Transformer coupled multi-input two stage standalone solar photovoltaic scheme for rural areas[edit | edit source]
[30]D. Debnath and K. Chatterjee, "Transformer coupled multi-input two stage standalone solar photovoltaic scheme for rural areas," in IECON 2013 - 39th Annual Conference of the IEEE Industrial Electronics Society, 2013, pp. 7028–7033.
In this paper a transformer coupled multi-input dc-dc converter (TCMDDC) based solar photovoltaic system for standalone applications is proposed. The proposed TCMDDC can realize maximum power point tracking and battery charge control while maintaining proper voltage level. In the process it allows reduction in number of power conversion stages as compared to the existing standalone schemes. This leads to enhancements in efficiency and reliability of the proposed scheme. Further, it allows the use of low voltage levels for solar PV array and battery thereby eliminating concerns pertaining to the safety of personnel and equipment. A suitable control strategy that allows the TCMDDC to operate in different modes that are encountered in a standalone scheme is also devised. The viability of the scheme is ascertained through detailed analytical and simulation studies.
Notes:
- series connected PV modules increase voltage output but require complex control schemes or circuitry to track absolute MPP
- instead, use high-gain dc converter
- two stage topology
- MPPT, battery charge control, voltage boost all done by one converter
- isolation between input sources and load
- efficient battery charging (losses from only one converter)
- four operation modes based on MPP power in relation to load power
- increased efficiency through reduction of # of conversion stages, low PV voltage for increased safety, stable controller operation
A Two Stage Solar Photovoltaic based Stand Alone Scheme having Battery as Energy Storage Element for Rural Deployment[edit | edit source]
[31]D. Debnath and K. Chatterjee, "A Two Stage Solar Photovoltaic based Stand Alone Scheme having Battery as Energy Storage Element for Rural Deployment," IEEE Transactions on Industrial Electronics, vol. PP, no. 99, pp. 1–1, 2014.
Solar Photovoltaic (PV) based stand alone systems have evolved as a promising solution to the issue of electrification in areas where grid is not available. The major challenges in designing such systems are: a) extraction of maximum power from PV array, b) protection of battery from overcharge and over discharge, c) dc to ac conversion, and d) provision for adequate voltage boosting. As multiple objectives are required to be satisfied, the existing schemes for stand alone systems require a minimum of three converter stages leading to considerable reduction in reliability and efficiency of the system. In order to address this issue a two stage stand alone scheme consisting of a novel transformer coupled dual-input converter (TCDIC) followed by a conventional full bridge inverter is proposed in this paper. The proposed TCDIC can realize maximum power point tracking (MPPT) and battery charge control while maintaining proper voltage level at the load terminal. The small signal mathematical model of the TCDIC is derived. A suitable control strategy for the proposed TCDIC is devised. The operation of the scheme is verified by performing detailed simulation studies. A laboratory prototype of the scheme is developed. Detailed experimental validation of the scheme utilizing the laboratory prototype is carried out to confirm the viability of the scheme.
Notes:
- detailed analysis and experimental verification of system similar to [30] (two-stage, transformer coupled converter)
Optimal battery sizing for storm-resilient photovoltaic power island systems[edit | edit source]
[32]D. P. Birnie III, "Optimal battery sizing for storm-resilient photovoltaic power island systems," Solar Energy, vol. 109, pp. 165–173, Nov. 2014.
Photovoltaic systems with battery storage are analyzed from the perspective that they can operate as a local power island in circumstances of storm-damage or other grid outage. The specific focus is to determine the optimal battery size for a given solar array size, taking into account reasonable day-to-day and seasonal sunlight variations as well as efficiency losses when converting from DC to AC for connection to the grid, or for provision of power during island mode. Three locations in the United States are used as case studies (Newark NJ, Boulder CO, and Tucson AZ). These provide a wide range of sunlight characteristics and illustrate variability factors that will be similar to many locations in continental North America. The analysis of the probability distributions for sunlight brightness then allow for the establishment of a 95% confidence rating for the steady-state power output from a specific combined battery and solar array configuration when faced with a grid interruption. This rating system can be used as a guide for designing systems for future installation.
Notes:
- optimization of battery bank size for given solar array size for three different locations
A novel analytical model for optimal sizing of standalone photovoltaic systems[edit | edit source]
[33]A. Q. Jakhrani, A.-K. Othman, A. R. H. Rigit, S. R. Samo, and S. A. Kamboh, "A novel analytical model for optimal sizing of standalone photovoltaic systems," Energy, vol. 46, no. 1, pp. 675–682, Oct. 2012.
