[2026] PTE Academic Reading - Multiple Choice, Multiple Answers

Ocean thermal energy conversion (OTEC) is a renewable energy technology that exploits the temperature difference between cooler deep ocean water and warmer surface water to run a heat engine and produce electricity.This process is most efficient in tropical regions, where the temperature gradient between the surface and the depths is consistently large throughout the year.There are three main types of OTEC systems: closed-cycle, open-cycle, and hybrid.In a closed-cycle system, a fluid with a low boiling point, such as ammonia, is evaporated by the warm surface water to drive a turbine.The resulting vapor is then condensed back into a liquid using cold water pumped from several hundred meters below the surface.One of the secondary benefits of OTEC, particularly in open-cycle systems, is the production of desalinated fresh water as a byproduct of the condensation process.Additionally, the nutrient-rich cold water brought to the surface can be used for mariculture, supporting the growth of fish and shellfish.Despite its potential as a source of clean, continuous base-load power, OTEC faces significant technical and economic barriers.The high cost of constructing long, large-diameter pipes to transport deep-sea water is a major deterrent for many investors.Furthermore, the efficiency of OTEC systems is relatively low compared to other renewable sources like wind or solar, requiring massive facilities to generate significant amounts of power.Nevertheless, for remote island nations, OTEC represents a promising path toward energy independence and water security.