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.     

Solar photovoltaic charging of lithium-ion batteries

Solar photovoltaic (PV) charging of batteries was tested by using high efficiency crystalline and amorphous silicon PV modules to recharge lithium-ion battery modules. This testing was performed as a proof of concept for solar PV charging of batteries for electrically powered vehicles. The iron phosphate type lithium-ion batteries were safely charged to their maximum capacity and the thermal hazards associated with overcharging were avoided by the self-regulating design of the solar charging system. The solar energy to battery charge conversion efficiency reached 14.5%, including a PV system efficiency of nearly 15%, and a battery charging efficiency of approximately 100%. This high system efficiency was achieved by directly charging the battery from the PV system with no intervening electronics, and matching the PV maximum power point voltage to the battery charging voltage at the desired maximum state of charge for the battery. It is envisioned that individual homeowners could charge electric and extended-range electric vehicles from residential, roof-mounted solar arrays, and thus power their daily commuting with clean, renewable solar energy.     

Life cycle analysis for future photovoltaic systems using hybrid solar cells

Global climate change concerns have lead to growing demand for renewable energy sources (RES). However the viability of these sources is critically dependent on environmental, economic and technological considerations. This paper focuses on the environmental aspect of future photovoltaic (PV) systems which are assessed through life cycle analysis (LCA). Previous LCA studies on commercially available PV systems are reviewed. The sustainable evaluation methods used in these studies are also discussed. These methods are applied to the hybrid quantum dot (QD)-based solar cells currently under development within a project between the University of Manchester and Imperial College London. The aim of this project is to develop affordable solar cells with efficiencies up to 10% for micro-generation applications. Presently hybrid QD-based solar cells are not commercially fabricated; therefore the study is mostly based on very small laboratory-scale production. For easy comparability 10% conversion efficiency and 25 years lifetime are initially assumed. Lower conversion efficiencies and shorter lifetimes likely to initially characterise emerging PV technologies such as the hybrid QD-based solar cells are discussed. Comparable criteria for sustainability of electricity-generating systems namely net energy ratio (NER), energy pay-back time (EPB-T) and CO₂ emissions per unit generated during lifetime are found to be lower than current commercially available PV modules.     

A solar-powered,high-efficiency hydrogen fueling system using high-pressure electrolysis of water: Design and initial results

Hydrogen for fuel-cell electric vehicles (FCEVs) was produced using clean, renewable solar energy to electrolyze water. This report describes the design, construction, and initial performance testing of a solar hydrogen fueler at the GM Proving Ground in Milford, MI. The system used high-efficiency photovoltaic (PV) modules, a high-pressure (6500 psi, 44.8 MPa) electrolyzer, and an optimized direct connection between the PV and electrolyzer systems. This resulted in world-class solar to hydrogen efficiencies as high as 9.3% (based on H₂ lower heating value, LHV). The system could potentially supply approximately 0.5 kg of hydrogen per day from solar power for the average solar insolation in Detroit; more hydrogen would be produced in locations with more abundant sunshine. This is sufficient hydrogen to operate an FCEV for an average daily urban commute. Thus, the solar hydrogen fueler testing served as a “proof of concept” for clean, renewable hydrogen with potential applications including convenient, clean, quiet, small-scale home fueling of FCEVs (that can contribute to the growth of a future FCEV fleet) and fueling in remote locations where grid electricity is not available.     

Optimal operation of microgrid using hybrid differential evolution and harmony search algorithm

This paper proposes the generation scheduling approach for a microgrid comprised of conventional generators, wind energy generators, solar photovoltaic (PV) systems, battery storage, and electric vehicles. The electrical vehicles (EVs) play two different roles: as load demands during charging, and as storage units to supply energy to remaining load demands in the MG when they are plugged into the microgrid (MG). Wind and solar PV powers are intermittent in nature; hence by including the battery storage and EVs, the MG becomes more stable. Here, the total cost objective is minimized considering the cost of conventional generators, wind generators, solar PV systems and EVs. The proposed optimal scheduling problem is solved using the hybrid differential evolution and harmony search (hybrid DE-HS) algorithm including the wind energy generators and solar PV system along with the battery storage and EVs. Moreover, it requires the least investment.     

