Direct Normal Solar Irradiance Research Articles

Generation of synthetic solar datasets for risk analysis

In this paper, we present a method for the synthetic generation of long-term time series of coupled 1-min global horizontal solar irradiance (GHI) and direct normal solar irradiance (DNI). This method requires an input of 10–15 annual time series of hourly DNI and GHI values that can be retrieved from satellite-based irradiance databases, and produces 100 years of 1-min solar radiation values that can be used for risk analysis or as input for solar plants performance simulation in a wide range of scenarios.The method consists of the conjunction of three steps. The first one, based on a stochastic procedure, is used to generate 100 years of monthly DNI and GHI values. The second step consists of the subsequent generation of daily irradiation values. To that end we have used a bootstrapping technique. The synthetic daily sequences have the same serial correlation structure as the observed data. The last step consists of the generation of 100 years of 1-min solar irradiance data out of the daily values based on the non-dimensionalization of the daily profiles by the clear sky envelope approach. The method has been applied for the location of Seville showing satisfactory results in terms of cumulative distribution functions (CDFs) of the synthetic data. We obtain an average monthly KSI (Kolmogorov-Smirnov test integral) index of 0.11 kWh/m2 for GHI and 0.26 kWh/m2 for DNI. The minimum KSI value is 0.07 kWh/m2 for GHI and 0.15 kWh/m2 for DNI obtained in January. The maximum KSI value is 0.19 kWh/m2 for GHI and 0.34 kWh/m2 for DNI obtained in June and August respectively.

The Precision Solar Spectroradiometer (PSR) for direct solar irradiance measurements

A precision solar spectroradiometer (PSR) has been designed for high precision and accurate measurements of direct normal spectral solar irradiance in the wavelength range 300–1000 nm. Each PSR is radiometrically characterised and calibrated in the optical laboratory of PMOD/WRC. The calibration is traceable to SI through the primary spectral irradiance standard of the Physikalisch-Technische Bundesansalt (PTB), in Braunschweig, Germany. The expanded relative uncertainty for spectral solar irradiance measurements in the 350–1000 nm range is between 1.7% and 2.0%, with larger uncertainties below 400 nm which are mainly caused by the low signal levels and the uncertainties due to the straylight correction. A solar extraterrestrial spectrum was retrieved from solar measurements using the Langley-technique at a high altitude observatory and was found to be in excellent agreement with a literature solar spectrum (mean ratio 0.998±0.019). On two clear sky days solar measurements from 3 PSR and one independently calibrated spectroradiometer deployed during the International Pyrheliometer Comparison agreed to within their combined expanded uncertainties of 3%. Aerosol optical depth retrieved from the same solar measurements of the three PSR showed median differences with respect to the World reference for AOD between −0.010 and +0.014 at the center wavelengths 368 nm, 412 nm, 500 nm, and 862 nm. The instrument has a second auxiliary port for connecting different entrance optics for near coincident measurements such as global solar irradiance.

Thermodynamic analysis of a combined cooling, heating and power system based on solar thermal biomass gasification☆

The objectives of this paper are to propose a novel combined cooling heating and power (CCHP) system based on solar thermal biomass gasification, and to present thermodynamic analyses to effectively improve the utilization of distributed renewable energy sources. By adopting the Engineering Equation Solver software, the thermodynamic models of components were constructed, and the simulation procedures, mainly including the heat transfer of the solar cavity receiver and the biomass gasification, were presented. Based on a 100 kW electricity capacity, the design parameters of the CCHP system were obtained to simulate and discuss the thermodynamic performances and the energy and exergy flow diagrams in the cooling and heating operation modes. The influences of the key variable parameters, including the electric load ratio and the solar direct normal irradiance in the off-design work conditions on the thermodynamic performances, were analyzed and discussed. The simulation results indicate that the CCHP system achieves average energy and exergy efficiencies of 56% and 28%, respectively, and the energy ratio of solar to biomass is approximately 0.19 in the full load operating mode. Compared to the conventional biomass gasification CCHP system without solar energy, the increasing ratio of heating value of product gas based on the solar thermal biomass gasification reaches 55.09%, and the biomass saving ratios are approximately 9.22% and 2.02% in the cooling and heating modes respectively, which indicate that the proposed hybrid system is an effective and feasible method to improve the utilization efficiency of biomass energy.

