WP7 - Testing of PV devices and scribing process validation
WP7 will evaluate the quality of the process according to the particular patterning steps (P1, P2, P3) which are applied on thin film devices in different configurations (substrate/superstrate) and on different substrate materials (glass/flexible). Both CIS and CdTe materials families will be under analysis.
As first task (WP 7.1), the focus will be on identifying:
• on one side, the patterning steps which could be improved or substituted by using advanced fiber lasers concepts
• on the other side, the analytical methods which can help identifying laser-scribing patterning related problems in thin film solar modules, such as shunting paths between adjacent cells originating from a bad removal of the semiconductor material.
The following tasks (WP 7.2 to 7.5) will be directed to validate project samples of the following technologies:
• thin film cells/modules realised in a substrate configuration (CIS) on glass substrates
• thin film cells/modules realised in a substrate configuration (CIS) on flexible substrates
• thin film cells/modules realised in a superstrate configuration (CdTe) on glass substrates
• thin film cells/modules realised in a superstrate configuration (CdTe) on flexible substrates.
Preliminary and intermediate tests will be performed on laboratory scale mini-modules, to assess the performance level and guide further developments. Final tests will be done on industrial prototypes, to give evidence of overall project findings; industrial companies involved in the project will be therefore able to finalize research effort on a “ready for use” module, by means of small pilot lines specifically designed to encompass all the innovative laser issues.
The tests to be performed can be divided into three main categories:
• module calibration tests (IV curve, spectral response, temperature coefficient measurements..)
• module lifetime (climatic chambers for damp heat and thermal cycling, continuous light soaking facilities, ultraviolet exposure chamber, static load stress testing, hail testing, dry and wet insulation testing and visual inspection..)
• energy rating tests (real time performance monitoring as a function of environmental conditions).
Figures 1-4 show some examples of the experimental facilities of the European Solar Test Installation (ESTI), European Commission Joint Research Centre; ESTI acts as an independent European reference facility for photovoltaic technologies on fully traceable measurements.
Fig.1 shows typical outdoor racks for long term exposure testing of the photovoltaic modules: module positioning (inclination, support structure..) and cabling are designed in order to reproduce real operational conditions; test results shall then be related to the specific environmental conditions of the geographical area in which tests are performed.
Fig. 1: Outdoor racks for long term exposure testing.
Fig. 2 shows a solar tracking device for outdoor photovoltaic modules calibration measurements: being able to correctly determine the sun path in the sky and the module inclination angle for highest irradiation represents a preliminary issue for any measurement.
Fig. 2: Solar tracking device for outdoor measurements.
Fig. 3 shows a visual inspection experimental apparatus: modules are carefully inspected to detect, prior to tests or after specific ones, any cracks, bubbles or delaminations which may worsen and negatively affect module performance.
Fig. 3: Visual inspection experimental apparatus.
Fig. 4 shows an indoor solar simulator for photovoltaic cells: an appropriate lamp, whose spectral emission is designed in order to minimize the mismatch with standard solar spectrum, illuminates the sample under analysis and the outgoing IV (current-voltage) characteristic can be measured, by means of a dedicated electronic device.
Fig. 4: Indoor solar simulator for cells.
All the aforementioned tests are presented in details in the normative codes which are part Working Group 2 (“standards for flat-plate photovoltaic modules”) of International Electrotechnical Commission (IEC) standards, namely:
• IEC 60904-4 on calibration traceability (part of the 60904 series on measurement of I-V characteristics, requirements for reference solar devices, solar simulator performance requirements, etc.)
• IEC 61215 for crystalline silicon terrestrial photovoltaic (PV) modules - design qualification and type approval (edition 3 in preparation)
• IEC 61646 Thin Film terrestrial photovoltaic (PV) modules – Design qualification and type approval (edition 2 published in 2008)
• IEC 61853 Performance testing and energy rating of terrestrial photovoltaic (PV) modules series of energy rating standards (draft).