scholarly journals Evaluating solar radiation forecast uncertainty

2018 ◽  
Author(s):  
Minttu Tuononen ◽  
Ewan J. O'Connor ◽  
Victoria A. Sinclair
Keyword(s):  
Solar Radiation ◽  
Cloud Cover ◽  
Spatial Scales ◽  
Forecast Error ◽  
Surface Radiation ◽  
Cloud Base ◽  
Strong Impact ◽  
Positive Bias ◽  
Radiative Balance ◽  
Clear Sky

Abstract. The presence of clouds, and their characteristics, has a strong impact on the radiative balance of the Earth and on the amount of solar radiation reaching the Earth's surface. Many applications require accurate forecasts of surface radiation on weather timescales, for example, solar energy and UV radiation forecasts. Here we investigate how operational forecasts of low and mid-level clouds affect the accuracy of solar radiation forecasts. Four years of cloud and solar radiation observations from one site – Helsinki, Finland, are analysed. Cloud observations are obtained from a ceilometer and therefore, we first develop algorithms to reliably detect cloud base, precipitation and fog. These new algorithms are widely applicable for both operational use and research, such as in-cloud icing detection for the wind energy industry and for aviation. The cloud and radiation observations are compared to forecasts from the Integrated Forecast System (IFS) run operationally and developed by the European Centre for Medium-Range Weather Forecasts (ECMWF). We develop methods to evaluate the skill of the cloud and radiation forecasts. These methods can potentially be extended to hundreds of sites globally. Over Helsinki, the measured Global Horizontal Irradiance (GHI) is strongly influenced by its northerly location and the annual variation in cloudiness. Solar radiation forecast error is therefore larger in summer than in winter, but the relative error in the solar radiation forecast is more or less constant throughout the year. The mean overall bias in the GHI forecast is positive (8 W m−2). The observed and forecast distributions in cloud cover, at the spatial scales we are considering, are strongly skewed towards clear-sky and overcast situations. Cloud cover forecasts show more skill in winter when the cloud cover is predominantly overcast; in summer there are more clear-sky and broken cloud situations. A negative bias was found in forecast GHI for correctly forecast clear-sky cases and a positive bias in correctly forecast overcast cases. Temporal averaging improved the cloud cover forecast and hence decreased the solar radiation forecast error, but made little impact on the overall bias. The positive bias seen in overcast situations occurs when the model cloud has low values of liquid water path (LWP). We attribute this bias to the model having LWP values that are too low or that the model optical properties for clouds with low LWP are incorrect.

scholarly journals Evaluating solar radiation forecast uncertainty

2019 ◽  
Vol 19 (3) ◽  
pp. 1985-2000 ◽  
Author(s):  
Minttu Tuononen ◽  
Ewan J. O'Connor ◽  
Victoria A. Sinclair
Keyword(s):  
Solar Radiation ◽  
Cloud Cover ◽  
Spatial Scales ◽  
Forecast Error ◽  
Surface Radiation ◽  
Cloud Base ◽  
Strong Impact ◽  
Positive Bias ◽  
Radiative Balance ◽  
Clear Sky

Abstract. The presence of clouds and their characteristics have a strong impact on the radiative balance of the Earth and on the amount of solar radiation reaching the Earth's surface. Many applications require accurate forecasts of surface radiation on weather timescales, for example solar energy and UV radiation forecasts. Here we investigate how operational forecasts of low and mid-level clouds affect the accuracy of solar radiation forecasts. A total of 4 years of cloud and solar radiation observations from one site in Helsinki, Finland, are analysed. Cloud observations are obtained from a ceilometer and therefore we first develop algorithms to reliably detect cloud base, precipitation, and fog. These new algorithms are widely applicable for both operational use and research, such as in-cloud icing detection for the wind energy industry and for aviation. The cloud and radiation observations are compared to forecasts from the Integrated Forecast System (IFS) run operationally and developed by the European Centre for Medium-Range Weather Forecasts (ECMWF). We develop methods to evaluate the skill of the cloud and radiation forecasts. These methods can potentially be extended to hundreds of sites globally. Over Helsinki, the measured global horizontal irradiance (GHI) is strongly influenced by its northerly location and the annual variation in cloudiness. Solar radiation forecast error is therefore larger in summer than in winter, but the relative error in the solar radiation forecast is more or less constant throughout the year. The mean overall bias in the GHI forecast is positive (8 W m−2). The observed and forecast distributions in cloud cover, at the spatial scales we are considering, are strongly skewed towards clear-sky and overcast situations. Cloud cover forecasts show more skill in winter when the cloud cover is predominantly overcast; in summer there are more clear-sky and broken cloud situations. A negative bias was found in forecast GHI for correctly forecast clear-sky cases and a positive bias in correctly forecast overcast cases. Temporal averaging improved the cloud cover forecast and hence decreased the solar radiation forecast error. The positive bias seen in overcast situations occurs when the model cloud has low values of liquid water path (LWP). We attribute this bias to the model having LWP values that are too low or the model optical properties for clouds with low LWP being incorrect.

