WEBVTT
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Language: en

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We learn about
conservation of energy in school.

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How you can take potential energy,

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like the energy in the
chemicals in this battery,

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and you can then just convert
it to electrical energy.

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And then convert that to
whatever you can find a use for.

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A battery is just a store
of potential energy.

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And that potential energy
could be chemical,

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or it could be gravitational.

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This lake in this rainy bit of Wales
is part of the largest battery in Britain.

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And it's rechargeable.

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Welcome to Dinorwig Power Station,

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otherwise known as Electric Mountain.

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- What we have is a large reservoir
at the top of the mountain,

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a large reservoir at the bottom,

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and between the two, a power station,

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which converts that
potential energy into electricity.

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The power station itself is located
inside that mountain in deep caverns.

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We release that potential energy
through the station.

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It drives a turbine that spins round at
synchronous speeds, connected to the grid.

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It drives a generator,
converting that into electricity.

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We then export that
onto the National Grid.

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And then at nighttime, we just
reverse the whole process.

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The turbine turns into a pump.
The generator becomes a motor.

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And we push that water back up the hill
into the reservoir at Marchlyn Mawr,

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at the top of the mountain.

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The operating principle
here is that the generation

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that the station is able
to do during the daytime

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helps the nation meet those peaks
of electricity demand.

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And overnight, it's able to pump the
water back when prices are lower.

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In electrical terms, we have
around nine gigawatt-hours

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of storage at the top of the mountain.

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And in fact over the course of a day,

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the water passing through the
station is broadly equivalent

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to the total household
consumption of water in the UK.

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At full load, we can
be meeting the demand

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of around about two million homes.

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- This sounds like a really simple idea,

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but when there's this
much energy involved,

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the design challenges are ridiculous.

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If you've ever lived in a house
where you turn off a water tap

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and the the pipes go clunk,

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then you know about water hammer.

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Water isn't compressible, so closing a tap

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means that all the water
that is under pressure

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and rushing down the pipe
suddenly has nowhere to go.

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So if the pipes in your house
aren't secured properly,

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the crash and rebound of all that water

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can make the plumbing move and make noise.

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If that can happen with
just a tap in a house,

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imagine what could happen
when one of the valves here closes.

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At full capacity, there
is somewhere around

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a swimming pool every second

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rushing through the turbines down there.

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When that valve closes, all
that water heading down here

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suddenly has nowhere to go.

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The pressure would do
enormous amounts of damage.

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It would break everything apart,
if it wasn't for one extra bit of plumbing.

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A shaft hundreds of metres deep
that acts as a pressure release.

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We can't see anything, on the
surface or from down here, sadly,

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it all happens
deep within the mountain.

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But every time those valves move,

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[valve clanking]

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that surge pipe is what
stops the whole system

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from tearing itself apart.

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This station is not some
quirky old curiosity.

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This is serious engineering

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that keeps the lights
on around the country.

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- Dinorwig Power Station
is one of the largest

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power stations of its type in the world,

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and it's also one of the
fastest-acting power stations.

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So as well as being able to take advantage

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of the peaks and troughs
in the electricity market,

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it was essentially built, primarily,

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with the intent to provide very fast response onto the system

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in order to help the National Grid balance
supply and demand instantaneously

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on a second-by-second basis.

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So it has the capacity to be able to go
from zero up to its full capacity,

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maybe 2,000 megawatts,
within 10 to 30 seconds.

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When people talk about pumped storage,

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they tend to associate
it a lot with TV pickups,

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and National Grid, in analysing that risk,

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study the TV schedules and plan ahead
and put Dinorwig on standby, if you like,

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to be able to meet those pickups.

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Going back to the 80s and the 90s,

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everyone would be sitting
around the same TV channels

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with a limited choice, then.

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All the ingredients you need for a sort-of
collective putting-on of the kettle

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and opening of the fridge.
Pickups could be pretty significant.

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But since then, people are streaming
on YouTube, on Netflix,

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all the different plethora of channels
that we have, so that has changed

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that sort of coincidence
of viewing on one channel.

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The current environment that we're in,

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we have significant amount of renewable
technology on the system, which provides

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a level of unpredictability day to day.

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And actually, the
importance of storage now

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is that we can use it to help develop
the amount of renewables we have

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and allow us to fill in those gaps

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when the wind's not blowing
and the sun is not shining.

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So having storage is such an important
component of the modern grid system.

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- Thank you very much
to all the team at Engie

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who made this visit possible.

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Pull down the description
for more about them,

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and more about Electric Mountain.

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A battery is just... a store!...
of potential energy.