time of ~18 seconds, and an amplified, temperature-compensated silicon PV cell SolData SPC80 with an instantaneous response. Until autumn 2012, the measurements were logged every minute (as long as the irradiance was at least 30 W/m 2 ). Since then, measurements are logged not exactly every minute, but wait instead for stable irradiance. This is because the primary interest was to record good-quality current-voltage curves of the tested PV modules. Therefore, this data set is not just irradiance time series it contains I-V curve parameters of 10 PV modules. The site has had some problems with the fast sensor due to corrosion in the spring and summer of 2012, but the pyranometer data are reported to be ok. The measurement system uptime has been almost 100% in the years 2011 and 2012, but lack data from some days or parts of days in late 2013 due to computer hardware and software issues. The instruments have not been re-calibrated at the manufacturer, but in house calibration based on the self-referenced irradiance in several new PV modules has been carried out. The data from this station will be available by contacting Georgi H. Yordanov (georgi.yordanov[at]uia.no) Norut, Narvik Measurements of solar irradiance in Narvik are available from the Northern Research Institute (Norut). The station has installed PV modules from different suppliers. The PV modules are set up with a dual axis tracking system as shown in Figure 5-6. The tracking system is also equipped with a local solar irradiance sensor. The data is available with a 1 minute time resolution from June The pyranometers used are LI-COR Terrestrial Radiation Sensors, LI-200SA with a silicon photovoltaic detector. The spectral response of the LI-200 does not include the entire solar spectrum. The contact person at Norut is Øystein Kleven (oystein.kleven[at]tek.norut.no) 26/55

28 KVT/OB/2013/R046 Figure 5-6 Overview of Norut s PV system. (Source: NORUT) Norwegian Water Resources and Energy Directorate (NVE) NVE have carried out measurements of solar irradiance from automatic weather stations at Storbreen (from 2001), Midtdalsbreen ( ), Langfjordsjøkelen ( ) and Hardangerjøkulen ( ). The stations are operated by the Institute for Marine and Atmospheric research at the University of Utrecht. The stations carried out measurements of incoming and reflected solar radiation and incoming and outgoing longwave radiation. The instruments used are net radiometers from Kipp and Zonen, CNR1 (ISO9060 Second Class). The stations are inspected once per year. The analyses from these measurement campaigns are yet not finalized. Data may be made available upon request to Michiel van den Broeke or Rianne Giersen at the University of Utrecht Akershus Energi, Lillestrøm In relation to the Akershus Energipark at Lillestrøm, global irradiance data is available from two horizontally mounted pyranometers. Data is available since February 2013 every 5 seconds. Production data from the solar heat collectors are also available and can be presented e.g. as daily values in kwh. They have not yet implemented any routines for cleaning of the pyranometers. Data is available from Akershus Energi by contacting Torbjørn Kvammen (tk[at]aeas.no) 27/55

29 5.2.4 Brødrene Dahl, Larvik Brødrene Dahl has carried out measurments of global radiation at Ringdalsskogen in Larvik. Data is stored every 15 minutes. Data is available from May Cleaning routines and instruments used are unknown. Contact at Brødrene Dahl is Kåre Johansen (kare.johansen[at]dahl.no) Jotun, Sandefjord Global radiation has been carried out in Sandefjord by Jotun since The instruments have been delivered by Houm AS. Calibration and cleaning is performed once per year by IndaCo. The system is set up to log data every 10 minutes. In addition to solar radiation, temperature, precipitation, relative humidity wind speed and wind direction is also measured. The data can be made available upon request to Kjell Erik Flaten (kjell.erik.flaten[at]jotun.no) or Morten Eliassen (morten.eliassen[at]jotun.no) at Jotun Teknova, Kristiansand Teknova carries out mesurements of global end diffuse radiation on a horizontal plane in addition to pyranometer measurement on a tilted (20 degrees) plane. The site is located at the roof of Akershus Energi at Kjøita, Kristiansand. The instruments are Kipp & Zonen CMP11 and are ventilated with a CVF3. They use a Kipp & Zonen Solys2 sun tracker. The measurements started in May 2012, and are registered with a 1 minute interval. Temperature, wind speed and wind direction are also measured. The instruments are cleaned once per month. The data will not be distributed freely. For more information Anne Gerd Imenes at Teknova can be contacted (AnneGerd.Imenes[at]teknova.no) Glava Energy Center, Arvika Measurements of direct and diffuse radiation are available for Glava Energy Center, in addition to measurements of global irradiance on a horizontal plane, albedo measurements and measurements with pyranometers with 3 different inclination angles. The weather station at Glava Energy Center is also equipped with measurements of air pressure, temperture, relative humidity, precipitation, wind speed and wind direction. The instrumentation of the station is shown in Figure 5-7. Data is available with a 6 second frequency. Contact at Glava Energy Center is Magnus Nilsson (magnus.nilsson[at]aanc.se). 28/55

