The growth in turbine size that has driven huge reductions in the cost of wind power is expected to plateau once they hit 15MW, according to a new report commissioned by the Department for Business, Energy and Industrial Strategy (BEIS).
The study says the engineering challenges posed, the price of solving them and the cost-savings that can be achieved by mass producing larger numbers of smaller turbines will make it less attractive to go even larger.
The report, undertaken by DNV GL Energy, explores the likely changes to offshore wind load factors and costs out to 2035.
The largest wind turbines were typically around 3-4MW in the mid-2000s and by 2015 had reached 6-8MW. The most powerful currently on the market has a capacity of 10MW and will ready for delivery in 2021.
The report predicts that two further generations of even larger wind turbines will hit the market by 2035, with GE Renewable Energy’s 12MW Haliade-X model heralding the arrival of the first cohort.
But it adds: “It is expected that increases in turbine size will begin to slow, such that turbines of up to perhaps 15MW are expected by 2035 but that significant increases beyond this capacity are considered unlikely.”
Additional size increases will offer “diminishing returns” in terms of reduced energy costs, which may be better achieved through mass production. These economies of scale lower with turbine size as fewer are required to deliver a given amount of capacity.
The cost of developing and testing new designs would also need to spread over a fewer number of machines. “This is compounded by the requirement for new testing facilities, as very large turbines may soon exceed the capacity of even the largest current test benches,” the report adds.
Furthermore, the key components limiting turbine size will become increasingly important, “requiring more complex and more costly solutions, potentially undoing some of the cost reduction achieved by scale”.
The report cites the example of a gearbox, which it says would be difficult to economically engineer for a turbine with a capacity of more than 15MW, “particularly given that as rotor diameter increases, rotational speed decreases and therefore the torque in the drivetrain increases significantly.”
The results of the latest Contracts for Difference auction, which is expected to be dominated by offshore wind, are due to be published on Friday (20 September).