For years the conventional wisdom among environmentalists and policymakers has been the following: Desalination is too expensive, too energy intensive, too environmentally dangerous, and not scaleable. We disagree emphatically with all of these notions.
|A small desal system on the California coast.
The environmental impact of desalination is negligible if the brine is released into a major ocean current. Certainly on North America’s west coast, where the California current moves some 20-30 sverdrups per year past any outfall point, the impact of brine is a non-issue (ref. Sverdrups & Brine).
As for the impact of pipelines on the seabed to move brine 10-20 kilometers offshore, or the impact of sea wells and other intake technologies – we have been doing this for years for power plants and for pipelines to offshore terminals. The technology is safe. And any environmentalist or policymaker who thinks we should install marine current turbines on the seabed – at a paltry yield of maybe 5.0 megawatts per turbine – has no business concerning themselves with the seabed impact of a desalination complex that can deliver fresh water to millions of people.
Whether or not desalination is scaleable is arguable, of course, but current events seem to suggest it is. Worldwide, over 30 cubic kilometers of fresh water are already desalinated each year. In Ashkelon, Israel, the largest desalination plant to-date delivers .12 cubic kilometers of fresh water per year, and it was built at a cost of only $250 million (ref. Photovoltaic Desalination). So what are the costs to build and power a desalination plant, and what is the cost per household?
The online interactive spreadsheet “Desalination Costs” examines each of these questions in some detail. If you view the spreadsheet, you will note we have used very conservative assumptions. Water use per person per day, for example, is set at 200 gallons, which is about twice what a residential user on average consumes in any major U.S. city, Los Angeles in particular. The cost of the plant construction, assuming 1.0 cubic kilometer of fresh water output per year, is not set at $2.0 billion, which is what one would extrapolate from the cost of the Ashkelon plant, but at $5.0 billion, in order to make certain we stay conservative in our calculations. We then assume the project is financed on a 50 year bond at a rate of 10% – there is probably cheaper financing out there for a public/private project of this magnitude. Financed construction cost: $624 per acre foot.
The next section of the online calculator looks at the cost for energy. The productivity based on 2.0 kilowatt-hours per cubic meter of fresh water is well documented, and when paired with the very conservative price of $.20 per kilowatt-hour, yields a cost per acre-foot of $495. Double that amount for operations – in spite of the fact desal plants generally expend 70% of their variable costs just for energy, and the variable costs per acre foot are $990.
This equates to a total cost per acre foot using desalination of $1,613. For a family of four consuming 200 gallons per day per person, that is a monthly household water bill of $120. This price should represent the upper bound of what anyone should have to pay for water. It is well within the affordable range for any residential consumer in Los Angeles, for example, and could replace water they import from the north.
The potential of desalination, along with other green technologies that can deliver abundance, should be central to policy discussions, instead of controversial diversions.