3.            IMPLICATIONS

3.1        Energy Efficiency Implications

Though intermittent, electrical output from wave energy is more predictable than wind power output, as sea states (waves) are inherently more predictable than wind. This is because waves, once created, continue to transmit energy for some time and distance––around 8 h is the typical period of certainty within which sea state can be predicted accurately. Moreover, tidal currents flow according to a predictable diurnal pattern.

Because of limited experience with the marine renewables, it is difficult to be certain how effective and economic they will be if developed to a mature stage. There is experience (albeit limited) with tidal barrages, but their failure to take off speaks for itself. A rough indication of the relative capacities (load factor: hours during a year in which the facility operates at nominal capacity divided by the total operating hours in a year – 8760 hr/yr) and unit costs of some offshore technologies are given in the table below. Several of these options are already competitive in the context of niche markets, such as island communities using conventional small-scale diesel generation, which typically can cost from $0.10 to as much as $0.50 per kWh.

Current status of marine renewable energy technologies

Technology	Maturity	Load factor (%)	Installed capital cost ($/kW)	Unit cost of electricity ($/kWh)
Tidal barrage	Virtually abandoned	20-30	1,700-2,500	0.08-0.15
Wave-shoreline OWC	Experimental	20-30	2,000-3,000	0.10-0.20
Wave-near shoreline OWC	Commercial 2002-05	25-35	1,500-2,500	0.08-0.15
Wave offshore – Point absorber	Commercial 2010 or later	30-60	2,500-3,000	0.06-0.15
Tidal current turbine	Commercial 2005-10	25-35	2,000-3,000	0.06-0.15
OTEC	Commercial 2005-10	70-80	Unclear	Unclear

 

Source: "World Energy Assessment: Energy and the Challenge of Sustainability, Chapter 7: Renewable Energy Technologies - Published by UNDP, September 2000"

3.2        Social Implications

Depending on the scale of development, offshore energy projects can have significant impact on coastal communities. For example, in France there was strong opposition to tidal power from ecologists. On the other hand, there are regional development benefits, for example the La Rance scheme includes a road crossing linking two previously isolated communities and has allowed further development of the distribution network for raw materials and developed products.

The main issues, however, tend to be in conflicts with other users of the seas — for fishing, marine traffic, and leisure activities. Of these, fishing is perhaps the main potential area of conflict.

3.3        Environmental Implications

The offshore environmental impact of marine energy technologies tends to be minimal. Few produce pollution while in operation. One exception is tidal barrages, where the creation of a large human-made seawater lake behind the barrage has the potential to affect fish and bird breeding and feeding, siltation, etc. Another exception is OTEC, which may release carbon dioxide from seawater to the atmosphere. None of the technologies discussed seems likely to cause measurable harm to fish or marine mammals. But some — such as marine current turbines and wave power devices — may need small fishery exclusion zones to avoid entanglement with nets.

The environmental effects of tidal energy have always been recognised as a significant factor. The main environmental risks are due to the changes of water levels which modify currents, and sediment transport and deposit. The UK's previous tidal power programme devoted considerable effort to both specific and generic understanding of potential environmental changes that barrage schemes might induce. The programme concluded that no major environmental changes have so far been identified which would preclude further development of the technology. If a tidal energy scheme were ever to proceed to full-scale development it would require a detailed environmental impact assessment based on substantial local monitoring.

As with most renewable energy sources, wave devices produce no emissions during generation but the energy associated with the construction of the device does have small associated emissions.

Wave energy devices could have some environmental impacts in the following areas:

·         Hydrodynamic Environment: devices could act as coastal protection and change the flow patterns of sediment, which would require sensitive site selection;

·         Devices as Artificial Habitats: devices could attract and promote populations of various marine creatures;

·         Noise: this would come primarily from the Wells turbines of shoreline/nearshore OWCs, though they can be sound proofed;

·         Navigational Hazards: adequate visual and radar warning devices can be built into most devices;

·         Visual Effects: these would occur only for shoreline/nearshore devices;

·         Leisure Amenity: devices could provide calm waters thereby promoting some water sports (e.g. canoeing and scuba diving);

·         Conversion and Transmission of Energy: there may be visual and environmental impacts associated with the line required to transmit electricity to shore and to the grid.

With careful siting, most of these impacts would be small and easily reversible.