Integrating Wind – a Theoretical Example
Wind is a variable resource, and its output varies depending on the winds. But consumers demand the services of electricity at their convenience, not just when the wind blows. So how can an electrical grid accept wind power, and what is the effect of wind power on emissions from fossil generating plants?
The supply and demand for electricity must always be in balance. So when demand increases, more power must be generated. Similarly, when demand falls, generation must be take off line.
Lets assume that we have an island, that is not connected to any other power system. The island has a minimum demand of 50 MW, and a maximum demand of 100 MW. The average demand is 70 MW. The island has 21 natural gas fired generating stations, each 5 MW in capacity, and which can be run at any level from 0 to 5 MW. It takes 1 hour to start up any generating station. How can we ensure that demand always equals supply?
One way would be to always have all 21 generators running, so we are ready to increase electricity supply at any time. We would be able to increase supply to 100 MW any time we wanted, and we even have an extra plant running, in case one failed. This arrangement would of course be very wasteful of fuel, but if our demand varied quickly, and without notice, it might be what we need to do.
To save fuel, the grid operator studies the nature of demand. How quickly does demand increase or decrease? Is there a weather related pattern to demand? Does outdoor temperature matter? Does sun affect air conditioning load, or decrease heating load? Does wind cause wind chill effect in buildings, increasing heating demand? Is demand different at night, when people aren’t working? Do sunrise and sunset times affect lighting requirements? Are there different demand patterns on holidays, or weekends? If we can estimate demand with 100% accuracy, and with a 1 hour notice, then we would only ever run exactly the number of generating stations we need, with a huge savings in fuel.
Grid operators spend millions forecasting demand for exactly this reason. It allows a more efficient dispatch of generating stations, and therefore saves money.
Our island has smart grid operators, so they made the investment in forecasting. And they achieved an accuracy level that means they are never more than 10% in error. So how much extra generation do they need to run? Only 10 MW. That’s way better than the 35 MW average they had before forecasting.
Now lets introduce 20 MW of wind. The wind will produce 6 MW on average, or 9% of the average demand of 70 MW. And production will range between 0 and 20 MW, depending on the wind. What changes will this allow in our system? How much natural gas will we save?
If we have no forecasting, and if wind can go from 0 to 20 MW and back to zero instantly, then we have to burn just as much fuel as before. We still need to keep our 10 MW of margin available. After all, the output from wind could be zero in the moment that we need the 10 MW due to our demand forecast error.
But in practice, wind does not go from 0 to 20 instantly. Winds pick up, and drop back, but they do so over time. So our smart system operator will come up with forecasts of wind. With simplistic forecasting, you would simply make the assumption that the output next hour will be the same as the last hour. And with this type of forecast you would be within about 10% of the installed capacity, or 2 MW.
So, lets assume that our wind output never varies by more than 2 MW. How much generation do we need to add to firm up the wind? We need to add no new capacity, as we already have 105 MW of capacity to meet 100 MW of demand. And we change from needing 10 MW of extra generation to 12 MW running at any one time. We need the 12 MW when we had a simultaneous unexpected increase in demand of 10 MW, at the same time the wind dropped by 2 MW. In this scenario, fossil fuel use would drop by an average of 6 MW of wind production minus the 2 MW of extra reserve. So wind, in this simplistic example, would reduce fossil fuel use by 2/3 of the output from the wind, or 4 MW.
But remember, we have smart system operators. What can they do to reduce the 12 MW reserve, thus saving even more fuel? It turns out there is lots they can do. They can improve the wind forecasting. If our forecast ends up better than just using the previous hour’s output, we can reduce the 2 MW added requirement. They can interconnect to another jurisdiction. If you had two equal islands as described above, you could have only 41 natural gas plants, not 42, as one redundant plant may be able to back up both systems. And you could probably reduce your reserves from 10 MW per island to 7, as the odds of simultanous forecasting error is reduce. And the bigger your total system, the less variability wind has, as the wind doesn’t stop everywhere at once. You can install some “instant on” and “instant off” facilities. Waterpower often works in this way. If you had just 12 MW of “instant on/off” facilities, you could stop running extra generation altogether, and your windpower would be firm. You could implement load shedding, where hot water heaters, or air conditioners, or municipal water pumping facilities, or pool pumps, could be turned off when demand unexpectedly jumped. Ontario’s proposed smart meter program may allow some of this. If the system has pumped storage, you could run the pumps only when surplus electricity is available. The Cities of Guelph and Peterbourough used to have the ability to shut off all the hot water heaters on demand. This is neither new, nor far fetched, but it is an opportunity that Ontario has only recently begun to look at again. In the future, hydrogen production, or plug in hybrid vehicles may offer interesting ways to vary electricity demand at a moment’s notice.
