by Donald Jones, P.Eng.
A shorter version of this article appeared in the 2010 September edition of the BULLETIN, the journal of the Canadian Nuclear Society.
Coal-fired power plants in Ontario are to be phased out by 2014 and are being replaced by natural gas-fired power plants. Burning gas still results in large amounts of greenhouse gas (GHG) emissions. Wind turbine power plants are being built in the belief that they will reduce the GHG emissions from the gas-fired plants by reducing the amount of gas burned. Dispatchable coal is being replaced by dispatchable gas and not by non-dispatchable wind. Gas is not supporting wind, wind is interfering with gas, and with nuclear for that matter.
There is some doubt whether the billions of dollars being spent by Ontario’s electricity consumers on Ontario’s wind turbine power plants, on the supporting transmission and so called “smart grid” infrastructure, and on increased maintenance for the gas-fired and nuclear generators on the grid, will result in any appreciable, or even any, reduction in GHG emissions from the electricity generating sector. It is difficult to impossible for the layman to get a handle on this due to the highly complex way the grid is controlled by the Independent Electricity System Operator (IESO). If it were possible to frequently shutdown gas-fired power plants every time the wind picked up there might be some obvious GHG reductions but even then shutting down and then re-starting gas-fired units would eat into the amount of the reduction as well as increasing the amount of wear and tear damage to the units. Since the only people who know in detail how the generators on the grid are dispatched to accommodate wind are the people doing this job every day at the IESO they are the only ones who can come up with the answer to the question, “are wind turbine plants really reducing GHG emissions in Ontario and at what cost per tonne CO2 avoided?” This really is the bottom line. It should not be too difficult for them to use computer simulation to compare typical daily load profiles with and without various amounts of wind generation and with various water storage levels and compare emissions as a result of their usual dispatching procedures and knowledge of the technical specifications/operating characteristics of the gas-fired generators. While we wait for this to happen (!) let us look at scenarios that raise doubts about GHG reductions.
Ontario’s grid consists of many and varied generating stations located throughout the province feeding consumers through a network of high voltage transmission lines, transformers, switchgear, and low voltage distribution lines to major consumers including local utilities. Electricity cannot be stored in large amounts so generation and demand has to be kept in balance at all times. If demand exceeds supply all the generators on the grid slow down and the normal grid frequency of 60 Hertz (reversals per second of alternating current) will drop. All electric motors working off the grid would similarly slow down. If supply exceeds demand the frequency will increase. It is the job of the IESO to ensure that these frequency swings keep within very tight tolerances on a seconds to minutes time scale. It does this by dispatching generators (hydro, coal, gas, and even nuclear units as a last resort) on the grid at five minute intervals, not necessarily the same generator, to move power up or down. In the morning the power moves would generally be in an upward direction and in the evening in a downward direction but there can also be small reversals in the general trend. This brings the grid into a rough balance. In order to bring the frequency into its narrow operating range of around 60 Hertz the IESO automatically controls the output of a very small number of selected generators that have the capability to rapidly vary their output over a limited range. These are some hydro units at Niagara Falls and, in the past, some coal-fired units. This seconds to minutes control of frequency is called automatic generation control or AGC. The current AGC regulation service requirement from the IESO is for at least plus or minus 100 megawatts at a ramp rate of 50 megawatts per minute. This amount of AGC may have to be increased as more variable wind generation gets on to the grid. As well as frequency, voltage levels at points on the grid also have to be maintained but this is more complex and will not be discussed.
The hydro generators consist of run-of-the-river stations, like Niagara Falls, that run continuously and stations that depend on water storage, so have limited run times and are more dependent on precipitation. The run-of-the-river units would provide base load and the stored water units would provide intermediate load that looks after the normal daytime load cycle. Base load hydro accounts for about a third of the total installed hydro capacity. The hydro stations are extremely flexible when available and can quickly respond to changes in supply or demand on the grid. However there can be water management restrictions on the operation of the stored water units because of variations in upstream and downstream water levels and other concerns. Coal-fired units are less flexible but, when hot, much more flexible than the combined cycle gas turbine units that are replacing them and both can provide base load and intermediate load. A small amount of base load comes from some inflexible combined heat and power facilities. There is also a very small number (Aside: too small, maybe, in view of the coming huge increase in wind capacity) of simple cycle gas turbine units, much less efficient than combined cycle gas turbines, that can come on line from cold very quickly to help meet peak loads or other eventualities. Although combined cycle gas turbine plants are capable of operating simple cycle, by having the hot gases bypass the heat recovery steam generators, it is not known if the Ontario units have this flexibility. Present nuclear units are less flexible than hydro and gas and prefer to operate base load although they are regarded as dispatchable by the IESO. With low fuel cost and fixed costs that are independent of power level it makes economic sense at the present time to operate nuclear at full power to supply base load. Wind generation depends on the wind and is not dispatchable but is added to the base load supply whether needed or not.
