Calima and Wind Turbines: Navigating Dust and Erosion

Introduction

In the Canary Islands, a distinctive meteorological phenomenon blurs the boundaries between land and sky. It’s called calima, and it arrives with a flourish, carried on the winds from the Sahara Desert.

Calima is a recurring and increasingly noticeable phenomenon, marked by the arrival of significant amounts of suspended dust particles originating from the Sahara Desert. This dust has negative effects on the cardiovascular and respiratory health of the population. It also poses challenges for the region’s wind turbines, reducing energy production and accelerating equipment wear and tear.

The abrasion caused by airborne dust particles combined with dirt accumulation on turbine blades significantly reduces the energy efficiency of wind turbines. This happens because these factors damage the aerodynamic performance of the blades.

Example of type A calima over the Canary Islands. Image source: NASA

What does calima do to the wind turbines?

Calima remains an enigma. Research on its effects on wind turbines is notably limited and has been studied mainly in the form of dry dust inland, which is different from the heavily wet dust with sea spray that affects offshore wind turbines. As mentioned in the previous AIRE blog, most advancements in wind energy-related topics have originated in northern Europe, where calima is not a concern for wind turbines. Studies have primarily focused on the effects of dust accumulation on turbine blades and erosion caused by various particles, rather than specifically addressing calima’s effect on wind energy. If we think of calima for a wind turbine blade as the collision of dust transported by wind, it resembles a low-powered yet wide-coverage sand blasting gun. Consequently, research on the impact of this phenomenon relies on the understanding of the extent of damage caused to turbine surfaces.

Since the inception of wind turbines, particles such as raindrops, dust, ice crystals, hailstones, and insects have been major contributors to blade erosion and deterioration. These collisions affect turbine performance by altering airfoil surfaces. When particles strike the blades, existing cracks in the coating can propagate, leading to erosion, core delamination, and corrosion damage. This exposure of the internal composite structure can result in significant changes to the once-smooth blade surface. Increased roughness often leads to reduced power output [1].

While offshore wind farms offer benefits like higher wind speeds, they are also vulnerable to increased erosion from various particle impacts. Airborne sand particles, such as those from the northern regions of Africa during calima events in the Canary Islands, create tiny cuts and plow into coating materials upon blade collision, causing surface abrasion. This damage is most noticeable in the outboard sections of the blade, where relative velocity is higher compared to the inboard sections. [2]

Furthermore, exposure to environmental airborne particles can decrease aerodynamic efficiency due to an increase in the drag coefficient. Additionally, damaged blades may contribute to noise issues, as alterations to the blade surface disrupt boundary layer patterns, resulting in elevated noise levels, although studies already suggest cleaning periods for the blades to maximize their efficiency.

What things are being done to stop the damage of this phenomenon?

The calima phenomenon poses significant challenges for the wind energy industry in affected regions. To mitigate these adverse effects, various strategies and innovative technologies are being implemented to protect and maintain the operability of wind turbines against calima.

As an example, researchers at Jaume I University have developed a type of material with superior erosion resistance compared to current industry standards for wind turbine fabrication, along with new, highly durable coatings [3]. In 2018, they participated in a project called AeroExtreme, which sought to investigate various active and passive solutions for both the blades and internal structures of wind turbines. The goal was to maintain higher efficiency and durability despite extreme climate conditions. As part of this endeavour, they developed a material with erosion resistance surpassing any currently employed [4].

Additionally, the company envirofluid has developed two types of dust abatement solutions for addressing dust accumulation on wind turbines, which can impact both energy production and maintenance workers [5]:

Dust Suppression Plus: This bio-based, plant-derived chemical serves as a cost-effective dust suppressant agent specifically designed to combat dust during turbine maintenance.
Dust Suppression Nova: An eco-friendly polymer-based dust control solution crafted for application on tracks and open areas prone to dust generation, offering robust and long-lasting performance.

While these solutions do not directly address calima damage, they can effectively mitigate dust buildup on wind turbines following the phenomenon.

What does AIRE do?

AIRE aims to establish a comprehensive database containing calima measurements, leveraging this data to develop preventative solutions against potential damage. This database will be compiled using the PLOCAN wind turbine, equipped with a Vaisala meteorological station, a solar radiation sensor, a UV sensor and a LiDAR system.

To enhance understanding of mineral dust outbreaks, a phenomenon common in regions near deserts and subtropical climates, the PLOCAN site utilizes data from the University of Las Palmas de Gran Canaria. This includes a sampling network to measure aerosol particles resulting from the long-distance transport of mineral dust from the Sahara Desert. The LiDAR equipment will measure wind profiles during calima events, allowing for comparison with “clean wind” atmospheric boundary layer profiles. Additionally, PLOCAN will carry out blade inspections right after a calima event to complement this data. The data obtained from PLOCAN’s site will be used to estimate the blade distributed roughness and the loss of material during service life and how calima affects energy production.

AIRE will utilize mesoscale simulations and satellite data to create an erosion atlas for specific zones, including offshore regions, high-altitude areas, complex terrains, and airborne sand. This atlas will serve as foundational resource information in the developed toolbox. Additionally, engineers will design two airfoils optimized to withstand dust or precipitation conditions, enhancing the durability and resilience of the blades they are incorporated into.

Moreover, the blade damage model, which predicts how erosion evolves in wind turbine blades based on weather data and operational information, will undergo further development and validation using a high-fidelity experimental dataset. This model aims to characterize the impact velocity of particles and its subsequent impact on blade wear.

Thanks to the AIRE project, the adverse impact of calima on wind turbines will be mitigated. With its focus on practical solutions, the project strengthens the resilience of wind energy systems, resulting in greater economic, energy, and environmental efficiency.