Improving photovoltaic system sizing by using electrolyte circulation in the lead-acid batteries

Lead-acid batteries are, between all types of batteries, the most used today as storage systems for photovoltaic applications. The sizing of the lead-acid batteries is based on some external parameters, solar irradiation and load consumption, and some battery characteristics, charge capacity and efficiency, depth of discharge, operating voltage, and ageing effects. The improvement of any of these parameters will result in an improvement of the sizing of the lead-acid battery and, consequently, of the sizing of the photovoltaic array. We have studied in this paper the influence of the improved capacity of lead-acid batteries with electrolyte circulation onto the sizing of the lead-acid battery and the PV array. The experimental results have shown that the lead-acid battery capacity can be improved as much as 20% if electrolyte circulation is used. The improvement results in a reduction of up to 30% in the size of the battery if combined with the improvement in the reduction of the battery capacity due to annual cycling and ageing, another beneficial effect of the electrolyte circulation. The reduction of size is extended to the PV array which is affected not only by the above mentioned effects, but also by the higher charge efficiency of the electrolyte circulation battery. The reduction in sizing the PV array can be as much as 41% for the most exigent operating conditions, deep depth of discharge and high discharge rate. The use of an electrolyte circulation system is especially useful in lead-acid batteries for PV systems which must operate at very deep cycling and require a minimum size of the battery block.     

The partial state-of-charge cycle performance of lead-acid batteries

Negative plate lugs of flooded lead-acid battery were corroded during partial state-of-charge (PSoC) pattern cycle life tests simulated from stop and go vehicle driving.     

Techno-economic feasibility of photovoltaic,wind, diesel and hybrid electrification systems for off-grid rural electrification in Colombia

Electrification to rural and remote areas with limited or no access to grid connection is one of the most challenging issues in developing countries like Colombia. Due to the recent concerns about the global climatic change and diminishing fuel prices, searching for reliable, environmental friendly and renewable energy sources to satisfy the rising electrical energy demand has become vital. This study aims at analyzing the application of photovoltaic (PV) panels, wind turbines and diesel generators in a stand-alone hybrid power generation system for rural electrification in three off-grid villages in Colombia with different climatic characteristics. The areas have been selected according to the “Colombia’s development plan 2011–2030 for non-conventional sources of energy”. First, different combinations of wind turbine, PV, and diesel generator are modeled and optimized to determine the most energy-efficient and cost-effective configuration for each location. HOMER software has been used to perform a techno-economic feasibility of the proposed hybrid systems, taking into account net present cost, initial capital cost, and cost of energy as economic indicators.     

Performance of small-scale photovoltaic systems and their potential for rural electrification in Ethiopia

The performance of small-scale stand-alone photovoltaic systems is tested under the climatic conditions of Addis Ababa, Ethiopia. With climatic data obtained at a station in the Rift Valley, the photovoltaic system performance is estimated for those climatic conditions. The economics of small-scale stand-alone photovoltaic system applications under Ethiopian conditions are analysed. The potential of photovoltaics for the rural electrification of Ethiopia is discussed.     

Rural photovoltaic electrification program in Jordan

The photovoltaic (PV) technology potential for Jordan is high, based on the fact that many remote and isolated sites are located far away from the national electric grid and cannot be connected to it in the near future. Therefore, a rural PV electrification program—driven by quality-of-life improvement for the users—was launched in Jordan in 2002. An important element of the program is the access of low-income, rural consumers to essential electricity.This paper discusses and analyses the first stage of this program that is the electrification of a remote and small Jordanian village. Nine PV solar home systems (SHS) were installed in this village in order to provide lighting and power for radio and television.Feed back from the users of the installed systems indicates that the PV based electricity has been providing very satisfactory service to the consumers, and that it is an appropriate technology suitable for dissemination in the rural Jordanian areas.     

