Hybrid systems |
Adaptive mooring advances hybridisation
A novel automatic winch-equipped buoy from Fred. Olsen 1848 is enabling floating solar arrays to ride water-level swings in reservoirs and dams. Principal Development Engineer Even Hjetland and Chief Technical Officer Geir Grimsrud explain how the technology works and the challenges it solves
IN THE CONTEXT OF hydropower reservoirs and large-head dams, where water levels may fluctuate by several metres within hours or seasons, conventional fixed-mooring solutions for floating photovoltaic (FPV) arrays often struggle to maintain ideal tension, leading to stress on moorings, increased maintenance and reduced operational reliability. Enter the Tension Buoy from Fred. Olsen 1848 – a self-adjusting mooring buoy that integrates a motorised winch, depth-sensing and real-time tension monitoring to continuously adapt chain length and maintain consistent mooring tension. Designed specifically for variable-water-level environments such as reservoirs behind hydropower dams, the system promises to simplify hybrid solar- hydro deployments by ensuring steady anchoring through draw-down, refill and seasonal cycling. To explore how the system performs in real reservoir
environments, we spoke with the engineering team behind the Tension Buoy. Their insights shed light on the control architecture, load-management philosophy and practical considerations that make the technology suited to hydropower-scale fluctuations and hybrid- plant integration.
How does the Tension Buoy’s automatic winch system detect and respond to water-level changes in real time?
Below: Tension Buoy installed in Risør, Norway
Each buoy is individually equipped with a motorised winch, battery with solar charging and controller with wireless communication. As water level variations are slow, the winch is geared to suit a small motor and a correspondingly small battery.
The main task of the moorings is station keeping of the floating solar island. A GPS receiver located on the island routinely reports position to a centralised controller. In addition, a depth sounder monitors the water level at regular intervals and adjust the mooring lines accordingly to verify mooring line tensions are within expected range.
What are the design parameters for maximum and minimum water-level variation that the system can accommodate? Accommodating water-level variations is a matter of sizing the corresponding chain length. As variations grow, the weight of chain increases so the buoy size may have to be increased, but there are no maximum or minimum water-level variation limits for the buoy.
Can you elaborate on the load management design – how does the buoy ensure consistent mooring tension under varying hydrodynamic forces such as wind, waves, and current? The main objective of the mooring is to keep the FPV installation inside its position envelope, which it does by all tensioning buoys working on a collective centralised algorithm. However, monitoring of mooring line tension is also a key feature of the Tension Buoy product, as it will be affected not only by the instantaneous depth, but also by wind, waves and currents. To facilitate this, a load cell is fitted between the winch and the buoy, effectively reporting mooring line tension to the centralised controller.
18 | December 2025 |
www.waterpowermagazine.com
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