Life cycle assessment of photovoltaic electricity generation

The paper presents the results of a life cycle assessment (LCA) of the electric generation by means of photovoltaic panels. It considers mass and energy flows over the whole production process starting from silica extraction to the final panel assembling, considering the most advanced and consolidate technologies for polycrystalline silicon panel production. Some considerations about the production cycle are reported; the most critical phases are the transformation of metallic silicon into solar silicon and the panel assembling. The former process is characterised by a great electricity consumption, even if the most efficient conversion technology is considered, the latter by the use of aluminium frame and glass roofing, which are very energy-intensive materials. Moreover, the energy pay back time (EPBT) and the potential for CO₂ mitigation have been evaluated, considering different geographic collocations of the photovoltaic plant with different values of solar radiation, latitude, altitude and national energetic mix for electricity production.     

An evaluation on the life cycle of photovoltaic energy system considering production energy of off-grade silicon

In this study, single-crystalline silicon (c-Si) photovoltaic (PV) cells and residential PV systems using off-grade silicon supplied from semiconductor industries were evaluated from a life cycle point of view. Energy payback time (EPT) of the residential PV system with the c-Si PV cells made of the off-grade silicon was estimated at 15.5 years and indirect CO₂ emission per unit electrical output was calculated at 91 g-C/kWh even in the worst case. These figures were more than those of the polycrystalline-Si and the amorphous-Si PV cells to be used in the near future, but the EPT was shorter than its lifetime and the indirect CO₂ emissions were less than the recent average CO₂ emissions per kWh from the utilities in Japan. The recycling of the c-Si PV cells should be discussed for the reason of the effective use of energy and silicon material.     

Life cycle assessment of a solar thermal collector: sensitivity analysis, energy and environmental balances

Starting from the results of a life cycle assessment of solar thermal collector for sanitary warm water, an energy balance between the employed energy during the collector life cycle and the energy saved thanks to the collector use has been investigated. A sensitivity analysis for estimating the effects of the chosen methods and data on the outcome of the study was carried out. Uncertainties due to the eco-profile of input materials and the initial assumptions have been analysed.Since the study is concerned with a renewable energy system, attention has been focused on the energy indexes and in particular the “global energy consumption”. Following the principles of Kyoto Protocol, the variations of CO₂ emissions have also been studied.     

太阳能热力发电的生命周期分析

应用生命周期分析法(LCA)，对塔式太阳能热力电站所用设备材料的生产、运输、电站基本建设等3个过程进行了分析，分别计算出3个过程中的能耗及其对环境的影响，并与燃煤发电进行了比较。结果表明．太阳能热力电站每发电10MWh，即可节省能源3．78t标准煤，少向大气排放粉尘、CO2、NOx、SO2分别为498．7，9 933，49．94，78．75kg。太阳能热力发电具有显著的节能和环保效益。     

Life cycle assessment of a micromorph photovoltaic system

In this paper the results from a in-depth life cycle analysis of production and use of a novel grid-connected photovoltaic micromorph system are presented and compared to other thin film and traditional crystalline silicon photovoltaic technologies. Among the new thin film technologies, the micromorph tandem junction appears to be one of the most promising devices from the industrial point of view. The analysis was based on actual production data given to the authors directly from the PRAMAC Swiss Company and it is consistent with the recommendations provided by the ISO norms and updates. The gross energy requirement, green house gas emissions and energy pay-back time have been calculated for the electric energy output virtually generated by the studied system in a lifetime period of 20 years. A comparative framework is also provided, wherein results obtained for the case study are compared with data from literature previously obtained for the best commercially available competing photovoltaic technologies. Results clearly show a significant decrease in gross energy requirement, in green house gas emissions and also a shorter energy pay-back time for the micromorph technology.     

Life cycle assessment study of a 4.2 kWp stand-alone photovoltaic system

The energetic and environmental life cycle assessment of a 4.2 kW_p stand-alone photovoltaic system (SAPV) at the University of Murcia (south-east of Spain) is presented. PV modules and batteries are the energetically and environmentally most expensive elements. The energy pay-back time was found to be 9.08 years and the specific CO₂ emissions was calculated as 131 g/kWh. The SAPV system has been environmentally compared with other supply options (diesel generator and Spanish grid) showing lower impacts in both cases. The results show the CO₂-emission reduction potential of SAPV systems in southern European countries and point out the critical environmental issues in these systems.     

