The first Hydro proposal suggested that we take as much as possible from the stream, and so generate the maximum amount of power.
But this meant that we’d have a large intake, a large pipe, a large turbine, and a large cable to connect the turbine to the grid. And they would all get used to their maximum for only a few weeks each year.
So TGV Hydro came back with plan B:
| Plan A | Plan B | |
| Peak flow | 35 l/sec | 14 l/sec |
| Peak power | 13.7 kW | 7.2 kW |
| Average power over a year | 5.8 kW | 4 kW |
| Total cost | £115k* | £62k |
| Payback time | 9 years | 7 years |
*Plan A needed lots more electrical infrastructure before it could be fed into the grid. Which we ended up buying anyway, as the combination of PV and Hydro needed a bigger transformer.
They key number here is the payback time, which is a proxy for return-on-investment – they key measurement for the viability of the scheme.
So, we decided on the smaller scheme, with the higher ROI.
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