Generation of high-pressure hydrogen for fuel cell electric vehicles using photovoltaic-powered water electrolysis

Increasing the utilization of electric drive systems including hybrid, battery, and fuel cell electric vehicles (FCEV) will reduce the usage of petroleum and the emission of air pollution by vehicles. 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 emissions, as well as eliminating the dependence of the transportation sector on dwindling supplies of petroleum for its energy. Before FCEVs can be introduced in large numbers, a hydrogen-fueling infrastructure is needed. This report describes an early proof-of-concept for a distributed hydrogen fueling option in which renewably generated, high-pressure hydrogen is dispensed at an FCEV owner’s home. In an earlier report we described the design and initial characterization of a solar photovoltaic (PV) powered electrolyzer/storage/dispensing (ESD) system that was a proof-of-concept for a single FCEV home fueling system. In the present report we determined the efficiency and other operational characteristics of that PV-ESD system during testing over a 109-day period at the GM Proving Ground in Milford, MI, at a hydrogen output pressure of approximately 2000 psi (13.8 MPa). The high pressure was achieved without any mechanical compression via electrolysis. Over the study period the photovoltaic solar to electrical efficiency averaged 13.7%, the electrolyzer efficiency averaged 59%, and the system solar to hydrogen efficiency averaged 8.2% based on the hydrogen lower heating value. A well-documented model used to evaluate solar photovoltaic power systems was used to calculate the maximum power point values of the voltage, current, and power of our PV system in order to derive the coupling factor between the PV and ESD systems and to determine its behavior over the range of environmental conditions experienced during the study. The average coupling factor was near unity, indicating that the two systems remained coupled in an optimal fashion. Also, the system operated well over a wide range of meteorological conditions, and in particular it responded quickly to instantaneous changes in the solar irradiance (caused by clouds) with negligible effect on the overall efficiency. During the study up to 0.67 kg of high-pressure hydrogen was generated on a sunny day for fueling FCEV. Future generations of high-pressure electrolyzers, properly combined with solar PV systems, can offer a compact, efficient, and environmentally acceptable system for FCEV home fueling.     

Chemical treatment of crystalline silicon solar cells as a method of recovering pure silicon from photovoltaic modules

Photovoltaic technology is used worldwide to provide reliable and cost-effective electricity for industrial, commercial, residential and community applications. The average lifetime of PV modules can be expected to be more than 25 years. The disposal of PV systems will become a problem in view of the continually increasing production of PV modules. These can be recycled for about the same cost as their disposal.Photovoltaic modules in crystalline silicon solar cells are made from the following elements, in order of mass: glass, aluminium frame, EVA copolymer transparent hermetising layer, photovoltaic cells, installation box, Tedlar^® protective foil and assembly bolts. From an economic point of view, taking into account the price and supply level, pure silicon, which can be recycled from PV cells, is the most valuable construction material used.Recovering pure silicon from damaged or end-of-life PV modules can lead to economic and environmental benefits. Because of the high quality requirement for the recovered silicon, chemical processing is the most important stage of the recycling process. The chemical treatment conditions need to be precisely adjusted in order to achieve the required purity level of the recovered silicon. For PV systems based on crystalline silicon, a series of etching processes was carried out as follows: etching of electric connectors, anti-reflective coating and n-p junction. The chemistry of etching solutions was individually adjusted for the different silicon cell types. Efforts were made to formulate a universal composition for the etching solution. The principal task at this point was to optimise the etching temperature, time and alkali concentration in such a way that only as much silicon was removed as necessary.     

