Simulation Of Solar Energy Systems Research Articles

Resolution of the cloud enhancement problem for one-minute diffuse radiation prediction

For design and simulation of solar energy systems, quality information about all components of solar irradiance is crucial. In cases when only global irradiance measurements are available, separation models are a useful method to estimate DNI and diffuse irradiation. Several of such models have been developed since the 1960s, most of them aiming to deliver estimates in hourly resolution. For higher data resolution, such as in minute data, those models are not able to describe fast transient and cloud enhancement phenomena commonly observed in data with smaller time-steps. This paper proposes an adaptation of the BRL separation model, making it capable of delivering more precise irradiance estimates for higher resolution data. Two models result from this adaptation: one for Brazil and other for Australia. The proposed models yield a more precise DNI and diffuse fraction estimates to their respective countries, compared to other separation models commonly used in the technical literature. For example, using the recommended Combined Performance Index (CPI) as a single statistical indicator, the proposed model yields DNI estimates with CPI from 230 to 350% for Australia, and from 270 to 800% for Brazil, while the Engerer model, recently recommended as a ‘‘quasi-universal” 1-min separation model, yields DNI estimates with CPI from 500 to 700% for Australia, and from 600 to 1800% for Brazil.

Critical factors affecting the photovoltaic characteristic and comparative study between two maximum power point tracking algorithms

This paper presents the characterization and the modeling of the electric characteristics of currentvoltage and power–voltage of the photovoltaic (PV) panels. The philosophy behind digital simulation of solar energy systems is that experiments which normally should be done on real systems under high assembling costs can be done numerically in a short time on a computer, thus saving time and investments. The electric parameters of PV cells and the optimal electric quantities of PV panels have been analyzed (voltage and power) according to the meteorological variations (Temperature, solar irradiation …). The obtained results show that the diode parameters of the PV cells depend on solar irradiation: the current saturation increases with solar irradiation. This induces a decrease of the optimal voltage with solar irradiation; when the solar irradiation varies from 600 W/m2 to 1000 W/m2. By taking into consideration all the modeling results, the electric behavior of the cells association in parallels or in series, as well as the aging of a PV panel have been analyzed. Moreover, a comparative study between two types of MPPT techniques that are used in photovoltaic systems to extract the maximum power have been introduced which are Perturb and Observe (P &O) and Incremental Conductance (INC).

An Evaluation of Global Solar Radiation Empirical Formulations in Isparta, Turkey

Global solar radiation data are very essential for the design, evaluation, and simulation of solar energy systems. For this purpose, various empirical models for computing have been used to predict the monthly average daily global solar radiation on a horizontal surface around the world. The main objective of this article is to investigate 46 existing models and develop 4 models for estimating daily global solar radiation on a horizontal surface in Isparta, Turkey (37.47 N, 30.34 E). The collected existing models and developing models are compared on the basis of statistical error tests. According to the results, the developing model (Model 49) is showed the best estimation of the global solar radiation on a horizontal surface of Isparta by means of the R = 99.42, MPE = –0.254%, MBE = 0.00052 MJ/m2, and RMSE = 1.3284 MJ/m2.

A comparison of the UK Standard Assessment Procedure and detailed simulation of solar energy systems for dwellings

The drive to reduce worldwide carbon emissions that are directly associated with dwellings and to achieve a zero carbon home dictates that renewable energy technologies will have an increasingly large role in the built environment. The Standard Assessment Procedure (SAP), formulated by the Building Research Establishment (BRE), is the UK Government's approved methodology for assessing the energy ratings of dwellings. This article presents an evaluation of the advantage given to SAP ratings by the domestic installation of typical photovoltaic (PV) and solar domestic hot-water (SDHW) systems in the UK. Comparable PV and SDHW systems will also be simulated with more detailed modelling packages. Results suggest that calculation variances can exist between the SAP methodology and detailed simulation methods, especially for higher performance systems that deviate from the default efficiency parameters.

