Direct Normal Irradiance Values Research Articles

A hybrid MCDM optimization for utilization of novel set of biosynthesized nanofluids on thermal performance for solar thermal collectors

Recent advancements in solar technology have spurred researchers to develop a precise and cost-effective method for monitoring solar radiation across diverse environmental conditions. This study focuses on optimizing performance parameters by replacing conventional nanofluids, produced through chemical and physical processes, with biosynthesized counterparts. Biosynthesized nanoparticles, derived from biological sources like microorganisms or plants, offer a promising avenue for enhancing solar panel efficiency. Through the construction and testing of an integrated photovoltaic thermal system, varying operating parameters have been explored to maximize photovoltaic efficiency. The highest overall efficiency, reaching approximately 62 %, was achieved with biosynthesized Graphene oxide nanofluid under higher Direct Normal Irradiance (DNI) levels, while the lowest was observed with Aluminum oxide nanofluid at lower DNI values. Employing Multi-Criteria Decision methods such as Analytical Hierarchical Process (AHP) and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), nanofluids were ranked based on criteria including Exergy loss, Surface temperature, Overall efficiency, and Electrical efficiency, with weights of 49.58 %, 28.43 %, 13.45 %, and 8.54 % respectively. TOPSIS prioritized Graphene Oxide as the most favorable nanofluid, followed by Copper-Oxide and Cerium-Oxide, while Aluminum-Oxide received the lowest priority in optimizing PV panel performance.

A Method for Projecting Cloud Shadows Onto a Central Receiver Field to Predict Receiver Damage

This work demonstrates methods of mapping high-spatial-resolution direct normal irradiance (DNI) data from satellites, Total Sky Imagers (TSIs), and analogous data sources onto a heliostat field for characterizing the spatial and temporal variation of the incident flux on a central receiver tower during cloud transient events. The mapping methods are incorporated into an optical software module that interfaces with CoPylot–SolarPILOT’s python API– to provide computationally efficient optical simulation of the heliostat field and the solar power tower. Eventually, this optical model will be incorporated into optimization models whereby a plant operator can understand the effects of cloud transient events on overall power production and receiver lifetime due to creep-fatigue damage and therefore make better informed decisions about receiver shutdown events. By more accurately modelling the effects of cloud events on receiver flux maps, this work may determine the magnitude and frequency of thermal cycling on receiver tubes and panels using actual or realistic cloud shapes instead of averaged DNI values–which may undercount the total cycle number. This work may also prevent unnecessary plant shutdowns due to overly precautionary control strategies and characterize the relative impact of various cloud types on receiver life. We plan to eventually integrate this methodology into the System Advisor Model (SAM) to improve performance model accuracy during periods of cloudiness. In this paper, we demonstrate generating DNI maps and mapping them to a solar field in CoPylot using 10 m resolution data from publicly available Sentinel-2 satellite data over the Crescent Dunes plant.

Numerical Modeling and Experimental Validation of Heat Transfer Characteristics in Small PTCs with Nonevacuated Receivers

The development of small-sized parabolic trough collectors (PTCs) for processing heat production at medium temperatures (100–250 °C) represents an interesting approach to increase the utilization of solar thermal technologies in industrial applications. Thus, the development of simplified models to analyze and predict their performance under different operative and climatic conditions is crucial for evaluating the application potential of this low-cost technology. In this paper, we present a numerical method that by combining three-dimensional finite element simulations (implemented with COMSOL Multiphysics software version 6.1) with a one-dimensional analysis (based on a MATLAB script) allows for the theoretical determination of the power output of a small-PTC with a nonevacuated tubular receiver operating at a medium temperature. The finite element model considers both the nonuniformity of the concentrated solar flux on the receiver tube (evaluated using Monte Carlo ray-tracing analysis) and the establishment of natural convection in the air gap between the glass envelope and absorber tube. The model calculates, for several values of direct normal irradiance (DNI) and inlet temperatures, the thermal power transferred to the heat transfer fluid (HTF) per unit length. The data are fitted using the multiple linear regression method, obtaining a function that is then used in a one-dimensional multi-nodal model to estimate the temperatures and the heat gains along the receiver tube. The outputs of the model are the outlet temperature and the total thermal power transferred to the HTF. In order to validate the developed methodology for the assessment of the heat transfer characteristics in the small-PTC with a nonevacuated receiver, an experiment at the ENEA Trisaia—Solar Thermal Collector Testing Laboratory was carried out. This work compares the theoretical data with those acquired through experimentation, obtaining a good agreement, with maximum differences of 0.2% and 3.6% for the outlet temperatures and the power outputs, respectively.

