sobre la eficiencia de las placas fotovoltaicas

BP provide data for the installed solar photovoltaic (PV) capacity in a number of countries together with the amount of solar electricity consumed [1]. This allows for the solar load factor to be calculated. If you take the installed capacity and multiply that by 24 hours and 365.25 days this provides a theoretical maximum electrical output against which the actual output can be compared. The results, which are in part surprising (spurious?) are shown in Figure 1 and Table 1.

Figure 1 The solar PV load factor in the UK is less than 9% and less than 10% in Germany. In the countries ranked from the UK to Australia, load factors appear to vary in a way consistent with latitude and sunshine. But the large jump to over 20% in Portugal looks suspicious and the figure of 30% in Spain appears to be wrong. At the other end of the spectrum, the figures in the USA and China appear to be spuriously low.

In detail, understanding the efficiency of a PV panel is not straight forward. In fact what I am addressing here is the load factor comparing the actual output to the theoretical maximum output. It seems the panels are rated against sunshine falling directly (perpendicularly) onto the panel. So a 1 kW panel will only produce 1 kW if the Sun is shining directly on it. At higher latitudes this rarely / never happens since the efficiency at which the panels capture sunlight is influenced by the geometric alignment between the panel and the Sun, and this is continually shifting. On average, across an annual cycle, there is no Sun at all for half of the time (night time) and the maximum load a panel can have is therefore 50%. This may seem a terrible waste but it is in fact one of solar’s main strengths. The Sun shines and produces electricity during the day when electricity demand is highest.

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