The order, which previously had only preferred-supplier status, includes a five-year service contract.
The turbines have been optimised with a power mode to be able to deliver a maximum output of 8.3MW.
"Larger and more powerful wind turbines are a key driver of cost reduction. The use of an 8.3MW power mode with the large 164-metre rotor diameter provides an optimised rotor to generator ratio, demonstrating our ongoing focus on improving our technology, continuing to maximise value for our customers," said MHI Vestas chief executive Jens Tommerup.
