Relative performance of tracking versus fixed tilt photovoltaic systems in the USA

Tracking systems can increase the amount of electricity generated by photovoltaic (PV) modules, by actively orienting each module to intercept more solar energy. We find that horizontal one‐axis tracking systems can increase PV generation by 12–25% relative to south‐facing fixed mount PV systems with 25° tilts in the contiguous USA, and two‐axis tracking systems can increase PV generation by 30–45% relative to fixed mount systems. Tracking systems increase PV generation more significantly in arid regions such as the southwest USA than in humid regions with persistent cloud cover such as the Pacific Northwest and coastal Atlantic states. We find that fixed and tracking PV systems have similar interannual variability in their generation profiles, and this variability is primarily driven by project location. Tracking PV projects cost more than fixed tilt systems, per unit capacity, and we explore how much more tracking projects could cost while generating similar levelized costs of energy as fixed tilt systems. We define this as the breakeven additional cost of tracking and find that it is primarily driven by three factors: (i) regional tracking performance, (ii) fixed tilt system costs that tracking projects compete against, and (iii) additional tracking operation and maintenance costs. Using this framework, we explore the relative competitiveness of tracking systems for a range of fixed and tracking PV prices and evaluate how tracking competitiveness varies by region. Copyright © 2013 John Wiley & Sons, Ltd.     

Impact of photovoltaic orientation on its relative economic value in wholesale energy markets

Most calculations of optimum photovoltaic (PV) performance focus on maximizing annual energy production. However, given the seasonally and daily time varying electricity demand and resulting variation in price, the PV orientation resulting in maximum energy yield may not yield the maximum economic benefit. With the use of historical solar irradiance and wholesale market prices for several locations in the USA, we evaluate the benefits of a variety of orientations for fixed and tracking PV arrays. We find that orienting fixed arrays slightly to the west of due south generally increases their economic value in the simulated systems because the reduced generation on an annual basis is more than offset by increased generation in high‐value hours in late summer afternoons. However, this effect is small, typically providing an increase in value from 1% to 5%. The economic value of adjusting the orientation semi‐annually (May 1st and September 1st) and monthly shows a modest increase in value from 3% to 5%. Several other implications of this analysis are also discussed. Copyright © 2012 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.     

光伏电池铺设倾角的动态优化与分析

以单位面积全年接收的太阳能总辐射量最大为目标,根据某市典型气象年的逐时气象数据,建立随光照辐射强度变化的光伏电池板最佳铺设倾角动态优化模型。模型仿真计算结果表明,同一地点光照辐射强度的差异对最优倾角有显著影响,与同月固定最优倾角相比,采用动态优化的日固定倾角,光伏电池单位面积全年接收的太阳总辐射量增加57.13%。     

Power and energy [1999 technology analysis and forecast]

This article presents a power and energy technology analysis and forecast for 1999. The subjects covered include photovoltaics, PV power systems, solar arrays, nuclear power and free market spot electricity pricing     

On the role of solar photovoltaics in global energy transition scenarios

The global energy system has to be transformed towards high levels of sustainability in order to comply with the COP21 agreement. Solar photovoltaic (PV) offers excellent characteristics to play a major role in this energy transition. The key objective of this work is to investigate the role of PV in the global energy transition based on respective scenarios and a newly introduced energy transition model developed by the authors. A progressive group of energy transition scenarios present results of a fast growth of installed PV capacities and a high energy supply share of solar energy to the total primary energy demand in the world in the decades to come. These progressive energy transition scenarios can be confirmed. For the very first time, a full hourly modelling for an entire year is performed for the world, subdivided in 145 sub‐regions, which is required to reflect the intermittent character of the future energy system. The model derives total installed solar PV capacity requirements of 7.1–9.1 TWp for the electricity sector (as of the year 2015) and 27.4 TWp for the entire energy system in the mid‐term. The long‐term capacity is expected to be 42 TWp and, because of the ongoing cost reduction of PV and battery technologies, this value is found to be the lower limit for the installed capacities. Solar PV electricity is expected to be the largest, least cost and most relevant source of energy in the mid‐term to long‐term for the global energy supply. Copyright © 2017 John Wiley & Sons, Ltd.     

