Short-Term Deterministic Solar Irradiance Forecasting Considering a Heuristics-Based, Operational Approach

Solar energy is an economic and clean power source subject to natural variability, while energy storage might attenuate it, ultimately, effective and operationally feasible forecasting techniques for energy management are needed for better grid integration. This work presents a novel deterministic forecast method considering: irradiance pattern classification, Markov chains, fuzzy logic and an operational approach. The method developed was applied in a rolling manner for six years to a target location with no prior data to assess performance and its changes as new local data becomes available. Clearness index, diffuse fraction and irradiance hourly forecasts are analyzed on a yearly basis but also for 20 day types, and compared against smart persistence. Results show the proposed method outperforms smart persistence by ~10% for clearness index and diffuse fraction on the base case, but there are significant differences across the 20 day types analyzed, reaching up to +60% for clear days. Forecast lead time has the greatest impact in forecasting performance, which is important for any practical implementation. Seasonality in data gaps or rejected data can have a definite effect in performance assessment. A novel, comprehensive and detailed analysis framework was shown to present a better assessment of forecasters’ performance.

Estudio de las discrepancias en los tipos de cielo para análisis dinámico de la luz natural según los archivos climáticos disponibles. Caso Colombia

Para realizar un estudio de iluminación preciso es fundamental conocer los tipos de cielo predominantes de una localidad, pues estos son clave para estimar el desempeño lumínico de ambientes interiores. El objetivo de esta investigación es analizar las discrepancias en la valoración del desempeño de luz natural de espacios interiores según los archivos climáticos usados y considerando las diferencias en los tipos de cielo predominantes de acuerdo con los datos de radiación de estos. Para ello, haciendo uso del Clearness Index, de All Perez All Weather Sky Model, fueron estimados y comparados los tipos de cielo a partir de la información de radiación de archivos climáticos disponibles para trece ciudades colombianas. Adicionalmente, fueron realizadas simulaciones dinámicas de luz natural sobre ambientes hipotéticos, con diferentes archivos climáticos. Los resultados de la investigación evidencian, para cada ciudad analizada, notables diferencias en cuanto a los tipos de cielo predominantes según el archivo climático utilizado. Estas diferencias derivaron en notables discrepancias —en muchos casos, de más del 10 %— en la aplicación de métricas dinámicas haciendo uso de los archivos climáticos disponibles para cada ciudad. Si bien no es objetivo de la investigación concluir cuál de los archivos climáticos es más confiable, sí se resalta la necesidad de contar con datos de radiación confiables en los archivos climáticos, para favorecer la precisión en la valoración del desempeño lumínico de ambientes interiores a través de simulación computacional.

Relationship between photosynthetically active radiation and global radiation in Petrolina and Brasília, Brazil

ABSTRACT Photosynthetically active radiation (PAR) comprises the spectral range of global solar radiation (Rs) that is highly related to vegetation productivity. The study aimed to evaluate the relationship between PAR and Rs in Petrolina, PE, and Brasília, DF, Brazil, with data measured in 2011 and 2013 at two stations of the Sistema Nacional de Organização de Dados Ambientais located in Petrolina, PE and Brasília, DF, Brazil, and the obtained models were evaluated using the measurements of 2014. It was verified that the PAR, in instantaneous values (μmol m-2 s-1), can be estimated at 2.31 times the Rs (W m-2) measured in Petrolina, while for daily values of PAR (MJ m-2) is equal to 50% of Rs (MJ m-2). In Brasília, PAR (μmol m-2 s-1) is 2.05 times the Rs (W m-2) and, in daily values, equal to 44% of Rs (MJ m-2). The variability of the PAR/Rs ratio followed the local variations of clearness index (Kt) and Rs. The models presented an adequate performance based on statistical indices mean absolute error, mean relative error, and root mean square error and can be used to estimate PAR.

Spatial and Temporal Variation of Clearness Index in Iraq

This study deals with the spatial and temporal variation of clearness index (KT) in different meteorological stations, well distributed in Iraq, during the period between 1995 and 2015. The results indicate that the clearness index varies with the geographical location and period of the year. Monthly values of clearness index (KT) in the months of January and December show the lowest values of the index ranging between 0.38 and 0.64. Meanwhile, August shows the highest values ranging between 0.53 and 0.71. Seasonal variation of KT is well noted. The range of (0.40 to 0.58) has been measured in winter, while the range of (0.53 to 0.70) has been detected in summer season. The annual variation of KT shows a range between (0.47 - 0.64) in all stations. The standard deviation (SD) of the monthly values of KT ranged between (0.01-0.06) for all stations, while the coefficient of variation (CV) for the monthly values of KT ranged between (2-10) percent. Keywords: Clearness index, Global solar radiation, Extraterrestrial radiation, Time series, CV, SD.

Estimation of Global Solar Radiation on Horizontal Surfaces using Temperature-Based Model in Ilorin, Nigeria

In this study, the Solar Irradiation received was estimated in Illorin, Kwara, Nigeria, using the maximum and minimum temperature measured by an Arduino-based solar power parameter measuring system. The Extraterrestrial, Global and Diffuse Solar Radiation were estimated monthly using the Hargreaves and Samani model. This model also required the daily temperature, clearness index, and extraterrestrial solar irradiation in its use alongside the maximum and minimum temperatures. In using this model, we resolved the graphs of the three types of Solar Irradiation over ten days. For the selected days, the estimated extraterrestrial solar irradiation varies from 10.41kWh/m2 to 10.47 kWh/m2, while the mean extraterrestrial solar irradiation is 10.44 kWh/m2. The estimated global solar irradiation varies from 4.42 kWh/m2 to 5.677kWh/m2, while the estimated mean global solar irradiation is 5.19kWh/m2 per day. The estimated diffuse solar irradiation varies from 3.46kWh/m2 to 5.48kWh/m2, while the mean diffuse solar irradiation is per day is 4.61kWh/m2.

Study of Variability of Atmospheric Ozone over Jumla in Half Period of 24 Solar Cycle

This paper reports the variation of total ozone column (TOC) over Jumla (Lat.:-29.28° N, Long.:-82.16° E and Alt.:- 2300 m above sea level) from 2008 to 2014 derived from Total Ozone Mapping Spectrometer (TOMS) satellite observations. The monthly, seasonal, annual variations of TOC, solar insolation and clearness index have been analyzed. The result exemplifies that during the whole study period, the maximum value of monthly average TOC is 289.21 DU ± 10.75 DU in April, while the minimum value is 257.23 DU ± 11.25 DU in December. The results also show that TOC is highly seasonal dependent with larger TOC in spring 273.68 DU ± 14.92 DU and lower in the winter season (260.68 DU ± 15.25 DU). The average annual value of TOC exhibits slightly variable with a maximum in 2010 (277.52 DU ± 40.64 DU) and minimum in 2008 (267.19 DU ± 11.11 DU). The average values of solar insolation and clearness index for whole study the period are 5.10 86 kWh/m2/day ± 0.86 kWh/m2/day and 0.59 ± 0.12 respectively. The average value of TOC during the whole study period is 271.84 DU ± 14.19 DU, which indicates a good amount of stratospheric ozone content over Jumla.