This paper presents a novel analytical model for the determination of optimal sizing of standalone photovoltaic (PV) systems with least cost and predetermined reliability to satisfy load. Algebraic equations for optimal PV array area (Aopt), optimal useful battery storage capacity (Cu,opt) and the constant of integration (kopt) has been formulated. The proposed model provides the system output directly without going through the calculation of PV array capacity (Ca) and battery storage capacity (Cb). It is different from previous models, which only optimize the system parameters Ca and Cb without involving load. The isoreliability curves of proposed model are compared with other analytical and numerical methods with the pair of Ca and Cb in different environmental conditions without load involvement. The formulated model is also applied for the optimal sizing of a standalone PV system for domestic purpose at Kuching, Sarawak, Malaysia. The required optimal PV array area (Aopt) and useful battery storage capacity (Cu,opt) is determined with various load demands and loss of load probability (LLP). Proposed analytical model is more constructive due to incorporation of many useful variables namely desired LLP value, latitude and clearness index of location, load demand and unit cost of PV array and battery capacity. It is also rational in terms of power reliability and cost, and simple to implement for the size optimization of standalone PV systems as compared to existing models.
Notes:
- optimum useful battery capacity and solar array area calculated analytically using mean solar radiation data
- comparison to other models used in literature
- 10.09 m^2 and 39816 Wh - optimum array area and battery storage values for case study in Malaysia to supply 5000 Wh/day (up to 8 days running on batteries alone)
Sizing of a standalone photovoltaic/battery system at minimum cost for remote housing electrification in Sohar, Oman[edit | edit source]
[34]H. A. Kazem, T. Khatib, and K. Sopian, "Sizing of a standalone photovoltaic/battery system at minimum cost for remote housing electrification in Sohar, Oman," Energy and Buildings, vol. 61, pp. 108–115, Jun. 2013.
This paper presents a method for optimal sizing of a standalone PV system for remote areas in Sohar, Oman. PV array tilt angle as well as the size of the system's energy sources are designed optimally for better performance and lower energy cost. Numerical methods for optimization of the PV module tilt angle, PV array size and storage battery capacity are implemented using MATLAB and hourly meteorological data and load demand. The results show that for Sohar zone the tilt angle of a PV array must be adjusted twice a year. The PV array must be slanted at 49° in the period of 21/09–21/03 (n = 255–81), while it must be horizontal (tilt angle is zero) in the period of 21/03–21/09 (n = 81–255). This adjustment practice gains the energy collected by a PV array by 20.6%. As for the PV system size, the results show that the sizing ration of the PV array for Oman is 1.33 while the sizing ratio for battery is 1.6. However the cost of the energy generated by the proposed system is 0.196 USD/kWh.
Notes:
- orientation and tilt angle of panels greatly affects collected energy yield
- optimization algorithm for tilt angle presented and used to calculate optimum tilt
- monthly tilt adjustment improves output by 23.3%, annual by 10.3%, optimum angle 49 degrees Sept-Mar, 0 degrees Mar-Sept
- 0.196 USD/kWh
Optimum sizing of photovoltaic-energy storage systems for autonomous small islands[edit | edit source]
[35]J. K. Kaldellis, D. Zafirakis, and E. Kondili, "Optimum sizing of photovoltaic-energy storage systems for autonomous small islands," International Journal of Electrical Power & Energy Systems, vol. 32, no. 1, pp. 24–36, Jan. 2010.
The electrification of autonomous electrical networks is in most cases described by low quality of electricity available at very high production cost. Furthermore, autonomous electrical networks are subject to strict constraints posing serious limitations on the absorption of RES-based electricity generation. To by-pass these constraints and also secure a more sustainable electricity supply status, the concept of combining photovoltaic power stations and energy storage systems comprises a promising solution for small scaled autonomous electrical networks, increasing the reliability of the local network as well. In this context, the present study is devoted to develop a complete methodology, able to define the dimensions of an autonomous electricity generation system based on the maximum available solar potential exploitation at minimum electricity generation cost. In addition special emphasis is given in order to select the most cost-efficient energy storage configuration available. According to the calculation results obtained, one may clearly state that an optimum sizing combination of a PV generator along with an appropriate energy storage system may significantly contribute on reducing the electricity generation cost in several island electrical systems, providing also abundant and high quality electricity without the environmental and macroeconomic impacts of the oil-based thermal power stations.
