An extensive photovoltaic (PV) measurement comparison, carried out as part of an EU-funded FP7 project, demonstrates the ongoing need to share good practices in PV measurement, especially when it comes to new technologies or device structures, such as multi-junction cells and modules.
The results submitted by the participating laboratories were evaluated against the reference calibrations provided by the JRC’s European Solar Test Installation (ESTI). The outcome of this comparison has recently been published in an open-access paper in the journal Progress in Photovoltaics.
The study examined the broad range of expertise and facilities of the participating PV laboratories, both private and public. Based on the comparison to the reference calibrations, it clearly identifies improvement potential for the procedures implemented by several laboratories. Additionally, the results of this study highlight the importance of periodical comparison of individual measurement results versus those of reference laboratories. This ensures that claims of new achievements in performance and durability are backed by robust scientific evidence.
Following the new 55% greenhouse gas emissions reduction target that the European Commission proposes for 2030, as well as the increasing demand of energy supply in and outside Europe, renewable energies are gaining further momentum. Among them, solar and wind are currently at the forefront of this energy transition. Photovoltaics in particular has recently shown a rebound in installations demand as well as in the research and development of new technologies and new applications, a trend that was thoroughly discussed during the 37th edition of EU PVSEC. However, the successful deployment of photovoltaics, and its potential to contribute to the Paris Agreement objectives, needs to be supported by accurate and reliable performance assessments. While this applies to any PV technology, it is even more relevant to new products entering the market or products at developmental stage, which would need to meet the minimum requirements in order to reach industrialisation scale.
Crystalline silicon photovoltaic modules are approaching limit efficiency, due to the intrinsic characteristics of their semiconductor material. One solution to this bottleneck consists in combining silicon cells with other photoactive materials, thus creating a sort of multi-layer “sandwich” where each layer would respond to a specific band of the sunlight spectrum. In these multi-junction structures, the conversion efficiencies could in principle be tuned at much higher levels than single active materials. Moreover, multi-junction PV devices can be built entirely with photoactive materials whose physical and chemical properties substantially differ from those of crystalline silicon.
However, due to the intricate physical structure of multi-junction PV devices, the correct assessment of electrical performance and other characteristics involves measurement facilities and procedures that are more complex than those employed to test single-junction PV devices, of which traditional one-layer crystalline silicon modules are a classic example. Therefore, the aim of this measurement campaign was twofold: to verify the availability of such facilities and procedures in participating laboratories and to promote knowledge sharing of best practices in PV testing, with particular attention to the measurement procedures for multi-junction devices.
The paper also includes a summary section with general guidelines for the correct measurement of electrical performance of both single- and multi-junction PV devices. The broad application of these guidelines is expected to improve the consistency of future results inside the photovoltaic community.
- Publication date
- 5 October 2020