Parameters affecting the life cycle performance of PV technologies and systems

This paper assesses modeling parameters that affect the environmental performance of two state-of-the-art photovoltaic (PV) electricity generation technologies: the PVL136 thin film laminates and the KC120 multi-crystalline modules. We selected three metrics to assess the modules’ environmental performance, which are part of an actual 33 kW installation in Ann Arbor, MI. The net energy ratio (NER), the energy pay back time (E-PBT), and the CO₂ emissions are calculated using process based LCA methods. The results reveal some of the parameters, such as the level of solar radiation, the position of the modules, the modules’ manufacturing energy intensity and its corresponding fuel mix, and the solar radiation conversion efficiency of the modules, which affect the final analytical results. A sensitivity analysis shows the effect of selected parameters on the final results. For the baseline scenario, the E-PBT for the PVL136 and KC120 are 3.2 and 7.5 years, respectively. When expected future conversion efficiencies are tested, the E-PBT is 1.6 and 5.7 years for the PVL136 and the KC120, respectively. Based on the US fuel mix, the CO₂ emissions for the PVL136 and the KC120 are 34.3 and 72.4 g of CO₂/kW h, respectively. The most effective way to improve the modules’ environmental performance is to reduce the energy input in the manufacturing phase of the modules, provided that other parameters remain constant. Consequently, the use of PV as an electricity source during PV manufacturing is also assessed. The NER of the supplier PV is key for the performance of this scheme. The results show that the NER based on a PV system can be 3.7 times higher than the NER based on electricity supplied by the traditional grid mix, and the CO₂ emissions can be reduced by 80%.     

Life-cycle assessment of a photovoltaic system in Catalonia (Spain)

The life-cycle analysis (LCA) of photovoltaic (PV) systems is an important tool to quantify the potential environmental advantage of using solar technologies versus more traditional technologies, especially the ones relying on non-renewable fossil fuel sources.This work performs a life-cycle assessment on a 200 kW roof top photovoltaic (PV) system with polycrystalline silicon modules and evaluates the net energy pay-back and greenhouse gas emission rates. The performed life-cycle assessment “upstream” and “downstream” processes are considered, such as raw materials production, fabrication of system components, transportation and installation. The energy pay-back time ratio is determined for the installed technology and two other technologies of PV modules (monocrystalline and thin-film).The analysed PV system, located in Pineda de Mar (Catalonia, Spain), has an energy pay-back time ratio of 4.36 years. Furthermore, a sensibility analysis on solar radiation has been performed.     

Comparative life cycle assessment of hydrogen-fuelled passenger cars

In order to achieve gradual but timely decarbonisation of the transport sector, it is essential to evaluate which types of vehicles provide a suitable environmental performance while allowing the use of hydrogen as a fuel. This work compares the environmental life-cycle performance of three different passenger cars fuelled by hydrogen: a fuel cell electric vehicle, an internal combustion engine car, and a hybrid electric vehicle. Besides, two vehicles that use hydrogen in a mixture with natural gas or gasoline were considered. In all cases, hydrogen produced by wind power electrolysis was assumed. The resultant life-cycle profiles were benchmarked against those of a compressed natural gas car and a hybrid electric vehicle fed with natural gas. Vehicle infrastructure was identified as the main source of environmental burdens. Nevertheless, the three pure hydrogen vehicles were all found to be excellent decarbonisation solutions, whereas vehicles that use hydrogen mixed with natural gas or gasoline represent good opportunities to encourage the use of hydrogen in the short term while reducing emissions compared to ordinary vehicles.     

Solar energy—A look into power generation,challenges, and a solar‐powered future

Sun is an inexhaustible source of energy capable of fulfilling all the energy needs of humankind. The energy from the sun can be converted into electricity or used directly. Electricity can be generated from solar energy either directly using photovoltaic (PV) cells or indirectly using concentrated solar power (CSP) technology. Progress has been made to raise the efficiency of the PV solar cells that can now reach up to approximately 34.1% in multi‐junction PV cells. Electricity generation from concentrated solar technologies has a promising future as well, especially the CSP, because of its high capacity, efficiency, and energy storage capability. Solar energy also has direct application in agriculture primarily for water treatment and irrigation. Solar energy is being used to power the vehicles and for domestic purposes such as space heating and cooking. The most exciting possibility for solar energy is satellite power station that will be transmitting electrical energy from the solar panels in space to Earth via microwave beams. Solar energy has a bright future because of the technological advancement in this field and its environment‐friendly nature. The biggest challenge however facing the solar energy future is its unavailability all‐round the year, coupled with its high capital cost and scarcity of the materials for PV cells. These challenges can be met by developing an efficient energy storage system and developing cheap, efficient, and abundant PV solar cells. This article discusses the solar energy system as a whole and provides a comprehensive review on the direct and the indirect ways to produce electricity from solar energy and the direct uses of solar energy. The state‐of‐the‐art procedures being employed for PV characterization and performance rating have been summarized . Moreover, the technical, economic, environmental, and storage‐related challenges are discussed with possible solutions. Furthermore, a comprehensive list of future potential research directions in the field of direct and indirect electricity generation from solar energy is proposed.     

