Ramping of offshore wind parks from a TSO’s perspective

29-01-2018

Offshore wind is one of the main pillars in the decarbonisation of electricity in Belgium. The current installed capacity of 0.8 GW in the Belgian offshore area will significantly grow and reach 2.2 GW by 2020. In this changing context, Elia – the Belgian TSO – is concerned about large variations in the wind farms’ power generation which could be higher than the available regulation power. These large variations are caused by curtailment at high wind speeds or by sudden changes in velocity, and magnified by dense geographical clustering of the parks in the North Sea.

Commissioned by Elia, 3E performed a study on three axes. At first, a detailed statistical analysis of all ramping events and the quality of ramp forecasting was performed. In parallel, an international benchmarking was performed on mitigation measures for ramping of offshore wind parks. Combining both, 3E formulated recommendations on future measures.

Based on the historical wind and wind generation data, and extrapolation towards 2019, a statistical classification was made of the ramping of the Belgian offshore wind parks. Then it was analysed in relation to the timeframes and volumes of existing balancing products. Two different type of events were studied separately: ‘storm events’ caused by curtailment at high wind speeds, and ‘ramping events’ due to natural wind variability. Such storm events show a strong seasonality and occur generally only between September and March, while natural ramping occurs throughout the entire year.

Considering, e.g., a contracted volume of 150 MW for aFRR (organized in 15-minute products), ramping of the offshore wind parks currently seems to have limited impact on the operational reserve. On average, the combined ramping of the offshore parks exceeds this threshold value 1 day per week or around 0,2% of the time. In 2019, however, the ramping of 2 GW offshore wind would exceed this threshold value up to 5 days per week or in total around 3% of the time. Not adapting the contracted volumes to this new situation for balancing might thus impact the total cost of balancing.

For many TSOs, the topic of ramping of wind parks is of little to no importance and thus also not considered in their current operations. Energinet – the Danish TSO – is one of few including measures: facing significant challenges to integrate 5 GW of wind in a region with a peak demand of only 6 GW. Measures are defined in the Technical Regulation 3.2.5 for wind power plants above 11 kW, and imply constraint functions on the total injection, define maximum ramp rates, and expressing system protection and active power control requirements.

To conclude, recommendations have been formulated to improve the future situation. The effect of alternative ramp controls has been quantified, showing that an appropriate choice of storm controls and/or ramp limitations can result in major improvements. Additionally, the amount of data available for system operations is limited or has a limited quality, while also the predictability of ramping events has been found to be low. Improving the necessary data services are thus identified as a second major point of attention.