Category Archives: Hydro

Starting the Hydro

We’ve decided to take the plunge and start the process of getting a micro hydro setup. The TGV Hydro site has lots of pictures of what the various bits & pieces look like.

The full report from TGV Hydro was a long and involved affair, but the highlights are:

  • Water head is 60m (see positions on the map), connected via 690m of piping to the turbine house
  • Peak flow is 35 litres/sec, for a peak power of 14.3kW, average 5.8 kW over the year. Bear in mind that this covers several months of the year where nothing is generated, as there not enough water. This is because although the stream flows all year around, there’s a legal minimum of flow which must keep going down the stream, and for some of the year, that leave nothing for the hydro. So suddenly wet summers become a Good Thing.
  • Total power estimated at 50,000 kWh per year, which is enough for 11 homes
  • We have decided to export direct to the grid, as there’s a handy eletricity pole nearby to the turbine house, and running a cable from there all the way to the house would be a significant additional cost

hydro catchment

The clever part is that they work all this out just by combining the siting of the intake with rainfall records.

Then assuming that the rain that falls flows into the stream, it’s possible calculate the water that flows past the intake.


All this produces this idea of the flow across the year.

flow profile

The Numbers

  • About £100k to build!! made up roughly of:
    • 10k to TGV to get are the design & permissions
    • 83k construction:
      • 30 for the turbine house & its kit,
      • 18 for the pipeline,
      • 8k for the intake,
      • 16k to connect to the grid,
      • …plus lots of fees and PM costs
  • About £12k per year income which comes from
    • Generation Tariff: 18.8p / kWh for the Feed-in-Tariff
    • Export Tariff: 4.8p / kWh for the power exported to the grid
    • The TGV report has all kinds of assumptions about how these might vary of the life of the system.
  • All this has loads of assuptions and options, but these are the headline items.

So, on this basis, a 100k investment for a potential 12k annual payback seems reasonable, assuming that these really are the costs, and the government doesn’t change its mind about loving green energy. As if they would…


Hydro Update

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.