Case study on decarbonization strategies for LNG export terminals using heat and power from CSP/PV hybrid plants

The race towards decarbonization is driving major oil and gas companies to explore means to use renewable heat and power for their plants as part of their commitment to reduce their carbon intensity by 80% to 100% by 2050 (Holbrook, 2023). In terms of GHG (Greenhouse Gas) emissions, natural gas is considered the cleanest fossil fuel option available, and decarbonization of new LNG (Liquefied Natural Gas) projects is on the radar of many LNG projects developers. In addition, LNG cargos will have to be certified in the future by accredited authorities to meet defined GHG emission levels (Stern, 2019).This research study investigates a new concept of providing both heat and power from a PV (Photovoltaic) and CSP (Concentrated Solar Power) hybrid plant to meet the energy demand of an LNG export terminal. Two locations have been investigated for potential future LNG projects: Karratha in Australia and Ras Laffan in Qatar. Both locations have DNI values higher than 2000 kWh/m2/year, which is the minimum level required for CSP technology (Lovegrove and Stein, 2021).The LCCA (Levelized Cost of CO2 abatement) was used to compare the various solar configurations to select the option that will bring the greatest amount of CO2 reduction for the same investment cost (CGEP, 2020). The solar configurations technical parameters were defined based on the surface land available, natural gas feed composition and LNG plant design characteristics. The techno-economic assessment was carried-out taking into consideration the electricity price, the grid carbon intensity, and the CO2 tax in the region.Whilst in Australia a collocated single plant is favourable in terms of land availability and DNI (Direct Normal Irradiation) level, in Qatar, heat and power production have been separated into two distinct locations. Next to the LNG plant, a CSP plant provides heat only, whereas 130 km away, the hybrid PV/CSP plant located at Qurain EL Bawl provides electric power.The results indicate that the PV/CSP hybrid plant significantly accelerates the decarbonization of energy supply to the “All electric” LNG Plant. Depending on the solar field size, the quantity of CO2 emitted between 2025 and 2050 is reduced by 78–81% for Karratha (Australia) and by 82–88% for Ras Laffan (Qatar) compared to a grid connected plant.In addition, the economic assessment indicated that buying electricity from the grid during the period 2025–2050 would be more expensive for Australia then investing in a PV/CSP plant. In Qatar, the LCOE range of 93–110 US$/MWh is not competitive with the price of electricity in the region Qatar, mainly because of energy subsidies, however both the carbon tax and electricity price will need to be raised to the same level as in Australia to diversify and expand the power sector in the region.

Experimental and techno-economic analysis of two innovative solar thermal receiver designs for a point focus solar Fresnel collector

In this paper, techno-economic analysis and the experimental campaign for a new solar concentrating system are presented. Two novel receivers (Jet impingement receiver with mesh structure & helical channel receiver) are tested on a novel collector technology. The collector technology integrates the two established models of solar concentrating technologies, which are linear Fresnel reflector technology and central receiver technology, into the new concept called the Point Focus Fresnel Collector (PFFC). It is found that the PFFC system with jet impingement receiver and mesh structure provides higher thermal efficiency and manufacturing ease compared to parabolic dish systems. Maximum thermal efficiency of jet impingement receiver is highest at 87% whereas that for helical channel receiver is 83%. Average thermal efficiency of jet impingement receiver is 61% whereas that for helical channel receiver is 58%. Economic analysis of the system reveals that the discounted payback time for the PFFC system is only 5.5 years and less than one year compared to diesel and electricity powered steam generators respectively at an inflation rate of 2.5%. Substantial saving is predicted with PFFC system compared to diesel and electricity powered steam generator. For all discount rates in the range of 2.5–25%, the levelized cost of energy (LCOE) for PFFC system is much lower than that of LCOE in Saudi Arabia for conventional system. Since the LCOE in most of the Middle East and North Africa (MENA) countries is higher than the LCOE in Saudi Arabia, therefore, the PFFC system is also suitable for other MENA countries where average direct normal irradiation values are comparable to Saudi Arabia.

