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How Hydro Electric Power Works

By: Dr Gareth Evans - Updated: 15 May 2012 | comments*Discuss
 
Hydro Electric Hep Water Electricity

One thing we’re seldom short of in Britain is rain, and as a result, viewed from the air, much of our country is a wonderful glinting tracery of silvery rivers and lakes. It’s small wonder that the UK has been harnessing water power for hundreds of years – from driving local flour mills right up to now, when it is used to generate a small but significant amount of our electricity and provide a vitally important reserve for times of high demand.

We’ve all heard about hydro electric power (HEP) – but just how does it work?

Faraday and Generation

Back in 1831, the famous British scientist, Michael Faraday, discovered something which made most of our modern day generation systems possible. To put it very simply, he noticed that if you move a wire around in between two magnets, you generate an electric current.

Later to be named ‘Faraday’s law’ this forms the basis for a whole range of things, from wind-up torches and bicycle dynamos, to the alternator on your car – and hydro electric power too, of course. To understand how that bit works, however, we’d probably best take a quick look at another scientific law – the wonderfully named First Law of Thermodynamics.

Obeying the Law

Fortunately for all of those amongst us who flee screaming as soon as we hear the word ‘physics’ being mentioned, the First Law’s bark is much worse than its bite and despite the impressive sounding name, it’s actually not that hard to handle! All it really says is that you cannot just create energy out of nothing – you have to change one form of energy into another, or putting it another way, there isn’t any such thing as a free lunch!

From here on, the science behind hydro moves into much more generally familiar territory, with that Newton chap and his apple – and gravity is the key. Water, as we all know, flows down hill and it does so because of gravity – but if it’s moving it must have energy, and we know from the First Law that it didn’t suddenly get it from nowhere. In this case the water’s gravitational ‘energy-of-position’ – known as potential energy – has been transformed into ‘energy-of-motion’ – known as kinetic energy – and the rule of no free lunches has been obeyed.

Moving Water, Electric Power

So far, so good, but the energy swapping hasn’t finished here. If all that moving water now turns a paddle, attached to a shaft which is itself attached to a larger and more complicated version of Faraday’s wires and magnets, the end result is electrical power – and that is the science behind HEP in a nutshell.

HEP in Practice

There are three main types of HEP schemes:

  • Storage – a dam holds the water behind it in a reservoir and then channels it through the turbine and generator.
  • Run-of-river – akin to the old-fashioned mill wheels, the generator is driven by the natural flow of a river or stream; this is the system most often used for small scale HEP projects.
  • Pumped storage – this approach has two reservoirs, and uses off-peak electricity from the grid to pump water to the upper reservoir, usually at night, keeping it as a reserve and releasing it when demand is high.

In addition, tidal schemes such as surface barrages and submerged turbines, which use the movement of the tides to generate electricity, are a fairly new and growing form of HEP which may prove increasingly popular in the future.

Britain currently only generates around two per cent of its electricity from HEP, which seems a little surprising when you compare it with the quoted figures of nearly 100 per cent for Norway, and around 70 per cent for Iceland and Austria. With the rise of tidal flow schemes and the growing pressure to cut our dependence on imported gas, there seems to be a good reason for that to change; ours is, after all, a rather wet island, surrounded by water!

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