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The small photovoltaic solar plant at Proefhoeve, Melle

At the 1st of September 2001, when photovoltaic energy (PV) was not as prevalent as today, Ghent University installed a (small) PV demonstration project at the “Proefhoeve”, a farm used by the university for research and teaching. For research and demonstration purposes, two solar modules were installed on the roof of the cowshed. One module is orientated to the southwest (SW), the other to the northeast (NE). Obviously, the photovoltaic cells to the SW will produce more electricity than those to the NE. The cowshed is located in Melle, Belgium, at 50°58' N, 3°49'E. The inclination of the roof is 17 °.

Each of the two solar modules (7.5 m x 1.1 m) consists of 11 solar panels (660 mm x 1113 mm). Each solar panel has 4 x 9 = 36 solar cells in series. One solar cell measures 115 mm x 153 mm and was fabricated by Solarex from polycrystalline silicon. The nominal power output is 16.5 V x 5 A = 82.8 W under standard conditions (1000 W/m², 25 °C), i.e. an efficiency of 11 %. The solar power plant of the Proefhoeve thus consists of 792 solar cells, with a total area of about 16 m² (a very modest surface area, even for those days). The nominal yield is thus 1826 W. Two inverters (type Sonny Boy SWR 700 SMA Rule Werke) convert the 176 V dc to 230V AC voltage. This alternating current is plugged into the mains.

The following graph from 29 March 2002 shows the incident solar power (in W/m²) at a typical spring day. The red and blue line indicate the power from the incident solar power on the solar panel oriented to the NE and SW respectively.
We clearly see that the panel to the NE captures more sunlight in the morning while the panel to the SW will see more sun in the afternoon and evening. Obviously, this is because the sun rises in the east in the morning and sets in the west in the evening.

The following graph shows the 30th of June 2002, a typical clouded summer day.

I measured the solar plant from March 2002 till February 2004. The sunniest day measured in this period was the 1st of June 2002 with a total of 10.40 kWh AC power to the grid inserted: 4.72 kWh from the NE panel and 5.68 kWh from the SW panel. The sunniest moment, however, was on the 14th of May 2002 (at approximately 13h00), with an AC power of 1422 W delivered to the grid: 695 W from the NE panel and 727 W from the the SW panel.
The AC energy, delivered on the 230-volt distribution network, can be found on the following monthly statistics.

During the first year of follow-up data (from March 6, 2002 to March 5, 2003), 1270 kWh AC was produced. We note that 2003 was much sunnier than 2002. Still, the record day and the record time remain in May / June 2002. This is probably due to the temperature dependence of the solar cells. They like it sunny but cool.

A detailed analysis of this small solar plant can be found in this pdf (in Dutch).