Notes:
- optimized solar power system for small autonomous islands in the Aegean
A case study of solar photovoltaic power system at Sagardeep Island, India[edit | edit source]
[36]R. M. Moharil and P. S. Kulkarni, "A case study of solar photovoltaic power system at Sagardeep Island, India," Renewable and Sustainable Energy Reviews, vol. 13, no. 3, pp. 673–681, Apr. 2009.
The application of renewable energy in electric power system is growing fast. Photovoltaic and wind energy sources are being increasingly recognized as cost-effective generation sources for remote rural area isolated power system. This paper presents the performance analysis of solar photovoltaic (SPV) system installed at Sagardeep Island in West Bengal state of India. The technical and commercial parameters are used to carry out the performance analysis. The effect of the SPV installation on social life is also studied. SPV installations not only provide electricity to people but also raised their standard of living.
Notes:
- 3 state model of PV system (up, derated, down) based on radiation intensity
- PV implementation resulted in increased quality of life
- system viable for demand not exceeding 25 kW
Cascaded DC-DC converter connection of photovoltaic modules[edit | edit source]
[37]G. R. Walker and P. C. Sernia, "Cascaded DC-DC converter connection of photovoltaic modules," IEEE Transactions on Power Electronics, vol. 19, no. 4, pp. 1130–1139, Jul. 2004.
New residential scale photovoltaic (PV) arrays are commonly connected to the grid by a single dc-ac inverter connected to a series string of pv panels, or many small dc-ac inverters which connect one or two panels directly to the ac grid. This paper proposes an alternative topology of nonisolated per-panel dc-dc converters connected in series to create a high voltage string connected to a simplified dc-ac inverter. This offers the advantages of a "converter-per-panel" approach without the cost or efficiency penalties of individual dc-ac grid connected inverters. Buck, boost, buck-boost, and Cu´k converters are considered as possible dc-dc converters that can be cascaded. Matlab simulations are used to compare the efficiency of each topology as well as evaluating the benefits of increasing cost and complexity. The buck and then boost converters are shown to be the most efficient topologies for a given cost, with the buck best suited for long strings and the boost for short strings. While flexible in voltage ranges, buck-boost, and Cu´k converters are always at an efficiency or alternatively cost disadvantage.
Notes:
- 2 kW or less, single DC string with single inverter
- proposed - each panel has own converter, connected in series then connected to single inverter
- numerous advantages to converter for each panel setup, including individual module control and better data gathering
- Matlab script to calculate losses/efficiencies of converter topologies
- buck-boost and Cuk converters performed poorly due to high s.c. switching and conduction losses
- buck converter over 96% efficiency
Single-stage photovoltaic energy conversion system[edit | edit source]
[38]T.-J. Liang, Y. C. Kuo, and J.-F. Chen, "Single-stage photovoltaic energy conversion system," Electric Power Applications, IEE Proceedings -, vol. 148, no. 4, pp. 339–344, Jul. 2001.
For a photovoltaic (PV) array, the nonlinear output power relation of dP/dV against V and the near linear relation of dP/dV against I are discussed. Thus, using dP/dV as an index for current control is easier than for voltage control, allowing a simpler design. The current controller is employed in the PV energy conversion system to perform a rapid maximum power point tracking and to provide power to utilities with a unity power factor. As opposed to conventional two-stage designs, a single-stage PV energy conversion system is implemented, resulting in size and weight reduction, and increased efficiency. The proposed system performs a dual function; acting as a solar generator on sunny days and as an active power filter on rainy days. Computer simulations and experimental results demonstrate the superior performance of the proposed technique
Notes:
- dP/dV in relation to V and I for MPPT
- 3% increase in output power over P+O method, 35% decrease in time required to reach MPP
A battery management system for stand-alone photovoltaic energy systems[edit | edit source]
[39]S. Duryea, S. Islam, and W. Lawrance, "A battery management system for stand-alone photovoltaic energy systems," IEEE Industry Applications Magazine, vol. 7, no. 3, pp. 67–72, Jun. 2001.
