Financiers of green energy projects often claim in public filings that the energy generated by the projects they have financed has avoided some definite number of tons of CO2 emissions. Run the numbers, and you usually find they have assumed some annual capacity factor, say 35 percent in the case of a wind farm, and from that have estimated the megawatt-hours of electricity generated over a year. Then they assume some emission factor for the fossil generation, usually natural gas, that the wind generation is claimed to have displaced. The avoided CO2 they claim is the product of that emission factor and the amount of electrical energy their wind farm generated over the year.
So in the case of a 1,000 MW wind farm and the (generous) 35 percent capacity factor and assuming the displaced fossil fuel is combined cycle natural gas at 400 grams per kWh:
This is a simplistic and highly problematic way to estimate avoided CO2. It is like taking the mean income of five people: one who makes $1 million a year and four who each make $20,000. The mean in this case is $216,000 — a huge pay cut for the millionaire and the thousandaires think they woke up in heaven. The mean as a measure of economic well being in this case is… meaningless.
With electricity it is even more outlandish to claim displacement based on annual kilowatt-hours. Conditions on the grid change from hour to hour. The only way to get a meaningful idea of how much CO2 wind displaced—actually whether wind displaced gas at all—is to see when that might have happened. For this you need grid data at an appreciable frequency, and the higher the better.
The total value from the example above takes no account of wind’s tendency to not correlate with system demand. Wind blows when wind blows, and often that is not at the convenience of the system operator, whose mandate is to run the grid so that supply always matches demand, with no blackouts or brownouts. To give displaced fuel a CIPK of 400 grams assumes that wind displaces baseload supply, which is preposterous.
For example, here’s June 2019 in Ontario:
As you can see in the top plot, Ontario made more electricity than it used in almost every hour. Demand, generation, and the hourly “market” price (HOEP) showed much regularity. The HOEP scale is on the right side of the plot.
Wind, the next plot down, shows little regularity, and much volatility. It is erratic the whole month, with numerous sudden local peaks and valleys. And it is not an insignificant amount—the total wind fleet capacity is close to 5,000 MW. The volatility of output that wind shows through June 2019 makes you wonder what the system operator thinks it might have to do if wind suddenly spikes by more than the 1500 MW it does through the 9th, or suddenly plummets like it does the very next day.
The four plots below wind are the individual generators at the Sithe Goreway gas-fired station near Branpton. Obvious regularity, and interestingly in nearly every instance in which these units produced power they did so with overall generation exceeding demand by 2,000 MW or more. Was that to satisfy some external demand, from jurisdictions that import power from Ontario?
What an excellent question. The price (purple line on the top plot) during the majority of these instances was just over zero cents per kWh. (The mean of the 720 hourly prices reported in June 2019 was 0.36 cents.) If there were a strong demand for our power, wouldn’t that be reflected in the price? Export markets (and preferred in-province large users) pay this price, unlike us citizens of Ontario, who must cover the agreed contracted price of various sources, and trust me those are all many times more than 0.36 cents.1 So you could be forgiven for wondering if the price is connected with demand.
So why did Goreway produce any power at all during that time? Note that none of the plant units once produced at full power, and that in by far most of the operating hours they all produced at much less than half power.
Why run gas units at less than half power, which puts the CIPKs of the individual gas turbine units (G11, G12, and G13) well above the 569 grams they would achieve at full power. And again, why do that when it looks like none of our export markets is beating a path to our door to buy our power?
Is it because we have to over produce, and that export markets are where we dump our excess? I wonder. Was Sithe Goreway operation in June 2019 part of a proactive measure to handle the uncertainty posed by a hard-to-predict 5,000 MW source of power?
The 45 transmission-connected Ontario wind farms generated 381,528 megawatt hours in June 2019. Given that Ontario generated more than it demanded in nearly every hour that month, can we say that wind displaced any gas? Is it possible to say that it necessitated gas?
There were, obviously, many hours in June 2019 that the Goreway units produced nothing. Total supply exceeded demand in those hours, too. Most of the 56 hydro units showed great variability in output in June 2019; next post I’ll provide details on them.
Hmmm. There should be a way to separate the fuel consumption of the Goreway units into two separate terms:
1. The base gas consumption required to have the units on-line.
2. The gas consumption of the incremental kilowatt. This may vary across the power curve.
Charging much or all of the base gas consumption to wind/PV would seem to be appropriate. That would give a better idea of the possible emissions cuts which would result from replacement of “renewables” with nuclear.
Another thing is the issue of dump loads. Being able to dump power to an interruptible load would be a great way to manage issues of surges and sags in intermittent generation and create plenty of “spinning reserve”. So far nobody seems to be doing that.