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|
|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.