The Ontario grid has an installed capacity of around 35,000 megawatts and in 2009 nuclear provided 55.2 percent of Ontario’s generated electricity, hydro 25.5 percent, gas 10.3 percent, coal 6.6 percent and wind 1.6 percent. Other fuel types (biomass, solar etc) gave 0.8 percent. This shows 80 percent of Ontario’s electricity was supplied by non-GHG emitting nuclear and hydro putting Ontario’s electricity sector amongst the world leaders in the generation of “clean” electricity. Wind generation is expected to drastically increase over the next few years under Ontario’s Green Energy Act. Refurbishment of Darlington and Bruce nuclear units and increasing demand for electricity in the next few years will result in more base load operation of combined cycle gas turbine units. Burning natural gas for base load will be expensive, is wasteful of a non-renewable resource, and is unnecessary. This situation may be alleviated somewhat by construction of a new nuclear station at Darlington.
In the future large amounts of wind (Aside: present wind capacity is around 1,100 megawatts but eventually maybe up to 8,000 megawatts nameplate capacity when transmission links are completed) will have an impact on the grid in both high electricity demand and low demand scenarios. Wind is a preferred supplier under present government rules and must be accepted on to the grid when available. During daily operation when the demand on the grid is high and wind starts coming on to the grid other units on the grid will have to power down to maintain grid balance. The other units could be hydro or gas. If hydro is powered back it would help conserve water behind the dams but would not reduce GHG and other emissions from the gas units. If the combined cycle gas turbines are powered down there still might not be any significant GHG reductions since the units cannot be completely shutdown. Some will be held in their load dispatching range of around 70 to 100 percent of full power to be available for dispatching and some would fall below their load dispatching range, on hot standby, in case the wind dropped. A sudden drop in wind would ramp up the combined cycle gas turbine units that are in their dispatchable range, and bring on the few peaker simple cycle gas turbines, and hydro if available, until the combined cycle gas turbines on hot standby can power up enough to respond to dispatches. Any time gas turbine units operate at part load to accommodate wind the emissions per megawatt hour of generation will increase and there will be wear and tear damage dependent on the depth and frequency of the power changes leading to higher maintenance costs. Also high demand usually coincides with high ambient air temperatures that would reduce output and efficiency of gas turbine units. Output from the stored water hydro units can be restricted during the summer due to drought and, in the future, climate change leading to more gas-fired generation.
The more difficult scenario is the case of oversupply, which tends to occur in the spring and fall, overnight and on weekends. This is called Surplus Baseload Generation (SBG) when the demand is less than a base load supply that cannot readily be reduced because of technical or contractual reasons. There were many cases of SBG in the spring of 2009 caused by the economic downturn and a surplus of hydro power and even with the relatively small amount of wind generation on the grid at that time. SBG is expected to increase in the future, not helped by more self-scheduling wind, until an improving economy and growing population increases demand. As the wind generation comes on to a grid that already has low demand the gas units are powered down, base load hydro minimized and, if possible, exports are maximized but enough flexible hydro and gas must be available to handle grid load changes and be available in case the wind drops. Eventually if the wind generation keeps on increasing, or demand falls, the present approach is for selected nuclear units to be dispatched to make one significant power reduction to another constant power level or to completely shutdown and be replaced by more gas, and hydro if available. In the spring of 2009 nuclear units at Bruce made many such power reductions, using turbine steam bypass which is wasteful of energy and increases thermal emissions, and some shutdowns. When a nuclear unit is shutdown it will not be available again for up to three days because of nuclear physics reasons so if demand increases over this period it would have to be met with gas-fired generation. Shutting down or powering down nuclear units that produce relatively low cost reliable electricity without GHG emissions and replacing this electricity with higher cost energy from gas and wind makes little economic, technical or environmental sense. Shutting down and restarting nuclear units like this results in wear and tear and increased maintenance cost and puts the grid at risk.
For the newer wind turbine power plants under the Feed-In-Tariff (FIT) program, but not those under the earlier Renewable Energy Standard Offer Program, the IESO is offering financial incentives to the wind operators to shutdown their plants during times of SBG. Under this incentive (FIT) wind operators would get paid if they shutdown in response to an IESO request to do so. However this means that wind plant staff would have to be available at very short notice to open breakers at the turbine plant installations so there is no guarantee that the curtailment request would be followed by the wind plant operators. This could pose a real risk to the high voltage grid if there are large injections of wind generation unless Hydro One can selectively isolate the wind plants on instruction from the IESO.
