Instantaneous Irradiance Research Articles

Solar irradiance prediction with variable time lengths and multi-parameters in full climate conditions based on photovoltaic greenhouse

Photovoltaic power generation can provide energy for greenhouses and achieve high quality and high yield of crops. In reality, solar irradiance is fluctuating and intermittent. Thus, the key to ensure efficient photovoltaic power use under greenhouse environmental conditions is to provide an accurate prediction of solar irradiance. Yet, currently studies on irradiance prediction in terms of the variable time lengths, multi-parameter and full climate conditions are rather limited. To improve the comprehensive performance of the prediction model, this paper proposes models of irradiance time series prediction such as Pyraformer, Informer, Transformer and TimesNet. Those models were tested based on the synergistic combination of weather conditions (WC), sunshine time accumulation (STA/h), instantaneous total irradiance (ITI/(W/m2)) and irradiance daily accumulation (IDA/(MJ/m2)). The model performance was rigorously evaluated with 9 prediction lengths, 5 training days, 4 seasons and 5 days for 9 weather conditions. The results showed that the Transformer model had the best overall prediction performance for STA, ITI, IDA and WC at different time steps of 10 min to 24 h. All models were suitable for predicting time series within 1 h. However, TimesNet model was not suitable for predicting time series with steps outside 1 h. On the other hand, by using the sun combination dataset, the Transformer model had the best performance at a time step of 10 min. The mean absolute error (MAE), mean-square error (MSE), root mean squared error (RMSE) and coefficient of determination (R2) of ITI were 0.118 W/m2, 0.059 W/m2, 0.243 W/m2 and 93.9 %, respectively. When exploring the minimum dataset, with the increase of data samples, the prediction effect of TimesNet showed an increasing trend. While, Transformer had the best prediction effect for the dataset with one year of use. When exploring seasonality, Pyraformer model had the best prediction effect on winter and summer, and TimesNet had the best prediction effect on autumn and spring. Local prediction of 9 climate conditions showed that the effects of snow and dust storm were not ideal. The research results showed that the characterization factors that were closely linked to irradiance. The prediction scheme proposed in this paper combined the advantages of different time steps, different factor combination datasets, different data volumes and seasonality, which greatly improves the generalization ability of the model. This study can provide a reference for irradiance prediction and more refined management of photovoltaic (PV) greenhouse.

An experimental study on hybrid control of a solar tracking system to maximize energy harvesting in Jordan

Due to its capacity to maximize the power produced by photovoltaic (PV) panels, solar tracking systems have grown in popularity. However, erratic weather conditions, like cloudy or overcast days, change the panel's preferred orientation. On sunny days, the panel is turned to face the sun's radiation; however, on cloudy or overcast days, diffused radiation alters the optimal position. This has increased the necessity for new search algorithms that control the orientation of the panel to generate the most power feasible regardless of the weather conditions. This study aims at developing a sun-tracking system that can adjust the solar panel's orientation to generate the maximum possible electrical output from solar energy in Jordan, regardless of the local climate. To achieve this; a hybrid controller has been created that combines an open-loop sun monitoring system with a dynamic feedback controller built on an active search algorithm. The suggested algorithm is built on the real-time measurement of the PV panels' waning solar irradiance by using small solar cell 0.6 W. The system switches to the recently proposed circular path finding method to locate the Maximum Power Point Tracking (MPPT) if the instantaneous irradiance level falls below a predetermined threshold (DNI irradiance). As a result of the testing phase, the generated power of a solar panel increased by about 35%, confirming the effectiveness of the newly proposed sun tracker hybrid control system. During experimental test, positive irradiance current noises are appeared, using average filter taking the mean of 100 values for one measurement.