Test Reference Year Generation and Evaluation Methods in the Continental Mediterranean Area

Different meteorological data series called multiyear data, long-term average measured data series, or test reference years (TRYs) are required for solar energy system simulation. It is known that the use of the multiyear data approach requires a great effort in time and computation, long-term average measured data do not have the extreme values of weather data given along the year, and TRYs represent typical references rather than extreme conditions and facilitate the comparison in the performance of energy systems. In this paper, TRYs have been generated, using three different methodologies, from hourly meteorological data measured in two cities, Madrid and Valladolid (Spain). In order to evaluate them, the performance simulation of three solar energy systems (thermal, passive, and photovoltaic) with long-term measured meteorological data has been compared with estimated performance simulations with TRYs. Root-mean-square and mean bias errors and relative differences have been used as estimators to measure the performance deviation of TRYs from long-term measured meteorological data series. Results of the comparison show that the most appropriate method for generating test reference year depends on the characteristics of the station and varies from month to month. The Danish method (TRY5) gives better results in Valladolid than in Madrid for the photovoltaic and passive systems; the Argirious method (TRY6) gives better results in Madrid than in Valladolid for the photovoltaic system. The Pissimanis method (TRY4) is the best for simulating thermal and photovoltaic systems in summer.

Using satellite-derived insolation data for the site/time specific simulation of solar energy systems

In this paper, the question of satellite-derived irradiance is addressed on two levels. First, the question of physical accuracy is addressed by comparing satellite-predicted hourly/daily global and direct irradiance with controlled ground measurements in climatically distinct environments. This accuracy is compared to the error made as a function of distance when extrapolating the needed data from the closest ground measurement site. Second, the question of end-use accuracy is addressed by comparing satellite-derived, photovoltaic-utility load-match benchmarks with actual benchmarks for three US electric utilities where ground measurements were available.

Estimation of the diffuse fraction of daily and monthly average global radiation for Fudhaliyah, Baghdad (Iraq)

Separating the global solar radiation on a horizontal surface into direct and diffuse components is required in the simulation of solar energy systems. Many models have been developed for this purpose. The aim of this study is to establish, from the data collected over the period 1985–1986 at Fudhaliyah, daily correlations between (i) diffuse fraction of global radiation and clearness index; (ii) diffuse fraction and fractional sunshine duration; (iii) diffuse fraction and clearness index combined with fractional sunshine duration. In addition, the monthly average values of the above-mentioned correlations were established. Comparison with the most commonly used equation, Page's correlation, gives good agreement for monthly average of the relationship between diffuse fraction and clearness index. An equation for daily diffuse transmissivity values that incorporates a single physically based coefficient, which reflects the maximum clear-sky transmissivity at the study site is presented.

Correlation between hourly diffuse and global radiation for New Delhi

Estimation of hourly insolation on tilted surfaces is required in simulation of solar energy systems. This necessitates splitting of hourly global horizontal insolation into diffuse and direct components. Many models have been developed for this purpose, and the aim of this study is to develop a correlation between hourly diffuse ratio and clearness index for New Delhi. The correlation is developed on the basis of measured data for two years. The performance of this correlation was checked by calculating the difference between computed and measured diffuse radiation. The correlation proved to perform quite well. A comparison of the present correlation with those for other locations showed that such correlations are location dependent.

An improved computer code for the simulation of solar heating systems

A generalised solar energy simulation code, which represents a significant improvement over fixed step iterative simulation codes, is presented. The key features of the code are the simultaneous solution of all differential equations arising from closed loops in the system, and the technique for advancing the simulation from “control function” to “control function”. Computer time is minimised by the use of sparse matrix techniques together with automatic time step control generated from an error bound estimate. The application of the improved code to the simulation of solar energy systems is demonstrated on two example problems. In the first problem, emphasis is placed on predicting the temperatures of the fluids within the system and the controller actions, while in the second problem the emphasis is on predicting long-term system performance. The simulation results of both these problems demonstrate that the improved code is suitable for both detailed system control and long-term system performance studies.