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2nd Progress meeting on the APOLLON project

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2nd Progress meeting on the APOLLON project



In Piacenza, Italy, has been held the 2nd progress meeting of the APOLON Project, so far the biggest integrated Photovoltaic project of FP7 whose main final objective is the development of point focus (PF) and dense array (DA) systems with a target cost of 2 Euro/W. In order to answer to the industrial need to speed up the pre-qualification phase of the CPV systems, without risking hindering the path toward more attractive solutions, which require longer developing time, the APOLLON Project has been divided in two developing phases. In the first one (2 years), an optimization of the existing CPV technologies, from the cell component up to the system level, is foreseen, while, in the second one (3 years), the research towards more advanced solutions and a more substantial progress beyond the state-of-the-art is proposed.

Optimization of the CPV existing technologies


The DA and the PF systems have been first optimized starting from the core of such technologies: the solar cell. The main aim is to reduce the overall CPV-Cell Economical Performance Index, that is, to get solar cell with higher efficiency, concentrator factor and yield at reduced cost. A joint collaboration between ENEA and NAREC has brought to improve Silicon NAREC cell performances in infrared spectral response. Average efficiency have reached 20% with standard deviation= 0.14%. InGaP SJ cells and DJ InGaP/InGaAs cells have been optimized by ENE for the III-V target of the DA and for PF systems. The former best cells reached efficiency of 16,0% at 300 suns, yield around 96 %, while the DJ devices reached efficiency around 29 % @ 750 suns. TJ are under development. These results are expected to allow producing within the end of this year, DA module with efficiency higher than 22%, in agreement with target to be reached by the project.

It is worthwhile to point out that in order to reduce one the typical disadvantages of the DA systems, that is, the need for active cooling therefore a higher complexity of the thermal management, the concept of the spectrum splitting of the solar light is adopted. CPower, with the support of the University of Ferrara, is developing “Mirror Based Spectrum Splitting System (MBS3)” which makes use of mirror and diacroic optics, concentrating the solar radiation onto two separate dense array panels of photovoltaic cells, respectively made of “low gap” and “high gap” semiconductor material. The new MBS3 design allows dissipating the thermal energy which hits the sub-receivers just by using the mechanical structures, avoiding any active liquid cooler.  A thermal analysis has showed a maximum cell working temperature around 50°C

The activity of PF systems has been leaded by SOLARTEC INT and has concerned the optimization of the main components of this technology. Fresnel lenses have been optimized and secondary optics (SOE), developed by the State Enterprise Scientific Research Technological Institute of Instrument Engineering (SE SRTIIE) have been successfully integrated in the receivers, to allow obtaining 1° acceptance angle. The optimized Fresnel lenses will be compared also with the prismatic-hybrid lenses under ENEA development.

The optimization of the assembling technique plays an important role to reduce the cost of the CPV technology. For this reason, in order to get high-throughput assembling of CPV modules, a rotary head wedge bonder with pattern recognition system has been selected by SOLARTEC INT. Its outstanding robustness and the industry-leading throughput make it the most economic choice for demanding production.

Preliminary measurements carried out independently at ISE on the optimized SOLRTEC module (without SOE) have already showed very encouraging results in line with the project targets: the module efficiency value was, in fact, over 24%. The utilization of SOE is expected to bring further benefit to the module performances. TECNALIA has been also supporting SOLARTEC INT and CPower for the optimization of the existing tracker technology. TECNALIA, has worked on the electronic control logic and has also developed a web application for a full tracker remote control.


