Reliability of commercial triple junction concentrator solar cells under real climatic conditions and its influence on electricity cost

This paper proposes a methodology for assessing the concentrator solar cell reliability in a real application for a given location provided the results from accelerated life tests. We have applied this methodology for the evaluation of warranty times of commercial triple junction solar cells operating inside real concentrator modules in Golden (Colorado, USA), Madrid (Spain) and Tucson (Arizona, USA) for the period 2012–2015. Warranty times in Golden and Madrid, namely, 68 and 31 years, respectively, for the analysed period, indicate the robustness of commercial triple junction solar cells. Nevertheless, the warranty time of 15 years for Tucson suggests the need of improvement in the heat extraction of the solar cell within the concentrator module. Therefore, the influence of the location on the reliability of concentrator solar cells is huge, and it has no sense to supply general reliability values for a given concentrator product. The influence of these warranty times for the three locations on the levelised cost of electricity has been analysed. Cost of €c10–12/kWh can be achieved nowadays, while after 1 GW_p cumulative installed power, a dramatic reduction to levels of €c2–3/kWh is achievable. Copyright © 2017 John Wiley & Sons, Ltd.     

Development of concentrator modules with dome‐shaped Fresnel lenses and triple‐junction concentrator cells

The status of the development of a new concentrator module in Japan is discussed based on three arguments, performance, reliability and cost. We have achieved a 26·6% peak uncorrected efficiency from a 7056 cm² 400 × module with 36 solar cells connected in series, measured in house. The peak uncorrected efficiencies of the same type of the module with 6 solar cells connected in series and 1176 cm² area measured by Fraunhofer ISE and NREL are reported as 27·4% and 24·8% respectively. The peak uncorrected efficiency for a 550× and 5445 cm² module with 20 solar cells connected in series was 28·9% in house. The temperature‐corrected efficiency of the 550 × module under optimal solar irradiation condition was 31·5 ± 1·7%. In terms of performance, the annual power generation is discussed based on a side‐by‐side evaluation against a 14% commercial multicrystalline silicon module. For reliability, some new degradation modes inherent to high concentration III‐V solar cell system are discussed and a 20‐year lifetime under concentrated flux exposure proven. The fail‐safe issues concerning the concentrated sunlight are also discussed. Moreover, the overall scenario for the reduction of material cost is discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Experimental demonstration of high‐concentration photovoltaics on a parabolic trough using tracking secondary optics

A new approach to high‐concentration photovoltaics (HCPV) based on a parabolic trough primary concentrator is presented. The design diverges from the standard HCPV arrangement of a two‐axis tracking point‐focus concentrator, and rather employs a simpler parabolic trough primary concentrator to reduce cost. To break the 2D limit of concentration, and bring the system into the realm of HCPV, the system employs an array of rotating secondary concentrators is arranged along the focal line of the parabolic trough. The resulting line‐to‐point (LTP) focus geometry allows the system to achieve a geometric concentration of 590×, yet still maintains the advantages of having a linear trough primary concentrator, namely manufacturability, economy, and scalability. A full‐scale prototype of the system was constructed in Biasca, Switzerland. During on‐sun tests a flux concentration of 364 suns was measured at the exit of the secondary concentrator, the highest reported concentration for any parabolic‐trough‐based system. Moreover, the system reached a peak efficiency of 20.2%, the highest measured solar‐to‐DC efficiency for a parabolic trough‐based solar collector. Long‐term performance is estimated by means of a coupled optical‐electrical model validated vis‐à‐vis the experimental results. This work serves as an experimental proof‐of‐concept for high‐concentration trough‐based collectors, thereby opening new avenues for reducing the cost of HCPV systems. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrical performance evaluation of low‐concentrating non‐imaging photovoltaic concentrator

Second generation prototype photovoltaic facades of reduced costs incorporating devices with optically concentrating elements (PRIDE) incorporate 6 mm wide ‘Saturn’ solar cells at the absorber of the dielectric concentrator. The concentrators were made using injection moulding technique with potential to manufacture in large‐scale applications. Four different concentrator panels have been experimentally verified at outdoors to identify the non‐identical current–voltage (I–V) curves. The I–V curve, fill factor and solar to electrical conversion efficiency of four PRIDE concentrator modules have been evaluated from the 24 manufactured in the ‘IDEOCONTE’ project. The maximum solar to electrical conversion efficiency and the fill factor of the PRIDE concentrator were 9·1 and 70%, respectively. The mismatch loss of the ‘unit concentrators’ has been identified that occurred due to the lack of bonding between the concentrator unit and the solar cell and the rear glass. The average power concentration ratio of PRIDE concentrators manufactured by the improved method was 2·10 compared to a similar non‐concentrating panel and the optical efficiency of the PRIDE system was 83%. Copyright © 2008 John Wiley & Sons, Ltd.     