Field analysis of solar PV-based collective systems for rural electrification

This article analyses the long-term performance of collective off-grid photovoltaic (PV) systems in rural areas. The use of collective PV systems for the electrification of small medium-size villages in developing countries has increased in the recent years. They are basically set up as stand-alone installations (diesel hybrid or pure PV) with no connection with other electrical grids. Their particular conditions (isolated) and usual installation places (far from commercial/industrial centers) require an autonomous and reliable technology. Different but related factors affect their performance and the energy supply; some of them are strictly technical but others depend on external issues like the solar energy resource and users’ energy and power consumption. The work presented is based on field operation of twelve collective PV installations supplying the electricity to off-grid villages located in the province of Jujuy, Argentina. Five of them have PV generators as unique power source while other seven include the support of diesel groups. Load demand evolution, energy productivity and fuel consumption are analyzed. Besides, energy generation strategies (PV/diesel) are also discussed.     

Sulphation in discharged lead-acid batteries

The inability of lead-acid batteries to be efficiently recharged after prolonged storage in the discharged state has been studied. Experimental (three plate) cells have been fully discharged and stored for various periods (0,4, 8, 24 weeks) prior to being recharged by a constant voltage schedule. In addition, the electrolyte of some of the cells stored for 24 weeks was replaced by water before the cells were recharged.Current/time profiles, ampere-hour input, and capacity after recharge data have been recorded for the recharges after each storage period. Samples of active material have also been examined by S.E.M. chemical analysis.The results obtained confirmed that it becomes increasingly difficult to recharge as the period in store increases and that the crystal growth is greater on the positive PbO₂ electrode than on the negative electrode. The results also indicate that the increased size of the crystals may not be the complete cause of the inability to recharge.     

Antimony poisoning in lead-acid batteries

Linear potential sweep measurements were conducted using rotating lead-disc electrodes in sulfuric acid electrolyte containing antimony. Within the range investigated hydrogen evolution at the negative electrode is shown to be a monotonic function of the quantity of antimony deposited on the electrode surface. In the potential range −950 mV to −1150 mV versus Hg/Hg₂SO₄ the antimony deposition on lead electrodes is time dependent only; at more negative potentials the deposition rate decreases with over-voltage. At potentials <−1320 mV antimony purging occurs. Various additives to the electrolyte were investigated to determine their ability to suppress the hydrogen evolution; aromatic aldehydes and wood flour were found to be effective. A possible mechanism is discussed.     

Grid electrification challenges, photovoltaic electrification progress and energy sustainability in Lesotho

Lesotho's energy profile is characterized by a predominance of traditional biomass energy to meet the energy needs of the rural households and a heavy dependence on imported petroleum for the modern economic sector needs. As a result, the country faces challenges related to unsustainable use of traditional forms of biomass and exposure to high and unstable oil import prices. There are relatively abundant renewable energy resources in the form of hydro, solar and wind. The average daily solar radiation in Lesotho varies between 4.5 and 6.5 kWh/m², with some areas in the South West averaging over 7 kWh/m²/day. Under the UNDP/GEF-supported Lesotho Renewable Energy-Based Rural Electrification (LREBRE) Project, a total of 5000 solar home systems (SHS) will be installed by 2012. Since the start of the project, a total of 1537 SHS with a capacity of 65 W have been installed, and an estimated 500 SHS have also been independently installed as a result of the project's influence. This paper examines the role of PV technologies in the sustainable development process, with particular reference to UNDP/GEF-LREBRE Lesotho PV project, and the extent to which this project is impacting on the PV industry. The paper also analyses national grid electrification and energy provision in rural areas and shows that the problem of rural electrification could be tackled by conventional and non-conventional means.     

Options for rural electrification in Mexico

The author summarizes a study which examined 19 commercially available options for electrifying remote communities in Mexico. Characteristics of a typical community were defined and, using seven of the technologies, power systems were designed capable of supporting this community. The performance of these systems was evaluated, with respect to their ability to satisfy 11 technical design objectives, five socioeconomic objectives, and their impact on the environment. A photovoltaic-diesel generator hybrid system with a wind generator option was recommended for the typical community     

Heat tolerance of automotive lead-acid batteries

Starter batteries have to withstand a quite large temperature range. In Europe, the battery temperature can be −30 °C in winter and may even exceed +60 °C in summer. In most modern cars, there is not much space left in the engine compartment to install the battery. So the mean battery temperature may be higher than it was some decades ago. In some car models, the battery is located in the passenger or luggage compartment, where ambient temperatures are more moderate.     

