Research conducted by DNV GL on behalf of the Department for Business, Energy & Industrial Strategy (BEIS) suggests there is significant potential to increase the load factors of offshore windfarms in the UK
Load factor is the ratio of the amount of electricity produced by a windfarm to its total potential, based on nameplate capacity, over a set period of time (usually one year, to account for seasonal variability in output).
It is the product of availability (itself a result of the availabilities of the turbines, balance of plant and grid), system efficiency (such as the energy lost in cables), and wind capture, which is dependent on the wind speed, turbine capacity and rotor diameter, and wake efficiency of the windfarm. ‘Load factor’ is also referred to as ‘capacity factor’ and the terms are considered interchangeable.
BEIS commissioned DNV GL to examine long-term offshore wind load factor assumptions used in its modelling. The purpose of the research was to obtain a better understanding of ‘technological learning rates’ of offshore wind. This will enable better predictions of the long-term energy production potential and load factor of UK offshore windfarms. The study also assessed the levelised cost of new offshore wind technologies, considering the continued industry drive to reduce costs.
DNV GL reported that, based on an analysis of current operational offshore windfarms and on publicly available information, load factors ranging from 39% to 47% have been identified. The main conclusion from the study was that project load factors can be expected to increase to more than 50% in the period to 2035, primarily due to the deployment of larger and more efficient turbines and improved project design and operation. The industry also expects cost of energy to continue to fall in this period, albeit at a lower rate than has occurred to date.
“Overall, the industry expects that evolution of existing technologies will dominate in the UK market, over potential disruptive technologies,” said DNV GL, noting that, in addition to deploying the next generation of larger offshore wind turbines, improvements in load factor are expected to result from advanced windfarm design and control; and the combination of increased hub height and reduced wake losses result in increased energy production and therefore higher load factor.
“The magnitude of each individual improvement is relatively small, in low single-digit percentage points, but the aggregate impact will be more significant,” said DNV GL, noting that these improvements are expected in the next generation of windfarms, which will enter operation in the mid-2020s.
DNV GL also noted that existing offshore windfarms are already starting to revise operations and maintenance strategies to take advantage of new technology, and future projects are expected to learn from these improvements to achieve higher availability from entry into service. Improvements in availability are estimated to add up to two percentage points to load factor.
The research reviewed current technology and assessment of representative UK offshore wind load factor; identified future offshore wind technology with the potential for commercial deployment in the period to 2035; assessed the potential impact on load factor and cost of each technology, through comprehensive modelling of a hypothetical offshore windfarm; and contains a survey of industry stakeholders, providing industry opinion on future technologies and validation of the modelling results. It also assessed the potential for transfer of the identified technologies to the onshore wind industry and estimates the effect of technological development on load factors of UK offshore windfarms in the period to 2035.
The authors of the report said there are also several more radical technologies proposed for offshore wind, that are in earlier stages of technological and commercial development: these include two-bladed turbines, alternative turbine technologies such as vertical axis turbines, and floating foundations. These are not expected to gain a significant foothold in the UK offshore wind market in the timeframe of this study, which is to 2035, due to both the extent of technical development required and the inherent competition with incumbent technologies.