Sliver solar cells for concentrator PV systems with concentration ratio below 50

This paper links together two different yet complimentary technologies: concentrator photovoltaics (CPVs) and Sliver technology. Recent research and development and commercialisation efforts in concentrator technologies have centred on high‐concentration systems, encouraged by the availability of high‐efficiency, multi‐junction III‐V cells. In contrast, little attention has been paid to the potential of systems with low‐to‐medium levels of concentration. Arguably, this is due to the absence of any suitable, low‐cost concentrator cells, readily available at a commercial scale. Sliver technology is a candidate for the supply of commercial low‐cost cells suitable for systems with concentration ratios in the range of 5–50. This can be achieved via judicious choice of cell design parameters and with only minor changes to the fabrication process suitable for 1‐sun Sliver cells. Device modelling is used to show that Sliver cells are suitable for illumination intensities up to 5 W/cm², with unavoidable emitter resistance limiting performance for higher intensities. The best cells manufactured for operation at low and medium concentration had efficiencies of 18·8% at 9 suns (above 18·6% between 5 and 15 suns) and 18·4% at 37 suns (above 18·2% between 30 and 50 suns), respectively. Incorporation of sidewall texturing and SiN anti‐reflection coatings would yield efficiencies exceeding 20% for similar cells. Concentrator Sliver cells can be produced to almost any length and are perfectly bifacial, features which add significantly to their attractiveness to concentrator system designers. The availability of cheap concentrator Sliver cells could provide opportunities for new, low‐cost concentrator systems, which in turn has the potential to provide a pathway to low‐cost solar electricity. Copyright © 2009 John Wiley & Sons, Ltd.     

Operating regimes for second generation luminescent solar concentrators

In this paper, we introduce the concept of first and second generation luminescent solar concentrators. Traditional, first generation devices are characterised by their randomly oriented molecules that absorb sunlight and emit luminescence isotropically. By applying detailed balance to the absorbed and emitted photon fluxes we derive the Shockley–Queisser limit for these devices. It is found that they have inherently low efficiency due to optical losses (the well known reabsorption problem) and also that device performance is strongly affected by the areal ratio between the top and edge surfaces. This latter property makes it very difficult to achieve significant cost reductions because as the edge area is reduced (to lessen the amount of expensive photovoltaic material required for conversion), the efficiency of the system diminishes. First generation concentrators have now approached the fundamental limits which we predict here, thus to achieve a stand‐alone luminescent concentrator that enables significant cost reductions, second generation approaches are now needed. New, second generation devices are characterised by either directional emitters or photonic filters which enhance the waveguiding mechanism, allowing high efficiency and large sizes to be achieved simultaneously. Here we define the fundamental operating regime in which second generation technology must reach to surpass the limit of first generation devices. Copyright © 2011 John Wiley & Sons, Ltd.     

Development and experimental evaluation of a complete solar thermophotovoltaic system

We present a practical implementation of a solar thermophotovoltaic (TPV) system. The system presented in this paper comprises a sunlight concentrator system, a cylindrical cup‐shaped absorber/emitter (made of tungsten coated with HfO₂), and an hexagonal‐shaped water‐cooled TPV generator comprising 24 germanium TPV cells, which is surrounding the cylindrical absorber/emitter. This paper focuses on the development of shingled TPV cell arrays, the characterization of the sunlight concentrator system, the estimation of the temperature achieved by the cylindrical emitters operated under concentrated sunlight, and the evaluation of the full system performance under real outdoor irradiance conditions. From the system characterization, we have measured short‐circuit current densities up to 0.95 A/cm², electric power densities of 67 mW/cm², and a global conversion efficiency of about 0.8%. To our knowledge, this is the first overall solar‐to‐electricity efficiency reported for a complete solar thermophotovoltaic system. The very low efficiency is mainly due to the overheating of the cells (up to 120 °C) and to the high optical concentrator losses, which prevent the achievement of the optimum emitter temperature. The loss analysis shows that by improving both aspects, efficiencies above 5% could be achievable in the very short term and efficiencies above 10% could be achieved with further improvements. Copyright © 2012 John Wiley & Sons, Ltd.     

