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As noted in the Wind Turbine Basics chapter that Capacity Value is how much wind provides power when demand is highest. There are many different ways this is calculated (see here). The bottom line is that when we need the power the most how much can that power come from wind?
Peak demand can be broken up into a number of periods. In order from the highest demands: summer mid day, winter evenings, and fall/spring midday and evenings. What this chapter will look at is two things:
- The production from wind, highest output relative to those peak periods, and
- Zero output relative to those peak periods.
All peak demands will be within 10% of the highest demands, that is 90% to 100% demand for any given month.
Summer Capacity Value
Summer peak demand period is between noon and 5pm, the hottest part of the day. The following data is only between those hours and when demand is within 10% of peak for the month. This scatter plot is the average of the Hourly Capacity Factor for all farms for each year.
You can see that the values are heavily scattered at the low end of output. The averge of those averages is 17%. However, we know that using averages doesn’t work too well with data that is heavily skewed towards the low end of output.
Notice almost 20% of the time in the summer peak hours the output is zero. Nothing from wind contributing to running your AC units. Over 60% HCF is virtually non existant, and as we have seen, these spikes of high output lasts only a few hours, barely time to shutdown, then restart backup capacity. One has to wonder if doing that shutdown and startup is using more energy than if the wind didn’t exist in the first place.
As you can see the median is a much better candidate for assign the Capacity Value in the peak summer hours. Thus the Capacity Value in the summer is 10%.
Winter Capacity Value
Winter peak demand periods are between 4pm and 10pm. This is the scatter of all farm’s average HCF vs demand within 10% of peak.
This is much more spread out, which will increase both the average and the median.
As we saw with Port Alma’s occational high end output that some of them managed to occur when we were within 10% of peak demand. Notice zero output still dominates with almost 11% of those hours.
Using median for the Capacity Value means it’s 25.8%.
Spring Capacity Value
The highest demand periods in the spring is between 8am and 10pm, the widest range of the seasons.
This scatter of the spring HCF during peak hours shows many consentrated at the low end, with a few points above 70%. The count of HCF looks like this:
The spring Capacity Value is 17%. Zero output still hugely dominates at 12.5% of those hours.
Fall Capacity Value
Fall peak demand periods are between 9am and 10pm, just like spring’s. This is the scatter of all farm’s average HCF vs demand within 10% of peak.
This makes the fall Capacity Value at 19%. It also shows that the zero output is just over 14% of the time when demand is highest in the fall months.
Of course, these values will change from individual year to year. With 2010 being a bad year for wind those Capacity Values will be lower.
In this report there are additional measures of performance. On such measure is Forced Outage. This is when, regardless of reason, output is zero. As you can see the Force Outage ranges from 11 to 19% during high peak demand hours.
There is another measure that is used to calculate the reliability of the entire system, and that’s Loss of Load Probability. Basically that measurement is when demand is high what is the probability of loss of power due to forced outages. Because wind is so variant, with lots of zero output, wind is significantly affecting, to the up side, the Loss of Load Probability. That is, wind’s Force Outage is increasing the risk that the system can’t handle the demand at high peak times. Something the wind industry does not tell you.
Luckily in Ontario we have ample reserve capacity, for the time being, which is dumped to the US at a monitary loss. The optimim reserve capacity is 15%, but we are way over that since 2005. But this won’t last. When demand finally increases to use up that slack in the system, wind will start to become a threat to the risk of outages. Especially since wind will, or is expected to, increase in number and fraction of the mix. As wind is increased as a percent of the total mix, and because farms at distant locations experience the same Hourly Capacity Factors, that is outages at the same time, this significantly increases the risk that demand will be more than avialable supply.
In short, this means that in the near future when the wind doesn’t blow, is a large proportion of the mix, when demand is highest, expect the system to partly shut down and people will lose power. Make no mistake, the more wind we build in the province, the higher the risk that outages will occur when wind has Forced Outages. Exactly the opposite the wind industry is tell us.
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