What are the problems associated with OTEC?

Problems Associated with OTEC

1. Heat Exchangers (Evaporators & Condensers)

• Very Low Efficiency:
  • The maximum theoretical thermal efficiency is only around 3.4%, practical efficiency drops to 2.5% due to energy losses (like pumping deep seawater).
• High Flow Rates Needed:
  • To generate useful power, massive volumes of water must be pumped through the heat exchangers.
• Material Requirements:
  • Heat exchanger materials must be highly conductive, corrosion-resistant, and strong.
  • Common materials:
    • Titanium – Excellent but expensive.
    • Aluminium alloys – Cheaper but more prone to corrosion.
    • Copper-nickel alloy (90/10) – Used widely but unsuitable with ammonia.
    • Plastics – Corrosion-resistant but have low thermal conductivity; performance can be improved by adding graphite.

2. Biofouling

• Definition:
  • Accumulation of microorganisms, slime, and marine organisms on the surfaces in contact with seawater.
• Impact:
  • Reduces heat transfer efficiency, increases thermal resistance (“fouling factor”).
• Prevention & Cleaning:
  • Periodic cleaning (mechanical or chemical).
  • Maintain higher flow rates (but avoid erosion).
  • Design must account for biofouling, especially in the evaporator where warm water promotes growth.

3. Site Selection

• Temperature Difference:
  • Needs a minimum 20°C difference between warm surface water and cold deep water.
• Ideal Locations:
  • Tropical regions (between 20°N and 20°S latitude).
• Accessibility:
  • Offshore plants are typical, but steep shoreline locations can allow onshore construction.
• Biofouling Consideration:
  • Some sites may be more prone to biofouling than others.

4. Energy Utilization

• Transmission to Shore:
  • Efficient only if plant is within 30 km of the shore; otherwise, transmission cost rises.
• Alternative Uses Onsite:
  • Use electricity for:
    • Electrolysis of seawater → produces hydrogen & oxygen.
    • Ammonia production → used as fertilizer.