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Hydro-electric is not power on tap

Living "off-grid" is wonderful, but even a mill does not have the most reliable year-round power source

25 October 2010

This column is written by Marc Asker, head of EcoPower, a renewable energies company that he set up in 2007. He has been in the industry since 2003

A COUPLE – Fi and Giles Stonor – asked me recently about solar photovoltaic systems, which in itself is not unusual, but, given that they lived in a mill with a hydro-electric turbine, I was intrigued.

The Stonors moved from London to the Lot in 1999. They have a 13th-century water mill – at Moulin de Latreille, near Cales – and wanted to harness it to give power: however, they had not anticipated what problems would be entailed.

The mill is isolated and, in 2002, the FDE (Fédération Départementale Electricité du Lot) confirmed that they were eligible for a grant to fit a hydro-electric turbine, on the grounds that that would be cheaper than installing mains electricity.

After a study by Lyon company Sert, civil works started in 2004, when a turbine designed and built by Labarthe et Fils was fitted. The electronics were done by a company from Rodez, but a series of problems meant work was not completed until June 2006.

Living with the turbine had its ups and its downs, because the ever-changing weather means they cannot rely on it for an annual supply of electricity. Now they are making plans and saving for alternative methods.

The power that the turbine generates is governed by the height of the river, which means that, in winter, it can give up to 11 kilowatts of power while, in the summer, when the river is low, the average is 2-3kW for six hours a day.

However, they have to do some hard work cleaning the grills – which are there to stop debris from entering the turbine – three or four times a day. In autumn, the grills become blocked with leaves and weed, so they either have to shut down the turbine until the worst has passed or constantly clean the grills. It is hard physical work.

Because they know how much power the turbine is generating, they also know how much power they can use and that has made them very aware of heaviest consumers of electricity.

They have started running a chambre d’hôtes at their mill, and guests have given positive feedback on what they are trying to achieve. It has spurred them to continue to try to live as environmentally soundly as possible.

After visiting the mill (you gain an impression of the size of building at www.moulindelatreille.com and see what a challenge they faced), it became apparent there were two key areas to be addressed.

One is that Fi and Giles have no way of storing electricity while the mill is running at night or if they are using less power than they are creating. It is being wasted and the only way to address this is to store the power in batteries.

The second issue is that, as a chambre d’hôtes, at times of high occupancy, they simply do not have enough hot water.

Their hot water comes from a standard French ballon with immersion heater, which uses a great deal of electricity that they do not have with the lower river in summer.

This is being resolved by installing a solar thermal hot water system, driven by a small solar photovoltaic panel: they can rely on it all year round.

One final problem for the Stonors is that, if they leave the mill for three or more days, they have to stop the turbine for safety reasons. This means there is no power for the fridges and freezers, etc. A small battery bank and an extra solar PV system would allow them to leave the house with the electricity on.

Living “off-grid” is wonderful, but even a mill does not have the most reliable year-round power source. A mixture of technologies, solar PV, solar thermal, wind/water turbines etc is always the best approach. That way you are not reliant on any one particular type of system.

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