◊ Part of the ‘wind energy’ series of articles ◊
Two important measures of energy resources are ‘capacity’ and ‘capacity factor’ (utilization).
Capacity refers to the maximum output capability of the resource under a specified or standard set of conditions. In most cases it will be referred to as the ‘Nameplate Rating’. It is a value that is used for planning, design and operating contingency management.
Ontario’s wind capacity at the end of 2018 was 5,250 MW
Capacity factor is a measure of how the actual output of the resource over time compares to its stated nameplate rating. It is a reflection of how much the resource is actually utilized. It is usually stated as a percentage and will be between zero and 100. A resource that runs at its nameplate rating for 12 out of 24 hours a day, 365 days a year will have a 50% capacity factor for the year.
Ontario’s wind capacity factor at the end of 2018 was 27%
Capacity factor is important for system operation, determining the commodity cost and economic viability of generating facilities. The capacity factor of a wind turbine is influenced by geographic location, turbine rating, operating practices, electrical efficiency, prevailing winds, blade size, design and construction material.
According to IESO data the 2016 average capacity factor for all generation in Ontario was 52%.
Capacity factors are usually distinguished between on-shore and off-shore installations. The prevailing wind off-shore is generally accepted to produce higher capacity factors than on-shore. Wind turbine design and construction has improved over the last 10 years which has increased rated capacity factors compared to older designs.
Wind energy capacity factors may have daily values anywhere from 10% to 90%, however it is the longer term value which is most relevant to the viability of a wind turbine or farm. Using generator output data from the IESO for as many as 41 wind farms, the average capacity factor in Ontario from 2010 to 2018 was 26%.
Other jurisdictions
According to Hydro Quebec as of 2016 they have contracts with independent wind power producers that are expected to provide a 35% capacity factor. There is no data to validate that statement.
Statistics published by the Alberta Electric System Operator (AESO) show capacity factors ranging from 28% in 2010 to a 2017 high of 34.5%.
By comparison, using wind energy data from Texas as presented on Wikipedia, the average capacity factor for the period 2000 to 2017 is 28%. Note that an anomaly in 2001 is most likely due to the impact of tropical storm Allison on the region. Wikipedia data shows that the capacity factor for Texas in 2019 was 33.4%.
The trend toward higher factors beginning in 2009 is due to installation improvements and technology advancement in wind turbines.
At a higher level, the US Energy Information Administration (EIA), a government organization, publishes extensive data on electricity including wind. The 2010 to 2017 capacity factors for wind rolled up to the national level range from 29.8% to 34.6% with a slight upward trend.
Manufacturers and wind energy associations like CanREA (Canadian Renewable Energy Association) provide an industry perspective in support of increasing wind energy. Feel free to visit their website and view their material. Bear in mind that any information presented is heavily biased toward the expansion of wind energy because of who they represent.
Some hype
CleanTechnica reported in 2012 that capacity factors of 50% (for the GE Brilliant 1.6-100 turbine) are the new normal for the industry. I was unable to find any credible data from installations to support that number. The GE 1.6-100 turbines are installed at the Jericho Wind Energy Centre in Lambton County, Southwestern Ontario. The capacity factor for Jericho is in line with the Ontario average of 26%, nowhere near what the manufacturer claims of 53%.
The claim of 50% or higher capacity factor simply doesn’t play out in annual average statistics. Be careful how you interpret what you read.
Some hope
Existing trends show improvement from the values of 26% in 2010 to 35% in 2018 for actual North American installations.
Some truth
Given the typical capacity factors of wind energy it should be considered intermittent.
The cost of wind energy is directly tied to capacity factor. The higher the capacity factor, the more revenue for a power producer.
Ontario has a relatively low capacity factor compared to other jurisdictions like Alberta and Texas which have 40% higher averages.
Based on the capacity factor measure, Alberta and Texas should be able to offer wind energy for 40% lower cost than Ontario. That’s not very comforting for Ontario ratepayers but its the truth.
Derek
Previous article… The economic reality of wind – “down the rabbit hole”
Next article… Wind energy subsidies