30 Figure 5-7 Solar radiation measurement station at Glava Energy Center. The sun tracker with pyranometer and pyheliometer is seen in the middle of the picture. The pyranometers installed with different inclination angles can be seen on the right. (Photo: Øyvind Byrkjedal) 5.3 Cloud observations Norwegian Meteorological Institute, METAR Meteorologisk Institutt is responsible for collecting METAR data which is the meteorological data used for aviation. The data is typically collected at airports, but also at other stations. Since the data is intended for aviation cloud observations are an essential part of the METAR. Solar radiation is however not included in the METAR. A total of 68 METAR stations are found in the database from Norwegian Meteorological Institute. 5.4 Solar energy production data Akershus Energi, Lillestrøm The solar plant at Lillestrøm consists of m 2 of heat collectors, which is able to deliver 7-8 MW of solar energy. The plant was opened in Production data from the solar heat collectors available and can be presented e.g. as daily values in kwh or as temperature data. Data is available from Akershus Energi by contacting Torbjørn Kvammen (tk[at]aeas.no) Hedmark University College, Evenstad The roof of one of the buildings at Hedmark University College at Evenstad has been equipped with PV panels in A total of 455 m 2 of PV cells was installed, expecting to produce 64 MWh of electricity annually. The production data from this solar plant will most likely 29/55

31 become freely available according to Thor Chrisitan Tuv at FUSen (thor-christian[at]fusen.no) who has been the project leader for this installation an behalf of Statsbygg Production data from Swedish solar plants Production data from 41 solar plants located in Sweden are publicly available through the website These plants were commissioned between 1984 and up to present. Details regarding the location, maximal power and energy production of each plant are presented. Energy production data from 2010 on may be downloaded as daily, monthly or annual values through this database. 30/55

32 6 Summary and suggestions for future work This report has given an overview of the available data for resource mapping of solar radiation that presently exists in Norway. The report discusses the existing resource mapping products and the available measurements of solar radiation. Solar irradiance data have been collected and a database with all available data has been established at Kjeller Vindteknikk. Data from a total of 68 stations measuring global irradiance has been collected in addition to several stations measuring sunshine duration. 51 of the stations measuring global solar irradiance have more than 10 years of data. Most of these measurements are performed with Secondary Standard pyranometers, which are the highest quality pyranometer class defined by ISO9060. The tools to estimate the solar resources are either based on surface observations, satellite data, meteorological models or a combination of the different sources. The data based on the geostationary Meteosat satellite have limited coverage in Norway because of a low viewing angle. The data is quite coarse and data is not available north of 66 N. Comparison of different satellite products (Ineichen, 2011) showed that the best satellite product had low biases and low standard deviation compared to ground observations at 23 stations in Europe. None of the stations used for the comparison was in Norway. Hagen (2011) compared data from Meteosat with 10 ground stations in Norway and Sweden and found that the data from Meteosat compared well for several of the stations, but that for some stations differences arise from the fact that the satellite does not take into consideration the horizon as viewed at the measurement site. The satellite data thus overestimate the irradiance for some of the sites. Two of the tools to estimate the solar resources are based on ground observations. PVGIS is solely based on ground observations (north of 58 N) of solar irradiance. South of 58 N also satellite data is used. PVGIS is based on data from only 1 station in Norway (Bergen). The data from this station is interpolated with other ground stations in Sweden and the rest of Europe to a map of the solar resources in Norway. The methodology to interpolate the clear sky index between the different stations takes topography into account, but cannot differentiate the regions of different weather regimes such as the difference between western Norway compared to eastern Norway caused by the mountain range that separates the two regions. Crossvalidation of the PVGIS product shows small biases, however the validation is performed only for 1 station in Norway. Meteonorm is a product mixing ground observations and satellite data and has a database of 1200 stations that measures global irradiance worldwide. Only 3 of these stations are located in Norway (Bergen, Bodø and Tromsø). Meteonorm uses the ground observations to adjust the satellite data, and uses an interpolation technique to represent global irradiance at stations without global irradiance measurements. For both of these products (PVGIS and Meteonorm) the interpolation of ground based solar irradiance stations in Norway gives large uncertainties due to the low number of measurement stations that has been used. However from our screening of solar radiation data in Norway, we find a total of 68 stations that measure global irradiance in Norway. 22 of these stations have more than 10 years of data. We suggest using these data for validation purposes, improving the existing tools or developing new tools better suited to estimate the solar resources in Norway in the next stages of this work. 31/55

