Solar and photovoltaic forecasting through post‐processing of the Global Environmental Multiscale numerical weather prediction model

Hourly solar and photovoltaic (PV) forecasts for horizons between 0 and 48 h ahead were developed using Environment Canada's Global Environmental Multiscale model. The motivation for this research was to explore PV forecasting in Ontario, Canada, where feed‐in tariffs are driving rapid growth in installed PV capacity. The solar and PV forecasts were compared with irradiance data from 10 North‐American ground stations and with alternating current power data from three Canadian PV systems. A 1‐year period was used to train the forecasts, and the following year was used for testing. Two post‐processing methods were applied to the solar forecasts: spatial averaging and bias removal using a Kalman filter. On average, these two methods lead to a 43% reduction in root mean square error (RMSE) over a persistence forecast (skill score = 0.67) and to a 15% reduction in RMSE over the Global Environmental Multiscale forecasts without post‐processing (skill score = 0.28). Bias removal was primarily useful when considering a “regional” forecast for the average irradiance of the 10 ground stations because bias was a more significant fraction of RMSE in this case. PV forecast accuracy was influenced mainly by the underlying (horizontal) solar forecast accuracy, with RMSE ranging from 6.4% to 9.2% of rated power for the individual PV systems. About 76% of the PV forecast errors were within ±5% of the rated power for the individual systems, but the largest errors reached up to 44% to 57% of rated power. © Her Majesty the Queen in Right of Canada 2011. Reproduced with the permission of the Minister of Natural Resources Canada.     

Life cycle assessment and cost analysis of very large‐scale PV systems and suitable locations in the world

Although the Sahara region has a high potential for solar power plants, the amount of installed photovoltaic (PV) system remains relatively low. This paper aims to evaluate these potentials of PV system installation in terms of environmental and economic viewpoints with indices of cost, energy, and greenhouse gas (GHG) emission. Two 1‐GW very large‐scale PV systems are simulated at Ouarzazate in Morocco and at Carpentras in France. The evaluation was performed using life cycle assessment. The lowest energy consumption and GHG emission are obtained while assuming cadmium telluride module. The result of our simulation shows that energy payback time is 0.9 years and CO₂ emission rate is 27.4 g‐CO_2‐eq/kWh in the Ouarzazate case. In cost estimation, generation costs are 0.06 USD/kWh in Ouarzazate and 0.09 USD/kWh in Carpentras in the case of 3% interest rate and 0.5 USD/W for multicrystalline silicon PV module price. In addition, by adapting 15% internal rate of return for 20% of budget, the generation costs become 0.09 USD/kWh in Ouarzazate and 0.13 USD/kWh in Carpentras under the same condition. Furthermore, the selection for suitable locations to install solar power plants in term of GHG emission is identified using geographical information system. Very high‐potential locations (lower than 38 g‐CO_2‐eq/kWh) could be obtained in North Chili, east and west Sahara, and Mexico. Copyright © 2015 John Wiley & Sons, Ltd.     

The energy payback time of advanced crystalline silicon PV modules in 2020: a prospective study

The photovoltaic (PV) market is experiencing vigorous growth, whereas prices are dropping rapidly. This growth has in large part been possible through public support, deserved for its promise to produce electricity at a low cost to the environment. It is therefore important to monitor and minimize environmental impacts associated with PV technologies. In this work, we forecast the environmental performance of crystalline silicon technologies in 2020, the year in which electricity from PV is anticipated to be competitive with wholesale electricity costs all across Europe. Our forecasts are based on technological scenario development and a prospective life cycle assessment with a thorough uncertainty and sensitivity analysis. We estimate that the energy payback time at an in‐plane irradiation of 1700 kWh/(m² year) of crystalline silicon modules can be reduced to below 0.5 years by 2020, which is less than half of the current energy payback time. Copyright © 2013 John Wiley & Sons, Ltd.     