It is estimated that about 80% of all photovoltaic (PV) modules are used in stand-alone applications. Continuous power is obtained from PV systems by using a storage buffer, typically in the form of a lead acid battery. Batteries used in PV applications have different performance characteristics compared with batteries used in more traditional applications. In PV applications, lead acid batteries do not reach the cycle of lead acid batteries used in other applications such as uninterruptible power supplies or electric vehicles. The shortened battery life contributes significantly to the costs of a PV system. In some PV systems the battery accounts for more than 40% of the life cycle costs. An increase in the lifetime of the battery will result in improved reliability of the system and a significant reduction in operating costs. The life of a lead acid battery can be extended by avoiding critical operating conditions such as overcharge and deep discharge. This paper presents a battery management system for such applications
Notes:
- battery management system proposed which maintains the state of charge of the batteries to increase their lifetimes
- collected charge/discharge data to demonstrate performance
Comprehensive Approach to Modeling and Simulation of Photovoltaic Arrays[edit | edit source]
[40]M. G. Villalva, J. R. Gazoli, and E. R. Filho, "Comprehensive Approach to Modeling and Simulation of Photovoltaic Arrays," IEEE Transactions on Power Electronics, vol. 24, no. 5, pp. 1198–1208, May 2009.
This paper proposes a method of modeling and simulation of photovoltaic arrays. The main objective is to find the parameters of the nonlinear I-V equation by adjusting the curve at three points: open circuit, maximum power, and short circuit. Given these three points, which are provided by all commercial array data sheets, the method finds the best I-V equation for the single-diode photovoltaic (PV) model including the effect of the series and parallel resistances, and warranties that the maximum power of the model matches with the maximum power of the real array. With the parameters of the adjusted I-V equation, one can build a PV circuit model with any circuit simulator by using basic math blocks. The modeling method and the proposed circuit model are useful for power electronics designers who need a simple, fast, accurate, and easy-to-use modeling method for using in simulations of PV systems. In the first pages, the reader will find a tutorial on PV devices and will understand the parameters that compose the single-diode PV model. The modeling method is then introduced and presented in details. The model is validated with experimental data of commercial PV arrays.
Notes:
- AM1.5 - PV device tilted 37 degrees and facing sun rays
- Fig. 4 practical diagram of PV cell - possibly useful for simulation?
- detail of equations used to construct single diode PV I-V model
Design considerations about a photovoltaic power system to supply a mobile robot[edit | edit source]
[41]G. M. Tina, V. Cristina, A. Paolo, P. Luca, G. A. Dario, and P. Massimo, "Design considerations about a photovoltaic power system to supply a mobile robot," in 2010 IEEE International Symposium on Industrial Electronics (ISIE), 2010, pp. 1829–1834.
It is desirable that robots would be, as much as possible, autonomous and self-sufficient. This requires that they can perform their duties while maintaining enough energy to operate. This paper presents the preliminary results for the design of a power supply system of an autonomous robot. Robot design is divided into four primary areas: energy storage, actuation, power and control. It is obvious that there are many relationships among these phases so as matter of fact they have to be analyzed in parallel to optimize a robot, especially from the energetic point of view. In particular, a power supply solution that utilizes solar cells and a microcontroller have been chosen to power and control an hybrid robot, named TriBot. Finally, initial tests with a probe-loaded robot prototype have demonstrated the feasibility of the solution.
Notes:
- without PV system - robot lifetime of about 2 hours, possibly extended to 4.5 with PV system
- motor power consumption of ~9W during operation, ~12W while climbing
- 3.5W for controls during sensor operation
- c-Si and thin film a-Si cells considered
- c-Si likely best candidate for high(ish) efficiency, low cost, reliability, but lacks desirable flexibility
- further investigation needed on using lower power motion system and higher efficiency cells
Portable Photo-voltaic Stand-alone System, Operating at Very Low Power Conditions[edit | edit source]
[42]P. Del Vecchio and A. Timidei, "Portable Photo-voltaic Stand-alone System, Operating at Very Low Power Conditions," in International Conference on Clean Electrical Power, 2007. ICCEP '07, 2007, pp. 387–388.
A new approach to mobile photo-voltaic systems is proposed; the system described in this paper is of very low power (5 W) and is intended mainly for recharging or powering small portable electronics devices. The objects of this study are: (i) the optimization of photo-voltaic cells connection with regard to mobile conditions; a nonstandard topology is adopted, to compensate shadowing or non-optimal orientation; (ii) the introduction of a novel topology for battery and DC/DC converter, in which the battery voltage is optimized for photo-voltaic operation and a buck-boost converter can provide any voltage to the load. A good efficiency is achieved also in marginal condition of illumination (0.1 W). A prototype has been built with thin film photo-voltaic cells mounted on a flexible plastic support and integrated in a jacket. A series of measurements have been performed in a real-life situation, and the system has been characterized. The efficiency of the proposed system has been compared with a conventional system, in the same operating conditions.
