Friday, April 24, 2015

Bryan Leyland: Things you know that ain't so - wave power


Things you know that ain't so - wave power will soon provide substantial low-cost generation.” The first wave power machine was made in the early 1900s. It was mechanically complex and was a commercial and technical failure.

With the OPEC oil crisis in the 1970s, there was a resurgence of interest in wave power. The most notable of the of the prototypes was “Salter's Duck” that had a number of segments shaped floats rotating central axis. In theory, it looked really good. But Prof Norman Bellamy, who built a prototype and tested it, reported that the mechanical complexity was greater than expected and the power output was about one third of expected. He went on to develop a new device consisting of floating hinged steel tubes that faced into the waves and generated electricity from hydraulic rams at each hinge as the wave passed along the device. Prototype tests on Loch Ness revealed serious problems with designing and manufacturing a device that could withstand a storm and still generate useful amounts of power under normal wave conditions. So he abandoned that option and switched to a system with air bags that was much more promising. A prototype was built and was quite promising that he eventually abandoned it to pursue more attractive options.

When the global warming scare convinced many governments that renewable energy might be a way of solving the carbon dioxide problem, lots of money was made available for wave power development. One organisation revived Bellamy's hinged steel tube concept and spent millions of dollars trying to make it work. They went into administration a few months ago. Another organisation carried out further development on Prof Bellamy's airbag system but, it seems, without any prospect of generating electricity at a cost anywhere near conventional generation. 

A New Zealand organisation has developed yet another device that is more robust than most and may well have a use providing small amounts of electricity for offshore installations and, possibly, small communities where diesel power is seriously expensive. But, as with the other prototypes the tonnage of steel required per kilowatt of output is simply far too great.

Over the last few years Prof Bellamy has developed an entirely new concept based on a rubber tube with an internal diaphragm. It is moored head onto the waves and as a wave passes along it pumps air at a steadily increasing pressure from one end to the other. The compressed air is then piped to shore where it drives an air turbine generator. This system has a huge advantage that much of the expensive equipment is onshore and if the tube is lost in a storm, it is relatively cheap and easy to replace it. If the remaining technical and economic problems can be overcome, it could be producing commercial power in 5 -10 years time.

As with solar, wind and tidal power, it will need to feed power into a large system that can cope with the fluctuations in output or it will need substantial and very expensive energy storage systems.

The conclusion is that all but one of the systems now under development have severe mechanical and economic problems. If Prof Bellamy’s system is successful, all the other systems will be obsolete overnight.

The chances that wave power will produce a substantial amount of low-cost power in the foreseeable future are extremely small because, almost certainly, nuclear power and fossil fuels can provide a continuous supply of electricity at an equivalent or lower cost. (As the world has not warmed for the last 18 years, we can be confident that man-made carbon dioxide does not cause dangerous global warming.)

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