Recovery of discarded sulfated lead-acid batteries

The aim of this research is to recover discarded sulfated lead-acid batteries. In this work, the effect of two methods (inverse charge and chemical charge) on the reactivation of sulfated active materials was investigated. At the inverse charge, the battery is deeply discharged and the electrolyte of battery is replaced with a new sulfuric acid solution of 1.28 g cm⁻³. Then, the battery is inversely charged with constant current method (2 A for the battery with the nominal capacity of 40 Ah) for 24 h. At the final stage, the inversely charged battery is directly charged for 48 h. Through these processes, a discarded battery can recover its capacity to more than 80% of a similar fresh and non-sulfated battery.At the chemical charge method, there are some effective parameters that including ammonium persulfate [(NH₄)₂S₂O₈] concentration, recovery temperature and recovery time. The effect of all parameters was optimized by one at a time method. The sulfated battery is deeply discharged and then, its electrolyte was replaced by a 40% ammonium persulfate solution (as oxidant) at temperature of 50 °C. By adding of oxidant solution, the chemical charging of positive and negative plates was performed for optimum time of 1 h. The chemically charged batteries were charged with constant voltage method (2.66 V for the battery with nominal voltage and nominal capacity of 2 V and 10 Ah, respectively) for 24 h. By performing of these processes, a discarded battery can recovers its capacity to more than 84% of the similar fresh and non-sulfated battery. Discharge and cyclelife behaviors of the recovered batteries were investigated and compared with similar healthy battery. The morphology and structure of plates was studied by scanning electron microscopy (SEM) before and after recovery.     

Application of valve-regulated lead-acid batteries for storage of solar electricity in stand-alone photovoltaic systems in the northwest areas of China

Photovoltaic (PV) installations for solar electric power generation are being established rapidly in the northwest areas of China, and it is increasingly important for these power systems to have reliable and cost effective energy storage. The lead-acid battery is the more commonly used storage technology for PV systems due to its low cost and its wide availability. However, analysis shows that it is the weakest component of PV power systems. Because the batteries can be over discharged, or operated under partial state of charge (PSOC), their service life in PV systems is shorter than could be expected. The working conditions of batteries in remote area installations are worse than those in situations where technical support is readily available. Capacity-loss in lead-acid batteries operated in remote locations often occurs through sulfation of electrodes and stratification of electrolyte.In northwest China, Shandong Sacred Sun Power Sources Industry Co. Ltd. type GFMU valve-regulated lead-acid (VRLA) batteries are being used in PV power stations. These batteries have an advanced grid structure, superior leady paste, and are manufactured using improved plate formation methods. Their characteristics, and their performance in PV systems, are discussed in this paper. The testing results of GFMU VRLA batteries in the laboratory have shown that the batteries could satisfy the demands of the International Electrotechnical Commission (IEC) standards for PV systems.     

Porosity measurements of electrodes used in lead-acid batteries

A method is presented that determines the porosity of a complete electrode plate used in lead-acid batteries. It requires only elementary equipment and is simple to operate, so that laboratory workers can use it as a routine method during manufacturing to determine the complete electrode's average porosity over a range of electrode sizes and types of both flat plate and tubular configuration. The method makes use of Archimedes’ principle and uses glycerol as displacement medium. This allows for the porosity determination of both cured and formed positive and negative electrodes, without the detrimental effect of lead oxidation, which is common when using water as a displacement medium. The study showed that the method of using glycerol as a displacement medium gave on average, good repeatable results for both cured and formed positive and negative electrode plates used in the manufacture of automotive lead-acid batteries. The porosity results of the method were compared to the results obtained using Hg porosimetry, where a statistical paired t-test showed the two techniques to produce comparable results for all types of plates analyzed. The porosity of various plates was compared to the surface area of the respective active material of both positive and negative electrodes. These results showed unusual trends in that, depending on the manufacturing conditions, the surface area of formed positive electrodes could vary significantly from sample to sample of different batches without little change in its respective porosity. The surface area of different formed negative electrodes, however, would only vary slightly with significant changes in their corresponding porosity. The glycerol displacement method was also shown to be suitable to determine the effective porosity of cured and formed positive tubular electrodes.     