Stochastic optimal dispatch of integrating concentrating solar power plants with wind farms

Power systems face many challenges since the large-scale application of uncertain renewable energy. Concentrating solar power (CSP) plants with thermal energy storage (TES) can make solar energy a schedulable resource without increasing system uncertainty. Therefore, we consider manage uncertainty locally to integrate CSP plants with wind farms, reduce the uncertainty of output, and improve overall regulation efficiency and reliability. First, based on the energy transfer process between the modules of the CSP plant, we establish a CSP plant model in detail. And then considering the influence of solar direct normal irradiance (DNI) and wind power uncertainty on the dispatching operation, a stochastic optimal dispatch model is established. At last, the validity of the model is verified through an example. The analysis shows the advantages of combining CSP plants and wind farms, in addition to this, the influence of different confidence levels of chance constrained programming (CCP) on the entire system economy and spinning reserve capacity is also well illustrated.

Hybrid-CSP in India: Technological and Economic Aspects

India has an enormous potential for employing concentrated solar power (CSP) technology for energy generation. A great advantage of CSP is that it can be conveniently installed in parallel with existing fossil fuel power plants to deliver a synergetic setup, which will enable us to increase the efficiency of the existing plants without making major changes in the plant setup and machinery. India has not yet utilised this resource to its full capacity. This paper discusses the status of CSP in India and the possible ways in which we can hybridize it with the existing coal plants in Uttar Pradesh (A state of the India) by simulating and optimizing different CSP technology and their economic feasibility. In this various hybrid, CSP technologies linked with different energy resources are discussed in detail. Further, the methodology of the system and different factors and aspects of the technology are discussed, that affect the performance and efficiency of the system. Policies by the government also play a major role in the development of the solar technology in a country, without the support of the government it is very difficult for public and private sector companies to venture in this field of technology, as the initial investment is eminent. Jawaharlal Nehru National Solar Mission (JNNSM), its policies, and how it has exerted a major influence in renewable, especially the solar sector in India in the past decade has been established. The various environment conditions like solar direct normal irradiance, wind-speed, land availability and economic factors like fixed cost expenses, inflation have been considered and areas suitable for CSP technology has been identified.

Evaluation of the performance of different models for predicting direct normal solar irradiance

Evaluation of the performance of different models for predicting direct normal solar irradiance

Performance analysis of a CPV/T-DC integrated system adopted for the energy requirements of a supermarket

In this paper, a model that analyses the coupling of a concentrating photovoltaic and thermal (CPV/T) system with a desiccant cooling (DC) system used to satisfy the energy loads required by a supermarket, is presented. A detailed analysis of the supermarket electrical and thermal loads is conducted in different periods of the year: summer, winter and half seasons. A CPV/T system linear focus configuration is considered, and its sizing as a function of the solar Direct Normal Irradiance (DNI) is realized for each period of the year. Hence, an Artificial Neural Network (ANN) is used to model carefully the DNI adopting experimental data in the simulation process. The coupling between the CPV/T and DC systems allows to obtain energy and economic savings during the year compared with a conventional solution, considering accurately in the modelling: supermarket energy loads, solar radiation, environmental conditions, etc. In particular, the analysis of three case studies is performed, where the main aim has been to size the CPV/T-DC integrated system and to study how it can match the different supermarket energy needs. The three solutions are analyzed from an energetic and economic point of view in order to demonstrate the effectiveness of the solution proposed.

