Uniqueness verification of solar spectrum index of average photon energy for evaluating outdoor performance of photovoltaic modules

To analyze the effect of a spectral irradiance distribution of solar spectra on the outdoor performance of photovoltaic (PV) modules, an index for the spectral distribution is needed. Average photon energy (APE) which represents the average energy per photons included in a spectrum is one of these. In this study, the uniqueness of APE to the spectral irradiance distribution was statistically analyzed to assure that an APE value uniquely yields the shape of a solar spectrum. The similar methodology adopted in International Electrotechnical Commission to rate the spectral matching of a solar simulator was used for the analysis. The results showed that an APE value yielded a spectral irradiance distribution with quite small standard deviation. The analysis using APE showed that the outdoor performance of crystalline Si PV modules depended almost only on a module temperature, while that of amorphous Si ones mainly depended on APE. The behaviors were reasonable considering from the operation mechanisms of the PV modules. These results demonstrate that APE is a reasonable and useful index to describe the spectral irradiance distribution for evaluating the outdoor performance of PV modules.     

Output energy of a photovoltaic module mounted on a single-axis tracking system

In this study, the electric energy from a photovoltaic module was calculated theoretically at different azimuths and tilt angles in Taiwan. The gain of the module mounted on a single-axis tracking panel relative to a traditional fixed panel was analyzed. To simulate different operation environments, both types of radiation will be considered in addition to observed radiation, i.e. the extraterrestrial radiation and the global radiation predicted by an empirical model. The results show that the optimal tilt angle obtained from the observed data is flatter than those from other two radiation types and becomes flatter while the panel deviates from due south. The yearly gains obtained from the extraterrestrial, predicted and observed radiations are 51.4%, 28.5% and 18.7%, respectively, if a single-axis tracked panel is installed with the yearly optimal tilt angle; the similar gains are 45.3%, 25.9% and 17.5%, respectively, while the panel is adjusted to its monthly optimal angle each month. The amount of yearly energy in due west (or east) is less than its maximum in due south by about 11%, 10% and 5% for the extraterrestrial, predicted and observed radiation respectively. The yearly conversion efficiency of a fixed module is 10.2%, 9.2% and 8.3% for the extraterrestrial, predicted and observed radiation, respectively.     

Solar energy in Malaysia: Current state and prospects

Malaysia is situated at the equatorial region with an average solar radiation of 400-600 MJ/m² per month. It has a promising potential to establish large scale solar power installations; however, solar energy is still at the infancy stage due to the high cost of photovoltaic (PV) cells and solar electricity tariff rate. The Malaysian government is keen to develop solar energy as one of the significant sources of energy in the country. According to the 9th Malaysia Plan (9MP), a large allocation had been dedicated for implementation of solar PV systems. On 25th July 2005, a Malaysian Building Integrated Photovoltaic (MBIPV) project had been announced and it was planned to end by 2010. The project consists of three categories which include: BIPV demonstration, national “SURIA1000” and BIPV showcase. Greater emphasis will be placed on energy efficiency under the Tenth Malaysia Plan (2011-2015). This paper discusses present and future situation of solar power in Malaysia, utilization of solar energy and the strategies taken by the Malaysian government and Non-Government Organizations (NGOs) to promote solar energy thermal applications and electricity power generation in the future.     

Single-stage sine-wave inverter for an autonomous operation of solar photovoltaic energy conversion system

This paper proposes a high performance single-stage inverter topology for the autonomous operation of a solar photovoltaic system. The proposed configuration which can boost the low voltage of photovoltaic (PV) array, can also convert the solar dc power into high quality ac power for driving autonomous loads without any filter. An MPPT circuit with parallel connection is implemented so that the part of the energy generated is processed by the dc–dc converter to supply dc loads. The line current total harmonic distortion (THD) obtained using this configuration is quite reasonable. The proposed topology has several desirable features such as low cost and compact size as number of switches used, are limited to four as against six switches used in classical two-stage inverters. In this paper analysis, simulation and experimental results are presented.     

