Sink or swim

In an important programme set in motion by Philippines President Fidel Ramos, the country aims to ‘pole vault into the twenty-first century’ by becoming a net exporter of energy to countries in the Asia Pacific. Although May 1998 saw the end of Ramos’s term of office, that programme continues, and among the energy sources proposed to bring it to fruition is a tidal power scheme using technology developed and trialled in Canada.

The ‘tidal fence’ proposed by Vancouver-based Blue Energy uses multiple vertical axis hydro turbines, in a manner analogous to wind turbines. The technology has won the backing of the Asia Power Development Foundation, and Asia Power International, and together the companies have proposed a project to be installed at the San Bernando Strait, between the two Philippines islands of Samar and Leyte. The fence will supply 30MW average power, and up to 55MW at peak times, at an estimated capital cost of US$136M.

The plant will be built under a ‘build, operate, transfer’ scheme, and so will operate as a private power generator, feeding into the grid operated by the Philippines National Power Corporation. At this stage of development the fence is expected to provide power at a cost of US$0.085/kWh, although in later applications of the technology the price is expected to drop to US$0.06/kWh.

According to Barry Davies, chairman of Blue Energy, negotiations are proceeding ‘in a timely manner’. He adds, ‘Asia Power International has just signed a pre-commercial contract with the Department of Energy for the Philippine government. The contract approves the 30MW pilot project with an extension of over 600MW with completion of a feasibility assessment over the next six months. An energy conversion agreement with the National Power Corporation of the Philippines should be finished about six months later’.

Energy technologists have considered the possibilities of harnessing the power of the tides for many decades, but practical solutions have been few and far between. Those in operation, such as the La Ranche plant in France, have generally taken the approach of confining tidal flows as they surge, thus enhancing head and water speeds as the tides ebb so that conventional water power technologies can be used to generate power. While the La Ranche plant has operated successfully for many years, using this approach limits severely the number of sites suitable for generating power. To make full use of the tide in areas where the water cannot conveniently be confined, a new approach is required.

The tidal fence

One solution to the problem was the vertical axis catenary turbine, patented — but never built — by a French engineer, Darrieus, over a century ago. Blue Energy’s Davis turbine has its genesis in Darrieus’s work.

Major development work on the Davis turbine was carried out in the early 1980s. It consists of a series of vertical axis hydro turbines with straight blades mounted in a rectangular cross-section duct structure. The duct provides structural support for the rotor shaft’s top and bottom bearings and channels all the tidal flow through the turbines, increasing the velocity and improving the approach angle of the blades. The duct structure forms a tidal fence or sea wall. In the case of the Philippines project, the structure is expected to have 13 rotor systems in 13 ducts. The reinforced concrete base and column structure is installed on vibra screed aggregate.

According to Blue Energy the turbine operation is optimised using either four or five blades. Economy and simplicity mean that the four-blade configuration is preferred. The turbine blades can be made of solid or hollow, extruded or welded, aluminium, alloy steel or stainless steel. Blue Energy notes that the blades will undergo relatively low stresses, as the revolutions remain low. Tip speed ratios are typically three to five, with water velocities in the range of 2-5m/s. The blades are protected by a heavy urethane, ceramic or metal plasma coating, and additionally with anti-fouling paint.

Blade foil sections are based on wind turbine sections developed by the Sandia National Laboratory in New Mexico, US. Each blade is supported by two, three or four arms, depending on the blade aspect ratios (ie length to chord ratio).

The arms are attached to the blades and rotor shaft using proprietary methods which avoid any penetration of the blades or the rotor shaft, and transfer the large bending and torsion loads.

Integrated development

All the gearing, auxiliary equipment and electrical generators with their associated switchgear are mounted above high water level in a machinery room associated with each duct. They are therefore easily available for maintenance and repair.

The tops of the machinery rooms form a continuous surface and can support common facilities such as gantry cranes. As an incidental benefit, the continuous fence can support a roadway, railway, or provide a route for other infrastructure facilities such as electricity transmission lines. While this does not affect the economics of the tidal plant in isolation, the company believes it makes it highly attractive as part of an integrated development project. Blue Energy agrees that the efficiency of the tidal fence is somewhat lower than that of conven-tional turbines, but notes that this is balanced by the fact that the turbine gen-erates power on the surge and ebb tides.

The Davis turbine, despite its long development, has not so far been operated commercially. Development work has included field testing of a 20kW version, at Cornwall in Ontario, which was able to supply power to the Niagara Power Corporation. In a second field test a 100kW version also supplied the local grid, this time via Nova Scotia Power. Development work was interrupted

for some time, however, after work on renewable energy projects was scaled down by the Mulroney government.

A chance for new technology?

At this stage, the Philippines’s ‘pole vault’ to becoming an energy exporter looks to be some way in the future. The country has barely enough energy for its own requirements at present and, despite the recent dramatic slowdown in Asian economic growth, it will need to meet fast rising demand from its own population in the next few years. The practical problems of supplying a customer base distributed across thousands of islands should also not be underestimated.

The Philippines National Power Corporation considers that the best way forward is to legislate itself out of existence: to split its monopoly into competing generating companies and transfer them into the private sector. This plan is well advanced and the new assets of the successor companies have been sketched out. Indeed under the original timetable privatisation would have been completed this year.

Do projects such as the tidal fence have a role in the Philippines if and when the private sector takes over? The answer may be that it is perhaps the best chance for such projects.

Unconventional technologies are often best pursued by private companies. They do not have to convince the bureaucrats of a nationalised industry that they have chosen familiar, proven technology, and they do not have to carry the costs of that bureaucracy in the early phases of a project, when investment costs are also high. The company is free to focus on developing and applying its technology. In return, a well written power purchase agreement places risk on the shoulders of the project developer, where it should be, and protects the consumer from the consequences of trialling new technology.

There will be many opportunities for new power suppliers in the Phillipines in future. The Davis turbine may become an early example of new developments begun and completed in the private sector.