a b s t r a c tOcean energy has the potential to play a significant role in the future energy system, whilst contributing to the reduction of carbon emissions and stimulating economic growth in coastal and remote areas. Ocean energy has attracted increasing interest, particularly in the EU, which is currently at the forefront of ocean energy development.Tidal and Wave energy represents the two most advance types of ocean energy technologies. In the EU, the aim is to reach 100 GW of combined wave and tidal capacity installed by 2050. In order to achieve these targets the sector needs to overcome a series of challenges and barriers with regards to technology readiness, financing and market establishment, administrative and environmental issues and the availability of grid connections especially in remote areas. Currently these barriers are hindering the sector's progress; its ability to attract inwards investments and to engage with the supply chain to unlock cost-reduction mechanisms. A number of policy initiatives and mechanisms have been put in place to ensure that ocean energy technologies could become cost-competitive in the short term, in order to exploit the benefits that these technologies could provide to the EU.

No abstract

The SET-Plan declaration of intent for ocean energy has set ambitious targets for wave and tidal energy technologies. Tidal technologies are expected to reach a levelised cost of energy (LCOE) of 15 cEUR/kWh by 2025. To meet this target, technology costs need to be reduced by about 75 % from 2016 values. Cost-reduction of tidal technologies is expected to go hand in hand with technology deployment and further technology validation gained by the operation of first-of-a-kind tidal farms. In this paper we assess the learning investment needed to support the cost-reduction of tidal energy to meet the 2025 SET-Plan targets. The learning investment necessary to bring tidal energy to cost-competitiveness would be of about EUR 1.45 billion, requiring about 3.2 GW of installed capacity to achieve the LCOE target of 15 cEUR/kWh. Supporting the step growth for the sector requires the design of accompanying policies aimed at the industrialisation of the sector to support the creation of assembly and manufacturing facilities.

Consenting is still generally regarded as a non-technological barrier to the progress of the marine renewable energy industry, caused by the complexity of consenting processes and the lack of dedicated legal frameworks. Existing consenting systems for ocean energy projects tend to be based on procedures designed for other sectors and are seen as inappropriate for the specific needs of ocean energy. Licensing procedures are also viewed by developers as time-consuming because regulators see ocean energy as a new activity with unknown or uncertain effects and consequently often apply strong interpretation of the precautionary principle. Consenting processes for ocean energy are, nevertheless, evolving throughout Europe, driven by national and European policies and incentives on renewables, changing legal and administrative frameworks to facilitate development and more integrated marine governance. This review compares the consenting processes for ocean energy in different European countries, focusing on aspects thought to hamper operation of the process. It shows that different systems of governance across the EU Member States have resulted in diversity in the design of consenting processes, though common features can also be identified. This evidence-based review enables suggestions for streamlining consenting processes for wave energy.

Energy security for the EU is a priority of the European Commission. Although both blue and green water resources are increasingly scarce, the EU currently does not explicitly account for water resource use in its energy related policies. Here we quantify the freshwater resources required to produce the different energy sources in the EU, by means of the water footprint (WF) concept. We conduct the most geographically detailed consumptive WF assessment for the EU to date, based on the newest spatial databases of energy sources. We calculate that fossil fuels and nuclear energy are moderate water users (136-627 m 3 /terajoules (m 3 TJ -1 )). Of the renewable energy sources, wood, reservoir hydropower and first generation biofuels require large water amounts (9114-137 624 m 3 TJ -1 ). The most water efficient are solar, wind, geothermal and run-of-river hydropower (1-117 m 3 TJ -1 ). For the EU territory for the year 2015, our geographically detailed assessment results in a WF of energy production from domestic water resources of 198 km 3 , or 1068 litres per person per day. The WF of energy consumption is larger as the EU is to a high level dependent on imports for its energy supply, amounting to 242 km 3 per year, or 1301 litres per person per day. The WF of energy production within the 281 EU statistical NUTS-2 (Nomenclature of Territorial Units for Statistics) regions shows spatially heterogeneous values. Different energy sources produced and consumed in the EU contribute to and are produced under average annual and monthly blue water stress and green water scarcity. The amount of production under WS is especially high during summer months. Imported energy sources are also partly produced under WS, revealing risks to EU energy security due to externalisation. For the EU, to decarbonise and increase the share of renewables of its energy supply, it needs to formulate policies that take the water use of energy sources into account. In doing so, the spatial and temporal characteristics of water use and water stress should particularly be considered.