Monday, May 5, 2014

Desalination Works but It's Expensive

A recent large deployment of desalination in San Diego is useful to Hawaii where Oahu and Maui may approach the need for manufactured potable water in the next 20 years or so if population and tourism growth trends continue and appreciable sea water rise continues (e.g., 0.32 cm water rise was noted between 1993 and 2013, which, if remains steady, results in 32 cm or 13 inches mean sea level rise every 100 years.) Recall that as sea water rises it makes larger parts of the aquifer brackish, thus unusable for drinking and irrigation.

The project in San Diego was smartly located right next to a large powerplant which means that a comparable location for Oahu would be next to the Kahe powerplant and Electric Beach.  This is because desalination requires vast amounts of both water and electricity, and pumping requirements can be reduced by taking advantage of the seawater pumped into a pre-existing powerplant.

The deployment in San Diego is currently under construction. It is designed to produce 50 MGD of water, that is 50 million gallons per day. This amount of clean water can supply 112,000 typical single family homes or more than one third of the current s.f. homes on Oahu.  This would be the upper limit of desalination plant that would be needed for Oahu. This plant would require more than 30 MW of electricity which is what the H-Power plant was producing for decades, before its boiler capacity was doubled in mid-2013.

The budgeted price of San Diego's Carlsbad desalination plant?  One billion dollars including a 10-mile distribution pipe, if the project is completed on time and on budget in early 2016.  Come 2020, Oahu may need to start budgeting for such a large project.