PRecipitation atlas for Offshore Wind blade Erosion Support System (PROWESS)

WHY

The progress towards affordable energy is pushing wind turbines to greater extremes, longer operational life and extended exposure to harsh environments.

Blade lifetime and performance are two central concerns when operating offshore wind turbines. Leading-edge erosion has been identified as the key factor to significantly shorten the life of the wind turbine blades. Damage will lead to more frequent blade repairs, inspections and early replacements. The main cause of leading-edge erosion is precipitation. Different types of precipitation, for example, rainfall and hail, have been proven to cause erosion at different rates and severities. You can find more information on this topic from the earlier GROW project WINDCORE.

Damage to the blades from leading edge erosion can lead to a reduction in Annual Energy Production of 1 to 5%. Severe damage in the form of delamination and pitting into the composite material also affects the structural integrity of the blade, resulting in major expensive repairs or even blade replacement. Repairs must be made because if left too long irreparable structural damage to the blades can occur. The costs are high because these repairs and possible replacements have to be made in challenging offshore conditions and because of the energy production loss during repair. Both higher costs and lower annual electricity production increase the levelised cost of energy.

Current turbines are limited to tip speeds of up to 325 km/h (90 m/s). The aim is to increase the tip speed to improve the efficiency and performance of the wind turbine. Higher speeds also make it possible to use less heavy gearboxes, which saves costs. However, higher speeds also significantly increase leading edge erosion. This can be prevented by applying leading edge protection systems such as coating or by reducing the tip speed in certain harmful precipitation events.

Applying the right control strategy for wind turbines is currently not possible due to a lack of knowledge about the precipitation events that lead to erosion, namely the combination of different types of precipitation with different wind intensities (tip speeds). At the moment, no useful information is available about the type of precipitation and related weather conditions at the location of existing and future wind farms in the North Sea. This is mainly due to the lack of proper sensing and measurements. In addition, it is not yet possible to link precipitation types and data on erosion with other weather data, such as wind fields, sea water aerosols (salt spray up to the nacelle height is possible in certain conditions), temperature, and UV radiation level.

WHAT

Six partners form a unique collaboration to address the missing link between precipitation types and leading blade erosion. The consortium consists of the experienced project owners in the offshore wind industry Eneco, Shell and Equinor, the project coordinator TNO and the SMEs Whiffle and Sky Echo with relevant knowledge in the modelling and observation field.

In this project, we will measure and monitor the characteristics of the precipitation at different sites in the Dutch North Sea and coast in detail and correlate the precipitation accurately with other weather data. In concrete terms, a monitoring system network will be set up and implemented by determining the optimum weather monitoring strategy based on multiple sensors, radar systems and high-resolution meteorological modelling.

Based on this information we will develop an optimised weather atlas for precipitation and wind with a high spatial and temporal resolution for the Dutch part of the North Sea. Using data collected from the new and unique network of precipitation sensors, radar and modelling, the atlas will present erosion classes related to precipitation severity and wind conditions. We will also model with high resolution the correlation between the occurrence of leading-edge erosion and the predicted precipitation.

We will use the results of these activities to develop a decision-making tool. The tool will link the atlas to the operational and maintenance planning of a wind farm. The tool estimates the impact on costs and annual electricity production as a result of the expected leading-edge erosion for selected sites in the Dutch part of the North Sea.
The precipitation data and its relationship to the leading-edge erosion will be used to enhance site studies for future wind farms. The dataset will be publicly available.

EXPECTED RESULTS

The project will result in a new publicly available dataset on weather precipitation for the Dutch part of the North Sea. The dataset will provide a reliable source of information that can be used by multiple players in the wind industry such as equipment manufacturers, wind farm owners and operators, blade manufacturers and coating developers. The project will also result in an improved model to identify the optimal leading-edge coating system and in a model to assess the operational and maintenance costs and the loss in annual electricity production due to the occurrence of leading-edge erosion. We aim to keep the monitoring system network operational even after project completion.

Information on the following applications can be obtained from the results of this project:

• Characterization of precipitation regarding leading-edge erosion of the blades in the Dutch part of the North Sea.
• Improved accuracy of erosion models that advises on the leading-edge blade coating systems.
• Supporting the total cost estimate caused by erosion to reduce uncertainty in the investment decisions in the planning phase of the wind farm.
• Optimise operational and maintenance activities.
• Provide a pre-assessment for wind sites to optimise blade life, e.g. by applying certain leading-edge protection systems or by reducing the speed of the blades or switching off the turbine under certain weather conditions.
• Model developments on simulations of precipitation patterns with a better resolution using micrometeorological models and RADAR systems.