40% efficient sunlight to electricity conversion

Increasing sunlight conversion efficiency is a key driver for on‐going solar electricity cost reduction. For photovoltaic conversion, the approach most successful in increasing conversion efficiency is to split sunlight into spectral bands and direct each band to a dedicated solar cell of an appropriate energy bandgap to convert this band efficiently. In this work, we demonstrate conversion of sunlight to electricity in a solar collector with an efficiency value above 40% for the first time, using a small 287‐cm² aperture area test stand, notably equipped with commercial concentrator solar cells. We use optical band‐pass filtering to capture energy that is normally wasted by commercial GaInP/GaInAs/Ge triple junction cells and convert this normally wasted energy using a separate Si cell with higher efficiency than physically possible in the original device. The 287‐cm² aperture area sunlight‐concentrating converter demonstrating this independently confirmed efficiency is a prototype for a large photovoltaic power tower system, where sunlight is reflected from a field of sun‐tracking heliostats to a dense photovoltaic array mounted on a central tower. In such systems, improved efficiency not only reduces costs by increasing energy output for a given investment in heliostats and towers but also reduces unwanted heat generation at the central tower. Copyright © 2015 John Wiley & Sons, Ltd.     

Crystalline silicon solar module technology: Towards the 1 € per watt‐peak goal

Crystalline silicon solar module manufacturing cost is analysed, from feedstock to final product, regarding the equipment, labour, materials, yield losses and fixed cost contributions. Data provided by European industrial partners are used to describe a reference technology and to obtain its cost breakdown. The analysis of the main cost drivers allows to define new generation technologies suitable to reduce module cost towards the short‐term goal of 1 € per watt‐peak. This goal roughly corresponds with the cost level needed to enable ‘grid parity’: the situation solar electricity becomes competitive with retail electricity. The new technologies are described and their costs are analysed. Cost reductions due to scale effects in production are also assessed for next generation manufacturing plants with capacities in the range of several hundreds of megawatts to one gigawatt of module power per year, which are to come in the near future. The combined effects of technology development and economies of scale bring the direct manufacturing costs of wafer‐based crystalline silicon solar modules down into the range of 0·9–1·3 € per watt‐peak, according to current insights and information (the range results from differences between technologies as well as from uncertainties per technology). Copyright © 2008 John Wiley & Sons, Ltd.     

BICON: high concentration PV using one‐axis tracking and silicon concentrator cells

BICON is a two‐stage concentrator system developed at Fraunhofer ISE which is one‐axis tracked. The innovation of this one‐axis tracked system is that it enables a high geometrical concentration of 300 × in combination with a high optical efficiency (upto 78%) and a large acceptance angle of ± 23·5° all year through. For this, the system uses a parabolic mirror (40·4 ×) and a three dimensional second stage consisting of compound parabolic concentrators (CPCs, 7·7 ×). For the concentrator concept and particularly for an easy cell integration, rear‐line‐contacted concentrator (RLCC) cells with a maximum efficiency of 25% were developed and a hybrid mounting concept for the RLCC cells is presented. The optical performance of different CPC materials was tested and is analysed in this paper. Finally, small modules consisting of six series interconnected RLCC cells and six CPCs were integrated into the concentrator system and tested outdoor. A BICON system efficiency of 16·2% was reached at around 800 W/m² direct irradiance under realistic outdoor conditions. Copyright © 2006 John Wiley & Sons, Ltd.     

Maximization of conversion efficiency based on global normal irradiance using hybrid concentrator photovoltaic architecture

Maximization of module conversion efficiency based on global normal irradiance (GNI) rather than direct normal irradiance (DNI) was experimentally demonstrated using a hybrid concentrator photovoltaic (CPV) architecture in which a low‐cost solar cell (a bifacial crystalline silicon cell) was integrated with a high‐efficiency concentrator solar cell (III–V triple‐junction cell) to harvest diffuse sunlight. The results of outdoor experiments showed that the low‐cost cell enhanced the generated power by factors of 1.39 and 1.63 for high‐DNI and midrange‐DNI conditions, respectively, and that the resultant GNI‐based module efficiencies were 32.7% and 25.6%, respectively. © 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.     

Characterization of optical collectors for concentration photovoltaic applications

The design and characterization of the collector of a photovoltaic concentrator system is commonly carried out for a given receiver, the optical parameters of the collector being linked to it. This paper, which has substantial tutorial content, deals with the characterization of collectors for concentrator photovoltaic systems, independently of any receiver, and providing the necessary parameters for the design of a system. This strategy allows the parameters related to the collector and the receiver, which are usually manufactured by different industries, to be totally separated. It also allows the optical collectors coming from non‐photovoltaic industries to be evaluated. The information that the mirror and lens manufacturers should provide for a photovoltaic concentrator application can be summarized under three characteristics: overall optical efficiency; light distribution; and acceptance angle. Theory, equipment, and procedures to carry out the optical characterization of the collectors are explained. Copyright © 2003 John Wiley & Sons, Ltd.     

