7 Energy yield from PV systems

The annual and monthly amounts of energy that will be produced by a PV system depend on a number of factors, including:

• the annual total quantity of solar radiation available at the site
• the orientation and tilt of the PV arrays
• the peak power rating of the arrays
• the energy conversion efficiency of the PV modules
• the variation in the efficiency of the modules with temperature
• the power-reducing effects of array shading by trees, nearby buildings, accumulation of dirt etc
• the efficiency of the inverter, and any losses that occur in the wiring between the PV system and the final consumer.

The European Union’s Joint Research Centre [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] at Ispra, Italy, has produced PVGIS (PV Geographical Information System), an online tool giving solar radiation data and estimated PV outputs for Europe, Africa and parts of Asia. Users can input the geographic location, type of module, its power rating, array orientation etc., and the software will calculate the expected monthly and annual energy yield ((EU-JRC-IET, 2012)

Key aspects of this information are summarised in the map Figure 12

Maximise

Figure 12 Solar radiation map of Europe, showing annual energy yields of optimally oriented PV arrays in various European locations. (‘Performance Ratio’ is the ratio of actual to theoretical maximum PV array output.)

You’ll now look at the economics and environmental impact of energy from photovoltaics.