Design of tracking photovoltaic systems with a single vertical axis

Solar tracking is used in large grid‐connected photovoltaic plants to maximise solar radiation collection and, hence, to reduce the cost of delivered electricity. In particular, single vertical axis tracking, also called azimuth tracking, allows for energy gains up to 40%, compared with optimally tilted fully static arrays. This paper examines the theoretical aspects associated with the design of azimuth tracking, taking into account shadowing between different trackers and back‐tracking features. Then, the practical design of the trackers installed at the 1.4 MW Tudela PV plant is presented and discussed. Finally, this tracking alternative is compared with the more conventional fully stationary approach. Copyright © 2002 John Wiley & Sons, Ltd.     

PV thermal systems: PV panels supplying renewable electricity and heat

With PV Thermal panels sunlight is converted into electricity and heat simultaneously. Per unit area the total efficiency of a PVT panel is higher than the sum of the efficiencies of separate PV panels and solar thermal collectors. During the last 20 years research into PVT techniques and concepts has been widespread, but rather scattered. This reflects the number of possible PVT concepts and the accompanying research and development problems, for which it is the general goal to optimise both electrical and thermal efficiency of a device simultaneously. The aspects that can be optimised are, amongst others, the spectral characteristics of the PV cell, its solar absorption and the internal heat transfer between cells and heat‐collecting system. Another important level of optimisation is for the PVT device geometry and the integration into a system. The electricity and heat demand and the temperature level of the heat determine the choice for a certain system set‐up. With an optimal design, PVT systems can supply buildings with 100% renewable electricity and heat in a more cost‐effective manner than separate PV and solar thermal systems and thus contribute to the long‐term international targets on implementation of renewable energy in the built environment. Copyright © 2004 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.     

The performance of PV‐t systems for residential application in Bangkok

This paper focused on the performance of photovoltaic‐thermal (PVT) systems working in Bangkok for residential applications. The PVT system is one which produces both electricity and low temperature heat at the same time. This paper investigated the performance of PVT systems that use different types of commercial solar PV panels. The characteristics of the PV panels were used as input parameters in the simulation. Each system comprises 2 m² of PVT collector area. Water draw patterns are those with a typical consumption of medium size houses in Bangkok, and the measured monthly average city water temperature of Bangkok has been used to estimate the energy output. The results show that the optimum water flow rate is 20 kg/h for all types of PVT collectors and the effect of water flow can improve the cell efficiency of PV cells. Moreover, the total energy output from the PVT collectors, which had glass covers is very significantly higher than those without one. The c‐Si PVT panel gave the best performance with the highest rate of primary energy reduction. The payback time of each system is 6.4, 11.8, and 13.4 years for a‐Si, mc‐Si, and c‐Si types of PVT system, respectively. This investigation concludes that from the viewpoint of system performance, c‐Si PVT is the most promising type than whereas from the viewpoint of economy, a‐Si PVT has the fastest payback time. Copyright © 2012 John Wiley & Sons, Ltd.     

The present status and future direction of technology development for photovoltaic power generation in Japan

In 2004 NEDO established the PV Roadmap Toward 2030 PV2030 as a long‐term strategy for PV R&D. In this Roadmap, PV is expected by 2030 to supply approximately 50% of residential electricity consumption (cumulative installed capacity in the range of 100 GW). In terms of economic efficiency, electricity costs are targeted to equal commercial use, approximately 14 Yen/kW h, by 2020 and industrial use, approximately 7 Yen/kW h, by 2030. For future PV systems, it is essential to improve the stand‐alone capabilities of PV system with electricity storage and to develop community‐based PV systems using multi‐function inverters. Advanced technological innovations beyond the existing levels are also essential. Therefore, NEDO is undertaking 2‐year projects for preliminary research to make clear the next R&D of solar cells and PV system technology. Copyright © 2005 John Wiley & Sons, Ltd.     

