Objectives
The aim of this project is to extend the metric for an energy-based photovoltaic classification to roof-mounted photovoltaics as well as to the fast-growing fields of bifacial and building-integrated photovoltaics.
The specific objectives of the project are:
1. To define and realise standard testing conditions for the measurement of the power or the short-circuit current of bifacial solar devices Different approaches for laboratory measurements and for production line measurements will be developed, realised, compared, selected and standardised. This will form the basis for the extended energy rating and the standardisation of measurement of bifacial solar devices.
2. To improve the method of uncertainty evaluation of the spectral mismatch correction in the calibration of solar devices when combining the spectral irradiance and spectral responsivity, taking the correlation of the spectral data into account.
3. To develop traceable measurement methods for extending energy rating to bifacial solar modules and to modules (bifacial or monofacial) applied to or integrated into buildings. This will include the definition of a harmonised data format for solar device properties, required for PV Energy rating measurement standards.
4. To enable instantaneous measurement of the spectral radiance of the complete sky for improved determination of real outdoor measurement conditions and the irradiance spectral-angular distribution by hyperspectral imaging.
5. To develop more accurate measurement methods for traditional and emerging solar modules, including the spectral responsivity of the complete module, fast linearity measurements for modules, angular dependency of modules, with an uncertainty of <1 % for the angular dependency impact, <3 °C for the nominal operating module temperature (NOMT), <1 % for the impact of spectral responsivity and <1 % for the impact of non-linearity.
6. To facilitate the uptake of the technology and measurement infrastructure developed in the project by the measurement supply chain (NMIs, calibration laboratories), standards developing organisations and end users (photovoltaics industry).
Thus, the project addresses metrological problems of the European PV industry that have been identified by the consortium during standardisation meetings, workshops with industrial partners and conferences.
Progress beyond the state of the art and results
This project improves upon the most recently developed methods for the determination of the energy rating characteristics, yield prediction, and the energy rating of solar modules, which are currently not applicable to some emerging technologies. The existing methods and calculations do not take into account the irradiance that impinges on the rearside of the solar cell and thus are not applicable to bifacial solar devices.
Specifically, power rating measurements of bifacial solar devices have had deviations in excess of 10 % reported between ISO17025 accredited laboratories. This compares to less than 2 % for conventional technologies. This project will close this uncertainty gap by establishing appropriate measurement standards and verifying them by comparisons between the laboratories.
Building integrated photovoltaics (BIPV) are becoming a more common installation mode, but complex urban environments and interaction with the building envelope require better consideration of the albedo component and thermal operating conditions. PV-Enerate will adapt the methods included in the IEC61853 standards to deliver all data required for the yield prediction in a BIPV or BAPV mode.
Advanced metrology for the characterisation of solar modules will be developed as part of this project. One example for such development is a non-destructive method for the fast measurement of current-voltage (IV) characteristics of each solar cell within a module using digital light projection and other modulation techniques. Another is the application of one of the first LED-based solar simulators worldwide for modules (incorporating about 19000 LEDs in total, of more than 20 different types), which will be used for the realisation of the different radiation conditions experienced by a PV module across a typical year of operation and the comprehensive characterisation of modules as required for the energy rating.
Standardisation technical committees have identified that the nominal operating module temperatures (NOMTs) of solar modules are difficult to determine and that results from the outdoor method are highly site-dependent. For this reason, a comprehensive analysis of the effects will be performed. The project will use and include data from the world’s most advanced facility for simultaneous measurement of sky spectra from over 100 different directions, using a hyperspectral imaging approach.