Developing off-design model of Yazd integrated solar combined cycle for analyzing environmental benefits of using solar energy instead of supplementary firing

An integrated solar combined cycle (ISCC) is analyzed at off-design operating conditions. Using the principles of thermodynamics heat and mass transfer a computer code is developed in FORTRAN programming language to simulate the system’s hourly performance under steady state conditions. Three scenarios are considered for the study. In the first one, only the combined cycle (CC) is studied. In the second scenario, two solar heat exchangers are added to the system (ISCC) to produce some extra steam fed to the steam turbine for more power production. In the third one, as that of the ISCC scenario, a supplementary firing is used instead of solar heat exchangers to produce the same power. The main performance parameters are calculated for the hourly variation of solar direct normal irradiation intensity (DNI) and ambient air temperature for analyzing environmental benefits of using solar energy instead of supplementary firing. Results show that the contribution of solar energy in the annual produced power by the ISCC scenario is 75.14 GWh, which is 2.1% of the whole. In addition, it is found that using solar energy leads to an annual reduction of 36.13 Kton in the produced CO2 and an annual fuel saving of 3.76 ton.

Thermal Performance Analysis of an Absorption Cooling System Based on Parabolic Trough Solar Collectors

Solar radiation intensity significantly influences the cooling loads of building, and the two are correlated and accorded to a certain extent. This study proposes a double effect LiBr–H2O absorption cooling system based on the parabolic trough collector (PTC) of solar heat energy. Thermodynamic models including PTC and absorption chiller are constructed, and their accuracy is verified by comparing the simulation results and the experimental data. Subsequently, the impact of variable design parameters on the thermodynamic performance is analyzed and discussed. The analysis of a solar cooling system in a hotel case study is related to its operation in a typical day, the average coefficient of performance of the absorption chiller is approximately 1.195, and the whole solar cooling system achieves 61.98% solar energy utilization efficiency. Furthermore, the performance comparison of a solar cooling system in different types of building indicates that higher matching and a higher correlation coefficient between the transient solar direct normal irradiance and cooling load is helpful in decreasing the heat loss and improving systemic performance. The solar cooling system in the office building exhibits a correlation coefficient of approximately 0.81 and achieves 69.47% systemic thermal efficiency.

Probabilistic assessment of concentrated solar power plants yield: The EVA methodology

Understanding the long-term temporal variability of solar resource is fundamental in any assessment of solar energy potential. The variability of the solar resource (as shown by historical solar data) plays a significant role in the statistical description of the future performance of a solar power plant, thus influencing its financing conditions. In particular, solar-power financing is mainly based on a statistical quantification of the solar resource. In this work, a methodology for generating meteorological years representative of a given annual probability of exceedance of solar irradiation is presented, which can be used as input in risk assessment for securing competitive financing for Concentrating Solar Thermal Power (CSTP) projects. This methodology, which has been named EVA, is based on the variability and seasonality of monthly Direct Normal solar Irradiation (DNI) values and uses as boundary condition the annual DNI value representative for a given probability of exceedance. The results are validated against a 34-year series of net energy yield calculated at hourly intervals from measured solar irradiance data and meteorological, and they are also supplemented with the analysis of uncertainty associated to the probabilities of exceedance estimates. Relations between DNI and CSTP energy yields at different time scales are also analyzed and discussed.

Comparison of potential control strategies for an impinging receiver based dish-Brayton system when the solar irradiation exceeds its design value

Potential control strategies for an impinging receiver based dish-Brayton system have been presented for protecting the key components from the risks of overheating when the solar irradiation exceeds its design value. Two of them are selected for a detailed study: changing the effective diameter of the shading device and changing the inlet temperature. A rope-pulley shading device is developed for controlling the shading area in the center of the dish, and the change of the inlet temperature is achieved by applying a bypass at the cold side of the recuperator for reducing the heat transfer rate. Both control strategies can manage the peak temperature on the absorber surface within 1030 °C with an outlet temperature fluctuation between −4.1 and 15.1 °C, so that the impinging receiver can work for long time at any solar direct normal irradiance value. Furthermore, the temperature differences on the absorber surface are between 137.1 °C and 163.8 °C. The cases that are achieved by changing the shield effective diameter are significantly lower (11–26 °C) than the corresponding cases that are achieved by changing the inlet temperature.