scholarly journals Variabilidade Espacial da Radiação Solar na Região de Manaus - AM durante o Experimento GOAmazon 2014/15 (Spatial variability of solar radiation in Manaus-AM region during GOAmazon Experiment 2014/15)

2017 ◽  
Vol 10 (6) ◽  
pp. 1802
Author(s):  
Alice Dos Santos Macedo ◽  
Gilberto Fisch
Keyword(s):  
Solar Radiation ◽  
Spatial Variability ◽  
Rural Areas ◽  
Cloud Cover ◽  
Global Solar Radiation ◽  
Horizontal Gradient ◽  
Strong Impact ◽  
Wet Season ◽  
E 600 ◽  
The City

Este trabalho realizou um estudo da variabilidade espacial em 2014 da irradiância solar na região de Manaus-AM, através de dados observacionais, inserido no Projeto GOAmazon 2014/15. Também, como forma complementar, foi realizada a análise da cobertura de nuvens, chuva e aerossóis e suas interrelações com a irradiância solar. Como resultado, observa-se que os menores valores médios da irradiância solar ocorreram na área urbana,o que é justificado, em parte pela urbanização que altera os fluxos envolvidos, diminuindo a irradiância solar à superfície. Os valores típicos são entre 400 e 600 Wm-2na estação chuvosa (fevereiro/março) com um desvio padrão de 200 e 380 Wm-2e entre 650 e 800 Wm-2na estação seca (agosto-setembro) com desvio padrão de 190 e 300 Wm-2. A B S T R A C T   The solar radiation is an important climatic element in the Amazon region, as it has a strong  impact for ecological (by the preservation of the biodiversity) and technological (as a renewable energy) areas. Consequently, this study contributes for these themes, conducting an observational study of the spatial variability of the solar irradiance for Manaus-AM area, with data collected during the project GOAmazon 2014/15. The cloud cover and rainfall and their relationships with solar radiation were also analysed. The maximum values observed for the wet season (february and march) are in the range 450 and 600 Wm-2 with high standart deviation (300 - 350 Wm-2 ), while they are in the range from 650 and 800 Wm-2  during the dry period (august - september) with lower standart deviation (200 - 300 Wm-2).  These values are directly associated with cloud cover and rainfall. In general, the urban area (Manaus city) showed the low values of solar radiation at the surface compared with its neighborhood, inducing a horizontal gradient of clouds/rainfall and solar energy between the city and the semi rural areas.  Keywords: piranometer, global solar radiation, cloud cover, total sky imager

Terrestrial Solar Radiation

2017 ◽  
pp. 191-293
Keyword(s):  
Solar Radiation ◽  
Horizontal Plane ◽  
Cloud Cover ◽  
Weather Conditions ◽  
Clear Sky ◽  
Solar Tracking ◽  
Sky Conditions ◽  
The Impact ◽  
Estimation Models

After shading a light on the extraterrestrial solar radiation in the chapter 3 it is important to evaluate the global terrestrial solar radiation and its components. The information on terrestrial solar radiation is required in several different forms depending on the kinds of calculations and kind of application that are to be done. Of course, terrestrial solar radiation on the horizontal plane depends on the different weather conditions such as cloud cover, relative humidity, and ambient temperature. Therefore, the impact of the atmosphere on solar radiation should be considered. One of the most important points of terrestrial solar radiation evaluation is its determination during clear sky conditions. Therefore, in this chapter, the equations that determine the air mass basing on available theories are given and the clear sky conditions are introduced with shading a light on the previous work in identifying clear sky conditions. Taking into consideration that, clear sky solar radiation estimation is of great importance for solar tracking, a detailed review of main available models is given in this chapter. As daily, monthly, seasonally, biannually and yearly mean daily solar radiations are required information for designing and installing long term tracking systems, different available methods are commented regarding their applicability for the estimation of solar radiation information in the desired format from the data that are available. An important accent is paid also on the assessment and comparison of monthly mean daily solar radiation estimation models.

scholarly journals Measuring Cloud Cover and Brightness Temperature with a Ground-Based Thermal Infrared Camera

