The order for 171 of Siemens' upgraded 7MW direct-drive offshore wind turbines is, however, still "subject to contract signing and to the final investment decision by the customer", Siemens said in a statement.
The wind park off the east coast of England will have a total capacity of 1.197GW, Siemens added.
Hornsea 1 is one of the UK's blockbuster Round 3 offshore wind projects, and was awarded support by the country's government in April last year under its new contracts-for-difference (CfD) support mechanism.