In periods of high demand and in periods of low demand dispatchable and hot standby gas generation will be powered down as far as is prudent for grid reliability as more (FIT) wind generation comes on to the grid and then it is wind that has to be curtailed, not gas. It would be the IESO’s job to cobble together enough gas (combined cycle and simple cycle) and hydro generation to be available if, say, 5,000 megawatts or even 8,000 megawatts of wind decided to quit – wind has a propensity to fade at the same time over a wide geographical area. If this cannot be done some (FIT) wind would have to be kept off line. It is the timely availability of this gas and hydro generation that will set the limit on wind penetration on the Ontario grid. Hydro generation that depends on precipitation is a valuable operating reserve and will not be wasted to support wind and imports from neighbouring jurisdictions may not be available if they also have a large wind component on their grids. When the wind drops it could take around five hours to get a big combined cycle unit up to full power from a cold start and around two hours from a warm or hot condition. Dispatching combined cycle gas turbine units is more complicated than dispatching coal-fired units due to the various operating configurations of the multiple gas turbines and the steam turbine. Up to 8,000 megawatts of wind, equivalent to the output from more than eight Darlington size nuclear units, could be potentially coming on to a grid that has a demand that varies seasonally from less than 12,000 to more than 25,000 megawatts. This could happen on the few occasions that wind conditions are optimum across the province and could put the grid at unnecessary risk. Even if wind is shutdown, if a SBG is deep enough nuclear plants would still need to be shutdown, or powered down to a reduced constant power level, with GHG emitting gas-fired plants taking care of dispatchable load following on the grid. For less deep SBG shutting down some wind might prevent nuclear power reductions and reduce wear and tear on these essential units.
As more controversial shale gas gets into the natural gas supply it raises the question of life cycle GHG emissions. Although a combined cycle gas turbine generator produces just over half the carbon dioxide of a similar sized coal-fired generator, taken on a life cycle basis GHG emissions from burning shale gas may approach or equal coal. In this case it would have made economic sense to keep operating the coal-fired stations with low sulphur coal and flue gas clean-up until new nuclear became available and skip this monstrously expensive and risky venture with gas and wind. Even the advantage in GHG emissions from combustion that conventional natural gas has over coal would be reduced if the methane leakage in collection, transmission and distribution were considered. Coal has a dispatchable range of 20 to 100 percent full power compared to around 70 to 100 percent for combined cycle gas, which means more non-GHG emitting nuclear would be shutdown (with consequent wear and tear costs) or powered down to avoid SBG by using gas than by using coal. This would lead to an increase in carbon dioxide emissions even though carbon dioxide emissions from a combined cycle gas turbine plant are just over half the amount from a coal-fired plant for the same output. For gas to provide the same dispatchable power as coal, with both operating at their respective minimum loading points, several times as much gas generation would have to be on line meaning very much more GHG emissions. Under these circumstances coal, rather than gas, would make a better partner for wind.
The availability and cost of conventional and shale gas in the next few years is unknown yet the Ontario government is betting our future on enough affordable gas being available to power our electricity generators, heat our homes, supply our petrochemical industry, supply our industrial sector, meet our potential transportation needs, and meet the demands of all other north American users. Shale gas, and imported liquid natural gas, will only replace the declining reserves of gas from north America’s conventional sources, and at higher cost and with higher life cycle GHG emissions.
The only sure way to reduce GHG emissions to near zero is to have a future Ontario grid with an energy mix of just hydro and nuclear. Unless sufficient and suitable demand response loads (e.g. thermal storage, hydrogen production) become available to enable nuclear to operate base load the new CANDU nuclear plants must be able to vary reactor power, with steam bypass if necessary, to meet daily and weekend changes in demand (Aside: in fact the IESO has stated that Ontario’s future generation supply mix will place an increasing reliability value on the flexibility of generating assets to provide load following capability, operating reserve and AGC – wind meets none of these requirements). It has to be this way eventually and this will provide reliable secure electricity at a reasonable and stable price that will encourage long term investment and jobs in the province. Erratic wind would have no place on this grid since it would cause unnecessary manoeuvring of the nuclear and hydro units.
Using a suitable mix of flexible nuclear and hydro would mean the end of load shifting incentives (time-of-use “smart” metering for home and industry) to bring down peak demand since supply will match demand at all times, day and night, with plenty of clean, pollution free, reasonably priced generation. At present peak demand during the day means running more expensive gas-fired GHG emitting generation. Quebec and Manitoba, whose utilities integrate generation, transmission and distribution, have around 98 percent of their electricity supplied by low cost, flexible, clean hydro day and night and do not have or need “smart” time-of-use metering. Ontario could do the same with nuclear/hydro. The only restriction to a clean nuclear/hydro grid could be the lack of sufficient transmission capacity into some high demand load centres, that needs to be fixed, which is evident from the building of neighbourhood gas-fired power plants. This lack of sufficient transmission into these load centres means that not all of the thousands of megawatts of wind that is to be installed will get to where it is needed anyway, which does not help GHG reduction.
France has been producing 80 percent of its electricity from its flexible nuclear fleet for many years with the balance from hydro and fossil fuels. France has 58 pressurized water reactor units on line so the national grid controller can select units that have been recently refueled so have the flexibility to provide dispatchable load following, load cycling, and AGC. There need not be a shortage of electricity anywhere, especially in Ontario. It can be produced reliably in abundance by nuclear energy at reasonable cost and can meet our needs for thousands of years.
Now the people at the IESO can see why at least some of us are confused about the need for wind, and gas for that matter. Is Ontario making a huge mistake?
Donald Jones, P.Eng.
Retired nuclear industry engineer
by Donald Jones, P.Eng.