Utility Week

12 | 27TH SEPTEMBER - 3RD OCTOBER 2019 | UTILITY WEEK Policy & Regulation Analysis T his week saw another major milestone for the wind industry in the UK as the government released the results of the third contracts for di erence auction. Multi- ple projects secured agreements at the record low strike price of £39.65/MWh. In the - rst year of the contracts, the gov- ernment expects the wholesale capture price for intermittent generators to average £48.13/ MWh, meaning wind generators will likely hand back almost £10 to consumers for every megawatt-hour they produce over the 12 months. The argument that renewables are too expensive to form the backbone of the UK's energy system has now been - rmly put to bed. "Renewables are blowing the competi- tion out of the water," says Jonathan Mar- shall, head of analysis at the Energy and Climate Intelligence Unit. The costs of o shore wind – the dominant technology in the latest auction – have plum- meted over recent years. Strike prices have fallen by almost two-thirds since the - rst auction in 2015. More than anything else, this trend has been driven by increases in turbine size. But a government-commissioned report, pub- lished shortly before the results of the latest auction raises questions over how long this can continue. The study by DNV GL Energy explores, among other things, how turbine technol- ogy will evolve out to 2035. According to the report, in the mid-2000s the largest installed wind turbines were typically around 3-4MW and by 2015 had reached 6-8MW. The most powerful turbines currently available on the market have a capacity of 10MW. It predicts that two further generations of even larger wind turbines will hit the mar- ket by 2035, beginning with GE Renewable Energy's 12MW Haliade-X model, which is expected to be commercially available in 2021. But the report 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 signi- cant increases beyond this capacity are consid- ered unlikely." Diminishing returns Additional size increases will o er "dimin- ishing returns" in terms of reduced energy costs, which may be better achieved through mass production. These economies of scale erode as turbine size increases because fewer turbines are required to deliver a given amount of capacity. The cost of developing and testing a new design would also need to spread over a smaller number of machines. "This is com- pounded by the requirement for new testing facilities, as very large turbines may soon exceed the capacity of even the largest cur- rent test benches," the report adds. Furthermore, the components limiting turbine size will become increasingly impor- tant, "requiring more complex and more costly solutions, potentially undoing some of the cost reduction achieved by scale". However, Chong Ng, head of applied research at the O shore Renewable Energy Catapult, believes turbines will go much larger than 15MW. He says the main limit- ing factor at the moment is not turbine tech- nology, but the size and availability of the cranes needed to install them, which are "very, very expensive". "As long as the industry can sort out how to assemble the turbines e ectively on shore and ship it out… the size of the turbine can go further," Ng adds. The report suggests there may be dif- - culty in building gearboxes for turbines of greater than 15MW, but Ng does not see this as a problem because "anything above 10MW, I believe, will not have a gearbox". He says direct drive turbines have now become "mainstream" and account for most turbines with a capacity of more than 8MW. Even with the current technology, Ng thinks turbines could feasibly reach 20MW. Beyond that, he accepts that new materials will be needed to make the turbine blades light and strong enough. As the report notes, the weight of a turbine blade is proportional to the cube of its length, meaning at a certain point it is no longer able to support itself. But Ng expects new materials will be developed, not least because they will also be required by other industries for di erent applications. He also sees an incentive to overcome the challenges of going bigger. The turbines themselves typically account for a minority of the lifetime costs of an o shore windfarm. The majority goes towards installation (12-15 per cent) and operations and maintenance (45 per cent). "That's a huge amount of money," Ng says. Fewer turbines mean fewer installations with fewer cranes. It also means fewer peo- ple getting on fewer ships to perform mainte- nance less frequently. For similar reasons, Ng believes ¨ oat- ing o shore windfarms, assembled in dry docks before being towed out and anchored to the sea bed, will eventually become cost- competitive: "The prediction is by 2050, the costs of ¨ oating wind will be similar to - xed- foundation wind." The report from DNV GL Energy is less optimistic about the prospects for ¨ oating windfarms in the UK. Although such wind- farms allow developers to take advantage of better winds in deeper waters, the report argues that this may be of limited value in the UK, which already has access to plenty of shallow water in the North Sea. It also points out that the additional costs of the "large, heavy" foundations may outweigh any ben- e- ts in terms of higher load factors. Despite their di erences, the authors of the report and Ng agree there are still many avenues to explore in terms of cutting cost. One day o shore wind will become a fully mature technology in its optimum form, but we are still some way from reaching that stage. Off shore wind: How big is too big? The past two decades have seen big leaps in the size and capacity of off shore wind turbines, but a new report warns that such increases are unsustainable. By Tom Grimwood.

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