## 9 Economic Viability  
According to the results that have been obtained from the multicriteria analysis, it would be acceptable to choose Norte in OWC as the most profitable solution based on three aspects: technical, economic and environmental points of view.  
Based on this, it might seem that this civil work will generate an environmental benefit of great magnitude, which will also be accompanied by an additional economic wealth at the time of selling the generated energy. However, one of the main problems that is presented in this project is that the works need initial investment to be carried out. If this initial investment is amortized by generating benefits during its useful life, it will be profitable. This is something that does not happen in all cases.  
The economical approach will have the following characteristics:  
* It will require an initial investment for its construction.
* It will demand for periodical maintenance and conservation costs/expenses for its maintenance and conservation.
* It will produce benefits from the sale of energy.  
Once the three previous variables are known, it can be determined whether the construction project is profitable or not, based on the common profitability indicators, such as the net present value (NPV), the internal rate of return (IRR), the return period on investment (payback), the ratio cost-benefit or the ratio benefit-cost-investment (BCI).  
Considering an investment of 16 million of euros (see Table 3) and periodic costs for maintenance around a 3% of the material execution budget (common value for the maintenance of this type of infrastructures like the existing Mutriku Dike), these are considered as the costs of the project. For the benefits, if the current sale price of electricity is 0.15 \(\upxi\)/kWh in the Spanish electricity market and the net production of the facility has been estimated in 1,726,971 kWh/year, the incomes will be valorated in 295,045.65 \(\upxi\)/year.  
After the appropriate calculations, the results show that this facility would not be profitable nowadays, as the NPV is valued in less than 10 million of euros, the IRR is negative, the payback would be 500 years, the ratio cost-benefit is less than one unit and the BCI is estimated to be 0.12.  
To sum up, it would be necessary to produce at least more than one million euros in the sale of energy to make these indicators favorable for the project. More than an order of magnitude improvement in cost of energy [39] will be needed to implement this technology. This increase could be possible if the length of the facility had been longer or the development of the OWC devices had not been yet in its infancy to harness the great potential of the sea. In addition, a solution of hybrid wind-wave systems is being developed, which are innovative solutions to combine the sustainable exploitation of multiple marine resources. The idea is to develop a hybrid system for monopile substructures, which are currently the prevailing type of substructure for offshore wind turbines, and more specifically to focus on the wave energy converter sub-system, which consists in an oscillating water column. [40]. This could lead to an economical solution and increase the energy sales. It also offers other advantages, as it occupies less space and makes a minor impact on the environment.