Increasing the Resolution and Spectral Range of Measured Direct Irradiance Spectra for PV Applications

The spectral distribution of the solar irradiance incident on photovoltaic (PV) modules is a key variable controlling their power production. It is required to properly simulate the production and performance of PV plants based on technologies with different spectral characteristics. Spectroradiometers can only sense the solar spectrum within a wavelength range that is usually too short compared to the actual spectral response of some PV technologies. In this work, a new methodology based on the Simple Model of the Atmospheric Radiative Transfer of Sunshine (SMARTS) spectral code is proposed to extend the spectral range of measured direct irradiance spectra and to increase the spectral resolution of such experimental measurements. Satisfactory results were obtained for both clear and hazy sky conditions at a radiometric station in southern Spain. This approach constitutes the starting point of a general methodology to obtain the instantaneous spectral irradiance incident on the plane of array of PV modules and its temporal variations, while evaluating the magnitude and variability of the abundance of atmospheric constituents with the most impact on surface irradiance, most particularly aerosols and water vapor.

Evaluation of aerosol optical depths and clear-sky radiative fluxes of the CERES Edition 4.1 SYN1deg data product

Abstract. Aerosol optical depths (AODs) used for the Edition 4.1 Clouds and the Earth's Radiant Energy System (CERES) Synoptic 1∘ (SYN1deg) product are evaluated. AODs are derived from Moderate Resolution Imaging Spectroradiometer (MODIS) observations and assimilated by an aerosol transport model (the Model for Atmospheric Transport and Chemistry – MATCH). As a consequence, clear-sky AODs closely match with those derived from MODIS instruments. AODs under all-sky conditions are larger than AODs under clear-sky conditions, which is supported by ground-based AErosol RObotic NETwork (AERONET) observations. When all-sky MATCH AODs are compared with Modern-Era Retrospective analysis for Research and Applications (Version 2; MERRA-2) AODs, MATCH AODs are generally larger than MERRA-2 AODs, especially over convective regions (e.g., the Amazon, central Africa, and eastern Asia). This variation is largely due to the differing methods of assimilating the MODIS AOD data product and the use of quality flags in our assimilation. Including AODs with larger retrieval uncertainty makes AODs over the convective regions larger. When AODs are used for clear-sky irradiance computations and computed downward shortwave irradiances are compared with ground-based observations, the computed instantaneous irradiances are 1 %–2 % larger than observed irradiances. The comparison of top-of-atmosphere clear-sky irradiances with those derived from CERES observations suggests that AODs used for surface radiation observation sites are 0.01–0.03 larger, which is within the uncertainty of instantaneous MODIS AODs. However, the comparison with AERONET AODs suggests that AODs used for computations over desert sites are 0.08 larger. The cause of positive biases in downward shortwave irradiance and in AOD for the desert sites is possibly due to the dust particle size and distribution, as defined by the MATCH transport model, and the transfer of that information into the radiative transfer model.

Albedo increment as a scalar of the sunny-shady slope effect of roadway embankments in permafrost region

Roadways in permafrost region are usually built on embankments that are placed on the natural ground to reduce construction-induced thermal disturbance. The embankment alters the thermal regime of the soil under natural ground such that the soil under the south-facing side slope is warmer than that under the north-facing one. While this sunny-shady slope effect (SSE) has been well documented, how to mathematically describe this effect remains unknown. This study derives a simple straightforward scalar ΔR to characterize the SSE of an embankment in permafrost region. The scalar ΔR correlates to the internal factors such as the side-slope albedo, the side slope angle, and the embankment orientation etc., and to the external factors such as the instantaneous and seasonal solar irradiance and the sky cleanness factor. Increasing albedo of the south-facing side slope in a value of ΔR eliminates the SSE. The scalar ΔR was verified by simulating an east–west embankment with a side-slope angle of π/4 and an initial side-slope albedo of 0.25. The simulation revealed that the SSE is apparent in case of business-as-usual scenario but is eliminated in case if albedo of the south-facing side slope increases ΔR = 0.21. It is expected to study if ΔR correlates to the embankment differential settlement, the underlying permafrost temperature and the pavement longitudinal cracks.