Improved photovoltaic energy output for cloudy conditions with a solar tracking system

This work describes measurements of the solar irradiance made during cloudy periods in order to improve the amount of solar energy captured during such periods. It is well-known that 2-axis tracking, in which solar modules are pointed at the sun, improves the overall capture of solar energy by a given area of modules by 30-50% versus modules with a fixed tilt. On sunny days the direct sunshine accounts for up to 90% of the total solar energy, with the other 10% from diffuse (scattered) solar energy. However, during overcast conditions nearly all of the solar irradiance is diffuse radiation that is isotropically-distributed over the whole sky. An analysis of our data shows that during overcast conditions, tilting a solar module or sensor away from the zenith reduces the irradiance relative to a horizontal configuration, in which the sensor or module is pointed toward the zenith (horizontal module tilt), and thus receives the highest amount of this isotropically-distributed sky radiation. This observation led to an improved tracking algorithm in which a solar array would track the sun during cloud-free periods using 2-axis tracking, when the solar disk is visible, but go to a horizontal configuration when the sky becomes overcast. During cloudy periods we show that a horizontal module orientation increases the solar energy capture by nearly 50% compared to 2-axis solar tracking during the same period. Improving the harvesting of solar energy on cloudy days is important to using solar energy on a daily basis for fueling fuel-cell electric vehicles or charging extended-range electric vehicles because it improves the energy capture on the days with the lowest hydrogen generation, which in turn reduces the system size and cost.     

Design and simulation of the power control system of a plant for the generation of hydrogen via electrolysis, using photovoltaic solar energy

The gradual exhaustion of natural resources, particularly energy sources, and the various problems involved in their life-cycle, makes it necessary to promote a renewably derived hydrogen economy, in which hydrogen is produced from clean sources.

In this paper, the control system for an installation for producing hydrogen via electrolysis using only a 250 kWp photovoltaic generator is presented. Computer simulation was used to design and confirm its correct performance.

The results obtained ensure the installation's high energy yield.     

Desalination of underground brackish waters using an electrodialysis system powered directly by photovoltaic energy

The aims of this paper are: to demonstrate the feasibility of the desalination of brackish water from aquifers (total dissolved solids=2300-5100 g m⁻³) by means of an electrodialysis system powered directly by photovoltaic solar panels, and improve the mathematical model developed in a previous work in order to apply it to real brackish waters. The application of this model allows to predict the behaviour of the electrodialysis-photovoltaic system under different operational and meteorological conditions, and the time required to reach a given final concentration. Finally, the cost of electrodialysis-photovoltaic systems for small applications in isolated locations with lack of electric grid has been estimated.     

Design optimization of a large scale rooftop photovoltaic system

This paper presents the optimization process of a grid connected photovoltaic (PV) system, which is intended to replace a large-scale thermal solar system on the rooftop of a Federal office building. A PV energy conversion model is described. Based on this model, array surface tilt angle and array size are optimized. The optimization method is based on maximizing the utilization of the array output energy, and, at the same time, minimizing the electricity power sold to grid. An effectiveness factor is introduced that takes into account both of these parameters. The array configuration and the output parameters are determined by comparing several PV modules. A 43.2 kW PV system is designed and operational problems such as harmonic effects and anti-islanding are discussed. Finally, the system performance is simulated and through economic analysis it has shown that the cost of PV system can be recouped in 13 years under the current renewable energy incentive program by the state of Illinois.     

Investigation on abundant photovoltaic power generated by 40 kW PV system in Wakayama National College of Technology

We investigated the output characteristics of 40 kW photovoltaic (PV) power system installed at Wakayama National College of Technology. The total amount of PV power measured from our 40 kW PV system was 53 431.5 kW h/year. This abundant PV power was attributable to the greater amount of solar radiation and low temperature of the PV module.     

Diagnostic technology and an expert system for photovoltaic systems using the learning method

Diagnostic technology for photovoltaic (PV) systems was developed, using the learning method to take each site’s conditions into account. This technology employs diagnostic criteria databases to analyze data acquired from the PV systems. These criteria are updated monthly for each site using analyzed data. To check the shadows on the PV modules and pyranometer, the sophisticated verification method was also applied to this technology. After the diagnosis, a basket method provides maintenance advice for the PV systems. Based on the results of precise diagnoses, this expert system offers quick and proper maintenance advice within a few minutes. This technology is highly useful, because it greatly simplifies the servicing and maintenance of PV systems.     

