Extract from full Energy Strategy report that ISIS commissioned from Fulcrum. Published with their kind permission…
4.6 HYDRO POWER
The [Community] Vision  recommended that the potential of micro-hydro power on Brentford’s two weirs, one near the Thames Lock and the other near Brentford Gauging Locks and Basin, should also be explored. In fact it is worth noting that the weir by Brentford’s gauging lock was home to “Bax’s mill” prior to the construction of The Boatman’s Institute. A simple broad-brush estimate can be made on the potential flow rates and head available.
For instance, considering the Basin weir, British Waterways have advised that the fixed weir level is 4.75m AOD18, given the tidal variations it would be more difficult to guess the level below the weir, however for sake of ease a head of 2m is assumed. Obtaining flow rates is similarly difficult without actual measurement data, however the average discharge19 for the River Brent at Costons Lane, Greenford is 1.32 m³/s, whilst Monks Park is 1.00 m³/s. Thus if a head of 2m and a flow rate of 1.00 m³/s are achievable then:
Potential power available = flow rate x density x g x head x efficiency
= 1.00 m³/s x 1000 kg/m³ x 9.8 m/s2 x 2m x 85%
Although small this is equivalent to about 8 kettles. Obviously flow rates change according to season and canal use, and further more detailed analysis would need to be done before certainty could be had.
Successful installations of hydro-power have been done on canal/river/weir sites. The Guildford Hydro Project20 undertaken by Guildford Borough Council (GBC) is a helpful example. This involved the redevelopment of a neglected turbine house in Guildford; it was originally built in 1897, and was a working water mill until 1952. As of September 2009 the turbine has generated 500,100 kilowatt hours. The turbine at full power is rated at 68 HP (50kW) at a 6 ft head21. At full power the turbine passes 3.5 m³/s. During the summer when there is little rain and high pleasure boat activity through the adjacent lock this drops to somewhere between 0.5 and 1.0 m³/s. Real time output in the winter averages about 35kW and in the summer between 5 – 10kW.
The installation cost £340k, including £120k to refurbish the grade II listed building which had fallen into serious disrepair. GBC obtained grants totalling £80k which offset some of the cost.
The lower weir at the Thames Lock may present a more difficult site due to the tidal variation of the Thames; in fact it may be more suitable to use a tidal power system rather than a run of river, although this would bring added complications. The House Mill on the River Lea near Bromley-by-Bow is an example of an old tidal mill and a feasibility study has shown that it could be converted to power generation.
The rough calculations above have shown that some potential exists, however further study would have to be performed to understand the feasibility, particularly regarding flood risk issues and impacts to the canal operation. Nevertheless, even if 30kW could be generated this would be a small scale system and only contribute a small amount to local energy demands.
18 From WYG Draft FRA
21 Information provided by Roy Coverly, Senior Engineer at GBC.