33 The first step that should be carried out should be to use these data to validate the solar resource calculations that are carried out in the different software available (such as PVGIS, Meteonorm and others). Questions that need to be answered are: How well do these models represent the solar radiation that is observed in Norway? Are the models biased? How large are the uncertainties in the existing models? The validations should be performed by comparing the modeled values from the tools with the observed irradiance at the different sites. As part of this work it is important to carry out quality control of the observed data at each station. There will be periods with poor data that needs to be removed. The different stations should also be intercompared to check the homogeneity of the data series. Any effects from shadowing must also be considered for each station. Based on the validation for several of the ground stations in Norway one can reach conclusions regarding the biases and uncertainty levels in each of the models. Secondly, one should consider if it is necessary to develop models better suited for Norway. If the validation of the existing model shows that the uncertainties are unsatisfactorily high or that the models are biased, one needs to proceed to improve the existing models or develop better tools to calculate the solar energy resources. Several methodologies should be investigated. A possibility is to use the available ground stations by following the methodology of PVGIS. A similar tool as PVGIS could be developed for Norway, but with a far better selection of data as a basis (using 68 stations instead of 1).This work could be performed in cooperation with PVGIS in order to achieve an overall improvement of the existing model. A combination of satellite and ground based observations could also constitute an improvement compared to utilizing only the PVGIS method. The use of data from polar orbiting satellites should then be investigated. The polar orbiters deliver a high spatial resolution, while the geostationary satellites can contribute as a reference to describe the diurnal variation with minute resolution. The STRÅNG database from SMHI is developed based on mesoscale simulations. It has rather low spatial resolution, and an uncertainty that is quite high. However, combined with ground observations, this can also be used as a long term reference for stations with short time duration. Similar mesoscale model products such as STRÅNG can also be developed for Norway using higher resolution data that already exists today (Kjeller Vindteknikk has developed a mesoscale data base for Norway with 4km x 4km resolution). Cloud observations and observations of sunshine duration can also be useful to validate such models, and should be carried out as a supplement when using models as long term references. Thirdly, when one has agreed on a solar resource map with acceptable low uncertainty, one can develop mapping products directed toward the users. One example of such a mapping study is the mapping that has been performed for the roof tops in Stockholm (Figure 4-5). For solar energy purposes it is also important to describe the solar radiation at an incident angle relevant for the solar panels that will be installed. The models to carry out such calculations have not been investigated here. The distribution of the solar radiation as diffuse and direct components should be investigated. How well do the existing models describe these two components? Any errors in the energy calculations that arise from errors or biases in the separation of global energy in diffuse and direct parts will be amplified at higher latitudes compared to lower latitudes. A validation of the existing models can be performed at the stations where diffuse or direct irradiance measurements are collected. This can also be validated at the stations were tilted pyranometer measurements exists. Stations where 32/55