Model-Based Power Management for Smart Farming Wireless Sensor Networks

A model-based strategy for an efficient power supply control used in a wireless sensor network is presented. The strategy, based on Pulse-Skipping Modulation, regulates the current charging a battery, delivered by a photovoltaic source, resulting in an accurate current regulation and highly efficient power management. The strategy is implemented on a microcontroller unit and compensates for the microcontroller self-absorbed current. The modulation signal is generated through a full software interface, reducing the requirement for external components. Experimental validations, performed on a charger prototype by using a laboratory photovoltaic device simulator, proved that both regulation accuracy, regulation resolution and converter efficiency achieved are superior to the classic Pulse-Width Modulation. The approach results in a simple practical implementation, carries over the advantages of an up-to-date model for the photovoltaic device, and serves the auxiliary purpose of using the photovoltaic source as an instantaneous solar irradiance sensor.

Impact of instantaneous solar irradiance on refrigeration characteristics of household PCM storage air conditioning directly driven by distributed photovoltaic energy

AbstractMature and inexpensive ice thermal storage was employed to replace battery bank in energy storage, and photovoltaic directly driven technology was also combined in this paper. A 3HP household air conditioning assisted with ice thermal storage was investigated in four operating conditions. First, directly driven by photovoltaic arrays, the (COP)rs were almost 6.31% than that of refrigerator driven by power grid for the instantaneous solar irradiance, and the stored cooling capacity decreased 18.63% under the intermittent influence of solar irradiance. Moreover, the (COP)r of refrigerator operating in out‐of‐box mode was about 1.38 times that of operating in ice storage mode. Next, the inevitable compress motor fluctuation, caused by instantaneous solar irradiance, was investigated by experiment and simulation. In three typical weathers, compressor fluctuating time was approximately 65.22 s, 197.05 s, and 270.48 s in full irradiance range. When the lower solar irradiance limit was optimized from 150 to 80 Wm−2, refrigerator operated stably and continuously in any weather conditions. The ice production and the (COP)r were improved by 40.91% and 12.36%, respectively.

Shortwave Radiance to Irradiance Conversion for Earth Radiation Budget Satellite Observations: A Review

Observing the Earth radiation budget (ERB) from satellites is crucial for monitoring and understanding Earth’s climate. One of the major challenges for ERB observations, particularly for reflected shortwave radiation, is the conversion of the measured radiance to the more energetically relevant quantity of radiative flux, or irradiance. This conversion depends on the solar-viewing geometry and the scene composition associated with each instantaneous observation. We first outline the theoretical basis for algorithms to convert shortwave radiance to irradiance, most commonly known as empirical angular distribution models (ADMs). We then review the progression from early ERB satellite observations that applied relatively simple ADMs, to current ERB satellite observations that apply highly sophisticated ADMs. A notable development is the dramatic increase in the number of scene types, made possible by both the extended observational record and the enhanced scene information now available from collocated imager information. Compared with their predecessors, current shortwave ADMs result in a more consistent average albedo as a function of viewing zenith angle and lead to more accurate instantaneous and mean regional irradiance estimates. One implication of the increased complexity is that the algorithms may not be directly applicable to observations with insufficient accompanying imager information, or for existing or new satellite instruments where detailed scene information is not available. Recent advances that complement and build on the base of current approaches, including machine learning applications and semi-physical calculations, are highlighted.

Worldwide evaluation and correction of irradiance measurements from personal weather stations under all-sky conditions

Personal weather stations (PWS) are gaining popularity since they provide open meteorological data with high spatial resolution. However, a number of factors may affect the quality of the measurements of these stations. PWS provide irradiance measurements using silicon-photodiode sensors, which are a low-cost and lower-maintenance option compared to thermopile-type pyranometers. Silicon-photodiode sensors present, however, several limitations related to the spectral bandwidth, the device’s temperature and other affecting factors, which increase the error in the measurements. This article evaluates the accuracy of irradiance measurements from PWS under all-sky conditions. We propose a calibration method to reduce the uncertainty in the measurements based on the solar zenith angle, the temperature of the device and the clear-sky index. The proposed calibration model is evaluated in 30 personal weather stations from different producers located in 5 climate zones worldwide over several years. An average reduction of the relative mean bias error from 18.4% to 2.8% is achieved based on 5-min instantaneous irradiance samples for clear-sky instances and it is within a ±5% tolerance for all-sky conditions, where other metrics are also improved 1–4%. This study helps understanding the nature of uncertainty of irradiance measurements in this increasingly used data source and provides a practical calibration method to increase accuracy of PWS data.