Clustering of solar energy facilities using a hybrid fuzzy c-means algorithm initialized by metaheuristics

Abandoned areas with substances potentially harmful to the environment or human health have raised numerous concerns around the world. The objective of the present study is to analyze the possibility of building solar power plants capable of capturing solar energy in unproductive areas, both contaminated and uncontaminated. For this purpose, American data from the National Solar Radiation Database (NSRDB) were used, a collection of hourly solar radiation measurements and meteorological data, as well as data from the RE-Powering America's Land project, run by the United States Environmental Protection Agency (EPA). In the analysis, the information about “mapped area”, “distances to the transmission lines”, “solar direct normal irradiance on a utility scale” and “off-grid direct normal irradiance” were considered. To define the best locations, the data were initially pre-processed. A new hybrid fuzzy c-means (HFCM) algorithm was then applied, initialized, comparatively, by three metaheuristics: Differential Evolution (DE), Genetic Algorithm (GA) and Particle Swarm Optimization (PSO), for the data clustering. The number of clusters obtained was validated by three metrics: Calinski-Harabasz Criterion, Davies-Bouldin Criterion and Silhouette Coefficient, with all three unanimously indicating two clusters as the ideal number: one cluster for locations with greater potential for allocating facilities to capture solar energy, and another for locations with a lower potential. With the new approach, an increase of 23.3% in the training velocity of the HFCM algorithm was identified, which required fewer iterations to achieve the same value of the objective function. Else, a round of experiments was conducted with six different datasets (instances from literature) and the results showed that the proposed method can achieve better results (faster convergence and smaller solution cost) than the classic FCM. Visually, the predominance of the allocation of facilities was perceived in states with a greater average incidence of solar radiation. Therefore, this was the predominant factor in the convergence of the algorithm, which is in accordance with expectations for solar energy. Finally, the social, economic and environmental gains were considered with the revitalization of unproductive land with the possibility of implementing solar power plants in these areas.

Methodology to synthetically downscale DNI time series from 1-h to 1-min temporal resolution with geographic flexibility

In this paper, we present two methods for the synthetic generation of 1-min Direct Normal solar Irradiance (DNI) data from hourly means that can be applied globally without any local adaptation, which are based in the modelling of the stochastic component of DNI, and in the normalization of the daily profiles. The similitude between measured and generated DNI distributions has been evaluated through the Kolmogorov-Smirnov test Integral (KSI), and its performance on the thermal power produced by a parabolic trough (PT) plant has been assessed using the daily normalized root mean square deviations (NRMSD) with respect to site measurements. The generation methods provide, for an annual 1-min synthetic data set, KSI values of ∼3.3 W/m2 and ∼12.9 W/m2 (depending on the generation method used), and daily NRMSD of ∼0.9% and ∼3.4%, respectively. Sites selected for validating these methods are located at different climates and latitudes, suggesting their global applicability.

Effects of geometrical parameters of a dish concentrator on the optical performance of a cavity receiver in a solar dish-Stirling system

Dish-Stirling concentrated solar power (DS-CSP) system is a complex system for solar energy-thermal-electric conversion. The dish concentrator and cavity receiver are optical devices for collecting the solar energy in DS-CSP system; to determine the geometric parameters of dish concentrator is one of the important steps for design and development of DS-CSP system, because it directly affects the optical performance of the cavity receiver. In this paper, the effects of the geometric parameters of a dish concentrator including aperture radius, focal length, unfilled radius, and fan-shaped unfilled angle on optical performance (ie, optical efficiency and flux distribution) of a cavity receiver were studied. Furthermore, the influence of the receiver-window radius of the cavity receiver and solar direct normal irradiance is also investigated. The cavity receiver is a novel structure that is equipped with a reflecting cone at bottom of the cavity to increases the optical efficiency of the cavity receiver. Moreover, a 2-dimensional ray-tracking program is developed to simulate the sunlight transmission path in DS-CSP system, for helping understanding the effects mechanism of above parameters on optical performance of the cavity receiver. The analysis indicates that the optical efficiency of the cavity receiver with and without the reflecting cone is 89.88% and 85.70%, respectively, and former significantly increased 4.18% for 38 kW XEM-Dish system. The uniformity factor of the flux distribution on the absorber surface decreases with the decreases of the rim angle of the dish concentrator, but the optical efficiency of the cavity receiver increases with the decreases of the rim angle and the increase amplitude becomes smaller and smaller when the rim angle range from 30° to 75°, So the optical efficiency and uniformity factor are conflicting performance index. Moreover, the unfilled radius has small effect on the optical efficiency, while the fan-shaped unfilled angle and direct normal irradiance both not affect the optical efficiency. In addition, reducing the receiver-window radius can improve the optical efficiency, but the effect is limited. This work could provide reference for design and optimization of the dish concentrator and establishing the foundation for further research on optical-to-thermal energy conversion.

