2.3.2. OPEX

The OPEX relates to all expenditures associated with the operation of a WEC farm from the moment a takeover certificate is issued, including the cost of all operation and maintenance (O&M) activities as well as the cost associated to site leasing and insurance. Table 1 summarises the cost breakdown for the OPEX obtained from the literature review presented in [26]. The main two cost centres are the site lease and insurance, accounting for 6% of the OPEX, and the O&M, accounting for the remaining part of OPEX.

**Table 1.** OPEX breakdown of costs.


For a wave energy farm for which data is scarce, the annual OPEX can be estimated as a percentage of the CAPEX. As shown in the literature, estimates of the total OPEX per year roughly range from 1.5% to 9% of the CAPEX [29,33,48,49]. This is due to different factors (e.g., single prototype or utility-scale project, distance to shore, floating or submerged WEC, innovative or traditional O&M techniques applied, etc). For example, the OPERA project [25] has shown that when specific innovative O&M techniques are applied, the OPEX can be as low as 1.8% to 2.2% of the CAPEX, depending on the deployment location and size of the array. If a utility-scale project is considered, then the experience from the offshore wind energy sector (with the annual OPEX as 4.5% of the CAPEX [6] and the annual OPEX as 3% of the CAPEX [50] ) can be used.
