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Offshore wind – big but less than hoped?

A new study from the LUT University energy team in Finland assesses offshore wind power's techno-economic potential through hourly simulations & cost calculations, considering three different turbine spacings.  The results indicate ‘increasing economic potential at various cost thresholds, driven by declining floating turbine cost’, with regional variations depending on ‘water depth and distance to high-wind resources’.  However, turbine spacing in arrays is all important: ‘sparse installation density yields higher economic potential under 30 €/MWh due to reduced wake losses’.

Wake interactions have recently become an important concern, since they reduce the amount of energy that can be captured by large wind arrays and tall turbines, with research  under way on this in the UK, and elsewhere.  For example, a Belgian study claims that one in five offshore wind farms in the North Sea could suffer from energy losses of 10% or more, in some cases up to 18%, over the next five years as a result of ‘wake shadows.’ 

The effects can certainly be quite significant, although it evidently depends on the location. For example, a detailed study by Orsted of wind farm sites in the Irish sea puts the energy losses at between 0.16% and 5.3%. But it’s not a trivial thing, with the wind wake caused by wind turbines sometimes stretching for more than 100km behind the turbines though more usually 10 km. So wind wake losses and accidental or planned so called ‘wind theft’ issues, are becoming quite significant in defining wind farm location and array layout.  

The losses can obviously be reduced by wider turbine spacing, although that also reduces the total energy-take per unit of area. Other ideas that have been mooted include the novel one of running some of the turbines anti-clockwise - they are usually (and it seems arbitrarily) run clockwise looking from the front. 

The LUT study adopts a quite conservative 25% limit to the available area ‘to allow for wind farm wake recovery and to account for other miscellaneous uses and obstacles, including undersea cables, fisheries, military zones, and recreational areas’, and then looks at the resultant capacity of wind plant that might be operated globally and its likely cost.  Overall it estimates that there is up to ‘27.3 TW of installable capacity within 370 km of shore, in waters less than 1000 m deep, with 25% area utilisation and 66,200 TWh of electricity generation potential.’  Although this is significantly lower than a previous study with similar spatial limitations, which put the potential at 85.6TW, and others without the 25% limit,  LUT say that ‘this potential would be sufficient to fulfil the electricity demand of mid-2020s even if all energy sectors were to be electrified.’ 

However, that’s the maximum ‘technical capacity’, and doesn’t take costs into account. For example, LUT notes that ‘grid costs grow rapidly beyond 200 km’ out from shore, and that, although the highest technical capacity is achieved with tight wind turbine spacing, ‘spacing the turbines farther apart decreases the wake losses and increases the full load hours of a farm, thus decreasing the cost and increasing the economic potential under certain thresholds’. Specifically, it says ‘spacing with 8 rotor diameters shows the highest economic potential below 100 €/MWh, whereas 11 diameters show the highest potential below 50 €/MWh with 4750 TWh, and 17 diameters delivers the most electricity below 40 €/MWh with 300 TWh’.

So there are trade-off between spacings, costs and outputs, and although LUT does assume that cost can be below a €100/MWh competitive bench mark, it puts the economic potential much lower than the technical potential.  And it adds that ‘no configuration shows potential under 20 €/MWh, limiting offshore wind power's competitiveness with onshore renewables’. But it notes that the value to energy systems may be higher if there is smoother power output & proximity to coastal demand centres. Though otherwise, onshore wind, with its lower capital cost, is likely to have the edge in some locations. 

Nevertheless, LUT say that floating wind systems may become economically viable for sites previously unsuitable for bottom-fixed installations, if cost projections hold true. And they also have lower eco- impacts. ‘Away from wind obstructing land masses, with minimal surface roughness, floating turbines have access to stronger winds, potentially yielding high and consistent power output. Below 50 €/MWh, floating turbines represent 60% of the total potential, but the potential under 40 €/MWh is still dominated by bottom-fixed turbines.’

The bottom line is that offshore wind is doing well with costs falling, but, despite recent costs rises, onshore wind is doing better in LCOE terms, actually besting PV solar of late. So offshore is still quite costly, compared to solar PV and on shore wind, which they say ‘already deliver electricity below 40 €/MWh in solar PV based power purchase agreements and below 25 €/MWh for lowest cost tenders across various countries’. And it is not suited everywhere.  LUT warns that, their results imply that ‘offshore wind power is not a viable option for certain regions, as higher and more consistent offshore winds may be outweighed by the costs arising from complexities in grid connections and deep-water installations.’

Even so it says ‘offshore wind power can play a crucial role in regions with limited land availability, such as islands or coastal areas with high electricity demand, where access to inland low-cost renewable electricity incurs high transmission costs’, for example Belgium, Netherlands, the UK, People's Republic of China, Taiwan, Republic of Korea, Japan, and the USA. It says they ‘can already access offshore wind power below 100 €/MWh, due to good wind resources and shallow waters’ and, it concludes ‘the same regions can expect to tap into offshore wind power below 50 €/MWh by 2050’. 

Interestingly, the UK and Ireland come out looking like winners (606TWh at below 50€/MWh), while New Zealand does even better (914TWh), the highest economic potential in 2050 assuming spacing of 8 rotor diameters. The US only has 16 TWh of potential, unless installed farther apart, which increases the potential to 26 TWh. The low-cost potential in China is limited to 73 TWh, but with 2770 TWh below 100 €/MWh.  And finally, LUT says that the islanded nations of Japan, South Korea, and Taiwan can tap into 1580 TWh, 1000 TWh, and 470 TWh of offshore wind electricity below 100 €/MWh, respectively.

Lots to digest then, with some interesting implications- offshore wind may not always be a winner everywhere. Although it is still a very large resource. The full data is freely available on Zenido. There is also an AI generated podcast . Evidently the findings align with Jacobson & Archer’s earlier study: they estimated wind potentials based on kinetic energy, although without the same spatial limitations.


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