Estimation of Aerosol-Corrected Surface Solar Irradiance at Local Incidence Angle over Different Physiographic Subdivisions of India and Adjoining Areas Using MODIS and SRTM Data

AbstractSurface solar irradiance is considered as an important component of the surface radiation budget and constitutes one of the essential climate variables. In the present study, clear-sky instantaneous solar irradiance was estimated over 15 physiographic regions of India during January. Dewpoint temperature profiles were extracted from Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard the Aqua satellite to calculate actual vapor pressure following Clausius–Clapeyron equation, which was further used in the Zillman parameterization for solar irradiance. The effect of terrain slope and aspect on direct radiation was taken into account by modifying the parameterized incoming shortwave flux by introducing the local incidence angle. A significant positive correlation was found between terrain-corrected MODIS irradiance and measured radiation data but the RMSE was very high (187 W m−2). Further, the effect of aerosol extinction was introduced by multiplying the terrain-corrected flux by a transmission factor obtained from satellite-derived aerosol optical depth and Ångström exponent. Due to the inclusion of the aerosol transmittance, the correlation was significantly improved (R2 = 0.84) and RMSE was reduced (31 W m−2). Further the effect of surface orientation on surface irradiance was evaluated on six hilly subdivisions. A large variation in the flux (135 to 161 W m−2) was noticed among different aspect classes. The variability was highest in the Eastern Himalayas subdivision (>250 W m−2) and was a minimum in the Eastern Hills subdivision (<28 W m−2). In absence of ground radiation data in hills, Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), was used for validation of model output but it performed poorly and got saturated at higher surface irradiance values.

Annual benthic irradiance levels at the Northwestern Cuban shelf

This study, aimed at determining the average annual benthic light irradiance in the northwestern shelf to later calculate its macrophytobenthos total primary production, is the first and only one ever conducted on this subject in Cuban waters to date. Organic mud constitutes 39% of all bottom types, sand is 37%, and the remaining 24% is made up of carbonate mud, hard bottom, rubble, coral, and their combinations. The water average depth is 7.9 m (2 to 28 m range), with an average color 6 (2 to 14 range) in the Forel-Ule scale. Average water temperatures are 28.1 ºC at bottom, and 28.4 ºC at 0.5 m depth, indicating a well-mixed water column; the average bottom water currents speed of 0.116 m s−1 is unremarkable. Visible down to bottom in 73% of all stations, the average Secchi disk depth is 7.1 m (90% transparency) at the remaining 27% stations. The value of the diffuse attenuation coefficient of down welling irradiance “k” is affected by the hour of day, seasons, water color, runoffs, distance from the coast, and depth where it is determined. With an average surface-to-bottom “k” (k0−bottom) value of 0.13 m−1, this shelf water is 34% less transparent than nearby open ocean water. The bottom light illumination is 49% of that at surface, allowing an instantaneous irradiance energy at bottom of 0.31 kW m−2, which is almost twice the average energy most abundant macrophytobenthos species require to reach maximum photosynthesis rates.

Outdoor assessment of solar irradiance using camera: experimental proof of concept and application to MPP identification

In this paper, a novel image-based concept for estimating solar irradiance received on a photovoltaic (PV) array under normal conditions of irradiance is proposed. The approach is based on the variation of colors intensity in the images of the PV array with respect to solar irradiance. The images of the PV array, which are taken using fixed standard camera and undergo appropriate processing (filtering and intensity averaging), allow the approximation of the instantaneous solar irradiance. The effectiveness of the proposed approach is supported by series of outdoor experimental tests. The results demonstrate that the proposed approach has a good accuracy. As a direct application of the proposed concept, the instantaneous P-V curve of the PV array is approximated using analytical model of the PV array, measured temperature and the estimated irradiance. Once the P-V curve is available, the Maximum Power Point (MPP) can be easily located in real time and then the operating point of the system can be maintained at the MPP.

