Monday, September 25, 2006

Offshore Desal Is Better

In my video commentary to the Nevada State Engineer concerning the Southern Nevada Water Authority water grab applications, I stated that I would be sending them more information about desalination and new developments. This is what I sent:

Science magazine has just reported that:

A water desalination system using carbon nanotube-based membranes could significantly reduce the cost of purifying water from the ocean... The new membranes, developed by researchers at Lawrence Livermore National Laboratory (LLNL), could reduce the cost of desalination by 75 percent, compared to reverse osmosis methods used today”

The researchers estimate that these membranes could be brought to market within the next five to ten years. They claim:

"The challenge is to scale up so we can produce usable amounts of these membrane materials” ... and the fabrication process is "inherently scalable."

Actually, desalination is already much cheaper than just a couple of years ago. A company called Aqualyng is claiming energy consumption rates of 2.0 kWh/M3 – half that of some others.

So far, to my knowledge, SNWA has not even considered a fleet of offshore, wave powered, desalination barges.

Back when Southern Nevada Water Authority (SNWA) compared a pipeline to desalination, they assumed that a Big Factory type of desalination plant would be the best option. Typically, due to economies of scale, bigger plants generally make cheaper fresh water. But, SNWA made their comparisons before new membrane designs, new wave power generators, and lower energy use desalination units (for ships) were available. In other words, things have changed significantly – quite recently. Nowadays, a Big Factory type of plant isn't nearly as good an option as designers once thought. And mass produced smaller plants, operating offshore, might be a much better option.

A Big Factory desalination plant has a number of costs, impacts, and risks that can be avoided by utilizing a Barge Armada of desalination units with wave generated power. For instance:

  1. A big plant is a big commitment, with the risk that you overbuilt – or better technology will leave your plant obsolete. Whereas, a fleet of small, offshore barge desalination plants can be built as needed, utilizing the latest technology.

  2. A big onshore plant would need acres and acres of beach front property to build a massive facility, canals, and pipelines – and typically, a massive onshore coal fired power plant (which has been the only option considered). A barge armada would only need dock front property to house the facility to assemble and repair the desalination units and wave power generators – just big enough to hold a few barges.

  3. Construction and maintenance costs for an intake canal for a big onshore desalination plant would likely range from $5 million to $40 million. But, barges would need no intake canal – since the barges would be about 3 miles out to sea.

  4. An onshore plant would require more pre-filtering than offshore barges.

  5. The costs for a pipeline to distribute tons of brine offshore would be about 10% of construction costs for a big onshore plant. However, since the barges would be already offshore, and the plants on each barge are small enough not to effect local sea salinity, no pipeline would be necessary.

  6. Industry experts estimate that power expenses will amount to about 30% of total costs for a big, onshore desalination plant. But, the risk in projecting these estimates is high. The price of coal will likely go up. The price of electricity will likely go up. And, just in case you don't remember Enron, these expenses could go way up, fast. If, however, you generated your own power, from waves; you're set. The price of waves will always be free.

  7. As mentioned earlier; new, lower pressure Reverse Osmosis membrane technology has been developed that could lower the energy costs of desalination by 75%. But the membranes, so far, are small. As they are scaled up, Big Factory desalination plants would have to wait the longest for the technology. Conversely, small desalination plants would be the first to benefit. The spare electric power generated by the wave generators could then be sold, turning power costs into power profits.

There's more. A Barge Armada is far less vulnerable to earthquake, tsunami, and terrorist damage. They also have far less negative impacts on beach communities. Giant sea snakes and boats far off in the distance would be far more welcome than a big factory plant and a big power plant.

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