Underwater turbine spinning for 6 years off Scotland's coast is a breakthrough

Tidal potential, geography & role in the mix

• Tidal power is praised as predictable, reliable and complementary to solar, since lunar and solar cycles differ.
• Commenters note the UK’s especially favorable coastlines and phase diversity, allowing near‑constant aggregate output if sites are distributed well.
• However, strong tidal ranges and currents are geographically limited (bays with chokepoints, straits, shelves, some estuaries), so global technical potential is said to be ~1/10 of offshore wind.
• Some see “geographically constrained” as a feature (local boon) rather than a flaw; others stress it limits economies of scale and doesn’t tap China’s manufacturing strengths.

Performance, maintenance & economics

• The 6‑year no‑maintenance run is seen as a major proof‑of‑concept, but only 1 of 4 turbines achieved this; others needed retrieval for upgrades/maintenance.
• Debate over whether those retrievals indicate fundamental reliability problems or normal R&D and planned upgrades.
• Harsh conditions (saline corrosion, abrasion, high-flow currents, debris, biofouling) make underwater engineering especially difficult and expensive.
• Comparisons: a 1.5 MW tidal unit is roughly in the range of older large wind turbines; commenters criticize media claims about “homes powered” for mixing nameplate capacity with average household use.
• Skeptics argue that, per kWh, offshore installation/maintenance and subsea cabling are likely far costlier than ground-based solar, especially given solar’s rapid cost declines.

Environmental and ecological concerns

• Serious concern about marine life: past tidal plants have killed fish (e.g., dam-like designs), and a large Korean project was reportedly canceled over ecological risks.
• Questions raised about collisions for fish, dolphins and whales, and nursery disruption in chokepoint fisheries; calls for robust impact studies rather than assumptions.
• Some suggest mitigations (protective cages, shutdown on detection of animals), though these add cost and complexity.
• Others argue impacts are likely small relative to fossil fuels and that infrastructure excluding fishing could even benefit ecosystems.

Relation to other energy sources & system planning

• Several see future grids dominated by solar/wind (plus geothermal where possible), with nuclear and storage smoothing variability; tidal might be a niche but valuable, highly predictable supplement.
• Lifecycle analysis is emphasized as the correct lens for comparing technologies, rather than intuition about “ocean tech pollution” or visual intrusiveness.

Long-term physics & “renewable” semantics

• A side discussion explores that tidal energy ultimately comes from Earth–Moon rotational/orbital energy, so it’s not “renewable” in a literal infinite sense.
• Most agree the effect of human-scale extraction on Earth’s rotation or the Moon’s orbit would be utterly negligible on human timescales, making this a theoretical curiosity rather than a practical constraint.