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Each week Ontario's Independent Electricity System Operator (IESO) publishes a report, with selected metrics for the week (IESO uses Wednesday as the first day of a week). This is a report for the same intervals which contains my estimates of many of those same metrics, and additional metrics either to provide a comparative context, to the prior year, or to provide information on supply mix issues, including estimates quantifying the generation curtailed in Ontario. 

Section 1 of the IESO report is reportedly to "provide a quick reference for all market stakeholders."  I've added in the data for the corresponding week in the previous year, as a quick, contextual, reference to demonstrate trending.  Individual weeks will vary depending on weather, and holidays - but generally the trend is visible.

The change in demand, since the corresponding week in the previous year, is indicated by the difference between the area and linear graphs in this chart. Graphing only the difference provides a simpler picture indicating the growth, or, more likely, reduction in demand within Ontario.  The relative amplitude of the change in total market demand indicated whether trade is growing or contracting.

The import/export figures graphed here are from the "Hourly Import Export Schedules" file (as updated weekly).  These figures also match the IESO's weekly reported, as demonstrated by comparing the figures in the next table, for the current year, to the IESO weekly report.

The figures in the IESO's "Hourly Import Export Schedule", update weekly, do not always match the figures in the IESO's "Intertie Schedule & Flow Report", which is updated hourly - in fact there is a frequent variance in exports moving through the interties. 

Evidence strongly suggests the difference in the two IESO data sets is primarily hydroelectric production that is fed directly into Quebec's grid.  It is unknown how, or if, Ontario is compensated for curtailing the supply on it's grid by feeding output directly into Quebec's.  When Quebec's reservoirs are low this may be Ontario's preferred supply curtailment option, but it's also used to boost exports (in winter - as Quebec is a winter peaking jurisdiction); the following chart may be capturing curtailment, but it may also demonstrate "off the books" export transactions that are not curtailment.

Other known maneuvers occur at Bruce B reactors (steam bypass), and paying non-utility generators to go offline.  These curtailment actions are estimated on the following graph, as negative values, and shown along with wind output.  Again, the approach is simply programmed to show when generators are operating in the range they would be operating in during curtailment (they may be operating in that range for other reasons, and it will still show on the chart).
Not shown on the graph are the total removal from service of nuclear reactors during high supply/low demand periods.

Wind is included here because it's important to note that, while it is frequently cited as being important in replacing coal, we don't actually use much coal but continue to add industrial wind turbines.  We do frequently have more baseload supply than our domestic market can handle - and curtailment actions indicate we also increasingly have more supply than export markets are willing to absorb.
Baseload takes a number of forms in Ontairo: including nuclear that has the same costs at full output as at reduced output (probably less), run-of-the river hydro with a fixed cost, and sources that are contractually guaranteed payment for supply whenever it is produced.  These sources are not only the newer solar and wind contract holders, but historical non-utility generators (NUGs).  The following graph shows the hourly contribution of sources I have considered baseload, and all other sources that can be shown through manipulation of IESO data (solar cannot):

Simplified, graphing only the 'baseload' generation, as indicated in the preceding graph, against Ontario Demand is the simplest graphical indication of the Surplus Baseload Generation condition - although it is still imperfect, as water conditions also determine what the 'baseload', or minimum generation without spilling, is for hydro, and many thermal plants may be more efficiently run overnight, than stopping and starting only during demand spikes during the daytime periods.
I updated this graph (September 24, 2014) to show both the produced baseload power, and the total inclusive of my estimates of baseload generation that was curtailed. This gives a better picture of the surplus that must be dumped on export markets, or paid to curtail production.

The next graph illustrates the differences in weekly supply, and demand, over the same week in the previous year.  Net Imports are almost always negative in Ontario (only one day in nearly 18 months saw total imports exceed exports), so when the change in net imports is positive, it indicates reduced exports.  Similarly, a reduction in Ontario Demand is shown as a positive "Demand Reduction" figure.  Along with changes by different fuels sources, this produces a graph that essentially balances the growing, and declining, elements of the system.

The following graphs have been added to this page since week 18 of 2014.  The first graph includes estimated values for embedded generation for solar, and wind. 

Ignoring embedded generation is a growing weakness of official Ontario reporting as clearly solar is now impacting market pricing, and reported demand (the untracked embedded generation reduces what the IESO reports as demand).  The solar estimates are based on day-ahead "Variable Generation Forecasts" from the IESO along with estimates of how much capacity is considered in those estimates, and how much overall solar is estimated to be contracted and in service (by the OPA).
There is also a growing amount of "embedded" wind capacity in Ontario - which I've estimated as 12.5% of the figures reported by the IESO.


The reason the estimates for solar and wind are particularly apparent if estimates are shown for hourly costs - in the same format.  Currently there is little reporting on solar generation; what reporting there is indicates that in 2013 total solar generation was 0.8% of Ontario supply (OEB) and the cost of procuring that 0.8% was ~5.1% of total supply costs ("Generation Cost by Resource" tab of OPA "Cost of Electricity Service" spreadsheet).


Weekly reports are not archived in this format, but the weekly spreadsheets with the embedded data, and graphs, are archived in this folder.