Wind measurement at sea: LiDAR measuring buoys in offshore use.

Photonics for energy transition

No matter where you look, photonics is the silent enabler behind the drive to create sustainable forms of energy: from the construction of wind-energy systems and wind farms to photovoltaic production.

They continue to grow longer and longer. Ten years ago, the longest rotary blades for wind turbines covered a distance of 60 meters end to end. Today, the first 100-meter blades have entered the picture. Precision is the essence of the process used to produce these huge structures made of glass and carbon fiber reinforced plastic (GFRP/CFRP), objects that will be subjected to extreme mechanical stress during their service lives. The reason is simple: These blades must stand up to the tremendous forces caused by winds blowing up to 80 meters per second, squalls and lightning strikes for at least 20 years. At the same time, it is the intricate design perfected during extensive simulations that ultimately determines the energy yield and acoustic emissions of a wind turbine. Weight, costs, stability and the functionality of the rotary blades all depend on the precision that goes into creating the form optimized during the simulation process.

Exact positioning with the help of laser technology

But how do manufacturers pull off the trick of precisely positioning the glass and carbon fiber reinforced plastic mats with minimal overlap in the casting molds of a rotary blade half shell formed in a 3D process? What sort of compass is used in these structures that stretch for more than 100 meters? The answer is found in photonics. Laser systems draw on CAD construction data and project the patterns for the fiber mats, down to the very last millimeter, onto the curved surfaces. These projections then create process certainty and reproducibility in the manual laying process. A number of different teams can also securely get their bearings in the same half shell, an ability that speeds up the entire manufacturing job. In addition to lines, the systems based on fiber or diode lasers can also project instructions and numbers onto the huge structures to walk untrained or new employees through the manufacturing process.

But lasers do more than just help manufacturers produce rotary blades with high precision. For years now, they have become indispensable members of teams that position the generators, gear boxes, shafts and couplings of wind turbines. Tower manufacturers also use state-of-the-art, laser-supported measuring systems to verify the smoothness of flanges used in tower segments. Because these steel structures can be up to six meters in diameter, the laser measurement job is performed in segments before software is called on to combine the results and produce an overall conclusion. By contrast, laser processes can be used to measure smaller rotary blade flanges in one step. The fundamental aim is: The wind industry can use the precise optical measurements to minimize the risk of manufacturing errors, increased wear and tear and yield-lowering vibrations.

LiDAR technology assists yield analysis and the search for locations

Before the planning of a wind farm takes concrete shape, operators analyze local wind conditions as precisely as possible. Measurement towers used to be the gold standard. Today, however, flexible and less costly LiDAR systems are being employed. Unlike masts, these systems do not require a building permit to be erected. These systems are set up on the ground or on buoys at sea and measure wind speeds, wind direction and turbulence by shooting laser beams into the sky. The light hits particles in the wind and is reflected. These reflections can be used to precisely determine wind conditions at various heights. Even when masts are used, LiDAR technology is still called on to measure higher atmospheric layers. This technology also has one other strength: For months at a time, it can track the movements and exact attitudes of birds at a planned location to determine whether the site is used as a migration route.

The use of lasers does not stop once a wind farm has been erected. LiDAR measurements are used as the basis of detailed analysis of the aerodynamic effects produced during wind turbine operations. This analysis is used to optimize the distance between individual wind turbines and their positions with the aim of producing maximum yields and the lowest amount of turbulence possible in the future. Laser systems also monitor the vibrations created by the rotors, towers and turbines during operations by showering them with beams from a long distance. Camera systems capture the projected laser points on the structures and generate precise vibration analysis based on the motions. The technology is particularly interesting for offshore operations. At sea, operators have also begun to use hyperspectral camera systems to inspect the underwater portions of wind farms. In the past, it has been difficult for inspectors to distinguish corrosion from algae and other vegetation that form on the units. With the help of contactless hyperspectral methods, they are always up to date.

Photonics fuels progress in photovoltaics

The contribution that photonics is making to energy change is not just limited to wind power. In photovoltaics—a technology that is essentially photonic—laser and optic technologies continue to power progress. Lasers structure, cut, insulate, dope, solder and drill solar cells. Imaging systems facilitate fully automated, error-free manufacturing. The makers of state-of-the-art organic thin-film solar cells use ultrashort pulse (USP) lasers to do the delicate, µm-precise structuring of the active layers of their solar film. USP systems also help boost the efficiency of conventional silicon cells. With the aim of achieving the maximum absorption of sunlight, they create the finest structures on the cells’ surfaces.

No matter whether it is used to add nano- or micro-level structuring or to facilitate the quality-assured production of rotary blades that extend for more than 100 meters and steel towers that weigh several tons: Photonics frequently makes important, but overlooked contributions to the increased efficiency of renewable energy—and thus to the success of energy change.

Incidentally, the English version of the study “Light as the key to global environmental sustainability” that was conducted by Messe München and the industrial trade association SPECTARIS in cooperation with the Fraunhofer Institute for Laser Technology and the Fraunhofer Group for Light & Surfaces can now be downloaded.

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