|Previous Chapter||Next Chapter|
Of course the output is entirely dependant on the wind available. The Ontario Government has these two maps of wind speed in the Province (see)
Of course, this is over all for the year, and obviously, as you will see below and in subsequent chapters, changes radically in the summer from “optimal” performance.
The over all wind output on a percent Hourly Capacity Factor vs number of hours for all turbines looks like this:
Not all the wind farms started at the same time. This is the beginning time and number of records used to make that graph.
The plot only uses the number of hours of existing data to get the Hourly Capacity Factor, including hours of no output.
Notice the large number of hours of no output. At 15.8% of the hours it dominates the plot. The next column (between .09 and 1.0 % name plate) which is the second largest number of hours, is a mere 3.9% of the hours.
You can clearly see that the average, what the industry uses for Capacity Factor, has no physical meaning on this plot. It’s not in the middle, it’s not exceptional, it’s not unique in any way. It’s just a calculation of the average.
The median, however, is the point where half the hours are below that value. Overall then, the median of 14% means this: Fifty percent of the time output from wind in Ontario is less than 15% name plate. Half the time the output is 14% OR LESS. From this point on this point will be referred to as the Median Capacity Factor.
The other significant number here is the Standard Deviation. 65% of all values are in the first Standard Deviation noted on the graph. That number is the Median plus the Standard Deviation of 27.4%.
Skewness is a complex calculation (see), but important number because it tells us how far the median is from the average. Consider it the “pull” on the bell curve in one direction. A positive number is to the left, towards smaller percent of name plate. If the skewness was negative, the median would be to the right of the average, more into the high percent of name plate.
This graph shows the changes in the Capacity Factor (not the Median Capacity Factor) for all the farms over each month. The Median Capacity Factor (where 50% of the time output is lower) is about half these numbers.
Notice the significant drop off in Capacity Factor during the summer months. Fall 2009 to 2010 was a particularly low year for wind production.
This graph is the Median Capacity Factor for each month for each farm. The summers clearly show very low MCF below 10% for almost all the farms. In the summer time, all the farms half the time produce less than 10% name plate. Notice some of the winter months come very close to the Capacity Factor, which will show up as near zero skewness for that month.
This plot of skewness per farm per month is the opposite of the above graphs. Very low skewness in the winter months, but very high skewness in the summer. This means that in the summer time the use of Capacity factor is further away from actual output. The spread of the output for each month, the range of the Hourly Percent Name Plate, is the Standard Deviation.
Notice that the range of values is much more spread out in the winter (higher SD) than in the summer.
So summers tend to be small MCF, with high skewness and narrow range of hourly percent name plate output, while winters tend to be higher MCF, with low skewness (closer to the CF), but with a very wide range of hourly name plate values (thus more intermittent and with unpredictable swings than in the summer).
This is the data that produced the top graph:
|HCF||Count Of Hours||Accum Hours||% of the time|
|Previous Chapter||Next Chapter|