Notes:
- traditional systems - load determines battery voltage, charge controller is step-down converter, high voltage from series string of PV modules (not ideal due to shading)
- proposed - battery voltage chosen to optimize efficiency, parallel module connection, bypass circuits, buck-boost converter independent of battery voltage
- low self-consumption, high efficiency at low power (5W)
- 4 strings of 3 a-Si cells sewn to a jacket and tested through direct and diffuse radiation
- proposed system improves over traditional, but could be further improved by increasing # of parallel connections in PV circuit
A simple PV array modeling using MATLAB[edit | edit source]
[43]M. A. Bhaskar, B. Vidya, R. Madhumitha, S. Priyadharcini, K. Jayanthi, and G. R. Malarkodi, "A simple PV array modeling using MATLAB," in 2011 International Conference on Emerging Trends in Electrical and Computer Technology (ICETECT), 2011, pp. 122–126.
This paper presents the general overview on the requirement of renewable energy mainly the solar power. We have also dealt with the types of solar power available and the basic modeling of solar energy system mainly the photo voltaic type has been discussed. MATLAB Simulink has been used as a tool to provide the I-V and P-V plots of the system.
Notes:
- PV module modeled as a current source in parallel with diode and shunt current and in series with series resistance
- in ideal PV cell, Rseries->0 and Rshunt->infinity
- real PV cell, Rseries varies from 0.05-0.10 Ohms, Rshunt from 200-300 Ohms
- small change in Rseries can impact output power substantially
A modular strategy for isolated photovoltaic systems based on microcontroller[edit | edit source]
[44]A. M. Pernía, J. Arias, M. J. Prieto, and J. Á. Martínez, "A modular strategy for isolated photovoltaic systems based on microcontroller," Renewable Energy, vol. 34, no. 7, pp. 1825–1832, Jul. 2009.
Many different types of commercial regulators can be found in the market. These devices can be basically divided into two categories according to their operation mode: those which modulate the input voltage using PWM (pulse-width modulation) in order to generate the output voltage required to charge the batteries; and those which make the PV (photovoltaic) array operate in their MPP (maximum power point), which can be tracked in several different ways. The former are normally used for low-power applications, whereas the latter can provide an increase of power up to 25% as compared to their PWM counterpart. This paper presents a regulator which can operate in the maximum power point of PV arrays by means of a microcontroller. A simple, highly-accurate algorithm suitable to be implemented in a low-cost microcontroller has been developed in order to make PV arrays track and operate in their maximum power point. The control strategy proposed allows parallel connection of different regulators, thus making it possible to keep and integrate previous equipment.
Notes:
- proposed - parallel connected regulators which operates at MPP regardless of weather conditions and allows for PV connection with 12V or 24V batteries
- MOSFETs chosen over Schottky diodes to reduce conductive losses
- power consumption of 100W, voltage ripple of .5V
- MPP error less than 2%
- 95% power stage efficiency
Developing a mobile stand alone photovoltaic generator[edit | edit source]
[45]R. Soler-Bientz, L. O. Ricalde-Cab, and L. E. Solis-Rodriguez, "Developing a mobile stand alone photovoltaic generator Developing a mobile stand alone photovoltaic generator," Energy Conversion and Management, vol. 47, no. 18–19, pp. 2948–2960, Nov. 2006.
This paper describes a recent work developed to create a mobile stand alone photovoltaic generator that can be easily relocated in remote areas to evaluate the feasibility of photovoltaic energy applications. A set of sensors were installed to monitor the electric current and voltage of the energy generated, the energy stored and the energy used by the loads that may be connected to the system. Other parameters like solar radiations (both on the horizontal and on the photovoltaic generation planes) and temperatures (of both the environment and the photovoltaic module) were monitored. This was done while considering the important role of temperature in the photovoltaic module performance. Finally, a measurement and communication hardware was installed to interface the system developed with a conventional computer. In this way, the performance of the overall system in real rural conditions could be evaluated efficiently. Visual software that reads, visualizes and saves the data generated by the system was also developed by means of the LabVIEW programming environment.
