## System Performance

The Photovoltaic System performance is presented here as a series of graphs, updated automatically on a daily basis.

Daily Performance

Figure 1 represents the total insolation in the plane of the 48.6 m2 collector and the electrical energy produced, in 15-minute-average kW, as a function of the time of the day.

This data is combined in Figure 2 to give the efficiency - electricity produced ÷ insolation on the collectors - in 15-minute intervals. Also shown on Figure 2 is the footprint efficiency - the electrical energy produced divided by the global horizontal insolation on the footprint area* of the array.

* The footprint area is defined as two times the area of the collectors when projected on the horizontal, i.e. 2 x (the collector area) x Cos25 ° which is approximately equal to 88.1 m2.
Twice the collector area is used in the above calculations since it represents the total horizontal area required by the collectors. The collectors are mounted at 25° to the horizontal.
The efficiency based on the horizontal insolation is useful since the horizontal insolation is known in many parts of the globe. As a result, we will have an idea of how this system will perform in these regions without actually moving the set-up there.

In Figure 3 the air temperature, in ° C, is plotted as a function of the time of day.

Performance every thirty days

This graph shows the performance of the array for each day for the past thirty days. In Figure 4 the daily insolation in the plane of the collector and the electrical energy produced, in kWh per day, are plotted vs. the day of the year. Also shown is the sum of the daily horizontal insolation on the footprint area of the collector (as defined above), in kWh per day, vs. day of the year. The corresponding daily efficiencies are presented in Figure 5.

Finally, the corresponding average daytime temperatures are presented in Figure 6.

Cumulative Performance

Figure 7 shows the cumulative energy produced, in kWh, vs. day of the year for the past six months. Figure 7 also shows the cumulative insolation in the plane of the collector and the cumulative horizontal insolation on the footprint area of the collector, both in kWh, vs. day of the year. The corresponding cumulative efficiencies are presented in Figure 8.

 Year Electrical Output (kWh) In-plane Insolation (kWh) Global Horizontal Insolation (kWh) In-plane Efficiency (%) Footprint Efficiency (%) 1996 5353 66250 102833 8.1 5.2 1997 4380 57646 86197 7.6 5.1 1998 4750 54536 82737 8.7 5.7 1999 5776 67794 103241 8.5 5.6 2000 5411 64278 99706 8.4 5.4

The total energy produced by the Photovoltaic System since January 1996 is 25670 kWh.