For the technically minded, the key data is as follows:
1) Power generation formula: P = H x Q x G x E, where:
P is the power generated in kW,
H is the ‘head’ or drop in water levels at the sluice,
Q is the flow of water in m3/sec,
G is gravity, and
E is the efficiency of the screw.
2) H on our site is 1.6 meters, Q is a complex issue so is described below, G is 9.81 m/sec and E for the equipment to be installed is 74%.
3) As regards the flow, largely using data from Enslow just downstream – the river can be taken to be in flood a certain amount of the time and a flow of water must also be maintained in a different channel under the mill house and an overspill channel. Also the screw needs a minimum flow for it to work. The result of all this is that it is calculated not to work for 109 days per annum. In the remaining 256 days, it is calculated to work at varying amount from full capacity to low capacity to give an average figure for Q of 1.6 m3/s. The maximum will be 3.25 m3/s.
On an annual basis P is therefore 1.6 x 1.6 x 9.81 x 0.74 x 24 x 365 = 162,000 kWh (or thereabouts!).
The screw has to be designed to have a maximum capacity of 1.6 x 3.25 x 9.81 x 0.74. = 37 kWh.
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