Offshore wind: Techniques
Monopiles hammered into seabed versus platforms moored in deep water
What this tab covers The methods used to capture this energy: how each works, and how they compare on efficiency, cost, life-cycle emissions, maturity and scale.Offshore turbines either stand on foundations fixed to the seabed in shallow water, or sit on floating platforms moored in deep water. Fixed-bottom is commercial and growing; floating is in early commercial deployment.
Comparison
| Method | Efficiency | Cost | Life-cycle emissions | Maturity | Scale |
|---|---|---|---|---|---|
| Fixed-bottom offshore23457 | 41% global average capacity factor for 2025 projects | USD 78/MWh global average LCOE, installed cost USD 2,931/kW (IRENA, 2025 USD); US reference project USD 117/MWh and USD 5,411/kW (NREL, 2023 USD) | Median 12 g CO2e/kWh, range 8-35 (IPCC AR5); 12-23 g CO2e/kWh (UNECE 2022) | mature | 9.3 GW added in 2025; about 92.5 GW of offshore wind installed worldwide at end of 2025, with more than 50 GW under construction |
| Floating offshore38 | 38.2% net capacity factor for the US reference project | US reference project USD 181/MWh and USD 7,349/kW (NREL, 2023 USD) | No IPCC or UNECE figure specific to floating foundations | early commercial | Largest farm: Hywind Tampen, Norway, 88 MW from eleven 8 MW turbines on floating concrete structures in about 260-300 m of water, supplying about 35% of the power for nearby oil and gas fields |
Offshore wind costs more than twice as much per MWh as onshore (USD 78 against USD 33 globally in 2025) because foundations, cables and installation vessels are expensive, but its cost has fallen by 63% since 2010 (IRENA) and it gives higher, steadier output close to coastal cities. Floating wind is about 55% more expensive than fixed-bottom in NREL's US estimates (calculated: USD 181 against USD 117), reflecting its early stage. Life-cycle emissions of fixed-bottom offshore wind are similar to onshore wind.
How each method works
Fixed-bottom offshoreLarge three-blade turbines are mounted on steel monopiles hammered into the seabed, or on lattice jackets or concrete gravity bases. Each turbine feeds an array cable to an offshore substation, which steps up the voltage and sends power ashore through a subsea export cable. Installation uses specialised jack-up vessels.23457
Floating offshoreThe turbine sits on a buoyant platform (a spar, semi-submersible or tension-leg design) held in place by mooring lines and anchors. This allows wind farms in water too deep for fixed foundations, where much of the world's offshore wind resource lies. Platforms can be assembled in port and towed out.38
Sources
- Renewable Power Generation Costs in 2025 (Executive summary, Figure S1) IRENA, 2026
- Cost of Wind Energy Review: 2024 Edition (NREL/PR-5000-91775), reference projects in 2023 USD National Renewable Energy Laboratory, 2025
- Climate Change 2014: Mitigation, Annex III Technology-specific cost and performance parameters, Table A.III.2 (life-cycle emissions, min/median/max) IPCC AR5 Working Group III, 2014
- Carbon neutrality in the UNECE region: integrated life-cycle assessment of electricity sources (ECE/ENERGY/141) United Nations Economic Commission for Europe, 2022
- GWEC unveils offshore wind plan as global capacity hits 92.5 GW (reporting GWEC Global Offshore Wind Report 2026) Modern Power Systems, 2026
- 'Largest' floating offshore wind farm comes online in North Sea (Hywind Tampen) POWER Magazine, 2022