Turning the tide in our favour
The Council for Sustainable Development has suggested wind power as a renewable energy source for Hong Kong, together with solar power and energy from burning waste.
Hong Kong Electric has announced plans to build a 600 kilowatt wind turbine on Lamma Island. This is projected to generate 700 megawatt hours of electricity a year, reportedly enough to meet only 3 per cent of Lamma's needs.
Is wind power our best option? Advanced wind turbines are simple, rugged and reliable. The technology is proven, and thousands are generating power in other countries. But the noise from the rotor blades and visual pollution of the landscape are disadvantages, as is the uncertain power output. The wind is free, but fickle. Its speed fluctuates, and power generation is unpredictable. Too little wind, or too much, and output can drop to zero. Another disadvantage is cost. According to the council, land-based wind-generated electricity will cost 20 to 35 cents per kilowatt hour and power from offshore turbines about double.
Hong Kong is small and densely populated, and we value our country parks. Based on the projected output from the Lamma turbine, it would require 3,300 two-megawatt turbines to meet just 20 per cent of our electricity requirements. It is questionable whether land-based wind turbines would ever be permitted to make a significant contribution to our energy needs. Offshore wind farms are more acceptable and would benefit from stronger wind conditions, but the extra construction and maintenance costs are significant. Wind and solar radiation are products of the sun, and we are accustomed to thinking of it as our source of energy. Fossil fuels, natural gas, light and heat, all come from the sun. Even hydroelectric power depends on solar radiation to evaporate water and create the rain that fills the rivers and reservoirs. But instead of power from the sun, why not take advantage of Hong Kong's geography and tap the gravitational power of the moon? Month in, month out, the moon circles our planet, its gravitational attraction dragging the oceans behind it. Those who use our ferries will be familiar with variations in sea level. Twice each day we have a high tide, followed by a low tide. Less obvious are the tidal currents that flow through our harbour and wash our coastline Marine-current turbines are coming. Water is 800 times denser than air and a marine turbine can access five to 10 times as much energy as a wind turbine of the same size. A prototype turbine off the coast of England has exceeded its performance targets, and a twin-turbine model is being developed.
Unlike the wind, tidal currents are absolutely reliable, allowing predictable power generation. Marine turbines are silent and almost out of sight. Conditions under the sea in a storm are relatively benign, so the technology is fairly immune to storms and waves, unlike offshore wind turbines. This results in reduced costs.
Can we use this new technology? One possible location is Tolo Harbour. Linked to the sea by the 1km-wide Tolo Channel, it covers an area of almost 50 sq km. The average tidal range is about 1.5 metres and a daily average of some 300 million cubic metres of water flow through the channel at speeds of up to five knots. The channel could be further narrowed to increase the speed of flow, and hundreds of turbines could be installed, hidden beneath the sea.
Tidal-current power generation could also play a role in meeting China's power needs. Although tidal flows stop and reverse four times a day, this happens at different times up and down the coast, thus permitting continuous power generation. Marine-current turbines could be the answer to our need for pollution-free electricity; a lunar, but not lunatic, source of power.
Robert Wilson is a financial consultant and president of the Hong Kong, China Rowing Association