Characterization and Reliability


A key issue facing the CPV technology is to overcome its perceived lack of reliability. In the APOLLON Project, accelerated testing of the different CPV system components are foreseen to assess the reliability of the proposed CPV technology (also following the tests standard described in the IEC 62108 concerning the “design, qualification and type approval of CPV systems”). Furthermore, taking into account that testing has a research purpose in its own right, testing methodologies related to concentrator cells and systems are under development and verification. Round-Robin testing methodology is adopted among the partners and the testing activity of cells and modules occupies a relevant role in the project. A protocol for out-door testing has been prepared by the University of Cyprus, while a translation formula to compare the IV performance of the module obtained at different environmental conditions to a certain standard conditions has been proposed by ERSE and is under verification by the other partners. If validated, the translation formula will be proposed to be discussed in the IEC TC82 WG7 for CPV standard. JRC has set up a solar simulator to measure solar cells under concentration level till 1000 x and a spectral system apparatus has been completed. This will allow a comparison between in-door and out-door measurements. An accurate thermal characterization has been carried out by ERSE on PF modules. It has been shown that less copper and aluminum material (up to 50% less) could be used for the receiver in order to reduce module’s costs without affecting junction temperature.


Environmental aspects


What is the environmental impact of the PF and MBS3 in their full life cycle? What is the impact on global warming effect? What is the energy payback time? What are the possible improvement options? The APOLLON project has also started to answer these questions. Partners have contributed to supply to ECN the relevant data about the CPV starting technology that is: material consumption, waste produced, emission to the environment, energy production, cost figures. Preliminary calculations bring to consider the C02 emission of about 30 gr per kWh. This value is about one order of magnitude lower than the emission value of C02 produced by hard coal power plant with an integrated gasification combined cycle. Energy pay-back time is around 1.5-2.5 years. Since SOLARTEC INT and CPOWER CPV systems are still under a developing phase, further improvements are expected on system efficiency and reduction of utilized materials which will bring to reduction of the CPV environmental impact.



Progress beyond the state-of-the-art


More advanced solutions to boost solar cell efficiency in 2nd generation CPV systems have been exploring by CNRS and ERSE by modeling and developing epitaxial germanium cells grown by MOCVD. The epitaxial germanium growth opens the path towards totally epitaxial grown quadruple junction (QJ) InGaP/InGaAs/Ge/Ge solar cells and the realization of pseudo-quaternary material to replace 1eV InGaNAs cells. Ge carry-over into III-V subsequent layers and residual n-doping (Arsenic) in intrinsic Ge layers (contamination caused by the use of the reactor for III-V depositions) have been studied and could be solved with a proper selection of buffers, cell polarity, MOCVD reactor set up. As far as this last aspect is concerned, AIXTRON is finishing of setting up a new growth chamber, with a made on purpose new inlet reactor design for the epitaxial Ge growth. The rector chamber will be ready on next October 2010 and will be also equipped with a new heating system to allow getting uniform surface temperature on curved wafers and a new in-situ monitoring system to allow the determination of the two orthogonal components of the wafer bow (three beam measurement apparatus under development). ERSE, ENEA, TECNALIA and CRP are implementing the development of “intelligent modules”, incorporating tracking devices and new low F/# optics, utilizing the experience of automotive lighting. Optimized assembly techniques based on Chip on board (COB) and Chip of flex (COF) technologies are under evaluation to further improve the thermal dissipation, reduce the assembling cost and improving the precision of cell positioning in the receivers.  




The APOLLON project has reached its second year of life time, having started on July 2008. In this first two years, the Consortium has almost completed the first phase of the project and has already started few activities related to the second generation CPV systems. Cell, optic, receiver, tracker, assembling, testing all the key issues related to CPV system have been considered to reduce cost and guarantee reliability and long life time. At the end of this year full prototype MBS and PF systems will be ready to be installed at Catania (Sicily-Italy) within ENEL photovoltaic field for an accurate electrical analysis. Mismatch losses and module misalignment will be monitored all the time in order to select new solutions to raise further the CPV systems performances.


















APOLLON Partners



Ginaluca Timò, project coordinator will be speaking at the 3rd Concentrated Photovoltaics Summit EU on the 18-19 November in Seville. For more details visit: www.cpvtoday.com/eu and the APOLLON project’s website: www.apollon-eu.org


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