Fabrication technology for large-area a-Si solar cells

The fabrication process technology for large-area a-Si photovoltaic (PV) modules and their performance are reviewed. Our present technology enables us to provide 10% efficient large-area submodules with a stabilized efficiency of 8.5%. To study the practicability of the a-Si solar panels, we carried out an outdoor test for our a-Si modules. The results show that the a-Si solar PV modules generate power very efficiently in outdoor systems. The advantage of the a-Si modules under outdoor uses is presented and discussed.     

Predicting efficiency of solar powered hydrogen generation using photovoltaic-electrolysis devices

Hydrogen fuel for fuel cell vehicles can be produced by using solar electric energy from photovoltaic (PV) modules for the electrolysis of water without emitting carbon dioxide or requiring fossil fuels. In the past, this renewable means of hydrogen production has suffered from low efficiency (2–6%), which increased the area of the PV array required and therefore, the cost of generating hydrogen. A comprehensive mathematical model was developed that can predict the efficiency of a PV-electrolyzer combination based on operating parameters including voltage, current, temperature, and gas output pressure. This model has been used to design optimized PV-electrolyzer systems with maximum solar energy to hydrogen efficiency. In this research, the electrical efficiency of the PV-electrolysis system was increased by matching the maximum power output and voltage of the photovoltaics to the operating voltage of a proton exchange membrane (PEM) electrolyzer, and optimizing the effects of electrolyzer operating current, and temperature. The operating temperature of the PV modules was also an important factor studied in this research to increase efficiency. The optimized PV-electrolysis system increased the hydrogen generation efficiency to 12.4% for a solar powered PV-PEM electrolyzer that could supply enough hydrogen to operate a fuel cell vehicle.     

Study on the incorporation of photovoltaic systems as an auxiliary power source for hybrid and electric vehicles

We investigate the use of photovoltaic systems as auxiliary power generators in hybrid and electric vehicles. This technology provides an as yet unexploited possibility with the advantages of a new power source, which is light, noiseless, maintenance-free and continuously working. A notable reduction of air emissions can be achieved through a synergy of various technological breakthroughs, such as the method we present of introducing photovoltaic arrays and additional electrochemical energy storage capacity in vehicles. Solar cars are also considered as a case study in order to demonstrate the use of solar panels in electric cars. However, solar cars cannot be used extensively in practice, while hybrid and electric cars have already been used for many years and their market share is increasing. In order to reduce further the fuel consumption and emissions from hybrid vehicles we propose the use of solar panels and additional battery capacity. Finally, we examine if the reduction in the fuel consumption and air emissions from the use of solar panels compensates for the additional cost involved.     

串并联太阳能电池弧形光伏组件的发电性能研究

将弧形光伏组件安装在建筑和汽车上获取电能,已受到人们越来越多的关注。为获得更高的输出功率,有必要研究由互连太阳能电池组成的、电流不匹配的弧形光伏组件的特性。研究重点关注由串并联太阳能电池组成的弧形光伏组件的发电性能,设计了不同曲率的非平面微型光伏模块,并通过测量获取光伏模块的参数。与平面光伏模块相比,弧形光伏模块的发电量较小。此外,利用二极管模型分析了光伏模块的特性,说明并联比串联功率高的原因。最后研究了实际应用中太阳能电池的互连问题。结果表明,在理想模型下并联能获取更多电能,但大尺寸的光伏模块会产生更大电流,可能会在实际运行中产生额外损耗。因此,在实际应用中设计弧形光伏组件时也应考虑太阳能电池的互连。     

The coupling factor: A new metric for determining and controlling the efficiency of solar photovoltaic power utilization

