OTEC and salinity power: Resources and labour

Rivers of seawater, kilometre-long pipes and vast membrane areas

What this tab covers The natural resources (land, water, materials, fuel or feedstock) and the labour needed to capture this energy, per unit, with the reason each is needed.

OTEC needs very large seawater flows, pipes and heat exchangers; salinity plants need enormous membrane areas and both fresh and salt water.

Natural resources

Resource	How much	Why it is needed
Seawater	About 100,000 m3 an hour for a 10 MW OTEC plant¹	Each cubic metre carries little usable heat across a 20 °C gap.
Cold-water pipe	About 10 m diameter and 1,000 m long for 100 MW¹	Cold water must come from about 1 km down with little warming.
Heat exchangers	USD 200-800 per m2¹	Small temperature differences need very large surfaces; they must resist corrosion and biofouling.
Membranes (salinity)	At least 2 million m2 for a 2 MW plant, replaced about every 5 years²	Power per square metre is low, so area must be huge.
Fresh water (salinity)	Not quantified²	River water or treated sewage provides the low-salt side; it is returned, not consumed.

Labour

Phase	How much	Skills	Why it is needed
Manufacturing	Not quantified¹²	Heat-exchanger and membrane manufacturing	These components dominate cost.
Construction	Not quantified¹	Offshore pipe installation, marine engineering	A 10 MW cold-water pipe of 4-7 m diameter has not yet been demonstrated.
Operation	Not quantified¹²	Plant operators, membrane cleaning	Biofouling must be controlled continuously.
Decommissioning	Not quantified¹	Marine salvage	Pipes and moorings must be recovered.

No studies of jobs per MW were found for either technology.

Sources

Ocean Thermal Energy Conversion: Technology Brief IRENA, 2014
Salinity Gradient Energy: Technology Brief IRENA, 2014