Beyond the horizon – enhancing UK offshore wind ambitions

Professor Seamus Garvey, at the University of Nottingham, UK, says refocusing on home-grown technology can propel the UK offshore wind market.

The UK has 10.4GW of offshore wind turbines installed – more than any other country. The government committed recently to reaching 40GW by 2030. With so-called capacity factors around 50%, this fleet will deliver ~175TWh of electrical energy in 2030 – ~50% of current annual electricity consumption. The UK truly is the leading customer for offshore wind farms globally.

The UK does less well as a supplier. After Great Britain, the three countries with most offshore wind are Germany, China and Denmark. Unlike the UK, each of those countries hosts one or more major wind turbine manufacturers supplying into its own market.

Published in early 2019, the government’s Offshore Wind Sector Deal aspires to achieve 60% of UK content in wind farm lifetimes and has encouraged the sector to establish the Offshore Wind Growth Partnership to support this.

The direction is good, but the aspiration could, and should be, higher. To appreciate market size, think about each 1GW of installed capacity costing ~£2bln. The combination of unequalled engineering heritage and singular offshore wind resource per-capita should drive an expectation that the UK would become a significant exporter of offshore wind technology, in addition to serving high proportions of its own requirements.

The UK is unlikely to grow its own manufacturer of offshore wind turbines now. The global industry is consolidating towards fewer, larger manufacturers. As examples, take Siemens Gamesa Renewable Energy, Mitsubishi Vestas Offshore Wind and GE’s purchase of the Alstom wind turbine business. However, the industry continues to evolve strongly and, where there is evolution, there is opportunity.

In the UK, offshore wind projects are supported by commitments from the government called Contracts for Difference (CfDs). Under the CfDs, the wind-farm operator effectively accepts a constant strike-price for each MWh of energy generated. The lowest CfD strike prices agreed in the 2015, 2017 and 2019 auction rounds were 114.40, 57.50 and 39.65 (£/MWh), respectively. This strong cost reduction drives towards exploiting more offshore wind resource and this, in turn, presents two very interesting and important opportunities.

Firstly, as any country achieves high penetrations of wind power, reconciling electricity supply with demand will become a major technical challenge. The Offshore Wind Industry Council formed a taskforce in May 2019 to consider this and its report, Offshore wind and hydrogen: Solving the integration challenge, was published in October 2020. It recommends primarily that electrolysis be used to absorb electricity when wind generation exceeds demand, and that electricity is re-generated from hydrogen when wind-power resource falls below demand. Batteries are indicated to have a small role for short-term flexibility.

The report is right to suggest that hydrogen will play an important role in future zero-carbon energy systems, but quite wrong to imply that hydrogen should dominate the provision of flexibility for high penetrations of wind. Hydrogen is very suitable for storing energy over very long periods, for direct use in powering HGVs or trains and for manufacturing ammonia and steel.

In a March 2020 event, entitled Medium-Duration Energy Storage, it was shown that in a largely renewables-powered UK, in which energy storage provided all of the flexibility, approximately 92% of the energy passed through storage would have continuous charge/discharge periods in the range 4–200hrs. These time periods are too long for batteries. Two arguments militate against using hydrogen for electricity storage over these relatively short durations: (1) the power requirements would lead to high marginal costs and (2) the turnaround efficiencies (<40%) are unacceptably wasteful.

Thermo-mechanical energy storage technologies, like compressed-air, liquid-air, pumped-thermal and pumped-hydro are perfect for this duty, but these have been neglected in energy policy until recently. There are some excellent opportunities for integrating such storage energy approaches directly with wind turbines, and this is one broad area where the UK has potential to excel and ultimately export. The present structure of the CfDs strongly impedes the commercial development of these technologies by forcing, in effect, a flat return for each MWh of electrical energy generated from wind turbines. Although the CfD system served well to initiate the introduction of low-carbon generation, this system needs comprehensive revision now.

A second area of major promise for the UK lies in floating platforms for offshore wind turbines. There are presently three, fully mature, floating platform designs – all foreign. Other designs of equal, or higher, suitability to UK waters are possible.

Thus far, floating offshore wind platform designs have emulated onshore wind turbines – using a tall slender tower to support the nacelle via a yaw bearing. Significant economies are possible for floating wind by having platforms that are fully three-dimensional spaceframes right up to the nacelle and turning the entire platform over the water to orient the turbine axis into the wind. These body-yawing semi-submersible (BYSS) platforms always experience the downwind thrust force in the same direction relative to the structure, and this accounts for a major reduction in how much material is required for the platform.

In the offshore oil and gas industry, floating platforms were resisted as long as possible, but once the industry began to embrace them of necessity, the entire philosophy changed. Where originally floating platforms were regarded as an expensive but unavoidable necessity where water depths were too great for fixed-foundation arrangements, they became the preferred choice wherever the water was deep enough. When BYSS platforms begin to take hold, the same transformation may happen for offshore wind.

The UK already has high ambitions for offshore wind if we consider only the planned expansions in installed capacity. Our ambitions should reach further towards developing technologies both to serve our own captive market and to export globally.