As part of my Ph.D. thesis, I conducted an analysis on grid congestion, to determine the best substations where to connect more wind parks.
These are some of the graphics that show that congestion is not an immediate issue for wind power developers in some places in Portugal.
Graph 1 shows wind power output and the resulting grid congestion as more wind power capacity is added:
Graph 2 shows the daily variations of power demand over a year, in a region of Portugal. The variations in power demand impact grid congestion. If power demand is large when non-dispatchable units (as wind parks in Portugal) are producing large amounts of power, there will be no grid congestion -assuming grid capacity is at least equal to the peak of power demand. But if for example, power demand is low when wind blows the most (say at 2 in the morning), grid can get congested because not all power produced is consumed.
Finally, graph 3 shows wind power and demand frequency plots. Grid capacity is a function of these two variables and others (not shown here).