The value of cooperatives in rural electrification

The electricity sectors of many developing countries underwent substantial reforms during the 1980s and 1990s, driven by global agendas of privatization and liberalization. However, rural electrification offered little by way of market incentives for profit-seeking private companies and was often neglected. As a consequence, delivery models for rural electrification need to change. This paper will review the experiences of various rural electrification delivery models that have been established in developing countries, including concessionary models, dealership approaches and the strengthening of small and medium-sized energy businesses. It will use examples from the USA, Bangladesh and Nepal, together with a detailed case study of a Nepali rural electric cooperative, to explore the role that local cooperatives can play in extending electricity access. It is shown that although there is no magic bullet solution to deliver rural electrification, if offered appropriate financial and institutional support, socially orientated cooperative businesses can be a willing, efficient and effective means of extending and managing rural electricity services. It is expected that this paper will be of particular value to policy-makers, donors, project planners and implementers currently working in the field of rural electrification.     

Charging of lead-acid batteries using electrolyte circulation

The charge and discharge rates of lead-acid batteries are limited primarily by the mobility of current carrying ions in the electrolyte. An increase in ion mobility by forced circulation of the electrolyte is shown to improve the efficiency of the charging process and the effect of electrode spacing on charging rate is discussed.     

Energy gauge for lead-acid batteries in electric vehicles

This article proposes a new coulometric approach to calculate the state of charge of a lead-acid battery in electric vehicles. The main existing state of charge algorithms have two major defects: a state of charge definition not adapted to electric vehicle applications and the nonoptimal use of static performance of the accumulator to estimate its state under dynamic stresses. In order to improve these two weaknesses, we propose a new coulometric algorithm linked to the performance of the electric vehicle and where the ampere-hours virtually discharged are obtained by applying statistical equivalence coefficients to the real current profile. The evaluation of this new algorithm on real discharges reveals a significant improvement with less than 5% errors in all cases studied     

Advances in gelled-electrolyte technology for valve-regulated lead-acid batteries

In recent years, the valve-regulated lead-acid (VRLA) battery has been developed into a versatile and extremely reliable energy-storage device. When given a correctly specified battery design technology for the required product application, the VRLA battery will offer the end-user, some, if not all, of the following characteristics: high current capability; good reliability under cyclic, deep-discharge conditions (cycle life); good power density; high recharge efficiency; rapid rechargeability; resistant to overcharge; good charge stability (resistant to thermal runaway); no addition of water (topping-up) during service life (maintenance-free); long service life; wide operating temperature; robust design; low cost per Wh; high volumetric energy density (Wh/l); low self-discharge; high gravimetric energy density (Wh kg⁻¹); may be stored and used in any position (orientation); resistant to shock and vibration; no need to be recharged immediately after discharge and environmentally ‘safe’. The most commonly used gelling agent, fumed silica, has many disadvantages such as, contamination of the local working environment, particularly during paste-mixing, and occupational hygiene and handling problems. It is also bulky to transport and has long gel times unless used at very high concentrations. There is, therefore, an increasing demand for an alternative gelling agent for sulfuric acid in the production of gelled-electrolyte (GEL) VRLA batteries. Silica sols can provide a solution to all of these problems, and moreover at a lower cost to the battery producer.     

ANN modeling of water consumption in the lead-acid batteries

Due to importance of the quantity of water loss in the life cycle of lead-acid batteries, water consumption tests were performed on 72 lead-acid batteries with low antimony grid alloy at different charge voltages and temperatures. Weight loss of batteries was measured during a period of 10 days. The behavior of batteries in different charge voltages and temperatures were modeled by artificial neural networks (ANNs) using MATLAB 7 media. Four temperatures were used in the training set, out of which three were used in prediction set and one in validation set. The network was trained by training and prediction data sets, and then was used for predicting water consumption in all three temperatures of prediction set. Finally, the network obtained was verified while being used in predicting water loss in defined temperatures of validation set. To achieve a better evaluation of the model ability, three models with different validation temperatures were used (model 1 = 50 °C, model 2 = 60 °C and model 3 = 70 °C). There was a good agreement between predicted and experimental results at prediction and validation sets for all the models.     

Estimation of the lifetimes of valve-regulated lead-acid batteries

A method for estimating lifetime of valve-regulated lead-acid (VRLA) batteries used in float service under a variable-temperature environment was developed, and an effective means of shortening the period of an accelerated-lifetime test on a battery under cycle use was devised.