Effect of Tracking Error of Double-Axis Tracking Device on the Optical Performance of Solar Dish Concentrator

In this paper, a flux distribution model of the focal plane in dish concentrator system has been established based on ray tracking method. This model was adopted for researching the influence of the mirror slope error, solar direct normal irradiance, and tracking error of elevation-azimuth tracking device (EATD) on the focal spot characteristics (i.e., flux distribution, geometrical shape, centroid position, and intercept factor). The tracking error transmission law of the EATD transferred to dish concentrator was also studied. The results show that the azimuth tracking error of the concentrator decreases with the increase of the concentrator elevation angle and it decreases to 0 mrad when the elevation angle is 90°. The centroid position of focal spot along x-axis and y-axis has linear relationship with azimuth and elevation tracking error of EATD, respectively, which could be used to evaluate and calibrate the tracking error of the dish concentrator. Finally, the transmission law of the EATD azimuth tracking error in solar heliostats is analyzed, and a dish concentrator using a spin-elevation tracking device is proposed, which can reduce the effect of spin tracking error on the dish concentrator. This work could provide fundamental for manufacturing precision allocation of tracking devices and developing a new type of tracking device.

Performance analyses of Cu–Cl hydrogen production integrated solar parabolic trough collector system under Algerian climate

The potential of hydrogen production by thermochemical cycle in Algeria using solar radiation as heat sources is estimated under the climate conditions of the country. The study analyzes an integrated copper–chlorine (Cu–Cl) thermochemical cycle with solar parabolic trough system for hydrogen production. In order to determine the most promising solar sites available for deploying the integrated system, the direct normal solar irradiance (DNI) for horizontal tracking system oriented in North-South has been estimated and compared for different locations. Heat gain from parabolic trough collector model is evaluated under Algerian conditions. To describe the different steps of the Cu–Cl cycle for hydrogen production, we perform a thermodynamic analysis accounting for relevant chemical reactions and including the determination of the energy necessary to the cycle. A parametric study is conducted to investigate the effect of heat gain from the parabolic trough collector (PTC) on the hydrogen production rate. Furthermore, the rate production of hydrogen by the Cu–Cl cycle is analyzed and compared for performance improvement of the system for different climatic regions in Algeria. Simulation results reveal great opportunities of hydrogen production using Cu–Cl cycle combined with solar PTC in the south of Algeria with annual hydrogen production exceeds 84 Tons H2/year (around 0,30 kg/m2/day).

Analysis on the long-term relationship between DNI and CSP yield production for different technologies

Abstract Ground measured hourly data from the Solar Radiation Monitoring Laboratory of the University of Oregon over 34 years have enabled a detailed analysis of the relations between direct normal solar irradiance (DNI) and energy yield from concentrating solar thermal power (CSP) generation systems. Six different plant configurations have been selected for simulating the energy yields with System Advisor Model (SAM), based on different parabolic through and central receiver CSP and linear Fresnel commercial plants. The long-term yield energy of each CSP reference plant has been estimated by two different approaches: by modeling a typical DNI year estimated by the Sandia procedure for computing typical meteorological years, or by applying the Sandia methodology directly on the 34 years of hourly gross energy output resulting from multi-year modeling with SAM of the 34 years of meteorological input. Important differences are observed on the typical yield year resulting from each methodology. This work presents thus a complete analysis on how the statistical long-term characteristics of solar resource input might represent the statistical characteristics of long-term yield energy.

