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26 Introduction to SolarPowerfortheWorld
Annex: Some Facts on PV
• Thickness
The thickness of PV modules is essentially determined by
the supporting pane, normally glass. Solar cells are less than
1/3 mm thick when they are made of silicon crystals and not
more than 1/1000 mm thick when they are thin film.
• Areas
The area of a PV array of PV modules takes normally less
than 10 m 2 /kW. It depends on the cell efficiencies and the
packing density; 1 MW of PV occupies less than 1 ha (2.5
acres); 1 GW occupies an area of less than 10 km 2 (3.86
square miles).
• Electricity Production
For complete PV systems well oriented south at a fixed
inclination corresponding to the latitude of the site, the
annual electric energy production is better than 1000 kWh
for every kW installed, even at bad or mediocre solar
climates. The average for Germany in central Europe is
900 kWh/kW, a capacity factor of 11%. This takes into
account that a non-negligible part of the system park is
not perfectly oriented south, or that systems have technical
flaws. In parts of Germany with a better solar regime, up
to 1300 kWh can be produced in a year. In the south of
Europe, the yields are higher up to 2000 kWh. The same
is true in most of the United States. PV systems employing
solar tracking may yield some 15% to 30% more than
the corresponding fixed-plate arrays; on the other hand,
installation and operation costs are higher: a difficult tradeoff.
• Energy Payback Time for Solar Cells
Crystalline silicon cells have a payback time of less than
2 years, i.e. they are operated for less than 2 years at an