Education

The 2,000-year-old turbine

 By Robin Wylie

For most of its history (since at least 250 BC) the Archimedes screw has mostly been used in agriculture, to transport low-lying water into irrigation ditches. But in the last decade or so this ancient tool has acquired a new role as a hydroelectric turbine. Robin Wylie explains how Archimedes-style turbines are helping provide renewable energy in the present day and particularly useful for small to medium hydroelectric projects. This means that these turbines are well suited to environmentally-friendly “run of the river” hydro generation (the kind that doesn’t require damming)…

The story of renewable energy is usually one of advanced technology and modern ideas. But it can also involve looking at existing technology in a new light. A good example of this can be found in the hydroelectric sector, where an invention from the days of ancient Greece has recently been given a new lease of life.

The Archimedes screw sounds complex, but like many great inventions, it isn’t. It consists of an array of thin blades attached to a central shaft (resembling a giant strand of fusili pasta) and has been used for centuries as a simple water pump. For most of its history (which despite its name probably long predates Archimedes) the screw has mostly been used in agriculture, to transport low-lying water into irrigation ditches. But in the last decade or so this ancient tool has acquired a new role as a hydroelectric turbine.

The process is simple. The Archimedes screw is usually used to transport water from the bottom of the device to the top, by manually rotating the central shaft. But if flowing water is introduced through the top of the screw, the process is reversed: the water flows towards the bottom of the screw, rotating the shaft. Attach an off-the-shelf generator and presto — you’ve got a hydroelectric turbine.

And a turbine with substantial benefits. Its extremely simple design makes Archimedes-style turbines cheap, robust and easy to maintain. The blade orientation also allows aquatic debris — and even fish — to pass through the turbines without issue. This reduces the need to filter the water, cutting costs even further.

The Archimedes screw

Archimedes-style turbines are particularly useful for small to medium hydroelectric projects, as they perform best in slowly-flowing water (in technical terms, their performance is optimal when the “head” of the water flow is 5 m [16 ft] or less). This means that these turbines are well suited to environmentally-friendly “run of the river” hydro generation (the kind that doesn’t require damming).

The concept of using the Archimedes screw as a turbine isn’t new. The idea was patented in 1922. The recent popularity of this technology could reflect the growth of smaller, local hydroelectric projects. The Archimedes screw might be old news to farmers, but to those looking for cheap, green electricity, its potential is only just being tapped.

about the author
Robin Wylie
Freelance earth/space science journalist. Currently finishing off a PhD in volcanology at University College London.