Greenhouse gas emissions associated with photovoltaic electricity from crystalline silicon modules under various energy supply options

The direct and indirect emissions associated with photovoltaic (PV) electricity generation are evaluated, focussing on greenhouse gas (GHG) emissions related to crystalline silicon (c‐Si) solar module production. Electricity supply technologies used in the entire PV production chain are found to be most influential. Emissions associated with only the electricity‐input in the production of PV vary as much as 0–200 g CO₂‐eq per kWh electricity generated by PV. This wide range results because of specific supply technologies one may assume to provide the electricity‐input in PV production, i.e., whether coal‐, gas‐, wind‐, or PV‐power facilities in the “background” provide the electricity supply for powering the entire PV production chain. The heat input in the entire PV production chain, for which mainly the combustion of natural gas is assumed, adds another ∼16 CO₂‐eq/kWh. The GHG emissions directly attributed to c‐Si PV technology alone constitute only ∼1–2 g CO₂‐eq/kWh. The difference in scale indicates the relevance of reporting “indirect” emissions due to energy input in PV production separately from “direct” emissions particular to PV technology. In this article, we also demonstrate the utilization of “direct” and “indirect” shares of emissions for the calculation of GHG emissions in simplified world electricity‐ and PV‐market development scenarios. Results underscore very large GHG mitigation realized by solar PV toward increasingly significant PV market shares. Copyright © 2011 John Wiley & Sons, Ltd.     

Use of support vector regression and numerically predicted cloudiness to forecast power output of a photovoltaic power plant in Kitakyushu,Japan

The development of a methodology to forecast accurately the power produced by photovoltaic systems can be an important tool for the dissemination and integration of such systems on the public electricity grids. Thus, the objective of this study was to forecast the power production of a 1‐MW photovoltaic power plant in Kitakyushu, Japan, using a new methodology based on support vector machines and on the use of several numerically predicted weather variables, including cloudiness. Hourly forecasts of the power produced for 1 year were carried out. Moreover, the effect of the use of numerically predicted cloudiness on the quality of the forecasts was also investigated. The forecasts of power production obtained with the proposed methodology had a root mean square error of 0.0948 MW h and a mean absolute error of 0.058 MW h. It was also found that the forecast and measured values of power production had a good level of correlation varying from 0.8 to 0.88 according to the season of the year. Finally, the use of numerically predicted cloudiness had an important role in the accuracy of the forecasts, and when cloudiness was not used, the root mean square error of the forecasts increased more than 32%, and the mean absolute error increased more than 42%. Copyright © 2011 John Wiley & Sons, Ltd.     

Environmental life cycle assessment of roof‐integrated flexible amorphous silicon/nanocrystalline silicon solar cell laminate

This paper presents an environmental life cycle assessment of a roof‐integrated flexible solar cell laminate with tandem solar cells composed of amorphous silicon/nanocrystalline silicon (a‐Si/nc‐Si). The a‐Si/nc‐Si cells are considered to have 10% conversion efficiency. Their expected service life is 20 years. The production scale considered is 100 MW_p per year. A comparison of the a‐Si/nc‐Si photovoltaic (PV) system with the roof‐mounted multicrystalline silicon (multi‐Si) PV system is also presented. For both PV systems, application in the Netherlands with an annual insolation of 1000 kWh/m² is considered. We found that the overall damage scores of the a‐Si/nc‐Si PV system and the multi‐Si PV system are 0.012 and 0.010 Ecopoints/kWh, respectively. For both PV systems, the impacts due to climate change, human toxicity, particulate matter formation, and fossil resources depletion together contribute to 96% of the overall damage scores. Each of both PV systems has a cumulative primary energy demand of 1.4 MJ/kWh. The cumulative primary energy demand of the a‐Si/nc‐Si PV system has an uncertainty of up to 41%. For the a‐Si/nc‐Si PV system, an energy payback time of 2.3 years is derived. The construction for roof integration, the silicon deposition, and etching are found to be the largest contributors to the primary energy demand of the a‐Si/nc‐Si PV system, whereas encapsulation and the construction for roof integration are the largest contributors to its impact on climate change. Copyright © 2012 John Wiley & Sons, Ltd.     

Update of environmental indicators and energy payback time of CdTe PV systems in Europe

Thin film technologies undergo rapid developments for increasing the module efficiencies and improving production technologies or recycling processes which affect the environmental profile of PV power generation and Energy Payback Time (EPBT). Therefore, especially for the Life Cycle Assessment (LCA) of product systems with short development cycles, the environmental profiles need to be frequently updated to ensure the representativeness and validity of the environmental assessment. The update of LCA results in this paper demonstrates that considerable improvements were reached in the environmental profile of CdTe PV power and EPBT over the last four years. Depending on the location of installation in Europe, the corresponding Greenhouse Gas (GHG) emissions of PV power for ground mounted power plants are between 19 and 30 g CO₂‐equiv./kWh and between 0.7 and 1.1 years in terms of EBPT. Furthermore, for the first time, the environmental impacts due to an already applied recycling procedure of CdTe modules and it's relative contribution to the CdTe PV life cycle has been investigated. This paper presents the main approach, results and outcomes of the study. Copyright © 2011 John Wiley & Sons, Ltd.     