基于全生命周期的地热发电系统环境影响评价

为明确不同类型地热发电系统“获取、转化”环节的钻井、建设、运行、退役等不同过程对地热发电系统的环境影响贡献,本文建立了基于热力学优化模型的闪蒸/双工质地热发电系统全生命周期环境影响评价模型。进而,选取西藏羊八井、广东丰顺、华北油田及青海共和四种典型地热热储,整理和收集了我国地热发电系统的环境影响全生命周期环境影响清单,分析了地热发电站六个不同过程对三个主要环境影响潜值评价指标：酸化潜值、富营养化潜值和全球变暖潜值的影响规律。发现钻井完井过程分别平均占到地热电站酸化潜值、全球变暖潜值和富营养化潜值的46.28%、45.90%和27.52%,地下系统和地上系统的环境影响贡献相当;地热梯度与地热电站的全生命周期环境影响潜值有着负相关关系,梯度越大,环境影响潜值越低。。     

Environmental payback time analysis of a roof-mounted building-integrated photovoltaic (BIPV) system in Hong Kong

This paper reports the investigation results of the energy payback time (EPBT) and greenhouse-gas payback time (GPBT) of a rooftop BIPV system (grid-connected) in Hong Kong to measure its sustainability. The 22 kWp PV array is facing south with inclined angle of 22.5°. The hourly solar irradiance and ambient air temperature from 1996 to 2000 were used as weather data input. The annual power output was found to be 28,154 kWh. The embodied energy for the whole system in the lifespan was 205,816 kWh, including 71% from PV modules and 29% from balance of system (BOS). The percentage of embodied energy for silicon purification and processing reached 46%. The EPBT of the PV system was 7.3 years, and the GPBT was estimated to be 5.2 years considering fuel mixture composition of local power stations. This paper also discussed the EPBTs for different orientations, ranging from 7.1 years (optimal orientation) to 20.0 years (west-facing vertical PV façade). The results show that the ‘sustainability’ of a PV system is affected by its installation orientation and location. Choosing locations and orientations with higher incident solar irradiance is one key for the sustainability of BIPV technology applications.     

Life cycle assessment for photovoltaic integrated shading system with different end of life phases

The aim of this study is to conduct a novel life cycle assessment (LCA) process for a window-mounted building attached photovoltaic panel that is used as a photovoltaic integrated shading (PVIS) device, using GaBi software. Also, the study takes into consideration three different scenarios of the LCA process to reach the most environmentally-friendly system. The three scenarios differ mainly in the end of life processes phase, which in response affects the inputs of the stages within the LCA process. The newly proposed end of life phases are disposing the wastes in the landfill scenario, recycling scenario and recovery scenario. The results showed that the 30 Wp PVIS is environmentally wise to apply to buildings. For the three proposed scenarios, the highest emissions are generated during the production and end of life phases. Consequently, the recycling and the recovery scenarios are more environmentally-friendly in the long run compared to the landfill scenario.     

Life cycle assessment of electricity generation in Mexico

This paper presents for the first time a Life Cycle Assessment (LCA) study of electricity generation in Mexico. The electricity mix in Mexico is dominated by fossil fuels, which contribute around 79% to the total primary energy; renewable energies contribute 16.5% (hydropower 13.5%, geothermal 3% and wind 0.02%) and the remaining 4.8% is from nuclear power. The LCA results show that 225 TWh of electricity generate about 129 million tonnes of CO₂ eq. per year, of which the majority (87%) is due to the combustion of fossil fuels. The renewables and nuclear contribute only 1.1% to the total CO₂ eq. Most of the other LCA impacts are also attributed to the fossil fuel options. The results have been compared with values reported for other countries with similar electricity mix, including Italy, Portugal and the UK, showing good agreement.     

Life cycle assessment of earth-abundant photocatalysts for enhanced photocatalytic hydrogen production

Hydrogen (H₂) can play a critical role in global greenhouse gas (GHG) mitigation. Photocatalytic water splitting using solar radiation is a promising H₂ technology. Titanium dioxide (TiO₂) and carbon nitride (g–C₃N₄)–based photocatalysts are the most widely used photocatalytic materials because of their activity and abundance. Several attempts have been made to improve the photocatalytic performance of these materials in terms of their activity level, life span, response to visible radiation, and stability. However, the environmental impacts of these modifications are often not included in existing studies. This research, therefore, develops a cradle-to-grave life cycle assessment (LCA) framework to evaluate and compare the GHG footprints of four alternative pathways: TiO₂ nanorods and fluorine-doped carbon nitride quantum dots embedded with TiO₂ (CNF: TNR/TiO₂), g-C₃N₄, and g-C₃N₄/BiOI composite. Unlike most studies that focus only on certain stages such as laboratory-scale photocatalytic fabrication, this study includes utility-scale cell production, assembly, operation, and end of life to give a more accurate and precise environmental performance estimation. The results show that g-C₃N₄/BiOI has the lowest GHG footprint (0.38 kg CO₂ eq per kg of H₂) and CNF: TNR/TiO₂ has the lowest energy payback time (0.4 years). In every pathway, energy use in material extraction processes makes up the largest GHG contribution, between 83% and 89%. Sensitivity and uncertainty analyses were conducted under the impact of various input parameters on the life cycle GHG emissions of hydrogen production. Photocatalytic water splitting is highly feasible for adaptation as a mainstream hydrogen production pathway in the future.     