Solcast: Validation of a satellite-derived solar irradiance dataset

Solcast (https://solcast.com/) is a global solar forecasting and historical solar irradiance data company. Their datasets are important to the scientific community as substantial amounts of historical data is made freely available to researchers. Solcast’s hourly averages and sub-hourly instantaneous (10/15-min) global horizontal irradiance (GHI) estimates are validated at 48 BSRN ground stations that contain 1,014,792 valid hourly average measurements and 2,932,976 valid instantaneous measurements. The data are validated globally and across four climates under clear-sky, clouded-sky and all-sky periods, repeated for ‘all zenith angles’ (θ_z<85°) and high-sun zenith angles (θ_z<50°). A site-by-site validation is also performed for both hourly and instantaneous datasets. All validations and recommendations are impartial and unbiased.The hourly dataset validated similarly for both zenith angle scenarios, which is remarkable due to the added complexities at low-sun angles. In terms of rRMSE, the global performances of hourly GHI under clear-sky, clouded-sky and all-sky were 3.4%, 25.6% and 16.9%, respectively. With each ground station equally weighted, the overall bias was 0.33%, and standard deviation of biases at 1.7%. Solcast’s instantaneous GHI product validations were at times similar to the hourly validations though is naturally harder with increasing temporal resolution.The historical datasets from Solcast are found to be of good quality, thus, they are recommended for use by researchers. Identified areas for improvement herein will guide future developments of Solcast’s methodology.

Impedance matching control strategy for a solar cooling system directly driven by distributed photovoltaics

In this paper, an integrated control strategy for a solar cooling system directly driven by distributed photovoltaics (PVs) without a battery is proposed; this strategy matches the optimal operating impedance of the PV array by periodically perturbing the running frequency of the compressor. The theoretical working principle of the control strategy is explained, and two experimental processes are analysed under different solar irradiance levels. Furthermore, comparative tests of the control system with and without a controller were conducted to evaluate the performance of the solar cooling system. The results of the experiment under the impedance matching control strategy reveal that the average photoelectric conversion efficiency reached approximately 0.129 and improved by 83.7% relative to the control system without a controller. The coefficient of performance (COPsolar) reached 0.263 using an ice thermal storage model, which was an improvement of 60.4%. The compressor ran continually when the instantaneous irradiance exceeded 143 W/m2. The average efficiency of the control system reached 0.96, and the average three-phase power factor was approximately 0.71. The COP of the refrigeration unit was 2.10, and the total cooling capacity was 103.5 MJ, which was sufficient for cooling a 25.5-m2 air-conditioned room for 8.5 h.

Power balancing the multibeam OMEGA laser.

Multibeam lasers often require an output beam balance that specifies the degree of simultaneity of the laser output energy, instantaneous power, or instantaneous irradiance (power per unit area). This work describes the general problem of balancing a multibeam laser. Specific techniques used to balance the output power of the 60-beam pulsed OMEGA Laser System are discussed along with a measured reduction of beam-to-beam imbalance. In particular, the square-pulse distortion induced by a simple saturating amplifier operating with its output at some fraction of its saturation fluence is derived, and a method to exchange gain between saturated amplifiers in a single beam that have different saturation fluences to adjust balance is described.