How does this simple example apply to Ontario? Peak demand is 27,000 MW, minimum is 13,000, and average 17500. We have 31,000 MW of installed capacity. We have 14,000 MW of nuclear, and 1000 MW of natural gas co-generation, that cannot be either turned up or down. We have 6500 MW of coal that can be turned up, but requires a few hour lead time to get to full capacity. We have 7000 MW of waterpower, of which half can be turned up and down very quickly. We have about 4000 MW of gas that can be adjusted with about an hour’s notice. And we have 400 MW of wind.
Studies done on Ontario’s electricity system demonstrate that we can add 5000 MW of wind with virtually no need to add back-up capacity, load shedding, or “instant on” capability. And virtually all of the production from wind will reduce our use of fossil fuels. This proportion of wind has been added in other jurisdictions, also with almost no need to make other significant changes. Claims made by some that the cost of integrating wind is high are simply wrong. But it does depend on the grid, the amount of load shedding, and instant on facilities that exist, and the accuracy of forecasting. And there simply is no doubt that adding wind reduces the use of fossil fuels in any jurisdiction that makes electricity from fossil fuels.
Utility planners would be well advised to continue to refine their forecasting models (Ontario has this underway for demand), add wind forecasting to their models, and put a proper value on load shedding, instant on, or storage facilities. Only then can an optimal mix from both a cost and environmental perspective be achieved. And paying attention to these issues today allows maximum flexibility for future generation options.
January 10th, 2007 at 4:54 pm
Thanks Glen – this was most enlightening. I was wondering about these issues.
Don
January 12th, 2007 at 7:03 am
The example serves to illustrate what is being planned for Ontario’s electricity supply.
The plan is to install about 12,000 MW of natural gas fired generation in Ontario. Half has already been installed or is being built like the 1000 MW gas plant in Sarnia. The gas units will be run more often than not at about average 60% capacity to make up for when there is no wind generation.
The study conducted by GE for the Ontario Power Authority was very optimistic about wind capacity values for Ontario. GE did a study for New York State and found that capacity values were ~80% less than what was quoted for Ontario. There are limits to wind forecasting. We may end up having to run those natural gas units at more than 60% capacity if GE and the OPA are wrong about their Ontario guesstimates.
If wind’s capacity factor is 30%, then 70% of the energy needed to power those gazillion homes must come from another source. The policy of the Ontario government is to rely predominantly on natural gas for that source. The Americans have built 200,000 MWs of gas power generation in recent years. Natural gas power generation emits about 1/3 the GHGs of old coal. Half of Canada’s natural gas production goes to the US. Does anyone know how many years of proven gas reserves Canada has left? Do we burn it all up this generation? Meanwhile the Sierra Club & Co. oppose the proposed gas pipeline thru the Mackenzie Valley. Where will the gas come from to back-up all these wind mills that are being planned? Some people have warm and fuzzy concepts about pandas and forests but have no clue where their toilet paper and energy comes from.
There is no free ride. We’re back to having to consider all the pros and cons and deciding whether the 30%-70% wind –gas option is a better option than nuclear for Ontario. The OPA decided to take us down the 30%-70% wind –gas road before they held their bogus dog and pony road shows. It has not been determined that the 30%-70% wind –gas option is the better option for Ontario when it comes to reducing Ontario’s reliance upon carbon-based fuels, energy costs, energy security, job creation, the provincial economy and the environment.
January 12th, 2007 at 12:36 pm
We agree on concerns regarding gas. It is of course a finite resource, and should be used judiciously, and the less we burn, the better. And it does emit carbon.
The OPA is not proposing a 30% wind 70% gas mix. They are proposing a 50% nuclear, 25% hydro, 17% gas, 8% wind mix. And coal will be shut down.
If Ontario does indeed install 12,000 MW of natural gas, and this is there to “back-up” wind, then why are they proposing only 5000 MW of wind? Clearly you don’t need 2.4 MW of gas to back up 1 MW of wind, especially when you already have 3-4,000 MW of hydro to firm up wind, and 2,000-3,000 MW of imports to do the same. If the concern is saving gas, then wouldn’t you at least want the gas and wind installed in equal ratio, so that when the wind blows, you don’t have to burn gas?