Notes:
- photovoltaic generator, measurement system, and monitoring software
- 12V lead-acid batteries, charge controller, inverter, DC-DC converter (0-12V)
- two temperature sensors, Si photodiode radiation sensors, DC I and V transducers
- data collected by NI FieldPoint DAQ
- LabVIEW monitoring software to interface with PC
Synchronous Buck Converter based PV Energy System for Portable Applications[edit | edit source]
[46]B. ChittiBabu, S. R. Samantaray, N. Saraogi, M. V. Ashwin Kumar, R. Sriharsha, and S. Karmaker, "Synchronous Buck Converter based PV Energy System for Portable Applications," in 2011 IEEE Students' Technology Symposium (TechSym), 2011, pp. 335–340.
Synchronous buck converter based photo voltaic (PV) energy system for portable applications is presented in this paper; especially to charge the batteries used in mobile phones. The main advantage of using synchronous buck converter is to reduce the switching loss in the main MOSFET over conventional dc-dc buck converter. The switching loss is minimized by applying soft switching techniques such as zero-voltage switching (ZVS) and zero-current switching (ZCS) in the proposed converter. Thus the cost effective solution is obtained; especially in the design of heat sink in the dc-dc converter circuit. The DC power extracted from the PV energy system is synthesized and modulated through synchronous buck converter in order to suit the load requirements. The characteristic of PV array is studied under different values of temperature and solar irradiation. Further, the performance of such converter is analyzed and compared with classical dc-dc buck converter in terms of switching loss reduction and improved converter efficiency. The whole system is studied in the MATLAB-Simulink environment.
Notes:
- switching losses in conventional converter higher due to high MOSFET switching frequency
- replace freewheeling diode with MOSFET switch, incorporate that into main MOSFET with LC resonant circuits to obtain soft switching and lower switching loss
- proposed synchronous buck converter simulated to be 94% efficient, better than 87% efficiency from regular buck converter
- application to charging mobile phones
Solar photovoltaic system modeling and performance prediction[edit | edit source]
[47]T. Ma, H. Yang, and L. Lu, "Solar photovoltaic system modeling and performance prediction," Renewable and Sustainable Energy Reviews, vol. 36, pp. 304–315, Aug. 2014.
A simulation model for modeling photovoltaic (PV) system power generation and performance prediction is described in this paper. First, a comprehensive literature review of simulation models for PV devices and determination methods was conducted. The well-known five-parameter model was selected for the present study, and solved using a novel combination technique which integrated an algebraic simultaneous calculation of the parameters at standard test conditions (STC) with an analytical determination of the parameters under real operating conditions. In addition, the simulation performance of the model was compared with other models, and further validated by outdoor tests, which indicate that the proposed model fits well the entire set of experimental field test I–V curves of the PV module, especially at the characteristic points. After validation, this model was employed to predict the PV system power output under real conditions. The results show that the predictions agree very well with the PV plant field collected data. Thus, the operating performance of a standalone PV system located on a remote island in Hong Kong has been further evaluated with the aid of this model. It is found that the PV array power output is restricted by the status of the battery bank. This research demonstrates that the PV simulation model developed during the study is simple, but very helpful to PV system engineers in understanding the I–V curves and for accurately predicting PV system power production under outdoor conditions.
Notes:
- failing to include internal resistances does not result in an accurate I-V simulation
- 4-p model neglecting shunt resistance insufficient
- two diode model accurate but requires a lot of computing power compared to 5 parameter model (one diode)
- simulation in Matlab compared to other software results and onsite testing
- R^2 RMSE, and MBE values used to quantify comparison between simulation and measurements
- high correlation with measurements when solar radiation is higher (less cloudy)
Distributed photovoltaic generation and energy storage systems: A review[edit | edit source]
[48]O. M. Toledo, D. Oliveira Filho, and A. S. A. C. Diniz, "Distributed photovoltaic generation and energy storage systems: A review," Renewable and Sustainable Energy Reviews, vol. 14, no. 1, pp. 506–511, Jan. 2010.