MDBA: An accurate and efficient method for aiming heliostats

In a solar power tower plant, the role of the heliostat aiming strategy is to control the radiative flux distribution at the receiver surface to avoid thermally induced damage, while minimising spillage losses and maximising the receiver thermal efficiency. Flux limitations arise from factors including the heat transfer fluid stability limits, and thermo-mechanical stress limits in receiver pipes. Maximised flux, as close as possible to local flux limits, facilitates an overall smaller receiver with lower thermal losses. Methods exist to sequentially optimise aiming points of single heliostats, using fast convolution-based optical simulations to evaluate individual flux maps. However, to accurately determine receiver flux distributions, ray-tracing is preferred. Ray-tracing is computationally expensive and determination of the aim-points for every heliostat independently potentially leads to impractical simulation times. In this study, a new parameterisation of heliostat aim-point locations is introduced that significantly simplifies the aiming problem. The new aiming model, named Modified Deviation-Based Aiming (MDBA), enables efficient use of ray-tracing to optimise the aiming strategy and, together with receiver thermal and mechanical models, is able to closely match the flux distribution to local values of allowable flux on the receiver. This new parameterisation enables accurate aiming strategy interpolation, used to dynamically predict full field aim-points at different sun positions and values of direct normal irradiance (DNI). A reference case with a surround field and a cylindrical external receiver compatible with the Gen3 Liquid Pathway project is presented to test the capability of the method developed in this study.

Impact on solar radiation parameters in India during COVID-19 lockdown: a case study

ABSTRACT The current research objective is to explore changes in solar radiation variables across the Indian region during the lock-down period. Global Horizontal Irradiance (GHI), Direct Normal Irradiance (DNI) and Diffuse Horizontal Irradiance (DHI) were considered in order to determine changes in radiation. The reduction in DHI and the increase in DNI have been investigated. The radiation levels of GHI, DHI and DNI were compared to the previous month/year reference data for industrial and rural locations and observed the percentage difference in solar radiation during the lock-down period. Overall, the results of lock-down are evident in DHI and DNI industrial areas relative to rural/remote locations. Significantly, the DNI values raised from 1% to 12% in urban areas compared to previous years.

Comparative analysis of dish Stirling engine and photovoltaic technologies: Energy and economic perspective

Solar energy can be harnessed by direct conversion of solar energy to electrical energy by using photovoltaic (PV) technology or with the help of thermodynamic cycle by using concentrated solar power (CSP) technologies. The goal of this paper is to perform detailed comparative analysis for the two solar technologies namely: PV and dish Stirling engine (DSE). In order to ensure a fair comparison, the two systems are designed for the same rated capacity of 1 MW for Tabuk, Saudi Arabia. The average values of direct normal irradiance (DNI) and global horizontal irradiance (GHI) in Tabuk are 7.43 kWh/m2/day and 6.31 kWh/m2/day, respectively. The two technologies are analyzed based on several performance indicator factors such as capacity factor (CF), solar to electric efficiency, energy output, levelized electricity cost (LEC), and net present value (NPV). The comparative analysis of the two technologies shows that PV system has 6.9% better CF and 54% more energy output compared to DSE system. The LEC of PV systems is 3.39 ¢/kWh which is much better than the 11.74 ¢/kWh from the DSE system. The NPV of the PV system is positive while DSE system has negative NPV. This paper present useful insight of the two technologies which is helpful to choose a solar power technology for a power project.

Theoretical energy and exergy analysis of a combined cooling, heating and power system assisted by a low concentrated photovoltaic recuperator

Supporting energy generation systems with photovoltaic thermal systems is one of the important issues discussed in the literature. With photovoltaic thermal systems, some of the solar energy is directly converted into electrical energy, and the waste heat generated in the photovoltaic module is used for different purposes (heat source, preheater, etc.). In this study, unlike the literature studies, the integration of the photovoltaic module into a recuperator and its use in a combined cooling, heating, and power generation system was investigated thermodynamically. The fossil-fueled energy generation system consists of a Brayton cycle, an organic Rankine cycle, and an absorption refrigeration cycle. The photovoltaic recuperator was placed in the organic Rankine cycle to enhance cooling, heating, and electricity generation. The thermodynamic analyses were performed for different concentration ratios, direct normal irradiation values, mass flow rates, module lengths, and fluid saturation pressures. For the photovoltaic recuperator use, depending on the parameter values, enhancements were achieved in the range of 0–141% for cooling capacity, 32–35.5% for heating capacity, and 1.6–2.1% for net power output. Thus, the overall energy efficiency of the system increased. However, the low contribution of the photovoltaic recuperator to exergy output and the high exergy destruction rate in the photovoltaic recuperator caused the overall exergy efficiency of the system to decrease. The results showed that the location of the photovoltaic recuperator in the combined cooling, heating, and power generation system provided enhancements in a greater number of system outputs, given the results of the literature studies.