Impact of electricity tariffs on optimal orientation of photovoltaic modules

Maximum revenue (or cost saving) from non‐tracking photovoltaic (PV) modules used for distributed generation can be achieved by a module orientation that depends on how the electricity tariff varies with time of day and time of year. Many jurisdictions have real‐time market prices of electricity for large customers, time‐dependent tariffs or tariffs that depend on peak demand. This paper quantifies the impact of such tariffs on the optimal orientation of non‐tracking PV modules using example tariffs from California, Nevada and Ontario, and concludes that modules should be oriented to the west of south by 28°, 46° and 54° respectively. In order to focus on the impact of tariff, the results are based on simulations of a constant‐efficiency PV system operating under year‐round clear‐sky conditions. A generalized relationship between optimal azimuth and the on‐ to off‐peak ratio of time‐dependent tariffs is also presented. The paper quantifies the sensitivity of the dollar value of the power generated to non‐optimal orientation of the modules. Compared to conventional south facing modules tilted at an angle just under the latitude, the paper demonstrates that optimal orientation adds 4–19% to the revenue/cost savings, potentially affecting the economic viability of a PV installation. The peak demand components of the Ontario tariff have a much more substantial effect on the optimization and resultant revenues (cost savings) than variations in the real‐time market price of electricity. Copyright © 2015 John Wiley & Sons, Ltd.     

Initial field performance of a hybrid CPV‐T microconcentrator system

The first prototype of the hybrid CPV‐T ANU‐Chromasun micro‐concentrator has been installed at The Australian National University, Canberra, Australia. The results of electrical and thermal performance of the micro‐concentrator system, including instantaneous and full‐day monitoring, show that the combined efficiency of the system can exceed 70%. Over the span of a day, the average electrical efficiency was 8% and the average thermal efficiency was 50%. Copyright © 2012 John Wiley & Sons, Ltd.     

Efficient allocation of elastic interfederation encrypted streaming sessions

Audio and video (A/V) collaboration platforms often use Internet cloud technologies to ensure elasticity. They generally operate on a best‐effort basis, without quality or delivery guarantees. However, such guarantees are a premise of business‐focused platforms, which often rely on static/dedicated infrastructure and hardware‐based components. This article presents results obtained in the final stage of the Elastic Media Distribution (EMD) project, which targets the migration of a business‐focused hardware‐based A/V collaboration tool towards a more elastic, reliable, and secure cloud‐based model. The use case under investigation is an educational scenario: teachers and students located at distributed sites collaborate under different data encryption policies. An existing model of collaboration streaming is extended to accommodate encryption‐enabled streaming components, and new resource allocation heuristics are proposed to deploy these components under stringent service level agreement (SLA) constraints. An extended version of our evaluation framework, based on the CloudSim simulator, manages encryption‐enabled components. A resource usage dataset was obtained by prototyping selected streaming components and evaluating their performance on the Virtual Wall large‐scale test bed. This dataset is fed into the extended simulation framework. Simulation results show longer than expected delays when loading streaming components, an issue that jeopardises the user experience that can be alleviated by the algorithms proposed in this article. Results show that the proposed algorithms enable policy‐based secured communications under bandwidth and virtual machine (VM) cost increases of 48% and 23%, respectively, if compared with a nonencrypted previous solution, and with set‐up times remaining under the required 2‐second deadline.     

Heterogeneous Networks to Support User Needs with Major Challenges for New Wideband Access Systems

Third generation mobile radio systems are currently being deployed in different regions of the world. Future systems beyond the third generation are already under discussion in international bodies and forums such as ITU, WWRF and R&D programs of the European Union and in other regions. These systems will determine the research and standardization activities in mobile and wireless communication in the next years. Based on the experience from the third generation future systems will be developed mainly from the user perspective with respect to potential services and applications including traffic demands. This is directly related to the paradigm shifts from the first generation to systems beyond third generation. International bodies are already discussing basic system requirements. The basic system architecture of heterogeneous networks with different complementing access systems is from the today's perspective the most economic approach for systems beyond 3G to satisfy user and operator needs for reasonable cost. Such system architectures enable the deployment of system capacity according to the traffic requirements with the user experience ``Optimally Connected, Anywhere and Anytime' with seamless service provision between different access systems. New radio interface components with high data rate as additional components of systems beyond 3G are being proposed in international bodies. Key issues of such systems are coverage due to reduced range and the huge spectrum demand. In this paper the international context, the user perspective, revenue and traffic expectations are presented. This results in the basic system requirements and the potential system architecture of heterogeneous networks. Major challenges for the new wideband radio interfaces are the impact on range and spectrum demand. Basic investigations are presented on these issues to critically review requirements on future systems.     

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.     

高压部件测试安全性问题分析与预防

高压起爆引信技术是未来新型安全与引爆系统,其核心高压部件的安全可靠测试是该类产品生产必须解决的问题.本文对高压部件测试过程中的安全性问题进行分析与风险预测,制定措施实现高压部件的安全可靠测试.