A comparative study on cost and life‐cycle analysis for 100 MW very large‐scale PV (VLS‐PV) systems in deserts using m‐Si,a‐Si,CdTe, and CIS modules

This paper is a study of comparisons between five types of 100 MW Very Large‐Scale Photovoltaic Power Generation (VLS‐PV) Systems, from economic and environmental viewpoints. The authors designed VLS‐PV systems using typical PV modules of multi‐crystalline silicon (12·8% efficiency), high efficiency multi‐crystalline silicon (15·8%), amorphous silicon (6·9%), cadmium tellurium (9·0%), and copper indium selenium (11·0%), and evaluated them by Life‐Cycle Analysis (LCA). Cost, energy requirement, and CO₂ emissions were calculated. In addition, the authors evaluated generation cost, energy payback time (EPT), and CO₂ emission rates. As a result, it was found that the EPT is 1·5–2·5 years and the CO₂ emission rate is 9–16 g‐C/kWh. The generation cost was 11–12 US Cent/kWh on using 2 USD/W PV modules, and 19–20 US Cent/kWh on using 4 USD/W PV module price. Copyright © 2007 John Wiley & Sons, Ltd.     

Life cycle assessment of high‐concentration photovoltaic systems

The environmental profiles of photovoltaic (PV) systems are becoming better as materials are used more efficiently in their production, and overall system performance improves. Our analysis details the material and energy inventories in the life cycle of high‐concentration PV systems, and, based on measured field‐performances, evaluates their energy payback times, life cycle greenhouse gas emissions, and usage of land and water. Although operating high‐concentration PV systems require considerable maintenance, their life cycle environmental burden is much lower than that of the flat‐plate c‐Si systems operating in the same high‐insolation regions. The estimated energy payback times of the Amonix 7700 PV system in operation at Phoenix, AZ, is only 0.9 year, and its estimated greenhouse gas emissions are 27 g CO₂‐eq./kWh over 30 years, or approximately 16 g CO₂‐eq./kWh over 50 years. Copyright © 2012 John Wiley & Sons, Ltd.     

Formulation and analysis of a rule-based short-term loadforecasting algorithm

The formulation of rules for the rule base and the application of such rules are discussed. The classification of the load forecast parameters into weather-sensitive and nonweather-sensitive categories is described. The rationale underlying the development of rules for both the one-day and seven-day forecast is presented. This exercise leads to the identification and estimation of parameters relating load, weather variables, day types, and seasons. Sample rules that are the product of identifiable statistical relationships and expert knowledge are examined. A self-learning process is described which shows how rules governing the electric utility load can be updated. Results from both the one-day and seven-day forecast algorithms are presented, where the seven-day forecast is generated using both accurate and predicted weather information. The monthly average load forecast errors range between 2.97% and 10.71% for the seven-day forecasts. For the one-day forecasts, the average seasonal errors range between 1.03% and 1.53%     

Life‐cycle greenhouse gas emissions and energy payback time of current and prospective silicon heterojunction solar cell designs

Silicon heterojunction (SHJ) cells offer high efficiencies and several advantages in the production process compared to conventional crystalline silicon solar cells. We performed a life‐cycle assessment to identify the greenhouse gas (GHG) footprint, energy payback time (EPBT) and cumulative energy demand of four different SHJ solar cell designs. We analyse these environmental impacts for cell processing and complete systems for both current and prospective designs. On the basis of in‐plane irradiation of 1700 kWh/m², results for current designs show that life‐cycle GHG emissions could be 32 gCO₂‐eq/kWh for complete SHJ photovoltaic (PV) systems (module efficiencies of 18.4%), compared with 38 gCO₂‐eq/kWh for conventional monocrystalline silicon systems (module efficiency of 16.1%). The EPBT of all SHJ designs was found to be 1.5 years, compared with 1.8 years for the monocrystalline PV system. Cell processing contributes little (≤6%) to the overall environmental footprint of SHJ PV systems. Among cell processing steps, vacuum based deposition contributes substantially to the overall results, with 55–80%. Atomic layer deposition of thin films was found to have a significantly lower environmental footprint compared to plasma enhanced chemical vapour deposition and sputtering. Copper‐based compared with silver‐based metallization was shown to reduce the impact of this processing step by 74–84%. Increases in cell efficiency, use of thin silicon wafers and replacement of silver‐based with copper‐based metallization could result in life‐cycle GHG emissions for systems to be reduced to 20 gCO₂‐eq/kWh for SHJ systems and 25 gCO₂‐eq/kWh for monocrystalline system, while EPBT could drop to 0.9 and 1.2 years, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

