Sunday, 26 April 2009

Watermill research latest

The quest for finding a suitable turbine for our old watermill site continues. I have been reading about horizontal watermills in Bethold Moog's seminal work: The Horizontal Watermill: History and Technique of The First Prime Mover (1994, The International Molinological Society).

It seems that their a fair bit of debate about the first origins of watermills, but it is around a few hundred years b.c., probably around present day China. The technology gradually spread West, and by the 3rd century it moved from modern day Middle East to North Africa and around the same time to Southern Europe. Around the 8th/9th century a dotted line shows transfer of the technology moving NW from the Black Sea towards Scandanavia, and another line folliwng the Celtic trade routes, up to Ireland and Northern Scotland, including the Shetland Islands where writers have been inspired by them since the 1700s.

These were all horizontal watermills, similar to the type shown here (by a Galician architect). They used a vertical shaft to transfer power to the grinding mills in the room above.

The vertical watermill (with horizontal shaft) developed later, could be used in areas of higher flow and larger head (height difference) and probably delivered more energy to the shaft. Some were used for cutting wood. This shot taken in the early 20th centry on the Minho river (Northern Portugal, 2mins from where I am sitting!)

My research (for MSc thesis) is about the viability of using the traditional horizontal and vertical mill sites that are dotted around Portugal and many other parts of the world, to generate useful energy. That means electrical power, but also mechanical energy that can be useful in today's modernised / industrialsed economy.

There are important differences here. In Nepal and Northern India, horizontal watermills are still very much in use due to the lack of rural electrification /a national grid. I was amazed to see how similar in design the Nepalese "Ghatta" wheel was to some of the Portuguese mills. Even the grinding stones are similar.

Since the 1980s the Nepalese Centre for Rural Technology and various other partners have been trying to improve the efficiency of these old watermills.
The key difference here is that people were still using the mills, so there was a real social and economic drive to keep them working, get them performing better. They found that the efficiency of the systems were low: at around 20%. That means most of the energy captured from the falling water was being lost throughout the system. By improving the shaft, the rotor (horizontal spinning bit), introducing bearings (rather than river stones) and other changes, they were able to reach 50 to 60% efficiency. This may be a far cry from the 85 to 90% efficiency of a modern hydro electric turbine, but it's a major improvement nonetheless.

Ashden Awards have produced a short film about these projects in Nepal, and funded their further development. Nice film, watch it here

It mentions the addition of a small dynamo, or generator attached to the mill stone. I looked into this more and more, and found a plethora of experiments with hand-made spinning mill stone generators. UK Based IT Power participated in a project in Northern India to identify feasible upgrade to their local "gherat"mills.

The outcome of both projects has been an "Improved Watermill", otherwise known as a "Multi Purpose Watermill". This has got to be the best way forward: produce power with a small generator, but have the capacity to add in various other mechanical services. These could include: grinding grains, pressing oil (think olives for Portugal!), turning a potters wheel, a sharpening stone, a wood turning thing, a laithe (?). Of course the output of the electric generator would drop when you turned on one of these other systems, but power would have been stored in batteries, and would continue to run all night when other work is resting, so it wouldn't matter.

Of course such multi purpose watermills are not available in Europe to buy off the shelf. You would have to make it yourself.

But let's compare these with what's on the market for basic electricitiy generation. Finding a micro turbine for the kind of low head settings found in most watermill sites can be difficult. There aren't many systems out there, probably because the amount of energy that can be produced is quite little, around 4MWh/year, which is more or less the consumption of a modern house.

It's late already, so I'll summarise these in the next post...


Rupert Wolfe Murray said...

Really interesting and concise analysis. It's a subject that is easy to relate to as we all have memories of small energetic rivers and they provoke thought. I remember breaking into the abandoned water mill in Manor Valley, with Gavin, and we went down the shute where the grain would fall onto the stone. The bottom end of it was made of canvas and I can remember Gavin being caught in that and beaten by some enraged old man who was chasing us and was laying into gaga with a walking stick. Rupert

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