Tidal energy converts the kinetic energy from the predictable, cyclical movement of ocean tides into electricity. This process harnesses the gravitational pull of the moon and sun, providing a highly reliable output compared to weather-dependent sources like solar or wind. However, implementing large-scale tidal projects introduces substantial financial and environmental costs. These costs extend beyond the initial construction budget, impacting marine ecosystems and altering the physical dynamics of coastal environments.
Financial Investment and Infrastructure Requirements
The financial burden associated with tidal energy projects is often the most immediate obstacle to their widespread adoption. Building large-scale tidal stream generator arrays or tidal barrages requires an exceptionally high upfront capital expenditure (CapEx), which deters investors compared to more mature renewable technologies. The CapEx for tidal power can be several times greater than for solar or wind installations, with tidal stream projects estimated to cost between \\(4 million and \\)9 million per megawatt (MW) of installed capacity.
This substantial initial investment is driven by the complex engineering needed to construct robust infrastructure in harsh marine environments. A single commercial-scale tidal turbine, typically generating 1 to 2 MW, can cost between \\(3 million and \\)5 million before installation. Furthermore, the ongoing maintenance of equipment submerged in corrosive saltwater is also expensive.
Connecting remote tidal energy sites to existing electrical grids adds another significant layer of expense. New transmission infrastructure must be built to deliver the power to population centers, a cost that can range from \\(5 million to \\)20 million for a single project. This combination of high capital outlay, specialized hardware, and grid connection costs means that tidal energy was estimated to cost between \\(130 and \\)280 per megawatt-hour (MWh), substantially higher than onshore wind or utility-scale solar.
Ecological Disruption to Marine Habitats
Tidal energy installations pose biological costs, primarily impacting organisms and ecosystems within the deployment zones. The physical presence of structures, such as tidal barrages or turbine foundations, can lead to habitat displacement, affecting inter-tidal mudflats and salt-marshes that serve as feeding and nursery grounds. These structures also disrupt the established migration patterns of fish and marine mammals, which rely on specific routes for breeding and seasonal movements.
A major concern is the risk of blade strike mortality for marine life, especially migratory fish and marine mammals. While research suggests that many species actively avoid the rotating blades, the risk remains a central issue, particularly for endangered populations. The placement of large arrays could still create cumulative effects on fish populations, even if individual collisions are rare.
The construction and operation of tidal energy devices also generate underwater noise pollution, which is disruptive to sensitive species. Marine mammals, including whales and dolphins, depend on sound for navigation, communication, and foraging. Operational noise can interfere with their echolocation systems, and long-term exposure can cause behavioral changes, such as harbor porpoises avoiding areas where turbine flow speeds are increased.
Alteration of Local Hydrology and Sediment Flow
Tidal energy structures, particularly barrages, physically alter the non-living environment, incurring distinct physical environmental costs. A tidal barrage, a dam-like structure built across an estuary or bay, significantly changes the tidal range both upstream and downstream of the barrier. Studies on proposed barrages have predicted a decrease of 0.5 to 1.5 meters in maximum water levels upstream.
This alteration of water flow and velocity disrupts natural sediment transport processes in coastal and estuarine environments. Changes in currents modify how sand, silt, and other particles are carried and deposited, often leading to excessive sedimentation in one area and increased erosion in others. Barrages also reduce the volume of water exchanged with the sea, which decreases the water’s natural turbidity.
A reduction in water exchange can also lead to changes in local water quality and salinity within the impounded basin. Less water mixing can cause the average salinity to decrease, affecting ecosystems that rely on specific salt content. Furthermore, a decrease in the natural flushing rate of the bay can increase the concentration of pollutants and lead to greater seasonal temperature fluctuations in the water column.