Life cycle assessment of power generation alternatives for a stand-alone mobile house

This paper presents comparative life cycle assessment of nine different hybrid power generation solutions that meet the energy demand of a prototypical mobile home. In these nine solutions, photovoltaic panels and a wind turbine are used as the main energy source. Fuel cell and diesel generator are utilized as backup systems. Batteries, compressed H₂, and H₂ in metal hydrides are employed as backup energy storage. The findings of the study shows that renewable energy sources, although they are carbon-free, are not as environmentally friendly as may generally be thought. The comparative findings of this study indicate that a hybrid system with a wind turbine as a main power source and a diesel engine as backup power system is the most environmentally sound solution among the alternatives.     

Energy storage-based power buffering control for photovoltaic power generation system

光伏发电系统输出的最大功率随外界环境变化而波动,无法满足负荷的供电需求,针对该问题,建立了基于储能系统的光伏发电系统结构,介绍了光伏发电系统运行原理,分析了系统功率与直流母线电压的关系,设计了无源式储能系统和有源式储能系统对功率进行缓冲以满足控制目标.仿真结果表明,有源式储能系统较无源式储能系统有更好的功率调节作用,通过双向DC-DC变换器的储放能量自动切换控制,使得光伏发电系统输出的功率与负荷需求功率良好匹配,直流电压稳定.     

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.     

Life cycle CO2 emissions from power generation using hydrogen energy carriers

Hydrogen energy carriers such as liquid hydrogen (LH₂), methylcyclohexane (MCH), and ammonia (NH₃) are promising energy vectors in the clean energy systems currently being developed. However, their effectiveness in mitigating environmental emissions must be assessed by life cycle analyses throughout the supply chain. In this study, while focusing on hydrogen energy carriers, life cycle inventory analyses were conducted to estimate CO₂ emissions from the following types of power generation plants in Japan: a hydrogen (H₂) mono-firing power plant using LH₂ or MCH that originated from overseas renewable electricity; and NH₃ co-firing with fossil fuel and NH₃ mono-firing power plants using hydrogen energy carriers that originated from overseas natural gas or renewable electricity. Parameters related to the supply chains were collected by literature surveys, and the Japanese life cycle inventory database was primarily used to calculate the emissions. From the results, CO₂ hotspots of the target supply chains and potential measures are identified that become necessary to establish low-carbon supply chains.     

Life cycle assessment of solar PV based electricity generation systems: A review

Sustainable development requires methods and tools to measure and compare the environmental impacts of human activities for various products viz. goods, services, etc. This paper presents a review of life cycle assessment (LCA) of solar PV based electricity generation systems. Mass and energy flow over the complete production process starting from silica extraction to the final panel assembling has been considered. Life cycle assessment of amorphous, mono-crystalline, poly-crystalline and most advanced and consolidate technologies for the solar panel production has been studied.     

某15MW太阳能屋顶光伏发电工程的应用分析

在对太阳能屋顶光伏发电系统构成及发展意义阐述的基础上,通过对某15MW屋顶光伏发电工程大量实际数据的分析,表明太阳能屋顶光伏发电工程具有良好的社会、经济效益和广阔的发展前景。     

Life cycle assessment of high temperature electrolysis for hydrogen production via nuclear energy

A life cycle assessment (LCA) of one proposed method of hydrogen production—the high temperature electrolysis of water vapor—is presented in this paper. High temperature electrolysis offers an advantage of higher energy efficiency over the conventional low-temperature alkaline electrolysis due to reduced cell potential and consequent electrical energy requirements. The primary energy source for the electrolysis will be advanced nuclear reactors operating at temperatures corresponding to those required for the high temperature electrolysis. The LCA examines the environmental impact of the combined advanced nuclear-high temperature electrolysis plant, focusing upon quantifying the emissions of carbon dioxide, sulfur dioxide, and nitrogen oxides per kilogram of hydrogen produced. The results are presented in terms of the global warming potential (GWP) and the acidification potential (AP) of the system. The GWP for the system is 2000 g carbon dioxide equivalent and the AP, 0.15 g equivalents of hydrogen ion equivalent per kilogram of hydrogen produced. The GWP and AP of this process are one-sixth and one-third, respectively, of those for the hydrogen production by steam reforming of natural gas, and are comparable to producing hydrogen from wind- or hydro-electricity powered conventional electrolysis.     

Energy and carbon payback times for solid oxide fuel cell based domestic CHP

Fuel cells already provide heat and power to people’s homes with lower direct CO₂ emissions and fuel consumption than traditional methods. However, their whole life cycle, including manufacture and disposal, must be considered to verify that these environmental impacts are actually reduced and not merely shifted elsewhere. The total carbon footprint and energy payback times have been widely reported for other emerging microgeneration technologies, but have not previously been calculated for fuel cell systems.     

分布式光伏发电系统最大功率点跟踪技术比较研究

基于当前光伏阵列最大功率点跟踪技术的研究现状,介绍了适用于分布式光伏发电系统最大功率点跟踪的各种常用控制方法,阐述了每一种控制方法的技术原理,分析和比较了这些常用控制方法的特点,总结了各自的优点和缺点,最后对分布式光伏发电系统最大功率点跟踪方法的选择问题进行了探讨,并指出了具体选择方法时应综合考虑的各种因素。