Predictable Power, Prohibitive Price

Tidal and riverine currents represent one of the most predictable and reliable renewable energy sources available — highly forecastable, co-located with coastal demand centers, and available 24/7 unlike wind or solar. Yet hydrokinetic turbines (HKTs) that harvest energy from these flows remain far too expensive for commercial deployment. Current levelized costs of energy (LCOE) for tidal energy are $0.30–0.50/kWh, roughly 5–10 times higher than onshore wind. The problem is fundamentally structural: HKTs must survive extreme hydrodynamic loads, biofouling, corrosion, and debris impacts in underwater environments where maintenance is difficult and expensive.

The global tidal energy resource is estimated at 120–150 GW of extractable power, and riverine hydrokinetic resources could serve remote communities without grid connections. Unlike wind and solar, tidal energy is fully predictable years in advance, which would eliminate the need for backup generation or storage if cost-competitive. For island nations and remote coastal communities, tidal energy could provide baseload power without fossil fuel imports. ARPA-E invested $38M in the SHARKS program because the gap between resource quality and technology readiness represents a missed opportunity for grid diversity.

Early HKT designs borrowed heavily from wind turbine architectures (horizontal-axis rotors), which proved poorly suited to underwater operation — blades experience biofouling that degrades performance within months, saltwater corrosion attacks structural components, and the high density of water (800× air) creates extreme structural loads that require heavy, expensive foundations. Several demonstration projects (MeyGen in Scotland, Verdant Power in New York's East River) have shown technical feasibility but at costs far above grid parity. Vertical-axis and oscillating-foil designs reduce some structural issues but sacrifice efficiency. The fundamental challenge is that no integrated design approach has simultaneously optimized hydrodynamics, structural integrity, anti-fouling, and maintenance accessibility for the underwater environment.

ARPA-E's SHARKS program calls for integrated turbine co-design that simultaneously optimizes across hydrodynamic performance, structural engineering, and O&M logistics. Bio-inspired anti-fouling surfaces (drawing on marine biology), advanced corrosion-resistant composites, and autonomous underwater maintenance robots could each contribute. Control co-design — jointly optimizing the turbine, its mooring, and its power electronics as a single system — has shown promise in modeling studies but hasn't been implemented in hardware.

A team could develop and test a bio-inspired anti-fouling coating for turbine blades using accelerated lab-scale fouling protocols, or design a modular HKT concept optimized for rapid retrieval and maintenance in riverine settings. Ocean engineering, mechanical engineering, and marine biology students would find strong entry points.