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Solar and Wind Forecasting

Wind and solar resource forecasting predicts future energy output through numerical weather prediction models and statistical approaches. Resource forecasting is relatively new compared with system load forecasting, and it is not yet as accurate.

Experience suggests that the overall shape of wind energy production can be predicted most of the time, but significant errors in the level and timing of wind energy production can occur. Therefore, electric power system operators are interested in both the uncertainty of a particular forecast and the overall accuracy of forecasts in general.

The wind forecasts for the near term tend to be more accurate than forecasts for longer terms. For example, for a single wind power plant, forecasts one to two hours ahead can achieve accuracy levels of approximately 5%–7% mean absolute error relative to installed wind capacity, but this increases to 20% for day-ahead forecasts.

Wind forecasting also enjoys strong geographical aggregation benefits. Aggregating wind power plants over a region significantly reduces forecasting error. In Germany, for example, forecast error was reduced 50% from a single site prediction to a regional prediction of measured power production. In other research conducted in Germany, typical wind-forecast errors for representative wind power forecasts for a single wind project are 10%–15% root mean square error of installed wind capacity but drop to 6%–8% for day-ahead wind forecasts for a single control area and to 5%–7% for day-ahead wind forecasts for all of Germany. Combining different wind-forecasting models into an ensemble wind forecast can also improve wind-forecasting accuracy by up to 20%, as measured by root mean square error. More importantly, with aggregation, the impact of forecast errors on individual wind plants is not as severe because the aggregate forecast of all wind plants drives the committing and scheduling of generation.

The forecasting of solar energy production faces issues similar to those of wind. However, solar forecasting has significant predictability because the sun’s path through the sky is known. Nonetheless, solar resource forecasting is not as mature.

NREL is addressing solar and wind forecasting issues on the transmission system. For more information, see the following publications:


Bri-Mathias Hodge