The production of electricity and hydrogen in a renewable fashion, such as using solar energy, can provide a clean and sustainable energy source for electric-powered vehicles, including fuel-cell and battery-electric vehicles. Our research on generating hydrogen and charging batteries using renewable solar photovoltaic (PV) electricity has led to the development of a simple and convenient new metric called the coupling factor that describes the fraction of the maximum PV power transferred to electrical loads. The keystone of the coupling factor concept is a regression model to calculate the maximum PV voltage, current, and power as a function of the instantaneous incident solar irradiance and the photovoltaic module temperature. The coupling factor can range from zero to one, i.e., no transfer of power from the PV system to the load, to complete transfer of the PV power. We describe the derivation of regression models to compute important PV electrical output variables, such as the open circuit voltage, the short circuit current, the maximum power point voltage, the maximum power point current, and the coupling factor as a function of the fundamental measured variables affecting those quantities. The models are derived for PV modules used in our previous research to power an electrolyzer and charge high-voltage batteries. In addition, we develop models for other modules using PV cell technologies different from those used in our PV system. Some of the calculated quantities are compared to measurements for our PV system. The usefulness of these quantities, and especially the coupling factor, in rating the transfer of PV power to electrolyzer and battery loads, is illustrated. Finally, we discuss how the predicted maximum power point voltage can be used for real-time control and efficiency optimization of a dynamic PV-load system.     

Germanium-doped Czochralski silicon for photovoltaic applications

Germanium (Ge)-doped Czochralski (GCZ) silicon has been grown for photovoltaic (PV) applications. It is found that Ge doping improves the mechanical strength of CZ silicon, resulting in the reduction of breakage during wafer cutting, cell fabrication and module assembly. Boron-oxygen (B-O) defects that lead to the light-induced degradation (LID) of carrier lifetime are effectively suppressed by Ge doping. The decrease in the maximum concentration of B-O defects increases with an increase of Ge concentration. The efficiency of GCZ silicon solar cells and the power output of corresponding PV modules both exhibit smaller loss under sunlight illumination. The current work suggests that GCZ silicon should be potentially a novel substrate for thin solar cells with low LID effect.     

Impact of uneven shading and bypass diodes on energy extraction characteristics of solar photovoltaic modules and arrays

Solar photovoltaic (PV) energy is becoming an increasingly important part of the world's renewable energy. In order for effective energy extraction from a solar PV system, this paper investigates I–V and P–V characteristics of solar PV modules and arrays. The paper particularly focuses on I–V and P–V characteristics of PV modules and arrays under uneven shading conditions, and considers both the physics and electrical characteristics of a solar PV system in the model development. The article examines how different bypass diode arrangements could affect maximum power extraction characteristics of a solar PV module or array. It is found in this article that under uneven shading conditions, solar PV cells may perform in very different ways and a solar PV system may exhibit multiple peaks in its P–V characteristics. The study of this article also shows that the arrangement of largely distributed bypass diodes within a PV module could effectively improve efficiency and maximum power point tracking strategies for energy conversion of solar PV systems.     

Estimation of irradiance and outdoor performance of photovoltaic modules by meteorological data

Three environmental factors of irradiance, solar spectral distribution and module temperature greatly affect the performances of photovoltaic (PV) modules. If the environmental factors can be estimated by basic meteorological data (BMD) announced by an official organization in various areas, the performances of PV modules can be estimated easily. In this study, a relationship between the environmental factors and the BMD was analyzed. The performances of Si-based (crystalline Si and thin-film Si) PV modules were estimated by the relationship. As a result, errors between the estimation and actual performances in the crystalline Si and thin-film PV modules were within 1.88% and 0.58% in Kusatsu city, Japan (34°58′N, 135°57′E). This methodology can be useful for rating the performance of PV modules at various areas.     

基于光伏组件的太阳能资源观测

鉴于太阳能资源的测量和评价是太阳能开发利用的重要基础,按照光伏电池两种主要安装方式(倾斜固定和太阳跟踪),利用单晶、多晶和非晶三种典型的光伏组件设计进行了太阳能光伏资源观测试验,获得了各季节典型晴天条件下各类型光伏组件辐照度的日变化特征和倾斜面光伏组件一年中月均每日可发电量的极大值、极小值及其月份。通过对比各类型光伏组件在太阳跟踪器上和纬度倾斜面上光伏辐照度变化,得出跟踪光伏组件日均光伏曝辐量与倾斜光伏组件日均光伏曝辐量的相比较优势。根据光伏组件的观测结果推算出各类型光伏组件的光伏反演辐照度,与气象辐射观测用总辐射表的总辐射辐照度趋势非常一致,在太阳能光伏主要利用时段相对误差基本在10%以内。