Currently, in the field of operation and planning of electrical power systems, a new challenge is growing which includes with the increase in the level of distributed generation from new energy sources, especially renewable sources. The question of load redistribution for better energetic usage is of vital importance since these new renewable energy sources are often intermittent. Therefore, new systems must be proposed which ally energy storage with renewable energy generators for reestablishment of grid reliability. This work presents a review of energy storage and redistribution associated with photovoltaic energy, proposing a distributed micro-generation complex connected to the electrical power grid using energy storage systems, with an emphasis placed on the use of NaS batteries. These systems aim to improve the load factor, considering supply side management, and the offer of backup energy, in the case of demand side management.
Notes:
- current choices for energy storage from PV: supercaps, flow batteries, NaS, Li-ion, Ni-Cd, lead-acid, metal-air batteries, pumped hydro, compressed air, flywheels
- NaS likely the best option for PV due to scale, amount of time in use before recharge, energy management (load leveling and peak shaving), but they are expensive
- 3-5x energy density of lead-acid
- 98% of material can be recycled
- roundtrip AC energy efficiency of 76% from AEP NaS-based storage system
- PV system with storage has added value by being able to provide power during times of low insolation
Parallel-Connected Solar PV System to Address Partial and Rapidly Fluctuating Shadow Conditions[edit | edit source]
[49]L. Gao, R. A. Dougal, S. Liu, and A. P. Iotova, "Parallel-Connected Solar PV System to Address Partial and Rapidly Fluctuating Shadow Conditions," IEEE Transactions on Industrial Electronics, vol. 56, no. 5, pp. 1548–1556, May 2009.
Solar photovoltaic (PV) arrays in portable applications are often subject to partial shading and rapid fluctuations of shading. In the usual series-connected wiring scheme, the residual energy generated by partially shaded cells either cannot be collected (if diode bypassed) or, worse, impedes collection of power from the remaining fully illuminated cells (if not bypassed). Rapid fluctuation of the shading pattern makes maximum power point (MPP) tracking difficult; generally, there will exist multiple local MPPs, and their values will change as rapidly as does the illumination. In this paper, a portable solar PV system that effectively eliminates both of the aforementioned problems is described and proven. This system is capable of simultaneously maximizing the power generated by every PV cell in the PV panel. The proposed configuration consists of an array of parallel-connected PV cells, a low-input-voltage step-up power converter, and a simple wide bandwidth MPP tracker. Parallel-configured PV systems are compared to traditional series-configured PV systems through both hardware experiments and computer simulations in this paper. Study results demonstrate that, under complex irradiance conditions, the power generated by the new configuration is approximately twice that of the traditional configuration. The solar PV system can be widely used in many consumer applications, such as PV vests for cell phones and music players.
Notes:
- series connected PV array leads to rapidly changing local maxima of P-V curve, hard to track MPP
- parallel-connected PV cells, step-up converter, wide-bandwidth MPP tracker
- some serial connection required to increase voltage to converter
- parallel connection more suitable for highly mobile applications with inconsistent/changing illumination
- power generation increase by factor of ~2 using parallel over series under changing illumination
- shown by simulations and experimental evidence
Resistive Control for a Photovoltaic Battery Charging System Using a Microcontroller[edit | edit source]
[50]J. H. Lee, H. S. Bae, and B.-H. Cho, "Resistive Control for a Photovoltaic Battery Charging System Using a Microcontroller," IEEE Transactions on Industrial Electronics, vol. 55, no. 7, pp. 2767–2775, Jul. 2008.
A new control algorithm has been developed, consisting of a buck-type dc/dc converter, which is used in a parallel-operated photovoltaic battery charging system. From the past research, it has been analyzed that the current loop that is generally used in the parallel operation of the power conditioner has an inherent stability problem in the large-signal domain in the photovoltaic system. The proposed algorithm directly transforms the effective input characteristic of the converter seen by the solar array into a resistive load, which is controlled by a microcontroller-based unit. Thus, the resulting system eliminates the instability associated with the current loop in the photovoltaic system. In addition, it is simple, flexible, and easily expandable. To analyze the effects of the one-sample delay caused by the digital controller, the emulated function in the case of average current mode control is modeled using small-signal approaches, and the design criteria are presented. The experimental results from 180-W prototype hardware show that the proposed algorithm has a simple implementation structure and can stabilize the system in the entire region of the solar array.
Notes:
- novel control scheme transforms input characteristic of converter, increased stability
- advantages: resistive control always stable regardless of line inductance, each power stage can be separately controlled in parallel, no additional components
- 2 180W PV panels in series, 2 buck converters in parallel for current-mode control and proposed control experimentally tested
- simple implementation structure and improved stability of PV system