Estimation of Daily Average Downward Shortwave Radiation over Antarctica

Surface shortwave (SW) irradiation is the primary driving force of energy exchange in the atmosphere and land interface. The global climate is profoundly influenced by irradiation changes due to the special climatic condition in Antarctica. Remote-sensing retrieval can offer only the instantaneous values in an area, whilst daily cycle and average values are necessary for further studies and applications, including climate change, ecology, and land surface process. When considering the large values of and small diurnal changes of solar zenith angle and cloud coverage, we develop two methods for the temporal extension of remotely sensed downward SW irradiance over Antarctica. The first one is an improved sinusoidal method, and the second one is an interpolation method based on cloud fraction change. The instantaneous irradiance data and cloud products are used in both methods to extend the diurnal cycle, and obtain the daily average value. Data from South Pole and Georg von Neumayer stations are used to validate the estimated value. The coefficient of determination (R2) between the estimated daily averages and the measured values based on the first method is 0.93, and the root mean square error (RMSE) is 32.21 W/m2 (8.52%). As for the traditional sinusoidal method, the R2 and RMSE are 0.68 and 70.32 W/m2 (18.59%), respectively The R2 and RMSE of the second method are 0.96 and 25.27 W/m2 (6.98%), respectively. These values are better than those of the traditional linear interpolation (0.79 and 57.40 W/m2 (15.87%)).

Performance Analysis of Crystalline Silicon and CIGS Photovoltaic Modules in Outdoor Measurement

Abstract The outdoor measurements (during two months experiment) of photovoltaic silicon and CIGS modules as well as simulation of energy production during the period experiment are presented in this paper. This paper offer comparison of construction and electrical characteristics of multicrystalline silicon based modules and CIGS based modules. The measuring system for PV modules efficiency research is shown. The nominal power of installed modules is 250 W for m-Si and 280 W for CIGS modules. The energy production in outdoor conditions at direct current side and alternating current side of each photovoltaic panel was measured. Each PV panel was also equipped with temperature sensor for screening panel temperature. The photovoltaic panels were connected to the electrical network with micro inverters. To determine the influence of irradiance at sunshine on power conversion efficiency of PV panels, the pyranometer was installed in the plane of the modules. Measurement of the instantaneous power and irradiance gave the information about the efficiency of a particular photovoltaic panels. In the paper all data from research installation were analysed to present the influence of solar cell technology on the power conversion efficiency. The results of energy production show that m-Si module produced more energy from square meter (30.9 kWh/m2) than CIGS module (28.0 kWh/m2). Thin film module shows the higher production per kWp than multicrystalline module: 217.3 kWh/kWp for CIGS and 201.9 kWh/kWp for m-Si. The energy production simulation (made by PV SOL software and outdoor measurements test are in the good agreement. Temperature power coefficient for the CIGS module is twice lower than for the multicrystalline silicon module: 0.56%/°C and 0.35%/°C for m-Si and CIGS modules, respectively. The obtained results revealed strong influence of irradiance and temperature on energy production by PV panels. Performed studies have a large field of potential application and could improve designing process of PV installation.

Generation of spatially dispersed irradiance time-series based on real cloud patterns

Clouds, being complex components of the atmosphere, have significant effects on power generation by photovoltaic (PV) systems. For example, shadows caused by the cloud coverage over a geographically distributed PV power plant may cause significant fluctuations in power generation by leaving a number of PV panels unable to generate power and contribute to power generation by the plant at each time instant. Thus, investigation of the mentioned effects on PV power generation requires realistic spatial irradiance information. Such information should be evaluated based on the existing real cloud coverage and its light transmission characteristics. This also provides the opportunity to select appropriate coping strategies against the mentioned negative effects of partial shading on PV plant’s power output. This paper presents a modeling approach which generates Spatially Dispersed Irradiance Profiles (SDIPs) for PV arrays based on existing cloud patterns derived from local sky images taken at the application sites. The model gets the direct, diffuse and global irradiance values incident on a horizontal surface, which are primarily obtained utilizing a solar irradiance model (the Morf (2013) model), along with local sky images captured at the application sites and cloud transmittance values, as input data and yields site-specific Spatially Dispersed Irradiance Profiles (SDIPs) incident on the surface of inclined PV panels within PV application areas, as a result of process of the inputs. Utilization of local sky images and cloud transmittance values for different cloud types creates the opportunity for precise analysis of interactions of sunlight with the existing cloud type and hence, obtaining unique and site-specific irradiance profiles according to the existing cloud type and distribution in the sky. The model firstly detects the cloudy and clear-sky parts in the sky image and then instantly utilizes the most appropriate ellipse on the cloud layer associated with each solar panel through which the beam irradiance is received by the panel. The model also considers the light transmission characteristics of different cloud types as the parameter affecting the beam irradiance. The diffuse and ground-reflected irradiance components are assumed to be spatially constant and thus identical for all solar panels. Cloud base heights, as provided in the International Cloud Atlas (1987), are also utilized to calculate the ground area covered by each sky image. Daily irradiance sequences for different observation points in a PV array are simulated under partly cloudy sky conditions using a set of sky images and utilized for validation purpose of the proposed algorithm. It is demonstrated that instantaneous irradiance values, as well as daily irradiance sequences, differ from point to point in a geographically distributed PV application site depending on the distribution of clouds in the sky. The mentioned variable characteristic of the irradiance sequences received at different observation points, as well as the model’s capability to reflect the mentioned variabilities, is verified using irradiance data derived from satellite observations. The performance of the proposed model is validated using variability index (VI) metric as a measure of irradiance variability during a day. The modeled VI values are validated against the measured VI values for a reference point located at the center point of the generated irradiance profiles. Daily VI values calculated for both measured and simulated 1-min global horizontal irradiance (GHI) data are compared for a population of totally 117 days during April – August time period. The results of comparison show statistics of mean bias error (MBE) of 0.16, root mean square error (RMSE) of 2.394, correlation coefficient of 0.94 and mean absolute error (MAE) of 1.91. The validation results demonstrate capability and accuracy of the proposed model for estimation of irradiance values under cloudy sky conditions.