The gas, along with hydro, is there handle demand peaks. It is not being installed to firm up wind, as it is not needed for that. The system can already do that, with the small amount of proposed wind power, with no new investment required.
We can get much more from wind than is proposed, and we can get it sooner than is proposed. The plan calls for 5000 MW, but over the next 20 years. Building wind now would allow us immediately to use less coal or natural gas, surely a desirable objective.
The productivity of wind in Ontario is likely better than New York. The prevailing southwest winds in our province are ideally suited to our Great Lakes shorelines, and much less so for New York. I would expect a study to forecast higher winds for Ontario.
Keep in mind that 30% capacity factor does not mean that wind produces only 30% of the time. It produces 75-80% of the time, perhaps even more over a large geographic area, cutting gas use a majority of the time. 30% average is not the same as percent of the time producing.
January 15th, 2007 at 4:22 am
We’ve discussed some of these concepts in previous posts.
“Installed capacity is the maximum power that can be produced (nameplate capacity). Effective capacity refers to the expected contribution of that resource in meeting the annual system peak demand. In case of an intermittent resource such as wind power, the difference can be substantial-the Preliminary Plan considers only 17 percent of installed wind power capacity to be effective capacity.” OPA Integrated Power System Plan Discussion Paper 7-pg 19.
Your fridge’s motor doesn’t like running when supplied with less than 90% of its rated power at less than normal system frequency.
How much effective capacity must be provided from another source to back up 4000 MW of installed wind capacity in southern Ontario at peak demand?
Is gas not being installed to firm up wind?
“… the assumed gas-fired additions are expected to help support adequate response capability of Ontario’s power system, for example, with respect to ramping capability and operating reserve. It is expected that such capabilities will be of particular importance as more variable renewable resources, such as wind power, are added to Ontario’s resource mix. OPA Integrated Power System Plan Discussion Paper 7-pg 40
As for the difference in capacity values for wind in New York and Ontario, its hard to believe that comparing wind potential at best producing sites that there would be a 5 times difference in capacity values on account of the wind resource. The reason for the difference between the reports for Ontario and New York is on account of different criteria being used to arrive at the numbers ( to support the sought outcome in the case of the Ontario report).
If a wind tower must be backed for 83% of its name plate capacity by natural gas, how does building more wind farms reduce our reliance on a non-renewable GHG emitting fuel like natural gas?
The question comes back to “should we be replacing nuclear with the wind-gas mix”?
January 15th, 2007 at 11:21 am
It is interesting that the OPA paper discussed “effective capacity” for wind and water, but did not disclose the assumptions they make for nuclear. Nuclear does not work all the time. This morning, 4 out of 6 of the Pickering stations are off line for maintenance, reducing Ontario’s nuclear capacity by 2000 MW. What assumptions have been made about the “effective capacity” of nuclear, or fossil units? I haven’t been able to find it. We need to back up all sources of power to varying degrees. But the neat thing about it is that one back up source can often back up multiple stations. For example, we need to keep spinning reserve available to back up the loss of the largest generator – a 900 MW Darlington unit. This 900 MW back up is already in place, and it backs up all resources, including wind. Keep in mind we have only 400 MW of wind in Ontario today.
“If a wind tower must be backed for 83% of its name plate capacity by natural gas, how does building more wind farms reduce our reliance on a non-renewable GHG emitting fuel like natural gas?” Having backup facilities doesn’t mean you use them 83% of the time. When the wind is blowing, when the water is flowing, when the nukes are running, when demand is low, the back up facility is not operating. This may approach 100% of the time. That is how you save gas. The presence of the facility is not very closely related to the amount of fuel used.
“How much effective capacity must be provided from another source to back up 4000 MW of installed wind capacity in southern Ontario at peak demand? Is gas not being installed to firm up wind?” The back up is already in place. We have 3000+ MW of peaking gas plants and 3500 MW of peaking water power today. There isn’t any additional resources required. And if you build wind, you will burn less gas or coal. The gas is being installed to replace the swing values of the coal plants.
The question comes back to “should we be replacing nuclear with the wind-gas mix”? We aren’t replacing nuclear. In fact the OPA is planning on increasing nuclear. We are replacing coal, with wind, gas for peaking, other renewables, conservation, and nuclear. But I believe we have underestimated the amount that can be supplied by renewables and conservation.