Leonardo Micheli

Applicability of silicon micro-finned heat sinks for 500× concentrating photovoltaics systems

In concentrating photovoltaic (CPV) applications, the sunlight is focused onto solar cells up to thousands of times and, without an adequate cooling system, the cell’s temperature can dangerously raise over the operating temperature range in few seconds. In this study, an investigation on micro-finned heat sink for high concentrating photovoltaics has been conducted. The geometry of the system and the choice of the components play an important role in the thermal management of CPV. The size of cell, as well as the optics, can strongly affect the thermal behaviour of the CPV: the effects of the CPV geometry on the thermal performance of the heat sink are experimentally investigated and discussed in order to design an optimised system for passive cooling. A micro-fin array is developed to handle the heat generated by the cell and the system is studied in different conditions to prove the applicability of this passive solution to the harsh CPV conditions. It has been found that micro-fins are a suitable solution for passive cooling at concentrations up to 500×. Moreover, this kind of solutions shows the potential to achieve high mass-specific power values, proving its competitiveness in mobile or tracked systems, such as CPV.

Enhancing ultra-high CPV passive cooling using least-material finned heat sinks

Ultra-high concentrating photovoltaic (CPV) systems aim to increase the cost-competiveness of CPV by increasing the concentrations over 2000 suns. In this work, the design of a heat sink for ultra-high concentrating photovoltaic (CPV) applications is presented. For the first time, the least-material approach, widely used in electronics to maximize the thermal dissipation while minimizing the weight of the heat sink, has been applied in CPV. This method has the potential to further decrease the cost of this technology and to keep the multijunction cell within the operative temperature range. The designing procedure is described in the paper and the results of a thermal simulation are shown to prove the reliability of the solution. A prediction of the costs is also reported: a cost of 0.151

Comparison of methods for estimating the solar cell temperature and their influence in the calculation of the electrical parameters in a HCPV module

/Wp is expected for a passive least-material heat sink developed for 4000x applications.

Design, Development, and Analysis of a Densely Packed 500x Concentrating Photovoltaic Cell Assembly on Insulated Metal Substrate

The electrical parameters of a multi-junction solar cell are influenced by its operating temperature. Hence, the estimation of the cell temperature of a HCPV module is critical for its electrical characterization. However, measuring the cell temperature of a HCPV module is a complex task due to its unique features. This paper calculates the cell temperature in a HCPV module by using a number of methods to address this important issue. We conducted a comparative study of three methods used to estimate the cell temperature of a HCPV module: the Voc-Isc method, the thermal resistance method and the lineal method. The results show that all of the studied methods can be used to estimate cell temperatures with an acceptable margin of error.

Small-Volume Fabrication of a 144-Cell Assembly for High-Concentrating Photovoltaic Receivers

The paper presents a novel densely packed assembly for high concentrating photovoltaic applications, designed to fit 125x primary and 4x secondary reflective optics. This assembly can accommodate 144 multijunction cells and is one of the most populated modules presented so far. Based on the thermal simulation results, an aluminum-based insulated metal substrate has been used as baseplate; this technology is commonly exploited for Light Emitting Diode applications, due to its optimal thermal management. The original outline of the conductive copper layer has been developed to minimize Joule losses by reducing the number of interconnections among the cells in series. Oversized Schottky diodes have been employed for bypassing purposes. The whole design fits the IPC-2221 requirements. The plate has been manufactured using standard electronic processes and then characterized through an indoor test and the results are here presented and commented on. The assembly achieves a fill factor above 80% and an efficiency of 29.4% at 500x, less than 2% lower than that of a single cell commercial receiver. The novel design of the conductive pattern is conceived to decrease the power losses and the deployment of an insulated metal substrate represents an improvement towards the awaited cost-cutting for high concentrating photovoltaic technologies.

Technical issues and challenges in the fabrication of a 144-Cell 500× Concentrating Photovoltaic receiver

Concentrating photovoltaic (CPV) is a solution that is gaining attention worldwide as a potential global player in the future energy market. Despite the impressive development in terms of CPV cell efficiency recorded in the last few years, a lack of information on the modules manufacturing is still registered among the documents available in literature. This work describes the challenges faced to fabricate a densely packed cell assembly for 500× CPV applications. The reasons behind the choice of components, materials, and processes are highlighted, and all the solutions applied to overtake the problems experienced after the prototypes production are reported. This article explains all the stages required to achieve a successful fabrication, proven by the results of quality tests and experimental investigations conducted on the prototype. The reliability of the components and the interconnectors is successfully assessed through standard mechanical destructive tests, and an indoor characterization is conducted to investigate the electrical performance. The fabricated cell assembly shows a fill factor as high as 84%, which proves the low series resistance and the lack of mismatches. The outputs are compared with those of commercial assemblies. A cost breakdown is reported and commented: a cost of

Design and production of a 2.5 kWe insulated metal substrate-based densely packed CPV assembly

0.79/Wp has been required to fabricate each of the cell assembly described in this paper. This value has been found to be positively affected by the economy of scale: a larger number of assemblies produced would have reduced it by 17%.

Optimization of the least-material approach for passive Ultra-High CPV cooling

Concentrating Photovoltaics (CPV) aims to reduce the cost of photovoltaic applications by replacing part of the semiconductor material with a less expensive concentrating material. The significant increase in irradiance and the related reduction of semiconductor area introduce some criticisms that affect the design, fabrication and operating stages. The system needs to handle high power and current densities and high heat fluxes, without having repercussions on the cost, the size and the weight of the module. The concentrating photovoltaic is an increasing market and a number of commercial companies has started or is starting to produce CPV receivers. Many papers have been published on the improvement in cell efficiency and on new systems design, but there is a lack of information about the manufacturing stage. An in depth investigation into benefits and weaknesses of assembly methods need to be carried out. This paper describes all the issues and the challenges faced during the fabrication of a novel large densely-packed system.

Opportunities and challenges in micro- and nano-technologies for concentrating photovoltaic cooling: A review

The original design of a new 144-cell concentrating photovoltaic assembly is presented in this paper. It is conceived to work under 500 suns and to generate about 2.5 kWe. An insulated metal substrate was selected as baseplate, in order to get the best compromise between costs and thermal performances. It is based on a 2mm thick aluminum plate, which is in charge of removing the heat as quick as possible. The copper pattern and thickness has been designed accordingly to the IPC Generic Standard on Printed Board Design and to the restrictions of fit a reflective 125x primary optics and a 4x secondary refractive optics. The original outline of the conductive copper layer has been developed to minimize Joule losses by reducing the number of interconnections between the cells in series. Multijunction solar cells and Schottky bypass diodes have been soldered onto the board as surface mounted components. All the fabrication processes are described. This board represents a novelty for the innovative pattern of t...

Performance, limits and economic perspectives for passive cooling of High Concentrator Photovoltaics

The attention around Ultra-High CPV is increasing year by year, because of the potential cost-cutting achievable by increasing the concentration ratio. In these systems, an adequate thermal management becomes particularly important: cooling systems are required to be compact, reliable and efficient. In this work, the geometry of a passive heat sink for a 4000x CPV application is optimized to reduce the volume and the costs, limiting the effects on the thermal performance. The same approach is used to model the behavior of a UHCPV heat sink in New Orleans, LA (USA): the hourly cell temperatures are presented in the paper.