Wind Forecast Error Impacts on Efficiency 

… Wind generators are classified as intermittent generation and must submit a forecast of their hourly energy output.

Wind generation is offered into the market as price-takers (i.e. total forecast energy output is placed at the bottom of the offer stack).

Transition From Pre-Dispatch to Real-Time

In pre-dispatch the total estimate of wind generation is placed at the bottom the stack. However, in real-time, actual tele-metered output from wind generators is used. …

Impact on Efficiency

Wind forecast error could affect efficiency at 3 different time periods: 1-hour from real-time: scheduling of intertie transactions; 3-hours from real-time: SGOL [spare generation on-line] actions; day-ahead: DACP [day-ahead commitment process] commitments. …

1-Hour Ahead: Impact on Intertie Transactions

Under-forecast of wind generation could cause expensive imports to be scheduled in pre-dispatch which become uneconomic in real-time.

Over-forecast of wind generation: In real-time more expensive generation would be scheduled because cheaper imports were not scheduled in pre-dispatch or additional exports were scheduled in pre-dispatch.

3-Hours Ahead: Impact on SGOL Actions

Under-forecast of wind generation could lead to more generators scheduled under SGOL; generators under SGOL would be operating in real-time when cheaper resources could have been used.

Over-forecast of wind generation: SGOL participating generators would not be scheduled in advance; in pre-dispatch more expensive imports would need to be scheduled; or in real-time more expensive generation would be scheduled.

Day-Ahead: Impact on DACP Commitments

Under-forecast of wind generation: Over-commitment of imports and generators could occur; cheaper resources could be available in real-time.

Over-forecast of wind generation: Some imports and generation would not be committed in DACP; in pre-dispatch more expensive imports would need to be scheduled; or in real-time more expensive generation would be scheduled.

1-Hour Ahead Accuracy of Wind Forecast (2007)

Under-forecast frequency of 42%: 39MW average under-forecast.
Over-forecast frequency of 58%: 35MW average over-forecast. …

1-Hour Ahead Wind Forecast Errors: 2007 Costs of Inefficiencies

Inefficiencies occur when the most economic set of resources are not used to satisfy demand. Annual costs of inefficiencies: due to over-forecast: $186K; due to under-forecast: $25K.

Projection of Inefficiencies in 2009 Due to Wind Forecast Error

If we assume that the forecast error percentages remain the same in 2009 we could expect the annual costs of inefficiencies to increase: due to over-forecast: $866K; due to under-forecast: $37K. …

3-Hour Ahead Accuracy of Wind Forecast (2007)

Under-forecast frequency of 46%: 49MW average under-forecast.
Over-forecast frequency of 54%: 45MW average over-forecast. …

Day-Ahead Accuracy of Wind Forecast (2007)

Under-forecast frequency of 45%: 83MW average under-forecast.
Over-forecast frequency of 55%: 59MW average over-forecast. …

May 14, 2008

Hok Ng
IESO (Independent Electricity System Operator, Ontario)

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