PV power systems and the environment: results of an expert workshop

Photovoltaic (PV) power systems can lead to significant reduction of emissions to the environment. Contrary to conventional fossil fuel-based electricity production, the environmental aspects of PV power systems are mostly related to indirect processes such as cell and module manufacturing and ‘end of life’ waste management. Careful assessment of such environmental aspects throughout all life-cycle stages is required to reveal the contribution that PV power systems can make to environmental sustainability within the energy sector. An expert workshop was held in Utrecht, The Netherlands, on 25–27 June 1997 that addressed issues and approaches regarding the environmental aspects of PV power systems, including energy payback times, CO₂ mitigation potential, environmental life-cycle assessment and health and safety assessment and control. Various issues of environmental importance were identified during the workshop and recommendations were made for further work to ensure that PV power systems will indeed fulfil the promise of environmental sustainability. © 1998 John Wiley & Sons, Ltd.     

Future development promise for plastic‐based solar electricity

Plastic‐based photovoltaic (PV) technology, also known as organic photovoltaic (OPV), has the development promise to be one of the third PV generation technologies, practically where sunlight reaches a surface area both indoors and outdoors. This paper presents the economic forecast for solar electricity using OPV technology based on a 1 kWp domestic system. With reference to OPV roll‐to‐roll manufacturing, the paper discusses lifetime, efficiency, and costs factors of this emerging PV technology. Taking an outlook of historic PV technology developments and reflect future anticipated technology developments, the future levelised electricity cost is calculated using system life cycle costing techniques. Grid parity at levelised electricity cost below 25 c/kWh may already be reached within 10 years' time, and the technology would have been widespread, assuming a typical southern Europe average solar irradiance of 1700 kWh/m²/year. The influence of solar irradiance and the way the module performs over long periods of time expecting various degradation levels is studied using sensitivity analysis. Eventually, the financial attractiveness to mature silicon‐based PV technology may decline suddenly as financial support schemes such as the popular Feed‐in‐Tariffs dry out. This would give rise to other promising solutions that have already been proven to be less energy intensive and cheaper to produce but may require a different integration model than present technologies. This paper demonstrates that under no financial support schemes emerging PV technologies such as OPV will manage to attract business and further developments. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of initial power stabilization over crystalline‐Si photovoltaic modules maximum power

Measurements that suppliers offer in specification sheets are not always close to the actual power measured in independent laboratories such as CIEMAT. Independent measurements tend to be lower than those printed on the label sometimes even lower than the allowed tolerance indicated by the manufacturer on the same label. Furthermore, a potentially significant power reduction has been reported when Standard EN50380 (which requires photovoltaic (PV) modules to be exposed to more than 20 kWh/m² of sunlight prior to taking the measurements that appear on the label) is followed. This is the initial power stabilization and this work studies the power stabilization that tends to appear in crystalline PV modules. Crystalline PV modules usually decrease in power around 1%, but decreases >4% have also been reported. These power losses are only detected after the mentioned power stabilization. Copyright © 2010 John Wiley & Sons, Ltd.     

Optimal sizing and life cycle assessment of residential photovoltaic energy systems with battery storage

This paper presents the optimal sizing and life cycle assessment of residential photovoltaic (PV) energy systems. The system consists of PV modules as the main power producer, and lead–acid batteries as the medium of electricity storage, and other essential devices such as an inverter. Five‐parameter analytic PV cell model is used to calculate the energy production from the modules. Electrical needs for a family living under normal conditions of comfort are modelled and used within simulation of the system performance, with an average daily load of approximately 9·0 kWh. The system's performance simulations are carried out with typical yearly solar radiation and ambient temperature data from five different sites in Turkey. The typical years are selected from a total of 6 years data for each site. The life cycle cost of the PV system is analysed for various system configurations for a 20‐year system life. The role of the batteries in PV energy systems are analysed in terms of the cost and power loss. The system performance is analysed as a function of various parameters such as energy production and cost. It is shown that these change substantially for different system configurations and locations. The life cycle assessment of the energy system described was also carried out to determine the environmental impact. It was found that, with the conservative European average electricity mix, energy pay back time (EPBT) is 6·2 years and CO₂ pay back time is 4·6 years for the given system. Copyright © 2007 John Wiley & Sons, Ltd.     

