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CPVMatch Report Summary

Project ID: 640873

Periodic Reporting for period 1 - CPVMatch (Concentrating Photovoltaic modules using advanced technologies and cells for highest efficiencies)

Reporting period: 2015-05-01 to 2016-08-31

Summary of the context and overall objectives of the project

The EU-funded project Concentrating Photovoltaic modules using advanced technologies and cells for highest efficiencies (CPVMatch) will bring practical performance of high concentrating photovoltaics (HCPV) closer to theoretical limits. Leading European experts in their respective fields of science, technology and industrialization are engaged in the project to realize novel multi-junction solar cell architectures and innovative HCPV module concepts.

It has been proven that the only realistic path to close the gap between theoretical and practical ultra-high efficiency solar cells is the monolithic multi-junction (MJ) approach, i.e. to stack different materials on top of each other. Each material/sub solar cell converts a specific part of the sun´s spectrum and thus manages the photons properly. However, large area multi-junction cells are too expensive if applied in standard PV modules. A viable solution to solve the cost issue is to use tiny solar cells in combination with optical concentrating technology, in particular, HCPV, in which the light is concentrated over the solar cells more than 500 times. The combination of ultra-high efficient cells and optical concentration lead to low cost on system level and eventually to low levelised electricity costs, today well below 8 €cent/kWh and at the end of this project below 5 €cent/kWh. Therefore, to achieve an optimised PV system (high efficiency, low cost and low environmental impact), world-wide well-known partners in the field of CPV technology work together in this project to run and progress together the development of highly-efficient multijunction solar cells and the improvement of the CPV module technique.

The collaborative project started in May 2015 with a duration of three and a half years and an EC contribution of 4.95 M€. The consortium consists of four research institutions (Fraunhofer ISE, RSE, CEA, Tecnalia), one University (UPM), two industry partners (AZUR Space Solar Power, AIXTRON) and two SMEs (ASSE, Cycleco) and is coordinated by Fraunhofer ISE. The consortium addresses in their research all topics required to manufacture highly efficient CPV modules. This includes material issues, manufacturing and equipment aspects and production challenges. University and research institutes are working in close cooperation with industry partners in order to ensure fast industrial exploitation of all results within the whole value chain. The central objective of CPVMatch is to realise HCPV solar cells and modules working at a concentration level ≥ 800x with an efficiency of 48 % and 40 %, respectively (see picture), with a low environmental impact.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The first project period has been successful. All project partners have a high motivation to collaborate and to achieve high-level scientific results. Scientific results have already been achieved, which is also underlined by three journal papers and ten conference papers submitted in the first project period. The following presents highlights of results achieved within this period. Note that the description is not comprehensive and does neither present all highlights nor details.

Complex simulation using a transfer matrix method (TM) and realistic material parameters were carried out to optimize the GaInP/(Al)GaAs/GaInAs/Ge four-junction solar cell structure. A theoretical potential of 50.2% efficiency was identified. Through a comparison with experimental cells from previous projects the main loss mechanisms were identified and quantified, leading to a strategic development roadmap. An experimental analysis identified the most critical parameters during epitaxy and the bonding process and several new batches of four-junction solar cells have already been fabricated.

For the growth of SiGeSn suitable gas sources were identified based on literature reviews and experimental tests. For the first time, SiGeSn layer grown by MOCVD by using Si2H6, IBuGe and SnCl4 have been deposited. The energy gap of the ternary materials is in the range 0.87-0.97 eV, very near to the target value of 1 eV. Extensive CFD computations to optimize the MOVPE reactor configuration were carried out and new optimized hardware is currently being constructed. Moreover, nanostructured coatings for anti-reflection are being developed. First, available techniques and materials to be used for the nano-coatings were evaluated in terms of their optical properties, toxicity and usability. Then, a new apparatus for the deposition of nanostructured coatings, consisting of a rotating and tilting platform was assembled and mounted inside the evaporation chamber.

A new achromatic ‘biFresnel’ lens has been designed and manufactured within CPVMatch (see picture). The new design is based on ray-tracing simulations, experimental tests and discussions with optics manufacturers. It was produced with a new laminator set-up. Sub units of the new mirror-based module design were manufactured and tested indoor and outdoor (see picture), for which extensive simulations as well as experimental prototyping of the major components have been carried out. The smart module will include a novel positioning sensor and DC-DC converter.

To enable the characterization of four-junction solar cells measurement processes and evaluation algorithms were adapted. For the characterization of new CPV optics a test method that measures the spectrally resolved irradiance distribution for a concentrator photovoltaic (CPV) optical system has been developed, using the indoor characterization test bench, METHOD (Measurement of Electrical, Thermal and Optical Devices), which decouples the temperatures of the primary optical element (POE) and of the cell allowing to analyse their respective effects on optical and electrical performance (see picture). The Life-Cycle Assessment started by describing the CPVMatch system under study to realize a complete environmental study with the aim to reduce the environmental impacts, the energy consumption and the related costs. This resulted in a general process flow chart based on this system description. A questionnaire to collect qualitative data about the system has been developed to obtain data from the partners.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

In order to develop the targeted high performing CPV solar cells and modules a significant progress beyond the state of the art is required. Two strategies are adhered to (both for the multi-junction solar cell and module technology). The work on cells and module technologies is accompanied by a profound lifecycle and environmental assessment and the development of adapted characterization methods of new multijunction cells and HCPV modules. The following specific objectives have been defined for the project:

1. Development of a novel wafer bonded four-junction solar cell for better spectral matching with an efficiency of 48% using advanced materials and processes
2. Development of a lattice-matched multi-junction solar cell with high efficiency potential and low process cost, comprising nanostructured coatings and innovative lattice-matched materials, obtained by combing III-V and IV elements
3. Development of innovative, Fresnel lens-based HCPV modules
4. Development of smart, mirror-based HCPV modules
5. Life-cycle and environmental assessment of new multi-junction cells and HCPV modules
6. Assess the developments realized on solar cells and modules by means of adapted characterization methods

The central expected impact of this proposal is to significantly increase the technical performance of III-V multi-junction solar cells and HCPV modules and thus to lower the cost for PV energy. HCPV systems reach efficiency levels which flat-plate PV will never be able to reach cost-efficiently. In addition, CPVMatch will help to increase the reliability, maintainability, and lifetime of CPV while increasing simplicity and decreasing operation and maintenance costs. Therefore, this project will contribute to solving the global climate and energy challenge by improving one of the most promising solar energy technologies.

One of the central impacts of the project is also to reduce the life-cycle environmental impact of electricity generation. HCPV systems already have low energy payback times of 6 to 9 months in Southern Europe, which is mainly due to the smaller cell area and hence lower amount of energy needed for the production of cells in CPV systems. Moreover, higher efficiencies lead to lower energy payback times as more energy can be produced from similar system components. In order to optimize the environmental impact of CPV further, this project includes a work package on life-cycle assessment. Life-cycle aspects of the new technology will be analysed and a low environmental impact will be an aim of the design.

CPV power plants in Southern Europe could deliver predictable, low-cost and reliable electricity and hence improve EU energy security by lowering the need for energy imports of fossil fuels and nuclear material. This holds in particular as most of the CPV manufacturing value chain lies within Europe and includes several of the key enabling technologies, which were identified as essential for maintaining European competitiveness. Many start-up and smaller companies exist in Europe that can produce CPV systems, including cells, modules and other system components. Hence the success of this project will help to nurture the development of the European industrial capacity to produce CPV components and systems and to open new opportunities for companies and the strong research community in Europe.

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