H Nordic maritime turbines cut in at 2 m/s -- a speed below which most people would barely notice a breeze. At anchor or in port, generation depends entirely on the local wind speed at that moment. Underway, the combination of vessel forward motion and the venturi effect means conditions above cut-in speed are present for virtually the entire passage.
At anchor, the vessel is stationary. There is no forward motion to contribute apparent wind, and no vessel speed to drive the venturi effect. The turbines see only the ambient wind at the anchorage.
H Nordic turbines cut in at 2 m/s. The Beaufort scale classifies 2 m/s as a light air -- a condition where smoke drifts but a wind vane barely moves. Generation begins in conditions that would leave most conventional turbines idle.
Whether a specific anchorage produces useful generation depends on its exposure. Open roadsteads, exposed coastal anchorages, and locations with reliable sea breeze patterns will produce meaningful output. Sheltered harbour anchorages and river berths may produce very little.
For most commercial vessels, however, the anchorage contribution is not where the economics are made. Fuel savings are built during the 6,500 or more operating hours per year the vessel is underway -- not at anchor.
In port, generation again depends on local wind conditions. Port environments vary widely -- some exposed berths with prevailing winds produce useful output; sheltered inner docks with little airflow produce almost none.
H Nordic turbines are not designed or sized around port generation. Port time is also typically when scheduled maintenance occurs, and the battery storage -- 215 kWh for the 50 kW model, 430 kWh for the 100 kW model -- provides a useful buffer across periods of low generation.
Underway, the picture is fundamentally different. Two effects combine to ensure conditions well above cut-in speed are present for almost all of a vessel's sea passage:
Apparent wind from forward motion. A vessel cruising at 10 knots (approximately 5.1 m/s) generates 5 m/s of apparent wind from its own forward speed in completely calm conditions. On a typical commercial passage, the vessel is rarely in truly calm conditions -- but even if it were, forward motion alone keeps wind speed above the 2 m/s cut-in threshold.
The venturi effect. As the vessel moves through the air, its hull and superstructure compress and accelerate the airflow passing over the deck. At 3 m/s ambient wind -- a light breeze -- effective airflow at turbine positions reaches 9 m/s or more depending on vessel geometry. The venturi effect and forward motion are additive.
The practical result is that on a commercial vessel with 6,500 operating hours per year, turbines are generating for the vast majority of sea time. The exceptions -- rare periods of negligible wind in very low-speed coastal manoeuvring -- are short and infrequent.
Conventional grid-connected wind systems require a minimum wind speed before the inverter logic will synchronise with the grid. This effective minimum -- sometimes 3 to 4 m/s -- is higher than the turbine's physical cut-in speed, and means generation is lost in the light-wind range.
H Nordic's DC-direct architecture eliminates this constraint. Power routes from the DC generator through a DC/DC converter directly to the integrated battery, with no grid synchronisation requirement. Generation begins at 2 m/s and every unit of energy produced is captured in the battery immediately.
On a vessel where apparent wind from forward motion is frequently 3 to 5 m/s even in calm ambient conditions, this architecture captures generation that a grid-synchronised system would leave on the table.
See also: How the venturi effect works on vessels · Fuel savings methodology
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