Dynamic Paths: Towards high frequency direct normal irradiance forecasts

Direct normal solar irradiance (DNI) series of high-frequency time resolution permit an accurate modeling and analysis of transient processes in concentrating solar thermal power (CSTP) technologies. Numerical weather prediction (NWP) models provide an overall understanding of solar forecasting, but they are unlikely to cover a local statistical representativeness of the DNI high frequency dynamics. On the contrary, local statistical information derived from site measurements can provide statistical behavior, but may not necessarily yield an explicit model for all of the physical relationships involved. In this work, we propose a novel locally-adapted procedure for high-frequency DNI forecasting that connects these two extremes, proposing a hybrid approach in which low frequency (3-h) NWP outcomes act as boundary conditions (assuring a physical consistency with site climatic behavior) and are supplemented with Dynamic Paths of local high frequency (1-min) DNI series (assuring a statistical reproduction of site high frequency dynamics). This methodology is tested with ground measurements in 4 locations situated in different climates, and compared with a forecast base case. The analyses are carried out by classifying each measured time series into 6 categories according to its daily clearness index. Finally, metrics for adequately compare high frequency DNI forecasts are discussed.

Spatial analysis of solar radiation using computer vision technique and data assimilation

PurposeThe presence of broken clouds leads to frequent fluctuations in direct normal incident solar irradiation as well as diffuse radiation from the sky. This brings a lot of challenge for grid integration of solar power plants. The paper aims to discuss this issue.Design/methodology/approachA new model is presented to nowcast solar radiation by utilizing hourly global horizontal irradiance (GHI) over a large spatial grid. The spatial distribution of the GHI provides information on the presence of a cloud shadow above a given site. This information is extracted with the help of various data processing techniques. The spatial–temporal data analysis is employed to track the extracted cloud shadow image based on a dynamic model. A Kalman filter is applied for the assimilation of data in the tracking of the extracted shadow over a geographical location.FindingsThe proposed model can provide very good forecasting of solar radiation for various time horizons. However, the variation of shadow features between time steps must be included in the dynamic model to forecast accurate GHI values.Research limitations/implicationsIn this paper database used is on hourly basis; it can be further improved for the inter-hour level of ground data for more accuracy.Practical implicationsThe outcome of this paper would be useful in the field of solar energy application and for weather monitoring purposes.Originality/valueThe forecasted position of the shadow is utilized to prepare and forecast a GHI map for one hour time horizon. Results show that the model can be utilized to forecast solar radiation with accuracy consistent with the contemporary models.

Resource assessment for hybrid solar-biomass power plant and its thermodynamic evaluation in India

Hybrid solar-biomass thermal power generation systems are important for continuous power generation installations which supplement each other seasonally in India. In this paper, several aspects associated with hybrid biomass-solar power generation installations such as state wise availability of biomass resources, solar direct normal irradiance (DNI) has been discussed. Month wise daily average DNI is considered as 20%, 40%, 60%, and 80% and remaining heat is taken from biomass resource in the proposed hybrid plant. The thermodynamic evaluation (i.e. Energy and Exergy) of hybrid solar-biomass power plant have also been investigated. The total input energy of the proposed hybrid system is taken from the heat transfer fluid through parabolic trough collector (PTC) as per availability of solar resource and remaining from biomass to maintain the steam at superheated state of 500°C and 60bar and supplied to turbine at steam mass flow rate of 5kg/s. The energy and exergy analyses of 5MW hybrid system with series mode was carried out to identify the effects of various operating parameters like DNI, condenser pressure, turbine inlet temperatures, boiler pressure on net power output energy and exergy efficiencies.