Energy,cost and LCA results of PV and hybrid PV/T solar systems

Hybrid photovoltaic/thermal (PV/T) solar systems provide a simultaneous conversion of solar radiation into electricity and heat. In these devices, the PV modules are mounted together with heat recovery units, by which a circulating fluid allows one to cool them down during their operation. An extensive study on water‐cooled PV/T solar systems has been conducted at the University of Patras, where hybrid prototypes have been experimentally studied. In this paper the electrical and thermal efficiencies are given and the annual energy output under the weather conditions of Patras is calculated for horizontal and tilted building roof installation. In addition, the costs of all system parts are included and the cost payback time is estimated. Finally, the methodology of life cycle assessment (LCA) has been applied to perform an energy and environmental assessment of the analysed system. The goal of this study, carried out at the University of Rome ‘La Sapienza’ by means of SimaPro 5·1 software, was to verify the benefits of heat recovery. The concepts and results of this work on energy performance, economic aspects and LCA results of modified PV and water‐cooled PV/T solar systems, give a clear idea of their application advantages. From the results, the most important conclusion is that PV/T systems are cost effective and of better environmental impact compared with standard PV modules. Copyright © 2005 John Wiley & Sons, Ltd.     

A high‐efficiency LPE GaAs solar cell at concentrations ranging from 2000 to 4000 suns

III–V solar cells for terrestrial concentration applications are currently becoming of greater and greater interest. From our experience, concentrations higher than 1000 suns are required with these cells to reduce PV electricity cost to such an extent that this alternative could become cost competitive. In this paper, a single‐junction p/n GaAs solar cell, with efficiencies of 23ċ8 and 22ċ5% at concentration ratios of 2700 and 3600 suns respectively, is presented. This GaAs solar cell is well suited for use with non‐imaging optical concentrators, which possess a large aperture angle. Low‐temperature liquid phase epitaxy (LTLPE) has been the growing technique for the semiconductor structure as an attempt to use a simplified, cheap and clean technique, within a renewable energy perspective. The GaAs solar cell presented is compared with the highest efficiency tandem solar cells at concentration levels exceeding 1000 suns. The GaAs solar cell performance maintains high efficiencies up to 4000 suns, while tandem cells seem to drop very quickly after reaching their maximum. Therefore, single‐junction GaAs solar cells are a good candidate for operating at very high concentrations, and LPE is able to supply these high‐quality solar cells to work within terrestrial concentration systems, the main objective of which is the reduction of PV electricity costs. Copyright © 2003 John Wiley & Sons, Ltd.     

Distributed power generation versus grid extension: an assessment of solar photovoltaics for rural electrification in Northern Ghana

The competitiveness of distributed solar photovoltaic (PV) power generation for rural electrification in northern Ghana is assessed and compared with the conventional option of extending the national grid and increasing the capacity for centralised power generation. A model is constructed to calculate the life‐cycle cost (LCC) of the two options and to test the sensitivity of different parameters. All calculations are based on information from the GEF/UNDP pilot region in the East Mamprusi District. In addition to the economic aspect, issues of quality and environmental effects are discussed. The LCC of distributed PV is lower than that of a grid extension for an electricity demand corresponding to solar home systems of 140 W_p or smaller. Thus, distributed PV is cost competitive for purposes of lighting, entertainment, information and basic public facilities, such as schools and hospitals. The LCC for the option of grid extension with central power generation is dominated by the cost of low‐voltage micro‐grids within the communities. Important factors are the density of households and the penetration (fraction of households electrified), as they affect the line length per connected household. The relatively low cost of regional medium‐voltage grids makes the geographical location of each community less important than expected. Battery replacement every fifth year makes up the major part of the LCC of solar home systems and is also responsible for the large energy input in the production of the systems. This could limit both future cost reductions of distributed PV and its potential to mitigate greenhouse gas emissions. Copyright © 2002 John Wiley & Sons, Ltd.     

Novel applications of bifacial solar cells

Utilizing the light reflected by simple means onto the rear surface of solar cells is an effective way of lowering the cost of solar electricity, since more power is generated per cell. Innovative bifacial photovoltaic modules have been introduced, such as a multi‐functional bifacial PV sun‐shading element which is based on bifacially sensitive solar cells in combination with a white semitransparent reflector back sheet. Not only is sunlight collected by its front and rear surface efficiently converted into electricity, but also diffuse glare‐free daylight is provided. Other applications include relatively narrow bifacial modules installed at a certain distance in front of a reflecting background. In all cases power gains of more than 50% can be achieved with little extra cost compared with monofacial modules. Copyright © 2003 John Wiley & Sons, Ltd.     