Performance optimization of a photovoltaic induction motor pumping system

The performances of a photovoltaic pumping system based on an induction motor are degraded once insolation varies far from the value called nominal, where the system was sized. To surmount this handicap, an improvement of these performances by the optimization of the motor efficiency is described in this paper. The results obtained are compared with those of similar work pieces presented in the literature where the motor effeciency and air gap flux where optimized separatly. The simulation results show that the proposed system allows at the same time to combine the performances of the system with constant efficiency and the simplicity of implementation provided by the system with constant airgap flux.     

Solar photovoltaic charging of high voltage nickel metal hydride batteries using DC power conversion

There are an increasing number of vehicle choices available that utilize batteries and electric motors to reduce tailpipe emissions and increase fuel economy. The eventual production of electricity and hydrogen in a renewable fashion, such as using solar energy, can achieve the long-term vision of having no tailpipe environmental impact, as well as eliminating the dependence of the transportation sector on dwindling supplies of petroleum for its energy. In this report we will demonstrate the solar-powered charging of the high-voltage nickel-metal hydride (NiMH) battery used in the GM 2-mode hybrid system. In previous studies we have used low-voltage solar modules to produce hydrogen via the electrolysis of water and to directly charge lithium-ion battery modules. Our strategy in the present work was to boost low-voltage PV voltage to over 300 V using DC-DC converters in order to charge the high-voltage NiMH battery, and to regulate the battery charging using software to program the electronic control unit supplied with the battery pack. A protocol for high-voltage battery charging was developed, and the solar to battery charging efficiency was measured under a variety of conditions. We believe this is the first time such high-voltage batteries have been charged using solar energy in order to prove the concept of efficient, solar-powered charging for battery-electric vehicles.     

Optimization of the energy transfer in a system combining photovoltaic source to ultracapacitors

The optimal energy transfer is investigated for a system combining a photovoltaic module, a bank of ultracapacitors and a resistive load. Each ultracapacitor element is modeled with an accurate multibranch circuit composed of resistors and nonlinear capacitors which permit to reproduce its non-ideal behavior. The charge/discharge of ultracapacitors fed with the photovoltaic module into the resistive load is numerically simulated for irradiance of 1000 W m⁻² and cell temperature of 25 °C. The energy and the durations of the charge/discharge cycles are sought according to the low and high voltage thresholds of the controller switches. The cycle efficiency is found in the range [86.5%, 93.5%] and the best time ratio cycle is determined. Finally, the voltage thresholds of the controller switch which enable to transfer the maximal energy within an hour are deduced.     

Analysis of MPPT characteristics in photovoltaic power system

This paper describes characteristics evaluation of the power conditioner which has the function of Maximum Power Point Tracking (MPPT) by “mountain climbing method” through computer simulations. The generated power on the constant voltage control is compared to the one on MPPT with the load matching correction factor (Kpm). In this simulation, the following parameters are chosen, the rate of the voltage ΔV on changing the operating point and of the voltage ΔV_c on checking the maximum point.As a result, the influence of these parameters on Kpm is showed and it is made clear that we should decide the MPPT parameters with care.     

A system dynamics approach for the photovoltaic energy market in Spain

The goal of this paper is to contribute to understanding the behaviour of the photovoltaic (PV) sector in Spain and its expectations under possible scenarios. Currently, PV solar energy is not a profitable sector by itself. Therefore, the Spanish government, like the governments of other countries, has stimulated investment with subsidies. The spectacular increase of PV facilities exceeded all forecasts and the government decided to curb the trend. The present hypothesis is that continuing with this support to PV energy, the technological advances and the economy generated from the production of panels would be able to make the sector profitable in the future without the necessity of subventions. Based on this hypothesis, a computer simulation model was built using the system dynamics methodology. To test its utility, the model was challenged to fit the historical data and to explore several futures over the next few years. The model allows an understanding of the sector's behaviour under the latest policies of the Spanish government, thus helping to design future public policies. The simulation results are different depending on the adopted policy and the scenario. Therefore, these factors will determine the success or failure of the investments in this type of energy.     

Daily energy planning of a household photovoltaic panel

This paper puts forward an energy planning approach which offers a daily optimum management of a household photovoltaic panel generation (PVG) without using storage equipment. The approach considers the PVG of the last 10 days to estimate the one of the next day, using a Neuro-Fuzzy algorithm. The estimated PVG is planned according to the consumer’s needs so as to use the maximum of the generated energy. The algorithm decides by means of fuzzy rules the connection times of appliances, having different powers, to the photovoltaic panel (PVP) output during the day. The decision is made on the basis of optimization criteria with respect to different user operation modes. The approach is validated on a 260 Wp PVP and a set of four appliances of 30 W, 40 W, 60 W and 75 W. The system is installed at the National Engineering School, University of Sfax (ENIS) – Tunisia. The daily energetic assessment confirms that the PVG planning makes use of the estimated available energy in between 70% and 80%.     