Thermal performance analysis on steady-state and dynamic response characteristic in solar tower power plant based on supercritical carbon dioxide Brayton cycle

ABSTRACT Supercritical Carbon Dioxide (S-CO2) Brayton cycles and Concentrating Solar Power (CSP) plants are gaining increasing attention due to environment pollution problems and their higher efficiencies. At present, there is a lack of researches on the dynamic thermal analysis of CSP plants based on S-CO2 Brayton cycle, which needs to be resolved urgently. Therefore, a one-dimensional dynamic model of the printed circuit heat exchanger (PCHE) is developed, which is incorporated into transient model of the solar tower power plant. And the Modified Euler or Fully-implicit Runge-Kutta Method is used to complete the dynamic solution. The results indicate that the pressure ratio equaling to 3.5 and the zigzag PCHE regenerator with a diameter of 2 mm will be the best choice for our designed power plant to achieve the balance between larger net output work and power efficiency improvement, which provides the reasonable design parameter for more complicated three-dimensional transient models. By taking the binary nitrate working temperature limitation and common influences of temperature and pressure on S-CO2 thermophysical properties into consideration, as the direct normal irradiance (DNI) decreases, the S-CO2 heat transfer coefficient will increase. When DNI value changes between 780 W/m2 and 970 W/m2, the cold side S-CO2 outlet temperature of PCHE regenerator and S-CO2 Brayton cycle power efficiency will produce 114.65 K and 8% fluctuation in no more than 15 minutes.

Assessment of Direct Normal Irradiance Forecasts Based on IFS/ECMWF Data and Observations in the South of Portugal

Direct Normal Irradiance (DNI) predictions obtained from the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecast (IFS/ECMWF) were compared against ground-based observational data for one location at the south of Portugal (Évora). Hourly and daily DNI values were analyzed for different temporal forecast horizons (1 to 3 days ahead) and results show that the IFS/ECMWF slightly overestimates DNI for the period of analysis (1 August 2018 until 31 July 2019) with a fairly good agreement between model and observations. Hourly basis evaluation shows relatively high errors, independently of the forecast day. Root mean square error increases as the forecast time increases with a relative error of ~45% between the first and the last forecast. Similar patterns are observed in the daily analysis with comparable magnitude errors. The correlation coefficients between forecast and observed data are above 0.7 for both hourly and daily data. A methodology based on a new DNI attenuation Index (DAI) was developed to estimate cloud fraction from hourly values integrated over a day and, with that, to correlate the accuracy of the forecast with sky conditions. This correlation with DAI reveals that in IFS/ECMWF model, the atmosphere as being more transparent than reality since cloud cover is underestimated in the majority of the months of the year, taking the ground-based measurements as a reference. The use of the DAI estimator confirms that the errors in IFS/ECMWF are larger under cloudy skies than under clear sky. The development and application of a post-processing methodology improves the DNI predictions from the IFS/ECMWF outputs, with a decrease of error of the order of ~30%, when compared with raw data.

Overview of the integration of CSP as an alternative energy source in the MENA region

In this study, meteorological data from sixty-two locations in MENA (the Middle East and North Africa) region have been used to simulate the technical and the economic performances of a 50 MWe CSP (Concentrating Solar Power) power plant with parabolic troughs technology and two-tank storage system. As a first step, and due to the difference of the DNI (Direct Normal Irradiance) values in the different locations, the sizing of the optimum solar field and storage capacity has been done for each one of the sixty-two sites. After that, simulation of the electrical and economic output of the 50 MWe power plant has been conducted for all the sites. Furthermore, and for a clear representation of the results, maps of the region's electrical production and LCOE were created by interpolation of the site's simulation outputs and using a GIS software. Finally, a benchmarking of the region's production capacity against ANDASOL, the reference 50 MWe plants already operational in Spain, will be presented. Resultsshow that MENA region possesses a great potential to produce electricity from CSP with a competitive LCOE of 11.58 c€/kWh in comparison to Spain the leader on CSP production in the area. Those results can provide a good idea to the policymakers and investors in the field to push forward the installation of large-scale CSP plants in this region. This can lead to the creation of new job opportunities as well as sustainable development for the region's countries.

