By: Donald Jones, P.Eng., retired nuclear industry engineer.
The answer given by wind promoters to the intermittency question of wind, and to bolster their claim that wind (and now, they admit, with the help of frackgas) can replace nuclear in Ontario, is to say that any interruption in wind is no different from a nuclear unit coming unexpectedly off line. They also point out that the loss of wind does not occur suddenly like a nuclear unit and the geographic distribution of wind turbines means that wind is always generating somewhere. Wrong on all accounts. Wind is, and will increasingly be, a hindrance to the Ontario grid and it is also making the capacity factor of generators on the grid irrelevant as an indication of performance and reliability.
The Ontario grid has to maintain an operating reserve, some spinning and some not spinning, to handle the loss of the largest generating unit on the grid and loss of half the amount of the second largest unit (see Note 1). This typically means about 1,500 megawatts (MW) of operating reserve being available within 30 minutes with some of this being available within 10 minutes. A Darlington unit at 880 MW to the grid is the largest nuclear unit on the grid so normal operating reserve can easily handle a nuclear unit coming suddenly and unexpectedly off line. With wind likely to be over 6,000 MW nameplate capacity in the next few years wind is a different story. Operating reserve cannot be used to mitigate losses in wind production since that would make it unavailable for its intended use. While right now a reduction in wind output of 50 percent, say from around 2,000 MW to 1,000 MW, could be handled a reduction of 3,000 MW or more in the future would not. While the loss of wind generation would be less sudden than a loss of a nuclear unit it is still relatively sudden when considering that 3,000 MW or more of generation now has to be cobbled together over a relatively short period of time to replace the lost wind (see Note 2). The stability of the grid could depend on the accuracy of the information in the centralized weather forecasting system used by the Independent Electricity System Operator (IESO).
All gas-fired units on the grid, except for one flexible 393 MW simple cycle station, are relatively inflexible combined cycle gas turbine (CCGT) units or inflexible combined heat and power plants. Bearing in mind the time it takes to bring CCGT units into their dispatchable power range even from a warm condition and the limited amount of hydro storage available cobbling together enough replacement generation after loss of significant wind generation will be a major issue. It will result in limiting the amount of wind on the grid to what can be replaced in a short period of time. This means curtailment of wind will always be the case on windy high demand days and the wind generators would still have to be paid for their deemed generation (that did not get on the grid), based on the information provided to the IESO by the centralized weather forecasting system. This situation becomes more than a hindrance if wind generation starts to fall off during the morning ramp up to meet the increasing grid demand. A similar situation arises in the afternoon when solar is fading just as the late afternoon ramp up is getting underway. Besides wind curtailment the only other solution to accommodate more wind on the grid would be to add a few thousand MW of quick start simple cycle gas turbines to the operating reserve, call it wind reserve, that would not otherwise be needed (see Note 2). That makes no economic or environmental sense. Loss of wind is a lot worse than loss of a nuclear unit. Read the rest of this entry »