Model for energy conversion in renewable energy system with hydrogen storage

A dynamic model for a stand-alone renewable energy system with hydrogen storage (RESHS) is developed. In this system, surplus energy available from a photovoltaic array and a wind turbine generator is stored in the form of hydrogen, produced via an electrolyzer. When the energy production from the wind turbine and the photovoltaic array is not enough to meet the load demand, the stored hydrogen can then be converted by a fuel cell to produce electricity. In this system, batteries are used as energy buffers or for short time storage. To study the behavior of such a system, a complete model is developed by integrating individual sub-models of the fuel cell, the electrolyzer, the power conditioning units, the hydrogen storage system, and the batteries (used as an energy buffer). The sub-models are valid for transient and steady state analysis as a function of voltage, current, and temperature. A comparison between experimental measurements and simulation results is given. The model is useful for building effective algorithms for the management, control and optimization of stand-alone RESHSs.     

Techno-economic valuation and optimization of integrated photovoltaic/wind energy conversion system

Decentralized electricity generation by renewable energy sources offer greater security of supply for consumers while respecting the environment. But the random nature of these sources requires us to develop sizing rules and use these systems to exploit them. This paper proposes an integrated PV/wind hybrid system optimization model, which utilizes the iterative optimization technique following the Deficiency of Power Supply Probability (DPSP), the Relative Excess Power Generated (REPG), the Total Net Present Cost (TNPC), the Total Annualized Cost (TAC) and Break-Even Distance Analysis (BEDA) for power reliability and system costs. The flow chart of the hybrid optimal sizing model is also illustrated. With this merged model, the optimal size of PV/wind hybrid energy conversion system using battery bank can be performed technically and economically according to the system reliability requirements. Additionally, a sensitivity analysis was carried out in order to appreciate the most important parameters influencing the economic performances of the hybrid system. A case study is conducted to analyze one hybrid project, which is designed to supply small residential household situated in the area of the Center for Renewable Energy Development (CDER) localized in Bouzaréah, Algeria (36°48′N, 3°1′E, 345 m).     

Operation strategy of residential centralized photovoltaic system in remote areas

Photovoltaic (PV) systems have found fairly wide application in remote isolated area. However, each individual PV system usually supplies energy only to one consumer. In such a case we have several consumers that each one of them uses a stand-alone PV system. This situation would expose such stand-alone systems to transient excessive loads larger than the power generated by the PVs, and then the battery is bound to discharge even during the day. For overcoming this problem, we suggest an autonomous centralized PV system, comprising one battery bank and plural subsystems connected to each other. From solar radiation data and load profiles, the performance of the PV centralized system is simulated by using a time step scheme. The advantages of this system are found to be the large charging rate of power, high efficiency, and low cost compared with conventional individual PV systems and hybrid systems. In addition, the economic study shows that the life cycle cost and the price of kilowatt hour generated in the centralized system is lower than that for the individual systems.     

Enhanced control strategies for a hybrid battery/photovoltaic system using FGS-PID in grid-connected mode

This paper suggests improved control strategies using Fuzzy Gain Scheduling of Proportional-Integral-Derivative (FGS-PID) controller for a hybrid Photovoltaic (PV) and Battery Energy Storage (BES) system under different weather conditions. The proposed scheme is implemented using a two-level control system structure, combining the benefits of the PID as well as the fuzzy logic controller (FLC) for maximum power point tracking (MPPT). Ziegler-Nichols tuning method is also employed to select the initial values of PID gains. Within the period of steady-states and transients, FGS-PID adopts the gains to ensure the stability of the control scheme. It also damps out transient fluctuations and reduces settling time. Also, BES could be employed to provide a stable and reliable power from the output of PV sources to loads. It can enhance the performance of the entire power system during the grid-connected mode. The simulation results under Matlab/Simulink show that the suggested control strategies are robustness, fast transient response and proper steady-state performance in the grid-connected mode in comparison other presented methods.