Publications

Survey of Energy Resources 2007

OTEC - Introduction

Since the WEC Survey of Energy Resources (SER) 2004, the most significant - some would say substantial - change in the energy scene has been the very large increase in the price of oil from, typically, US$ 25-30/bbl to as much as US$ 70/bbl, with a possible "settling" point for the next few years of around US$ 50/bbl. Clearly this basic doubling of the oil price has a major effect on the comparative economics of all other energy supply systems - from all renewables to nuclear. As noted later, the climate change imperatives are also now accepted in a majority of countries, and these too have a direct impact on the costs of generation from all energy sources - for better or worse, depending on the particular energy source being considered. The costings in this chapter seek to take note of these changes.
Ocean Thermal Energy Conversion (OTEC) is a means of converting into useful energy the temperature difference between the surface water of the oceans in tropical and sub-tropical areas, and water at a depth of approximately 1 000 metres, which comes from the polar regions. Fig. 15-1  shows the temperature differences in various parts of the ocean, and for OTEC a temperature difference of 20oC is adequate, which embraces very large ocean areas, and favours islands (Gauthier & Lennard, 2001) and many developing countries.

The continuing increase in demand from this sector of the world (as indicated by World Energy Council data) provides a major potential market. Specifically the percentage of 'new' energies will grow - from a near-zero figure at the end of the 20th century to 6% by the year 2020, which translates into 'new' energies of some 12 000 MW a year, averaged over the period from 2000 to 2020. There is now a case for the use of OTEC power  in nations located in temperate zones, via the production and trans-shipment of liquid hydrogen, which will add to the 12 000 MW figure, but at this time a quantification cannot be reliably estimated  (Figure 15.2 OTEC).

The capital cost of OTEC plants has increased in the last 3 years, owing to the very significant rise in many material costs during that period, which must be added to the high costs resulting from the inherent low efficiency of this technology. Against this can be set reductions, firstly resulting from the lower interest rates in recent years and practically due to improvements in, for example, heat exchangers. This results overall in capital costs of the order of US$ 7 000-15 000/kW, still some ten times the capital cost for conventional power systems. The funding of all 'new' energies would therefore equate to a total sum each year in the region of US$ 75-150 billion: by any standards this is very substantial business, and for the construction, operational and financing sectors, an activity of very considerable interest. But the OTEC business will only develop if it is economically attractive to the utilities that will invest in and operate it - and this situation has now arrived for a number of potential locations.

Whilst the ocean thermal resource is relevant, particularly to many developing countries, there are a multitude of other factors to be considered before it can be said that a particular country or location is suitable for an OTEC installation. These include: distance from shore to the thermal resource; depth of the ocean bed; depth of the resource; size of the thermal resource within the Exclusive Economic Zone (EEZ); replenishment capability for both warm and cold water; currents; waves; hurricanes; sea bed conditions for anchoring; sea bed conditions for power cables of floating plants; present installed power, and source; installed power per head; annual consumption; annual consumption per head; present cost per unit - including any subsidy; local oil or coal production; scope for other renewables; aquaculture potential; potable water potential; and environmental impact - to name but a few. For completeness it would be useful to seek whole-life nuclear-power costings so that comparative capital and generating costs for all energy sources are clearly indicated.