Steam generation system operation optimization in parabolic trough concentrating solar power plants under cloudy conditions

Parabolic trough concentrating solar power with indirect thermal energy storage, as a promising application of solar energy, has been widely used in concentrating solar power plants. The exergy efficiency of thermal energy storage system and plant parasitic power consumption could change under cloudy conditions when the thermal oil distribution was adjusted to the live steam branch and reheat steam branch. However, the operating condition optimization of steam generation system has received insufficient attention. This study designed a detailed fixed-power-supply model of parabolic trough concentrating solar power plants to optimize the operation strategies under various conditions. The parametric constraints, which worked on the optimization, were investigated under various direct normal irradiation values. Simulation results indicated that the low reheat steam temperature, thermal oil mass flow rate of the live steam branch, and live steam pressure reduced the molten salt temperature at the discharging exchangers and plant parasitic power consumption. The distribution mode of preferentially satisfactory distribution of reheat steam branch demand had low molten salt consumption and high exergy efficiency of thermal energy storage. The molten salt consumptions under optimal conditions were 0.98%–13.68% lower than the consumption under original conditions with the decreasing direct normal irradiation from 300 W/m2 to 210 W/m2.

Recalibration of SPN1 pyranometers against pyrheliometer and its relevance for the evaluation of concentrating solar process heat plants

Accurate determination of direct normal irradiance (DNI) is essential for evaluating and monitoring of concentrating solar power (CSP) and solar process heat (SPH) plants. Currently, a bi-axially tracked Pyrheliometer (PHM) is the most accurate measuring device, but requires high maintenance effort and is cost-intensive. As an alternative, the cost-effective pyranometer SPN1 was investigated by comparing highly resolved minute mean DNI measurements of two SPN1 devices to a reference PHM at the Institute for Solar Technology SPF in Rapperswil (Switzerland). To reduce systematic errors, a linear and a quadratic correction function have been applied to four years of measurements. They reduced the root mean square error RMSE from 48.8 W/m2 (11.5% of mean PHM DNI = 426 W/m2) to 37.9 W/m2 (8.9%) and 29.6 W/m2 (6.9%), respectively. It is also shown that even recalibrations based on only one month of data already reduced the RMSE to maximum 33.4 W/m2 (7.8%), if conducted between April and September. Considering the impact of solar elevation and DNI range on the SPN1 accuracy by bifurcating the correction functions only resulted in a negligibly small improvement of the RMSE. Finally, the influence of SPN1’s DNI measurement accuracy on the performance analysis of a real SPH plant in Switzerland was evaluated. After recalibration and correction of DNI values, the evaluation of monitoring data yielded annual efficiencies that were 15% and 12% higher in 2014 and 2015, respectively. It is recommended to recalibrate SPN1 devices over a minimum of one month against a PHM according to the methods presented in this paper.

Direct normal irradiance predictions using broadband models for Indian stations

In this paper three parametric models CPCR2, MLWT2 and REST have been used to compute direct normal irradiance (DNI) for five Indian stations, namely New Delhi, Pune, Jaipur, Kolkata and Mumbai. Computed values of DNI have been compared with measured values in terms of percentage root mean square error (RMSE) and percentage mean bias error (MBE). It is observed that the average percentage RMSE for the year is the minimum for MLWT2 model for Jaipur followed by New Delhi and Pune and the values are 1.67%, 2.33% and 2.49%, respectively. But for coastal stations Kolkata and Mumbai the corresponding minimum values occur for CPCR2 model and REST model respectively, and the values are 2.62% and 2.76%, respectively. It shows that MLWT2 model performs better for most of the Indian stations except the coastal stations.

Optical Performance of a Novel Two-Receiver Solar Central Tower System

A novel idea of using two receivers on the same tower in a solar tower system is introduced and investigated. The idea is to have two receivers at the same tower at different heights and sharing the same heliostat field. The pointing strategy for each heliostat is to pick the receiver that gives the maximum optical efficiency. To investigate this idea, two receivers are placed on the tower, one at the top and one at the midway up the tower. The biomimetic “spiral” distribution scheme is used to design the heliostat field, and the particle swarm optimization (PSO) method is used to obtain the optimum field shape factors. The model equations for calculating the optical field efficiency are presented and coded using the matlab software. The code is validated against known cases. To quantify the effect of the idea introduced in this paper, a solar field for the 50 MWth solar tower system with a single receiver is designed for Ma'an, Jordan (Ma’an enjoys high values of direct normal irradiance). It is found that the annual weighted optical efficiency for the 50 MWth plant in Ma’an for a single receiver is 67.14%, while it reaches 67.64% using the two-receiver system. Furthermore, the study shows that having two receivers on the same tower could save two heliostats and 11,000 m2 of needed land area to obtain the same power as a single-receiver tower. The economic analysis for this 50 MWth plant shows that savings can be obtained from having an extra receiver on the same tower of the same quality as the main receiver when the specific land area exceeds 65 $/m2.

