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At some point in the future, all energy consumed on the earth will be derived from renewable sources. The timeframe for this fundamental move from fossil to sustainable fuels is debatable, but the end result is not.

It will occur for two reasons, one being environmental concerns and the effort to counteract climate change. The second reason is more unavoidable – simply put, the rate of use of the world’s fossil fuel resource outstrips its replenishment by a factor of millions.

The life expectancy of oil is estimated to be decades. For coal, it is a few centuries. Reserves of coal, oil, and gas will simply run out.

Many alternatives to fossil fuels exist, and in amounts that greatly exceed the current rate of human energy consumption. Perhaps the most underexplored, and certainly the most under-utilised, is that of ocean energy. It is estimated that the power in the ocean surpasses present human usage by a factor of more than 5000-fold. There are many different forms of possible ocean energy. This article will concentrate on two of the most familiar – waves and tides.

Waves alone (more correctly, surface gravity waves – the type we see breaking on the shoreline) have the theoretical potential to provide more than 30 terawatts on average, or twice the world’s current power usage, but the vast majority of this power is dissipated on beaches and headlands. If just a small percentage of this power was harnessed effectively, it would play a meaningful role in global energy production.

One of the most unique aspects of wave energy is the diversity of technology types for converting it to electricity. Devices range from pneumatic to hydraulic in terms of power off-take, fixed to floating in terms of their mooring, and buoyancy to pressure to gravity in terms of basic operation. No two devices seem to look the same. Indeed, some are as different as a hairdryer is from a lawn mower.

However, one similarity is that peak output per device is generally limited to the order of one megawatt or so. It is not possible to scale-up wave energy devices indefinitely, due to the physical constraints of the waves’ period and length, and the need to avoid the destructive interference of the waves with one another. However, scale-up to any desired capacity can be achieved very simply via multiple devices.

Several companies are now nearing commercialisation of their wave energy technologies. Although the majority of these organisations are in Europe and North America, three are based in Australia. Pelamis, Wavedragon and OPT are three of the more prominent northern hemisphere companies, each with their own technology. Oceanlinx, CETO, and BioWave are the only local Australian companies/technologies at present.

While the wind energy industry saw a reasonably rapid convergence of technological varieties into essentially one commercial style – the three-bladed, horizontal-axis turbine – the wave energy industry is yet to experience such a convergence. Some even say that the same level of convergence as seen by the wind industry will not occur with wave energy, due to certain fundamental differences in the resource. Time will tell.

The story for tidal energy is somewhat similar. While tidal technologies have been in commercial existence for many decades, the widespread emergence of an industry remains elusive.

The tidal resource is estimated to be about one-tenth that of wave energy, but this still equates to about 20 per cent of the current global power usage. And the tidal energy resource can be accurately predicted centuries in advance.

Tidal energy technologies come in two forms: tidal barrage and tidal stream.

Tidal barrage systems have been in place in some parts of the world for centuries. This involves letting the tide fill either a natural or artificial basin, then blocking the ‘opening’ at full tide with a barrage. Once the tide has retreated to form a head (the difference between the water level inside the basin to that outside the basin), the barrage is opened and the resulting ‘waterfall’ is used to drive a standard low-head turbine.

At low tide the system works in reverse, with the ensuing waterfall running in the opposite direction. Such a system has been operating in France at Mont Saint-Michel for many years, and a much larger project was mooted for the Kimberley region of Western Australia (although rejected due to the environmental concerns related to the twice-daily flooding and drying of the intertidal zone).

Tidal stream technologies are quite different again. These technologies are only just now being commercialised, although none is fully commercial yet. A tidal stream technology essentially operates like an underwater wind turbine. In fact, much of the development process for tidal stream turbines has called upon the knowledge and lessons learned from the wind industry.

Several companies, including Marine Current Turbines (MCT) and Verdant have turbines operating in the northern hemisphere. No such project is currently (no pun intended) operating in Australia, although some have been proposed.

As with any new industry, there are many hurdles for a technology to overcome on its way to general acceptance and use. Inevitably, there will be technical issues that must be resolved. No new idea is without its teething problems in this regard. Most new technologies also have commercial barriers to entry that need to be overcome.

Luckily for wave and tidal technologies (indeed, any renewable energy technology), the only significant commercial issue that needs to be addressed is price – the unit cost of electricity produced. Such is the appetite and demand for renewable energy, compared with its supply, that a technology’s ultimate competitiveness depends simply on its ability to be relatively cost-effective versus fossil fuel sources. And this is fundamentally a technical issue anyway.

Technical problems are overcome via a combination of funding and experience. With proper funding comes the opportunity to implement real projects in the real ocean. This opportunity results in the learning experience necessary for ensuing modifications and improvements to be made, with any technical issues and problems being solved along the way.

A new industry, such as marine energy, will initially attract interest, followed by funding, followed by experience. The experience inevitably includes some failures, which tends to dampen the initial enthusiasm.

This lessening of enthusiasm can result in a potential funding gap at a crucial stage in the technology’s technical and commercial development. For those technologies that can bridge this gap, the road to success becomes much smoother. Those that cannot bridge the gap will disappear.

The survival or demise of a technology is a tenuous thing. For any new technology with potential, it is vital that funding does not dry up at the critical time when lessons have been learned and mistakes corrected.

A few wave and tidal technologies are on the cusp of reaching this fork in the road to commercialisation or demise. Once the former is attained, the road will quickly become a highway.

Tom Denniss founded Oceanlinx in 1997, having earlier invented the core technology that has been commercialised by the company. He spent nine years as the company’s first CEO, and is now Chief Technology Officer and an Executive Director of the company. Tom has a PhD in Mathematics and Oceanography, and has had a varied professional career, including as a university lecturer and investment banker, prior to moving full-time to technology development in the field of wave energy.