Wind Energy Debate

Offshore and Onshore Wind Energy

There is no real argument against the fact that wind energy is now a successful form of renewable energy generation. Large onshore and offshore wind turbines are now commonplace and wind energy provided almost 12% of Europe's energy demands in 2017 (Wind Power in 2017 - Wind Europe).

The latest round of Contract for Difference (CfD) auctions saw offshore wind farms to be installed in 2022/3 bidding at £57.50/MWh, which is seriously cost competitive with fossil fuels and substantially less than the agreed £92.50/MWh for Hinkley C (Nuclear). It was just a few years ago that developers were scratching their heads and struggling to get below £150/MWh and really thought that wouldn't be possible. What changed?

Well the turbines still look broadly the same, so actually most of the savings occurred elsewhere. Yes, the turbines have got larger, in a bid to extract more power out of a single foundation and developments in blade structures, aeroelastic modelling and control algorithms have facilitated this, but the major gains have actually been elsewhere. There is not one distinctive factor standing out on its own, but a combination of many little improvements to operational and commercial aspects. One key aspect offshore was the development of an understanding of the installation process. In the early days the thought was "take a wind turbine and put it offshore" or "just another offshore installation", but over time those installing turbines have come to understand that it is really neither of those things and its own bespoke installation. A better understanding of foundation & cable installation as well as cable laying has led to better commercial arrangements and risk sharing to reduce the costs of these offshore operations. For all wind turbines the increase in number and proving of reliability has helped reduce the perceived risk for investors and resulted in better rates for capital investment and more competition for investment. Looking at all these factors is an essay in itself, so I will stop there having merely scratched the surface.

With more and more wind turbines being installed offshore, is there a shift in the industry direction? What potential does this open up for turbine developers?

 

There is around 12GW of onshore wind capacity in the UK, compared to approximately 6GW offshore (Source: Everoze LEAF). However, when you look at the future consented projects there is ~12GW offshore compared to only ~4GW onshore (Source: Renewable UK), so by the mid-2020s we will start to see more offshore wind turbines than onshore.

Offshore turbine installations are obviously associated with a greater capital cost, with an offshore foundation requiring fabrication and installation as well as sub-sea cable laying. The added costs are reflected in the material usage, take copper for example an onshore turbine uses 5.3t/MW while that value is 15.3t/MW offshore. These cost penalties are more than offset by the low turbulence resource and ability to install larger and larger turbines without serious consenting issues, in tandem with the cost reductions we have already discussed.

Onshore wind has also seen some of the benefits realised by offshore wind - blade technology development, control logic improvements, installation cost reductions, enhanced confidence, better risk sharing etc. However, the more challenging site modelling (due to topographical effects), enhanced turbulence (compared to offshore) and consenting challenges (no-one seems to want one in their back yard), mean that it is just so much easier to design for offshore and achieve roughly the same cost of energy.

Onshore Wind
Offshore Wind Turbine

With the reduced noise restrictions and lower turbulence there is potential for further engineering development of turbines offshore. To date, improvements in material understanding for composite blades and advanced control software has allowed turbines to become larger, but there is even more potential that is, as yet, untapped.

Typical permanent magnet generator systems used in wind turbines operate more efficiently at higher rotational speeds than that of the wind turbine rotor, therefore often a gearbox is used. Developments in technology have facilitated the use of some direct-drive devices, but the size of these generators needs to be large to facilitate efficient generation; making the nacelle larger in the process. Most onshore turbines are limited in rotational speed, due to these noise requirements. However, if the noise restrictions offshore are lower, that opens up the potential to have the turbine rotate faster.  To spin the rotor  faster, a move toward two bladed turbines could occur, again, facilitating even faster rotor speeds and therefore smaller direct drive generators. Moreover, two blades are (somewhat obviously) cheaper than three blades and you have removed a gearbox system which has a cost and reliability implications.

If you thought wind energy had already achieved some impressive cost reductions, we believe there are further cost reductions out there in the potential engineering advantages of operating offshore - watch out for these advances in the near future!

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