Why don’t we use more tidal power? - The Climate Question podcast, BBC World Service

Key Concepts

• Tidal Power: Renewable energy generated by the movement of tides (tidal streams, barrages, and lagoons).
• Baseload Power: A reliable, constant supply of electricity that meets minimum demand.
• Estuaries: Coastal bodies of water where freshwater from rivers meets saltwater from the ocean; critical ecosystems for biodiversity and carbon sequestration.
• Fish Disco: An acoustic deterrent system using ultrasound to guide fish away from dangerous industrial water intakes.
• Brackish Water: A mixture of freshwater and saltwater, essential for specific estuarine species.

---

1. Tidal Power: Technologies and Challenges

The panel discussed three primary methods for harvesting energy from the sea:

• Tidal Stream Generators: Underwater turbines that function like wind turbines. They can be fixed to the seafloor or suspended from rafts. Notable examples include research stations in Orkney, Scotland, which utilize "kite-like" turbines that move with the current.
• Tidal Barrages: Dams built across estuaries or bays. As tides rise and fall, water is trapped and released through turbines, functioning similarly to hydroelectric dams (e.g., La Rance, France).
• Tidal Lagoons: Enclosed coastal loops that trap water to generate power. A proposed project in Swansea Bay, Wales, is estimated to cost $1.6 billion.

Key Arguments & Constraints:

• Predictability: Unlike wind or solar, tidal power is highly predictable years in advance, potentially offering "firm" baseload power.
• Engineering Hurdles: Operating machinery in corrosive, salty, and high-pressure environments is technically difficult and expensive.
• Economies of Scale: Unlike solar panels or batteries, which are mass-produced, tidal projects are often bespoke, site-specific engineering feats, making them significantly more expensive.
• Geography: Tidal power requires specific conditions, such as narrow channels or a tidal range of at least five meters.

2. Environmental Impact and Mitigation

The discussion highlighted the tension between renewable energy development and wildlife conservation.

• Wildlife Risks: Turbines and barrages can disrupt fish migration and alter estuary water flow.
• The "Fish Disco": At the Hinkley Point C nuclear plant, scientists are using ultrasound speakers to deter fish from entering cooling water intake pipes.
  • Trial Results: In a study on twaite shad, the number of fish near intake pipes dropped from 14 to 1 when the ultrasound was active.
  • Critique: The system cost £15 million, leading to public criticism regarding the cost-to-benefit ratio of saving a relatively small number of fish.

3. Estuaries: Vulnerability and Resilience

Estuaries are identified as highly productive but fragile ecosystems.

• Vulnerability Factors: They are exposed to both oceanic and riverine climate changes. Their reliance on specific salinity levels (brackish water) makes them sensitive to environmental shifts.
• Human Impact: Beyond climate change, estuaries suffer from overbuilding, industrial pollution, and agricultural runoff (nitrogen fertilizers), which become concentrated in enclosed tidal areas.
• Ecological Importance:
  • They serve as nurseries for fish and protect coral reefs by trapping sediment.
  • They act as significant carbon sinks through seagrass and other vegetation.

4. Notable Quotes

• On the "Fish Disco": "It’s not a disco, it’s a fish alarm. It’s a siren. It’s really telling them to go away. It’s like a fish bouncer rather than a fish disco." — Graihagh Jackson
• On Ecosystem Recovery: "It shows what can be achieved when we put our mind to it... it’s a good reminder that there are all sorts of ecosystems which are being harmed by all sorts of other human activities... and ones that we can act on and try and protect." — Justin Rowlatt

5. Synthesis and Conclusion

The panel concluded that while tidal power offers a predictable, low-carbon energy source, it remains a "drop in the ocean" compared to other renewables due to high costs and engineering complexities. Similarly, while technological solutions like "fish discos" exist to mitigate industrial harm, they are expensive and highlight the broader challenge of balancing human infrastructure needs with ecological preservation. The discussion emphasized that local, small-scale conservation efforts—such as the restoration of nature reserves like Arne—can yield significant biodiversity gains, proving that targeted human intervention can successfully reverse environmental damage.