On the properties of aggregate clear-sky index distributions and an improved model for spatially correlated instantaneous solar irradiance

An important factor in grid integration of solar power is the so-called dispersion-smoothing effect, i.e., that differences in cloudiness over dispersed systems make the aggregate output less variable. This effect has been studied for irradiance step-changes on different time horizons, but not so much for instantaneous irradiance. In this paper, an improved probabilistic model is proposed for how instantaneous solar irradiance is correlated and aggregated over a network with arbitrary number of sites and dispersion. The model is fitted to irradiance data with a 1-s resolution from a network with 17 pyranometers in Hawai’i. A previously proposed three-state model of the instantaneous clear-sky index is partly confirmed by showing that clear and cloudy states can be separated and modeled by independent distribution models. It is also shown that the station-pair correlations for the instantaneous clear-sky index, as well as the shape of the distribution for the cloudy states, depend characteristically on the average degree of cloudiness, represented by the daily clear-sky index. For dispersed sites within the studied network, separated by distances up to 1km, and for daily clear-sky indices above approximately 0.5, the model performs better in reproducing the aggregate clear-sky index than non-spatial data. The proposed model could assist distribution system operators (DSOs) in grid planning and operation, as shown in a case study.

The Application of Sliding Mode Control of a Speed Induction Motor Pump using FPGA

Objectives: This paper shows the efficiency of using a sliding mode control of a photovoltaic pumping system, which is strongly non-linear. It contains several non-linear sub-systems (photovoltaic generator, DC/AC converter, an asynchronous three phase motor-pump, centrifugal pumps and two coupled tanks). The mathematical model of the whole system was achieved after the modeling of the various parts constituting it. Furthermore, an FPGA implementation on the map Xilinx Spartan 3A was performed to prove the effectiveness of the proposed sliding mode control of the motor-pump angular speed. Methods/Statistical analysis: The values of the irradiance and the temperature were respectively measured by the sensors (photo resistance and LM35). They vary according to the climatic conditions that change permanently during the year. Experimental results are compared with those obtained in Matlab. Findings: The motor-pump speed reached its maximum value when the irradiance is maximal. Likewise, a low irradiance allows a low speed. The FPGA board is responsible for finding the suitable frequency according to the instantaneous irradiance. This frequency will be the reference in the scalar control implemented on the DV51, which powers the motor-pump. Hence, we have carried out a real-time control according to the climatic conditions. Application/Improvements: Pumping is an alternative way of managing water resources in different areas (surface water, groundwater, desalination, agricultural use or industry).In the future work; we can control the water levels in the coupled tanks.