2008 ◽  
Vol 47 (2) ◽  
pp. 683-693 ◽  
Author(s):  
Stephen Smith ◽  
Ralf Toumi
Keyword(s):  
Brightness Temperature ◽  
Cloud Cover ◽  
Infrared Camera ◽  
Thermal Infrared ◽  
Cloud Base ◽  
Clear Sky ◽  
Brightness Temperatures ◽  
External Data ◽  
Infrared Cameras ◽  
Two Parameters

Abstract Thermal infrared cameras can be used to monitor clouds and the sky at high spatial and temporal resolutions. In particular, this study shows that, without the need for any external data, cloud cover can be retrieved both day and night over a field of view extending to zenith angles of ∼80°. Zenith clear sky temperatures are estimated for cloud cover up to 80%. During periods of 50% cloud cover or more the cloud-base brightness temperatures (CBBTs) can be calculated to an accuracy of ±1 K. These calculations are made possible by using a new parameterization for the variation of sky brightness temperature with zenith angle. Both clear and cloudy conditions are found to follow this simple empirical equation more closely than the widely used parameterization of Unsworth and Monteith. A simple, angle-dependent threshold system based on cloud transmittance can then be used to retrieve cloud cover, and clear sky temperature and CBBT are calculated using the two parameters resulting from the fitting process.

scholarly journals Clouds over Hyytiälä, Finland: an algorithm to classify clouds based on solar radiation and cloud base height measurements

2020 ◽  
Author(s):  
Ilona Ylivinkka ◽  
Santeri Kaupinmäki ◽  
Meri Virman ◽  
Maija Peltola ◽  
Ditte Taipale ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Global Radiation ◽  
Simple Algorithm ◽  
Cloud Base ◽  
Aerosol Formation ◽  
Detection Range ◽  
Clear Sky ◽  
Overall Performance ◽  
Sky Conditions ◽  
Cloud Base Height

Abstract. We developed a simple algorithm to classify clouds based on global radiation and cloud base height measured by pyranometer and ceilometer, respectively. We separated clouds into seven different classes (stratus, stratocumulus, cumulus, nimbostratus, altocumulus+altostratus, cirrus+cirrocumulus+cirrostratus and clear sky+cirrus). We also included classes for cumulus and cirrus clouds causing global radiation enhancement, and classified multilayered clouds, when captured by the ceilometer, based on their height and characteristics (transparency, patchiness and uniformity). The overall performance of the algorithm was nearly 70 % when compared with classification by an observer using total sky images. The performance was best for clouds having well-distinguishable effects on solar radiation: nimbostratus clouds were classified correctly in 100 % of the cases. The worst performance corresponds to cirriform clouds (50 %). Although the overall performance of the algorithm was good, it is likely to miss the occurrence of high and multilayered clouds. This is due to the technical limits of the instrumentation: the vertical detection range of the ceilometer and occultation of the laser pulse by the lowest cloud layer. We examined the use of brightness parameter, which is defined as a ratio between measured global radiation and modeled radiation at the top of the atmosphere, as an indicator of clear sky conditions. Our results show that cumulus, altocumulus, altostratus and cirriform clouds can be present when the parameter indicates clear sky conditions. Those conditions have previously been associated with enhanced aerosol formation under clear sky. This is an important finding especially in case of low clouds coupled to the surface which can influence aerosol population via aerosol-cloud interactions. Overall, caution is required when the parameter is used in the analysis of processes affected by partitioning of radiation by clouds.

scholarly journals Decadal variations in estimated surface solar radiation over Switzerland since the late 19th century

2012 ◽  
Vol 12 (18) ◽  
pp. 8635-8644 ◽  
Author(s):  
A. Sanchez-Lorenzo ◽  
M. Wild
Keyword(s):  
Solar Radiation ◽  
20Th Century ◽  
Cloud Cover ◽  
Decadal Variability ◽  
Sunshine Duration ◽  
Strong Increase ◽  
Surface Solar Radiation ◽  
Clear Sky ◽  
Decadal Variations ◽  
The 1950S

