Previous large-scale studies of this type are however very scarce. During the
first years of operation, the production is nearly constant, but subsequently
it begins to decline. Wind turbines constructed before 2007 lose around
0.15 capacity factor percentage points per year in absolute terms, corresponding
to a life-time energy loss of 6 %.
A gradual increase of downtime accounts for around 1/3 of the decline and
worsened efficiency for the rest. In comparison to results from the UK, Swedish
wind farms deteriorate much slower.
