Characterization of Crystalline Silicon PV Cells in Truck Transportation Environment
By Anderson Shu-Tsung Hsu, ITRI, Published at 2012 CPTIC Conference
The photovoltaics industry is expanding rapidly to meet growing renewable energy demands all over the world. PV cell breakage mostly depends on the stress induced in the processing, handling and transportation, but also relies on the presence of defects such as cracks or micro-cracks. In this paper, we present a test method of mechanical vibration for c-Si PV cells in a truck transportation environment. After the vibration test, we received the variances in performance in order to qualify c-Si cells during shipping, and to build the coherent relations between parameters and specific defects for reliability concerns.
Figure: test package of PV cell
For this project we used 1,000 pieces of crystalline solar cells, and each 100 pieces cells stacked in one block. There are 800 pieces to act as the experimental group and 200 pieces as the reference group for comparison. Therefore, 8- blocks acting as test blocks were arranged inside the test package, to sample the vibration response by setting an accelerometer on the top side of the test block. The other dummy blocks used 7-glass which had the same weight and dimension with the test block of real cells. In general, 10 blocks were arranged vertically in one box and 24 boxes in a test package. The total weight of test specimen near 335 kg, and its configuration is 110cm (L) x 93cm (W) x 127.5cm (H). Some conclusions were written as follows:
- Experimental data showed there are 6 pieces of broken cells and breakage rate for such case is below 1% (6/800), but failure rate due to all abnormal cells is near 4% (31/800). Few cells with visible defects in this status like cracks or micro-cracks are supposed to be induced in the process during transportation, but still keep good data of Ncell and Pmpp. Failure rate induced by more parameters (Ncell, Pmpp, Rs, Rsh, and FF) is robust than breakage rate (or efficiency) to qualify cells only. In order to make a solution of reliability for PV cell, PV module and PV system, to address cell performance drop and defect change coherently during transportation is necessary.
- Broken cells appeared at top layer firstly, where experienced more vibration response and higher grms value lead to the relative motion like drop or jump happened inside test package seriously.
- Random vibration test method with truck profile can simulate ground transportation condition well, that is helpful to evaluate test package to protect cells during shipping. Furthermore, drop or jump test would be necessary to monitor relative motion between blocks at each layer of test package. 3-Axis vibration test with 3-direction accelerometer shall be recommended to get the real response of test package.
- The improvement of package design relies on how to avoid resonance points happened at frequency range where easily excite package or cells to have more response lead to destroy during shipping. Detailed Sine-sweep resonance test are necessary to get resonance analysis for test package.
This paper was prepared in collaboration with SEMI International Standards Program, Taiwan Photovoltaic Technical Committee, and PV Cell Vibration Task Force. The paper is a result of extensive discussion in a series of task force meetings and exchanges over a period of a year. We would like to acknowledge the contribution of ideas from task force members during the discussions, and the opportunity to participate in the extensive experiment team. SEMI draft (activity no.5204) named “Test Method for Mechanical Vibration of c-Si PV cells in Shipping Environment” will join cycle 3 ballot submission in coming April, 2012. (PV Cell Vibration Task Force, contact window: firstname.lastname@example.org.
SEMI Standards Watch, March 2012