Stability and Performance of Photovoltaics (STAPP)

Definition of the performance of photovoltaics is normally reduced to the efficiency alone. However, this number contains no indication of key issues such as system component reliability, module stability or appropriate balance of system design -- all of which play a crucial role in determining the performance in terms of usability. The key indicator is the levelised cost of energy (LCOE). The main influences on this, and thus the viability of photovoltaic technologies, are not only in material science but also in the way systems behave in the long term, and the uncertainty in predicting their behaviour. The link between laboratory-based materials science and the LCOE is poorly understood, revealing gaps in scientific knowledge which will be filled by this project. The key outcome is improved understanding of the potential for deploying photovoltaics in different climatic zones. The biggest unknowns in the LCOE are: understanding of the stability and long-term performance of photovoltaic modules; how a holistic system performance can be described; and the uncertainty in life-time energy yield prediction. This is crucial, especially for newer thin film technologies, which have been shown to be more variable in degradation and often suffer inappropriate balance of system components. Close collaboration with manufacturers of thin film as well as crystalline silicon devices will ensure that these aspects are appropriately covered. Novel measurement and modelling approaches for the prediction of life-time energy yield of the modules will be developed and validated against realistic data in collected in different climatic zones. This will result in the development of accelerated test procedures. Uncertainty calculations will enable identification and minimisation of this, and thus reduce the LCOE. A holistic systems approach is taken, specifically looking at the effects of different inverters in different climates and the effects of the existing network infrastructure on energy performance. At the heart of this project is the development of models and their validation, all focused on predicting the lifetime energy yield. A measurement campaign will be undertaken using novel techniques to better monitor the long-term behaviour of modules. Detailed, spatially-resolved techniques will be developed and linked to finite element-based models. This then allows the development of improved accelerated tests to be linked to real environments. These models will be validated against modules measured in a variety of realistic deployments. Using a geographical information system, maps of environmental strains and expected degradation rates per year for the different technologies will be developed.The feedback from the grid is an often underestimated effect on photovoltaic system performance. Typically, the grid and power conditioning cause 5-10% losses in otherwise appropriately installed systems; in unfortunate cases this can rise to 60%. The underlying reasons need to be better understood, so specific models for the interaction with the grid and different control strategies will be developed with the overall aim to minimise these loss effects.This project will be crucial for both the UK and India to translate their ambitious installation plans into reality as it will deliver the tools required to plan the viability of installations via geographical information systems, underpinned by a robust science base. This will aid decisions on the use of appropriate photovoltaic technology for a given site, to include both the modules themselves and other system components, to maximise cost-effectiveness and reliability.

The outcome of this project will be a vastly improved understanding of how new and existing photovoltaic materials operate at the module and system level under different climatic conditions, represented by the UK and India (but with relevance to many other locations). Since the project focuses on energy yield and the levelised cost of electricity (LCOE), the results will be relevant to all sectors that are involved in the implementation of photovoltaics and the wider issues of energy in general. Nevertheless, we can define five sectors with specific interest in the results of the project, over and above the academic community, as shown below: 1. Companies involved in the manufacture of photovoltaic modules, the design of photovoltaic systems and the installation of photovoltaic systems 2. Organisations involved in the development of energy systems -- especially electricity distribution companies 3. Standards organisations dealing with the PV and electrical sector 4. Government and related organisations involved in the development of energy strategy, including policy decisions 5. Companies offering measurement equipment or service measurements. The project will impact all of the above communities, both in the short- and medium term. Whilst the project does not develop new materials directly, it will enable a deeper understanding of the operation of the newer PV technologies to a lower uncertainty of the energy yield and, therefore, of the LCOE of the systems. This will allow a significant reduction of LCOE through improved financing options; this will have a very significant impact on the PV industry. Reduced LCOE will enable the PV industry to achieve grid parity faster, i.e., reach the point where no further financial subsidies are required. Thus the project will positively impact on the speed of growth of the industry as a whole, and the project partners in particular. Two types of products are developed within the project and appropriate commercialisation partners are within the project. Firstly, there are novel measurement machines such as the measurement of localised QE in thin film multi-junction devices. This is equipment of great use to the PV industry, and by Perkin Elmer working closely with Loughborough University on this aspect, a commercial exploitation route is provided. Secondly, service type measurements will be developed, such as accelerated qualification tests. Among our partners, SEC is offering such tests commercially, in addition to Ipsol Test Ltd. Thus the commercialisation of these products will be ensured, creating employment in both the UK and India. Beyond these obvious commercialisation routes, the project is positioned around development of scientific models and pre-standardisation research. This tends to be difficult to commercialise directly. However, commercialisation of new technologies and progress of the industry would be adversely affected by the lack of such research. The development of accelerated tests and scientific models will allow a faster route to market for new and innovative technologies. The evaluation of novel products will reduce the risk of market introduction and early failure, which in turn increases the likelihood to succeed in today's difficult market. The project will also benefit the academic communities involved, as they can learn from each other. The project will educate a large number of performance specialists (the PDRAs, PGRAs and Research Students), which will enable both the UK and India to support the anticipated growth in installations. The lack of this would hinder progress, as there currently is a dearth of well-trained people in this field. The project will also improve the international standing of all partners involved.