This collection of data is the basis for a longitudinal comparison (from July 2008) of the performance of identical - to similar, photovoltaic (solar) arrays in Melbourne, Australia. The initial research question was whether performance of these systems was significantly impacted by the tilt angle of the panels. Was it better to be optimised for summer (shallow angle) or winter (steep angle)? The comparison of performance over 12 months showed that tilt angle of the panels was a NOT significant factor. The study has been extended to track the performance of the systems over time. The data also serves as a diagnostic tool for identifying underperforming systems and provides real world data for ground-truthing theoretical solar output estimates used to determine Government policy. At the end of each month, or the first day of each month, the numerical values displayed on the inverters have been recorded for two points of comparison: the monthly kWh output of each system (eTotal) and the monthly number of generating hours sensed by the inverters (hTotal). Data is listed for each system and systems are ranked by the tilt angle of the panels (lowest angel first). Each system is described by the code (e.g. SP-6-37-N) = Owner’s initials - number of panels - angle of panels - orientation. Raw data has also been normalised to show kWh output per panel. Various views of the data have been graphed to display the comparisons. These graphs are embedded in the spreadsheet. Background: Merri Solars is a loosely structured community group that began as a local Action Group in inner-suburban Melbourne in the late 1980s. In 2007, following a series of water audits and a group purchase of water tanks, a decision was made to make a group purchase of grid connected PV systems. This was when the Australian Federal Government was offering an $8,000 rebate, to anyone who installed a system greater than 1kW, with no means test. The grid-connected photovoltaic systems were installed on private houses in a small area within an inner suburb of Melbourne in mid-July 2008. 10 of the original group of 13 agreed to collect data from their inverters in order to compare the performance of what were very similar systems: 1. Similar panels (175W Siemens rebranded as Solar World) 2. Similar inverters (Sunnyboy) 3. Close proximity - therefore minimising climatic variations 4. Same orientation - all solar arrays face due north (except for one on a NW compound angle and later another with a NE orientation). Six members of the group installed 1kW systems with 6 x 175W panels. One member opted for 7 x 175W panels, two members had 8 x 175W panels, and one had 10 x 175W panels. 2 more households (local with 12 Schott 170W panels and in Brunswick with 8 x BP 165W panels) joined the group. Others have also joined and these systems serve as further points of comparison. Apart from the number of panels in each system, the main point of difference was the tilt angle of the panels (15 - 42 degrees). There has been vigorous discussion about whether it was better to be optimised for summer (shallow angle) or winter (steep angle). Half the systems needed frames; the other half followed the roof pitch angle. A comparison of performance over 12 months showed that tilt angle was a NOT significant factor. As annual data is collected, a performance comparison is able to be made between yearly outputs.
Dr Simon Pockley, research leader and co-ordinator
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