The Flying Shingle
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Green energy with a blue tinge
by Michael Mehta
Friday, October 23, 2009

Dear Editor,

In response to Jeremy Baker on the viability of water desalinization and tidal power

For many people it’s apparent that access to both clean drinking water and “green” energy pose real challenges. Although 71 per cent of the Earth is covered in water, only 2.6 per cent is fresh. In spite of abundant sources of energy including solar, wind, geothermal, and tidal power, many regions still rely heavily on large-scale hydroelectric plants, coal, oil, natural gas and nuclear. A tremendous opportunity exists on Gabriola to think outside of the box, and to perhaps find unique ways for solving both our fresh water and energy needs simultaneously. I would like to spell out my 2020 vision of how this might happen, and it involves a small-scale sea water desalinization plant coupled to a tidal generator.

Reducing the salt and mineral content of sea water is done through a process known as desalinization. Desalinization is the earliest form of water treatment, and its use is growing dramatically on a global scale. The Middle East and the Caribbean are the most aggressive users of desalinization technology, but even places like Tampa Bay in Florida have large facilities that can produce 25 million gallons per day of fresh water. Advances in membrane technology have made desalinization with reverse osmosis very cost-effective. For example, facilities in Israel produce water at $0.53 USD per cubic meter, while Singapore can do so for $0.40 USD per cubic meter (one cubic meter equals 264 US gallons). With small-scale plants available from companies like General Electric and Siemens, the energy inputs come in at 1.5 KW-hours per cubic meter of water. In other words, I can fill one of my 2800 US gallon cisterns for approximately $6 in water (plus transportation costs).

Tidal power is also a very old technology that dates back to 900 AD. Since then several advances have been made, and three general types of tidal generators exist. The first approach is to construct a barrage or dam where water is captured in a bay or estuary and when released it spins a generator to produce electricity.

Unfortunately, barrages can impede sea life migration and the silt built up behind them can adversely affect local ecosystems. The second approach is called a tidal fence and it involves a series of vertically oriented turnstiles that are placed between islands. Tidal fences may also interfere with migration, yet appear to be less environmentally damaging than barrages. The third approach involves using tidal turbines. Like wind turbines, tidal turbines spin as water moves through them, but much more efficiently due to the density of water. Most tidal turbines work best when currents are between 3.6 and 4.9 knots (4 and 5.5 mph), are anchored at depths of 10 to 30 meters, and have blades that vary in size between 3 and 17 meters in diameter. Tidal turbines have the best environmental performance, and are designed to spin slowly enough to allow marine mammals and fish to navigate safely around them or through a large opening in the center.

In December 2006 a small tidal turbine with a 3 meter diameter blade was installed in 13 meters of water off Race Rocks (10 nautical miles south-west of Victoria). This tidal turbine was commissioned to replace two diesel generating stations on the island. It produces 65 KW of electricity with a system that is highly efficient, simple (only one moving part), and with no visible surface structure. The cost of tidal turbines is often estimated at between $2000-3000 per KW of installed capacity, or 20 cents per KW-hour. Studies on tidal power in British Columbia suggest that about 4000 MW of potential exist – which is the equivalent of 2400 large wind turbines, or 8 large coal plants, or several high-capacity nuclear reactors.

My vision involves co-locating a water desalinization plant and a tidal turbine. Power from the tidal turbine can be used to produce fresh water from the desalinization plant, and any extra power can be used on the island for local purposes. At the moment, the federal government has several large-scale programs to fund projects like this. For example, the Clean Energy Fund and the Green Infrastructure Fund, both budgeted at $1 billion over the next five years, may apply. The twist here is that this combined facility should be owned by Gabriolans and structured to operate as a public utility. Profits, or dividends, from the operation of these facilities can be used to enhance school programs, elder care, provide funds for The Commons, and to support various artistic and other community events. Of course this vision is just one approach, and I invite Gabriolans to discuss this and other ideas with me.

Dr. Michael D. Mehta lives on Gabriola Island but works in Winnipeg. He is a Professor of Environmental Studies at the University of Winnipeg, and was founding Principal of Richardson College for the Environment. His website is

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