The exploitation of ocean energy is lagging behind other renewables such as solar and wind, but as costs decline it has the potential to contribute significantly to the global energy mix.
With an estimated potential in the range 20,000TWh to 80,000TWh, corresponding to 100% to 400% of current global demand, the resource is more than sufficient to meet projected demand well into the future, according to the International Renewable Energy Agency (IRENA) in a recent study.
Ocean energy resources
Ocean energies encompass ocean surface waves, tidal currents, tidal range, deep ocean currents, thermal gradients and changes in salinity. These require a diversity of technologies, with each distinctive in terms of technical design, operation and commercial maturity.
Currently the levelized costs of ocean energy technologies are substantially higher than those of other renewable energy technologies. Thus for most, the main challenge is to reduce the costs, along with improving the reliability and performance of systems.
While the long-term pathway to cost reduction is difficult to predict, due to limited available empirical cost data and wide variability in project cost strategies, commercial maturity is expected from the 2020s onwards. Up to then the cumulative installed capacity is expected to amount to only a few hundreds of megawatts. Deployment rates of ocean energy technologies to date have been slower than expected, and the lack of technical maturity can be attributed largely to challenges of working in an offshore environment. However, as has occurred with other renewable energy technologies, such cost reduction depends largely on deployment, investment, learning and innovation rather than just on time.
Ocean energy technologies
There is substantial activity on ocean energy across the globe, with the UK, France, USA, Canada, Japan, South Korea and Australia being some of the hotspots of activity.
The technologies of greatest medium-term relevance are tidal stream and wave energy converters, with full-scale prototype development of both types under way. [Engerati-First Grid-Connected Wave Energy Array Operates In Australia] With the exception of tidal range, these are also the most advanced ocean energy technologies available. While tidal range is a mature technology, with a proven track record stretching back to the 1960s, the very limited site availability, high capital investment and potentially significant ecological impacts have previously ruled this out for large scale utility projects in all but a couple of locations.
The other ocean energy technologies may become increasingly relevant over longer time horizons. However, so far there are few deep ocean current or salinity gradient projects, for example.
Overcoming barriers to ocean energy
IRENA makes more than 20 recommendations aimed to address the technical, economic, environmental, social and infrastructural hurdles to enable ocean energy to fulfill its potential.
• Technical challenges relate to the resource, device and array configuration. Addressing technical barriers should be a priority for ocean thermal energy conversion (OTEC), salinity gradient and ocean current technologies, since these are the least technically mature of the technologies. Although approaching commercial deployment, wave and tidal stream technologies also have a number of technical challenges to overcome before commercialization is realized.
• From an economic perspective policy makers and utilities are often under pressure to adopt least-cost and least-risk decarbonization technologies. Therefore, the next step, once technical concepts have been proven, is to reduce the cost and risk profile of the ocean energy technologies when compared with other renewable energy technologies in the market. The most significant barrier at present is the comparatively high cost of energy produced by ocean energy technologies relative to other renewables.
• The environmental/social burden on device developers at the prototype stage tends to be minimized by test centres through centralized studies and testing. However, once developers reach transition to commercial-scale deployment, environmental and social issues can come to the fore – particularly for tidal range systems.
• The infrastructural challenges for ocean energy technologies are twofold, relating to grid issues and the supply chain.
Above all, policy makers need to apply different approaches to ocean energy technologies, IRENA recommends. Given the diversity of ocean energy technologies, informed policy makers will examine their local resource, understand the technical maturity of each technology, and then tailor their ocean energy technology strategy accordingly. It will be the resulting policies targeted at selected ocean energy technologies that deliver their deployment success. A ‘one size fits all’ approach is unlikely to be ideal.