Short-term forecasts of GHI and DNI for solar energy systems operation: assessment of the ECMWF integrated forecasting system in southern Portugal

Solar energy is key factor in the demand for clean energy development and management. In particular, global horizontal irradiance (GHI) and direct normal irradiance (DNI) are the foremost important solar resource components that need to be well characterized in order to seek an efficient operation of photovoltaic and concentrated solar power plants, respectively. The objective of the present work is to assess the quality of short-term (24 h) forecasts from a global Numerical Weather Prediction (NWP) model regarding the GHI and DNI components for solar energy applications. Forecast accuracy for the Integrated Forecasting System (IFS), the global model of the European Centre for Medium-Range Weather Forecasts (ECMWF), was verified through the comparison of the predicted hourly values with the corresponding ground-based measurements in southern Portugal. In this study, results from one year of IFS data are analysed, yielding a general good agreement between model and four ground-based measuring stations. High correlations occur particularly for GHI whilst DNI simulations are predominantly hindered by cloud and aerosol representation (i.e. the radiative effects of clouds tend to be underestimated by the model and the radiative effects of the aerosols are overestimated by the model under very clear atmospheric conditions), being closely linked to the parameterization of absorption and scattering phenomena as function of cloud and aerosol type and dimension. Relative differences of annual availabilities for GHI are found between ∼0.16% to ∼2.12% whilst for DNI values ranging from ∼7% to ∼12% are found. The respective correlations coefficients are around 0.95 for GHI and between 0.65 and 0.77 for DNI. Regional irradiation maps of GHI and DNI are presented, showing that NWP predictions are an important tool for the operation of electricity generation systems based on solar energy.

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.

Representative Atmospheric Parameters in Multijunction Solar Cell Design

The representative spectrum selection approach is applied systematically to determine efficiency-maximizing multijunction solar cell (MJSC) bandgap combinations that also maximize energy yield (EY). The technique is performed using a complete, validated dataset of annual spectral irradiance measurements collected in Ottawa, Canada, and compared to the same calculation using simulated spectra with fixed representative atmospheric parameters. We confirm that representative atmospheric parameters exist, are identified with their median direct normal irradiance values, and show that they accurately predict maximized EYs at the MJSC design points. Representative spectra, for MJSCs of 2–8 junctions, are determined as a function of aerosol optical depth (AOD) and precipitable water (PW). Coefficients that describe the change in the EY and representative spectrum as a function of changing representative AOD and PW from one location to another are presented.

Short-range solar radiation forecasts over Sweden

Abstract. In this article the performance for short-range solar radiation forecasts by the global deterministic and ensemble models from the European Centre for Medium-Range Weather Forecasts (ECMWF) is compared with an ensemble of the regional mesoscale model HARMONIE-AROME used by the national meteorological services in Sweden, Norway and Finland. Note however that only the control members and the ensemble means are included in the comparison. The models resolution differs considerably with 18 km for the ECMWF ensemble, 9 km for the ECMWF deterministic model, and 2.5 km for the HARMONIE-AROME ensemble. The models share the same radiation code. It turns out that they all underestimate systematically the Direct Normal Irradiance (DNI) for clear-sky conditions. Except for this shortcoming, the HARMONIE-AROME ensemble model shows the best agreement with the distribution of observed Global Horizontal Irradiance (GHI) and DNI values. During mid-day the HARMONIE-AROME ensemble mean performs best. The control member of the HARMONIE-AROME ensemble also scores better than the global deterministic ECMWF model. This is an interesting result since mesoscale models have so far not shown good results when compared to the ECMWF models. Three days with clear, mixed and cloudy skies are used to illustrate the possible added value of a probabilistic forecast. It is shown that in these cases the mesoscale ensemble could provide decision support to a grid operator in terms of forecasts of both the amount of solar power and its probabilities.