OTEC

ECONOMICS OF OCEAN THERMAL ENERGY
CONVERSION
by
Luis A. Vega
PICHTR U.S.A.
The cost of producing electricity with OTEC plants is compared to the cost of electricity produced with fossil-fueled plants.
In the case of OTEC, when appropriate, the cost of electricity is estimated with credit for the desalinated water produced. The production cost of OTEC products are levelized over the life of the plant (nominal value: 30 years). Two generalized
markets are considered: industrialized nations and smaller, less developed island nations with modest needs. Scenarios under which OTEC could be competitive are established.
The scenarios are defined by two parameters: fuel cost, and the cost of fresh water production. In the absence of natural sources of fresh water, it is postulated that the cost of producing desalinated water from seawater via reverse osmosis (RO) be considered as the conventional technique. This approach yields a direct relationship between desalinated water production and fuel cost; and therefore, a scenario
defined with one aprameter.
It is postulated that OTEC should only be considered as a system to produce electricity and desalinated water, because OTEC-based, mariculture operations and air conditioning systems can only make use of a small amount of the seawater available, and therefore, could only impact small plants. The use of energy carriers (e.g.:Hydrogen) to transport OTEC energy generated in floating plants, drifting in tropical waters away from land, is determined to be technically feasible but requires increases in the cost of fossil fuels of at least an order of magnitude to be cost effective.
It is determined that plants of at least 50 MWe capacity would be required for the industrialized nations; and, that if desalinated water is required to reach wider scenarios, it is proposed that a hybrid plant be used, based on the closed cycle for the electricity production and a second-stage, for
desalinated water production, consisting of a flash (vacuum) evaporator and surface condenser. Closed cycle plants, without second-stage desalinated water production,
are found to be cost effective if housed in floating vessels, moored or dynamically positioned a few kilometers from land, transmitting the electricity to shore via submarine
power cables. The moored vessel could also house a hybrid OTEC plant and transport the desalinated water produced via flexible pipes. It is recommended that a floating 5 MWe and
7,500 cu m/day demonstration plant be designed, installed and operated prior to the commercialization of plants of at least 50 MWe capacity.