Coupling PV and CAES power plants to transform intermittent PV electricity into a dispatchable electricity source

This study investigates the transformation of photovoltaic (PV) electricity production from an intermittent into a dispatchable source of electricity by coupling PV plants to compressed air energy storage (CAES) gas turbine power plants. Based on historical solar irradiation data for the United States' south western states and actual PV and CAES performance data, we show that the large‐scale adoption of coupled PV–CAES power plants will likely enable peak electricity generation in 2020 at costs equal to or lower than those from natural gas power plants with or without carbon capture and storage systems. Our findings also suggest that given the societal value of reducing carbon dioxide and the sensitivity of conventional generation to rising fossil fuel prices, this competitive crossover point may occur much sooner. Copyright © 2008 John Wiley & Sons, Ltd.     

Experience with solar home systems in developing countries: a review

Solar energy is widely perceived as a promising technology for electricity generation in remote locations in developing countries. It is estimated that 1.3 million solar home systems had been installed by early 2000. An estimated one‐third of installed systems were backed by foreign donor support in government programmes and two‐thirds supplied by commercial dealers. The estimated growth in the deployment of solar lanterns is less than for SHS. One out of every 100 households that gain access to electricity in developing countries uses solar power. In spite of these successes, doubts have arisen about the effectiveness and suitability of small PV systems for rural development. Many organisational, financial and technical problems appear to present difficulties. A literature survey has been conducted to make an inventory of experience with solar PV applications for households in developing countries. The main finding is that an adequate service infrastructure is required to make projects viable. Household choice in system sizes is often too restricted in donor‐funded projects. Smaller systems sold for cash can be a good alternative to credit systems by offering to increased affordability. Gaps in existing knowledge have been identified, which could be overcome by field monitoring programmes. Copyright © 2001 John Wiley & Sons, Ltd.     

Solar based large scale power plants: what is the best option?

There are very few published data comparing performance and cost of thermal and photovoltaic (PV) based solar power generations. With recent intense technology and business developments there is a need to establish a comparison between these two solar energy options. We have developed a simple model to compare electricity cost using these two options without any additional fuel source of hybridization. Capital along with operation and maintenance (O&M) costs and other parameters from existing large scale solar farms are used to reflect actual project costs. To compete with traditional sources of power generation, solar technologies need to provide dispatchable electric power to respond to demand during peak hours. Different solutions for energy storage are available. In spite of their high capital cost, adding energy storage is considered a better long term solution than hybrid solar systems for large scale power plants. For this reason, a comparison between the two solar options is also provided that include energy storage. Although electricity storage is more expensive than thermal storage, PV power remains a competitive option. Expenses related to O&M in solar thermal plant are about ten times higher than PV, an important factor resulting in higher energy cost. Based on data from proven commercial technologies, this study showed that PV holds a slight advantage even when energy storage is included. Copyright © 2010 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.     

Performance,cost and life‐cycle assessment study of hybrid PVT/AIR solar systems

An alternative and cost‐effective solution to building integrated PV systems is to use hybrid photovoltaic/thermal (PV/T) solar systems. These systems consist of PV modules with an air channel at their rear surface, where ambient air is circulating in the channel for PV cooling and the extracted heat can be used for building thermal needs. To increase the system thermal efficiency, additional glazing is necessary, but this results in the decrease of the PV module electrical output from the additional optical losses of the solar radiation. PV/T solar systems with air heat extraction have been extensively studied at the University of Patras. Prototypes in their standard form and also with low‐cost modifications have been tested, aiming to achieve improved PV/T systems. An energetic and environmental assessment for the PV and PV/T systems tested has been performed by the University of Rome ‘La Sapienza’, implementing the specific software SimaPro 5·1 regarding the life‐cycle assessment (LCA) methodology applied. In this paper electrical and thermal energy output results for PV and PV/T systems are given, focusing on their performance improvements and environmental impact, considering their construction and operation requirements. The new outcome of the study was that the glazed type PV/T systems present optimum performance regarding energy, cost and LCA results. Copyright © 2005 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.