Abstract. Our knowledge on trends in surface solar radiation (SSR) involves uncertainties due to the scarcity of long-term time series of SSR, especially with records before the second half of the 20th century. Here we study the trends of all-sky SSR from 1885 to 2010 in Switzerland, which have been estimated using a homogenous dataset of sunshine duration series. This variable is shown to be a useful proxy data of all-sky SSR, which can help to solve some of the current open issues in the dimming/brightening phenomenon. All-sky SSR has been fairly stable with little variations in the first half of the 20th century, unlike the second half of the 20th century that is characterized also in Switzerland by a dimming from the 1950s to the 1980s and a subsequent brightening. Cloud cover changes seem to explain the major part of the decadal variability observed in all-sky SSR, at least from 1885 to the 1970s; at this point, a discrepancy in the sign of the trend is visible in the all-sky SSR and cloud cover series from the 1970s to the present. Finally, an attempt to estimate SSR series for clear-sky conditions, based also on sunshine duration records since the 1930s, has been made for the first time. The mean clear-sky SSR series shows no relevant changes between the 1930s to the 1950s, then a decrease, smaller than the observed in the all-sky SSR, from the 1960s to 1970s, and ends with a strong increase from the 1980s up to the present. During the three decades from 1981 to 2010 the estimated clear-sky SSR trends reported in this study are in line with previous findings over Switzerland based on direct radiative flux measurements. Moreover, the signal of the El Chichón and Pinatubo volcanic eruption visible in the estimated clear-sky SSR records further demonstrates the potential to infer aerosol-induced radiation changes from sunshine duration observations.

scholarly journals Cloudiness Information Services for Solar Energy Management in West Africa

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 857
Author(s):  
Derrick Kwadwo Danso ◽  
Sandrine Anquetin ◽  
Arona Diedhiou ◽  
Rabani Adamou
Keyword(s):  
Solar Radiation ◽  
Solar Energy ◽  
West Africa ◽  
Cloud Cover ◽  
Shortwave Radiation ◽  
Surface Solar Radiation ◽  
Clear Sky ◽  
Incoming Solar Radiation ◽  
Sahel Region ◽  
Sky Conditions

In West Africa (WA), interest in solar energy development has risen in recent years with many planned and ongoing projects currently in the region. However, a major drawback to this development in the region is the intense cloud cover that reduces the incoming solar radiation when present and causes fluctuations in solar power production. Therefore, understanding the occurrence of clouds and their link to the surface solar radiation in the region is important for making plans to manage future solar energy production. In this study, we use the state-of-the-art European Centre for Medium-range Weather Forecasts ReAnalysis (ERA5) dataset to examine the occurrence and persistence of cloudy and clear-sky conditions in the region. Then, we investigate the effects of cloud cover on the quantity and variability of the incoming solar radiation. The cloud shortwave radiation attenuation (CRASW↓) is used to quantify the amount of incoming solar radiation that is lost due to clouds. The results showed that the attenuation of incoming solar radiation is stronger in all months over the southern part of WA near the Guinea Coast. Across the whole region, the maximum attenuation occurs in August, with a mean CRASW↓ of about 55% over southern WA and between 20% and 35% in the Sahelian region. Southern WA is characterized by a higher occurrence of persistent cloudy conditions, while the Sahel region and northern WA are associated with frequent clear-sky conditions. Nonetheless, continuous periods with extremely low surface solar radiation were found to be few over the whole region. The analysis also showed that the surface solar radiation received from November to April only varies marginally from one year to the other. However, there is a higher uncertainty during the core of the monsoon season (June to October) with regard to the quantity of incoming solar radiation. The results obtained show the need for robust management plans to ensure the long-term success of solar energy projects in the region.

scholarly journals A Novel Approach for the Short-Term Forecast of the Effective Cloud Albedo

2018 ◽  
Author(s):  
Isabel Urbich ◽  
Jörg Bendix ◽  
Richard Müller
Keyword(s):  
Solar Radiation ◽  
Optical Flow ◽  
Spatial Scales ◽  
Surface Radiation ◽  
Estimation Methods ◽  
Short Term ◽  
Short Term Forecast ◽  
Cloud Albedo ◽  
Optical Flow Method ◽  
Term Forecast

The increasing use of renewable energies as a source of electricity has led to a fundamental transition of the power supply system. The integration of fluctuating weather-dependent energy sources into the grid already has a major impact on the load flows of the grid. As a result, the interest in forecasting wind and solar radiation with a sufficient accuracy over short time horizons grew. In this study the short-term forecast of the effective cloud albedo based on optical flow estimation methods are investigated. The optical flow method utilized here is TV-L1 from the open source library OpenCV. This method uses a multi-scale-approach to capture cloud motions on various spatial scales. After the clouds are displaced the solar surface radiation will be calculated with SPECMAGIC NOW which computes the global irradiation spectrally resolved from satellite imagery. Due to a high temporal and spatial resolution of satellite measurements the effective cloud albedo and thus solar radiation can be forecasted from 5 minutes up to 4 hours with a resolution of 0.05°. In the following there will be a brief description of the method for the short-term forecast of the effective cloud albedo. Subsequently evaluation results will be presented and discussed. Finally an outlook of further developments will be given.

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