The real cost of desalted water and how to reduce it further

Abstract

Freshwater scarcity on a worldwide level is now a burning problem, widely discussed in media interviews and in major newspapers. In this context, the majority of the media are underlining the importance of seawater desalination as an attractive and logical alternative source to fight the freshwater scarcity. Unfortunately the majority of all these discussions are providing a totally wrong picture of the real cost of freshwater production from seawater. Figures for desalted water costs from below 0.25 €/m 3 to over 0.6 €/m 3 for large-scale realisation are frequently quoted. In some media, however, the costs given for desalted water production are too prohibitive for large-scale applications. Many so-called experts are enhancing the confusion with incorrect or in incomplete statements. Even simple considerations, such as water cost ex desalination plant vs. water cost at consumer tap, are neglected. Yet another neglected point is that freshwater of any kind is either highly subsidised or overpriced to finance costs which are not water-related costs. Even in the EU Commission the real cost of seawater desalination is sometimes incorrectly perceived. In principle, the calculation of specific freshwater cost is simple and based on a few clear parameters such as investment cost for a given desalting capacity, energy cost, cost for distribution, amortisation period and concept, financing cost, inflation rate, operation and maintenance cost and, last but not least, plant availability and lifetime. A typical example to illustrate the reigning confusion is the primary energy cost. Today, the barrel of crude oil costs in the world market approximately 70 US$ or more. However, many tenders or BOT projects compare the water and energy cost on a 5 US$/barrel level. With this energy cost level and other unrealistic conditions even oldfashioned, low-GOR MSF plant can produce freshwater for a nominal cost of 0.60 €/m 3. With today's world market prices for crude oil, realistic cost and conditions for financing and all other costs fully covered, the real specific desalted water cost will exceed the 2 €/m 3 level for the same plant. It is clear that the freshwater has to be produced at socially acceptable cost and this would be about 1.0 €/m 3 or below. However, the calculation of the specific water cost has to be compatible with realistic parameters in order to be able to compare them and to draw correct conclusions and decisions. Therefore, in this paper an attempt has been made to calculate a realistic cost of freshwater from seawater for various types and sizes of desalination plants in combination with various energy sources and with comprehensible realistic conditions utilizing as a basis some older studies. The basic conclusion of our investigation is that large thermal and membrane desalination plants may reach in the future the same level of specific water cost and that a water production cost of 1.00 €/m 3, with energy cost of the year 2006 can be achieved with moderate R&D efforts. However, it is difficult (not impossible) to reach 0.50 €/m 3 and it will require time-consuming and intensive R&D work to achieve this goal.