Twenty Three HMG members crammed themselves onto the stones floor at Longbridge Mill.  This change to the usual accommodation at Longbridge seemed to be a big improvement:  the atmosphere of being in a mill with the convenience of a meal (and drinks) first, and excellent audibility.  It would certainly not work if the group was any larger.

Andy Fish thanked Lyn, the manager, and the staff at Longbridge for letting us use this area for our meeting.  He announced that the next meeting at Bursledon Village Hall on Friday 12 September 2014 will include an illustrated talk by Peter James on his project to rebuild Ockley Mill with the ultimate aim of living in it.

Andy then reported that the recent three day trip to Devon had been very successful and that next year we hope to arrange a three day visit to the Midlands in May.  If you are interested he would like to “put you on the list” to keep you updated with the itinerary.

David Plunkett said that the newly appointed miller at Eling Tide Mill (Mathew Painter) is currently receiving training at Alderholt and later at Longbridge.  Earlier in the day, several members had been working at Kingsley Mill where the replacement wheel is about to be rebuilt, starting next Wednesday, 18th June 2014.

Ros Plunkett thanked Peter Mobbs, Andy Fish, and Nigel Harris for information and items for the Newsletter, and reminded everyone that more contributions – particularly relating to Hampshire mills – are always welcome.

Andy Fish then introduced the speaker, Brendan Barrow of eWaterpower.  The talk, entitled “Mills and Hydropower”, was incredibly detailed and informative.

Brendan began by outlining his background, bravely declaring that his interest in the subject began at the age of 12 when he thought of using bike parts – a dynohub – in a local stream.  He then outlined the many stages in the complex process of planning, funding, gaining permission and finally building a variety of installations to generate electricity - using waterwheels, turbines, and Archimedean Screws.

Getting started:  This ideally begins with a desktop survey to assess the likely site, suitability, and viability.  Then, if the site has potential, an initial feasibility study is undertaken before an application for an extraction licence and planning permission can be submitted.  A bewildering array of factors need to be assessed and taken into account, including catchment modelling, ecological impact studies, flood risk assessment, eel and fish passage, and so on.  This may well cost up to £10,000, but start up funding is sometimes available from the EU.

Viability:   This depends on the power capacity of the site, which is calculated from Gravity (9.81ms^-2), Efficiency (66-74% can be realistically expected), Head (the difference between levels above and below the installation), and Flow (involving catchment modelling to reveal monthly and annual fluctuations).  The Environment Agency can assist with some data, for instance, there are 12 gauging stations on the Thames which record flow rates. 

Location:  These are usually existing wheel pits, new purpose-built channels, or structures in a weir.  The location and accessibility can have a significant impact on the cost.  Each solution has to be tailor-made for the site.

Types of installation:  Improved waterwheels of light construction can be 80% efficient, but generators and gearboxes reduce this.  An Archimedean Screw in the wheel pit, replacing an existing turbine or, in a new channel - is a popular choice and can be slightly more efficient.  Historic turbines and new ones of a variety of types (Kaplan, Crossflow, Francis, and so on) have been installed at various locations. 

Brendan gave numerous examples amongst them; Mapledurham, which has an Archimedean screw and; Shawford, which is using the original turbine.

Using the electricity:  There is the possibility of connecting your hydropower generator to the electricity grid.  However, this is not a straightforward topic.  Regarding costs, the export tariff (what the electricity company pays you for electricity) depends on many factors, while connecting to the grid may require a very expensive cable.  Also, for example, problems on the grid could require the generator to stop supplying the grid, either by shutting down the turbine or switching the supply to internal use.

At the very end of the talk, Brendan mentioned a very recent possibility, which is the construction of floating structures which use river flow rather than head.  (Sounds like a boat mill to me – nothing new there, then).

After this excellent talk and usual show of appreciation from the audience, Brendan answered questions from the floor and stayed to talk to individuals for a while.