Optimization of multilevel power adjustment in wireless sensor networks

Restricted to the limited battery power of nodes, energy conservation becomes a critical design issue in wireless sensor networks (WSNs). Transmission with excess power not only reduces the lifetime of sensor nodes, but also introduces immoderate interference in the shared radio channel. It is ideal to transmit packets with just enough power. In this paper, we propose a multilevel power adjustment (MLPA) mechanism for WSNs to prolong the individual node lifetime and the overall network lifetime. The energy conservation is achieved by reducing the average transmission power. The analytical model is built for the MLPA mechanism enabled with k distinct power levels (k-LPA). Under a free space loss (path loss exponent γ=2) model, the closed-form expression of optimal power setting is derived and the average transmission power can be minimized as (k+1)/2k of original fixed power. For wireless environment other than the free space loss model (γ≠2), a recursive formula expression set is established to acquire the optimal power configuration and the minimum average transmission power, which is 2P/(γ+2) as k approaches infinity. Furthermore, to reduce the computing complexity and the effort of measuring path loss exponent, two approximated power configuration methods are proposed. The analytical results show that both the proposed approximate methods are near-optimal solutions for most of the wireless communication environments. It can be shown that lim? _k→∞ P _avg ^～I (k,γ)=lim? _k→∞ P _avg ^～II (k,γ)=lim? _k→∞ P _avg ^min? (k,γ)=2P/(γ+2).     

Multi‐pronged analysis of degradation rates of photovoltaic modules and arrays deployed in Florida

The long‐term performance and reliability of photovoltaic (PV) modules and systems are critical metrics for the economic viability of PV as a power source. In this study, the power degradation rates of two identical PV systems deployed in Florida are quantified using the Performance Ratio analytical technique and the translation of power output to an alternative reporting condition of 1000 W m⁻² irradiance and cell temperature of 50 °C. We introduce a multi‐pronged strategy for quantifying the degradation rates of PV modules and arrays using archived data. This multi‐pronged approach utilizes nearby weather stations to validate and, if needed, correct suspect environmental data that can be a problem when sensor calibrations may have drifted. Recent field measurements, including I‐V curve measurements of the arrays, visual inspection, and infrared imaging, are then used to further investigate the performance of these systems. Finally, the degradation rates and calculated uncertainties are reported for both systems using the methods described previously. Copyright © 2012 John Wiley & Sons, Ltd.     

A novel power benefit prediction approach for two‐axis sun‐tracking type photovoltaic systems based on semiconductor theory

Photovoltaic (PV) systems incorporated with sun‐tracking technology have been proposed and verified to effectively increase the power harvest. However, the actual power generated from a PV module has not been investigated and compared with that analyzed from theoretical models of the PV material. This study proposes a novel method for estimating the power benefit harvested by a two‐axis sun‐tracking type (STT) PV system. The method is based on semiconductor theory and the dynamic characteristics, including maximum power point tracking of PV modules that can be integrated with the database of annual solar incidences to predict the power harvested by any STT PV system. The increment of annual energy provided by an STT PV system installed at any arbitrary latitude, compared with that by a fixed‐type system, can be accurately estimated using the proposed method. To verify the feasibility and precision performance of this method, a fixed‐type and a two‐axis STT PV system were installed at 24.92° north latitude in northern Taiwan and tested through long‐term experiments. The experimental results show that the energy increments estimated by the theoretical model and actual measurement are 19.39% and 16.74%, respectively. The results demonstrate that the proposed method is capable of predicting the power benefit harvested by an STT PV system with high accuracy. Using our method, a PV system installer can evaluate beforehand the economic benefits of different types of PV systems while taking different construction locations into consideration, thereby obtaining a better installation strategy for PV systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Enhancing the power output of PV modules by considering the view factor to sky effect and rearranging the interconnections of solar cells

The solar diffuse radiation incident on a photovoltaic (PV) module is unevenly distributed along the module's width because its solar‐cells “see” different view‐factor values with respect to their position. This fact causes PV modules to experience undesired power losses brought about by current mismatch. The paper addresses this issue and presents new interconnection strategies for the module's cells. The proposed interconnections are shown to introduce power gain vis‐à‐vis the all‐series connected module. Having established the theoretical framework, a case study is examined, comparing two sites with considerable different amounts of diffuse radiation with the aim of quantifying the power production enhancement with regard to the site's prevailing annual extent of diffuse radiation. It is found, for example, that by converting the all‐series cell interconnection into parallel strips in Desert Rock (NV, USA), each module can be supplemented with a 6.5 [kW_ph] annually on average. The study may have financial implications for the PV industry which strives to increase power generation while maintaining reduced costs. Copyright © 2017 John Wiley & Sons, Ltd.